//! The inventory, after Cataclysm's: everything on you, grouped by what it
//! is, with all about whatever's picked out; and beside it, when there is
//! one, another pile to move things to and from: your ship's lockers, what's
//! on the floor where you stand, or an armourer's rack to buy from and sell
//! to, with your armour to mend.
//!
//! Vim keys throughout: `j` `k` move, `gg` `G` go to the top and bottom,
//! ctrl-d and ctrl-u by half a page, `h` `l` between the lists, `/` finds.
//! `o` sorts both lists by something else (`Sort`), within each kind of
//! thing, and `O` turns the sort round. Every row shows what it weighs and
//! what it would fetch.
//! A count before a key does it that many times: `3d` drops three, `D` the
//! whole stack. `enter` lists everything you can do with what's picked out.
//!
//! It isn't a scene of its own. The scene you're walking about in opens it
//! over itself and carries out what it asks for (`Command`), since only
//! that scene knows what putting something down means there, and whether
//! it takes a turn.

use std::cell::Cell;
use std::collections::BTreeSet;

use ratatui::Frame;
use ratatui::crossterm::event::{KeyCode, KeyEvent, KeyModifiers};
use ratatui::layout::{Constraint, Layout, Rect};
use ratatui::style::{Color, Modifier, Style, Stylize};
use ratatui::text::{Line, Span};
use ratatui::widgets::{Block, Clear, Padding, Paragraph, Wrap};
use serde::{Deserialize, Serialize};

use super::keys;
use super::sky::rgb;
use crate::dungeon::armour::Armor;
use crate::dungeon::arms::{Condition, Dmg, Weapon};
use crate::dungeon::crawl::{Affinity, MEDPATCH_HEAL, MONSTERS};
use crate::items::{self, Category, Gear, Item, LOCKER_CAPACITY, Slot, Spot, Stack};
use crate::space::system::Rgb;
use crate::trade::{self, Terms};

const ACCENT: Color = Color::Rgb(240, 200, 110);
/// What something would fetch somewhere else: about this.
const GUESS: Color = Color::Rgb(184, 166, 120);
const DIM: Color = Color::Rgb(120, 124, 142);
const HEADING: Color = Color::Rgb(160, 166, 190);
/// Wider than this, the details sit beside the lists rather than below.
const WIDE: u16 = 110;
/// A list narrower than this shows what things fetch, but not what they
/// weigh.
const NARROW: usize = 30;
/// How far in things sit from the heading they're under.
const INDENT: &str = "   ";
const DETAILS_HEIGHT: u16 = 13;

/// How something looks lying about: a glyph and a colour.
pub fn look(item: &Item) -> (char, Rgb) {
    match item {
        Item::Weapon(w) => (if w.is_gun() { '}' } else { ')' }, w.dmg.rgb()),
        Item::Armor(_) => ('[', (170, 182, 204)),
        Item::Food(_) => ('%', (214, 176, 112)),
        Item::Medpatch => ('!', (240, 96, 96)),
        Item::Artifact(_) => ('*', (255, 214, 92)),
        Item::Salvage(_) => ('(', (150, 200, 222)),
    }
}

/// The pile beside you.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Beside {
    /// Your ship's lockers.
    Lockers,
    /// The floor where you stand: "on the floor", "on the deck".
    Floor(&'static str),
    /// An armourer's rack: what's for sale (see `View::shop`).
    Rack,
}

/// The armourer you're trading with, whose rack is the pile beside you.
#[derive(Clone, Copy)]
pub struct Counter<'a> {
    pub terms: Terms,
    /// What's in your ship's lockers: they'll buy from there too.
    pub aboard: &'a [Stack],
    pub scrip: u32,
}

/// What the lists are sorted by, within each kind of thing.
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum SortBy {
    #[default]
    Name,
    Weight,
    /// What it fetches, or here costs.
    Price,
    /// Price for its weight.
    Density,
    /// Armour, most worn first; the rest after.
    Durability,
    /// Weapons by their average damage, armour by what it guards.
    Strength,
    /// The order you came by things in.
    Newest,
}

impl SortBy {
    const ALL: [SortBy; 7] = [
        SortBy::Name,
        SortBy::Weight,
        SortBy::Price,
        SortBy::Density,
        SortBy::Durability,
        SortBy::Strength,
        SortBy::Newest,
    ];

    /// The sort after this one, round to the first.
    fn next(self) -> SortBy {
        let i = SortBy::ALL.iter().position(|&s| s == self).unwrap_or(0);
        SortBy::ALL[(i + 1) % SortBy::ALL.len()]
    }
}

/// How the lists are sorted: by what, and which way round.
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
pub struct Sort {
    pub by: SortBy,
    /// The other way round from usual: names z–a, the lightest first, the
    /// cheapest first...
    #[serde(default)]
    pub reversed: bool,
}

impl Sort {
    /// How it reads: "heaviest first", "by name".
    pub fn says(self) -> &'static str {
        match (self.by, self.reversed) {
            (SortBy::Name, false) => "by name",
            (SortBy::Name, true) => "by name, z–a",
            (SortBy::Weight, false) => "heaviest first",
            (SortBy::Weight, true) => "lightest first",
            (SortBy::Price, false) => "dearest first",
            (SortBy::Price, true) => "cheapest first",
            (SortBy::Density, false) => "most ¤/kg first",
            (SortBy::Density, true) => "least ¤/kg first",
            (SortBy::Durability, false) => "most worn first",
            (SortBy::Durability, true) => "least worn first",
            (SortBy::Strength, false) => "strongest first",
            (SortBy::Strength, true) => "weakest first",
            (SortBy::Newest, false) => "newest first",
            (SortBy::Newest, true) => "oldest first",
        }
    }
}

/// What something would fetch, or cost, as a row shows it.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
enum Price {
    /// What the armourer you're at asks or pays, and whether you can pay.
    Here(u32, bool),
    /// About what a buyer elsewhere would pay.
    About(u32),
    /// A scholar has yet to tell you what it is.
    Unknown,
    /// No one buys it.
    Nothing,
}

impl Price {
    fn amount(self) -> Option<u32> {
        match self {
            Price::Here(n, _) | Price::About(n) => Some(n),
            Price::Unknown | Price::Nothing => None,
        }
    }
}

/// What a scene shows the inventory, each time it asks it anything.
#[derive(Clone, Copy)]
pub struct View<'a> {
    pub gear: &'a Gear,
    /// The pile beside you, if there's one, and what's in it.
    pub beside: Option<(Beside, &'a [Stack])>,
    /// How you know monsters take each kind of damage.
    pub known: &'a BTreeSet<(&'static str, Dmg)>,
    /// Whether you can be hurt here, and so use a medpatch: only in a wreck.
    pub hurt: bool,
    /// The shop you're trading with, if you're at an armourer's.
    pub shop: Option<Counter<'a>>,
    /// How the lists are sorted.
    pub sort: Sort,
}

/// What the inventory asks the scene to do.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Command {
    /// Ready the weapon at this index in your pack.
    Ready(usize),
    /// Put on the armour at this index in your pack.
    Wear(usize),
    TakeOff(Slot),
    /// Eat one of the food at this index in your pack.
    Eat(usize),
    UseMedpatch,
    /// Put down this many of what's at a spot on you, where you stand.
    Drop(Spot, u32),
    /// Put this many of what's at a spot on you in the lockers.
    Stow(Spot, u32),
    /// Take this many of the `n`th stack in the pile beside you.
    Fetch(usize, u32),
    /// Buy the `n`th thing on the rack.
    Buy(usize),
    /// Sell what's at a spot on you.
    Sell(Spot),
    /// Sell the `n`th stack in your ship's lockers.
    SellAboard(usize),
    /// Have the armour at a spot on you mended.
    Mend(Spot),
    /// Have the armour that's the `n`th stack in your ship's lockers mended.
    MendAboard(usize),
    /// Have all your armour mended, on you and aboard.
    MendAll,
}

/// How the inventory answers a key.
#[derive(Debug, PartialEq, Eq)]
pub enum Reply {
    Stay,
    Close,
    Do(Command),
    /// Sort the lists this way from now on. Takes no time.
    Sort(Sort),
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
enum Row {
    Heading(&'static str),
    /// Something on you, or a slot to wear something in with nothing in it.
    You(Spot),
    /// The `n`th stack in the pile beside you.
    Beside(usize),
    /// The `n`th stack in your ship's lockers, when you're selling.
    Aboard(usize),
}

/// One thing you can do with what's picked out.
struct Act {
    key: char,
    what: String,
    command: Command,
}

pub struct Inventory {
    /// Whether the cursor is in the pile beside you, rather than on you.
    on_beside: bool,
    /// Where the cursor is in each list, counting only rows you can pick.
    cursor: [usize; 2],
    /// A count typed before a key.
    count: Option<u32>,
    /// `g` pressed once, waiting for a second.
    g: bool,
    /// Typing what to find, after `/`.
    finding: bool,
    filter: String,
    /// Picking from what you can do with what's picked out, on `enter`.
    menu: Option<usize>,
    /// What happened last.
    pub note: Option<String>,
    /// How many rows the lists showed when last drawn, for paging.
    page: Cell<usize>,
}

impl Default for Inventory {
    fn default() -> Inventory {
        Inventory::new()
    }
}

impl Inventory {
    pub fn new() -> Inventory {
        Inventory {
            on_beside: false,
            cursor: [0, 0],
            count: None,
            g: false,
            finding: false,
            filter: String::new(),
            menu: None,
            note: None,
            page: Cell::new(10),
        }
    }

    /// Opens with the cursor on the pile beside you: to pick things up.
    pub fn beside() -> Inventory {
        Inventory { on_beside: true, ..Inventory::new() }
    }

    fn matches(&self, item: &Item) -> bool {
        self.filter.is_empty()
            || item.label().to_lowercase().contains(&self.filter.to_lowercase())
            || item.category().heading().to_lowercase().contains(&self.filter.to_lowercase())
    }

    /// The rows of one list, headings and all.
    fn rows(&self, view: &View, beside: bool) -> Vec<Row> {
        let mut rows = Vec::new();
        let pile: Vec<(Row, &Stack)> = if beside {
            let Some((_, stacks)) = view.beside else { return rows };
            stacks.iter().enumerate().map(|(i, s)| (Row::Beside(i), s)).collect()
        } else {
            let g = view.gear;
            let mut worn = Vec::new();
            for slot in Slot::ALL {
                match g.worn.get(&slot) {
                    Some(a) if self.matches(&Item::Armor(a.clone())) => {
                        worn.push(Row::You(Spot::Worn(slot)));
                    }
                    None if self.filter.is_empty() => worn.push(Row::You(Spot::Worn(slot))),
                    _ => {}
                }
            }
            if !worn.is_empty() {
                rows.push(Row::Heading("WORN"));
                rows.extend(worn);
            }
            let ready: Vec<Row> = [(Spot::Melee, &g.melee), (Spot::Gun, &g.gun)]
                .into_iter()
                .filter(|(_, w)| self.matches(&Item::Weapon((*w).clone())))
                .map(|(spot, _)| Row::You(spot))
                .collect();
            if !ready.is_empty() {
                rows.push(Row::Heading("READY"));
                rows.extend(ready);
            }
            g.pack.iter().enumerate().map(|(i, s)| (Row::You(Spot::Pack(i)), s)).collect()
        };
        for category in Category::ALL {
            let mut these: Vec<&(Row, &Stack)> = pile
                .iter()
                .filter(|(_, s)| s.item.category() == category && self.matches(&s.item))
                .collect();
            if these.is_empty() {
                continue;
            }
            these.sort_by(|a, b| order(view, a, b));
            rows.push(Row::Heading(category.heading()));
            rows.extend(these.into_iter().map(|(row, _)| *row));
        }
        if !beside && let Some(shop) = &view.shop {
            let mut aboard: Vec<(Row, &Stack)> = shop
                .aboard
                .iter()
                .enumerate()
                .filter(|(_, s)| shop.terms.offer(&s.item).is_some() && self.matches(&s.item))
                .map(|(i, s)| (Row::Aboard(i), s))
                .collect();
            aboard.sort_by(|a, b| order(view, a, b));
            let aboard: Vec<Row> = aboard.into_iter().map(|(row, _)| row).collect();
            if !aboard.is_empty() {
                rows.push(Row::Heading("IN YOUR SHIP"));
                rows.extend(aboard);
            }
        }
        rows
    }

    /// The rows you can pick in one list.
    fn picks(&self, view: &View, beside: bool) -> Vec<Row> {
        self.rows(view, beside).into_iter().filter(|r| !matches!(r, Row::Heading(_))).collect()
    }

    fn side(&self, view: &View) -> bool {
        self.on_beside && view.beside.is_some()
    }

    /// The row picked out, if there's anything to pick.
    fn picked(&self, view: &View) -> Option<Row> {
        let side = self.side(view);
        let picks = self.picks(view, side);
        let i = self.cursor[usize::from(side)].min(picks.len().saturating_sub(1));
        picks.get(i).copied()
    }

    fn stack(view: &View, row: Row) -> Option<Stack> {
        match row {
            Row::Heading(_) => None,
            Row::You(spot) => view.gear.get(spot),
            Row::Beside(i) => view.beside.and_then(|(_, s)| s.get(i)).cloned(),
            Row::Aboard(i) => view.shop.as_ref().and_then(|s| s.aboard.get(i)).cloned(),
        }
    }

    /// Everything you can do with what's picked out, with `n` as the count.
    fn acts(view: &View, row: Row, n: u32) -> Vec<Act> {
        let mut acts = Vec::new();
        let Some(stack) = Self::stack(view, row) else { return acts };
        let mut act = |key, what: String, command| acts.push(Act { key, what, command });
        let some = n.clamp(1, stack.count);
        let how_many = |verb: &str| match (stack.count, some) {
            (1, _) => format!("{verb} it"),
            (_, 1) => format!("{verb} one"),
            (_, n) => format!("{verb} {n}"),
        };
        let offer = view.shop.as_ref().and_then(|s| s.terms.offer(&stack.item));
        match row {
            Row::Heading(_) => {}
            Row::You(spot) => {
                match (spot, &stack.item) {
                    (Spot::Pack(i), Item::Weapon(_)) => {
                        act('w', "ready it".into(), Command::Ready(i))
                    }
                    (Spot::Pack(i), Item::Armor(_)) => act('W', "wear it".into(), Command::Wear(i)),
                    (Spot::Worn(slot), _) => {
                        act('T', "take it off".into(), Command::TakeOff(slot));
                    }
                    (Spot::Pack(i), Item::Food(_)) => act('E', "eat one".into(), Command::Eat(i)),
                    (Spot::Pack(_), Item::Medpatch) if view.hurt => {
                        act('a', "use one".into(), Command::UseMedpatch);
                    }
                    _ => {}
                }
                // A ready weapon goes only if there's another to take its place.
                let spared = match spot {
                    Spot::Melee => view.gear.spare(false).is_some(),
                    Spot::Gun => view.gear.spare(true).is_some(),
                    _ => true,
                };
                if let Some(price) = offer.filter(|_| spared) {
                    act('s', format!("sell it for {price} ¤"), Command::Sell(spot));
                }
                if let Some(cost) = mend_cost(view, &stack.item) {
                    act('r', format!("mend it for {cost} ¤"), Command::Mend(spot));
                }
                if spared {
                    act('d', how_many("drop"), Command::Drop(spot, some));
                    if stack.count > 1 {
                        act('D', "drop them all".into(), Command::Drop(spot, stack.count));
                    }
                    if let Some((Beside::Lockers, _)) = view.beside {
                        act('m', how_many("stow"), Command::Stow(spot, some));
                        if stack.count > 1 {
                            act('M', "stow them all".into(), Command::Stow(spot, stack.count));
                        }
                    }
                }
            }
            Row::Beside(i) => match (view.beside, &view.shop) {
                (Some((Beside::Rack, _)), Some(shop)) => {
                    if let Some(price) = shop.terms.asking(&stack.item) {
                        act('b', format!("buy it for {price} ¤"), Command::Buy(i));
                    }
                }
                _ => {
                    act('m', how_many("take"), Command::Fetch(i, some));
                    if stack.count > 1 {
                        act('M', "take them all".into(), Command::Fetch(i, stack.count));
                    }
                }
            },
            Row::Aboard(i) => {
                if let Some(price) = offer {
                    act('s', format!("sell it for {price} ¤"), Command::SellAboard(i));
                }
                if let Some(cost) = mend_cost(view, &stack.item) {
                    act('r', format!("mend it for {cost} ¤"), Command::MendAboard(i));
                }
            }
        }
        if !matches!(row, Row::Beside(_))
            && let Some((n, cost)) = mend_all_cost(view)
            && n > 1
            && matches!(stack.item, Item::Armor(_))
        {
            act('R', format!("mend all {n} for {cost} ¤"), Command::MendAll);
        }
        acts
    }

    fn move_by(&mut self, view: &View, by: isize) {
        let side = self.side(view);
        let last = self.picks(view, side).len().saturating_sub(1);
        let cursor = &mut self.cursor[usize::from(side)];
        *cursor = (*cursor).min(last).saturating_add_signed(by).min(last);
    }

    pub fn key(&mut self, key: KeyEvent, view: &View) -> Reply {
        if self.finding {
            match key.code {
                KeyCode::Enter => self.finding = false,
                KeyCode::Esc => {
                    self.finding = false;
                    self.filter.clear();
                }
                KeyCode::Backspace if self.filter.is_empty() => self.finding = false,
                KeyCode::Backspace => {
                    self.filter.pop();
                }
                KeyCode::Char(c) => self.filter.push(c),
                _ => {}
            }
            self.cursor = [0, 0];
            return Reply::Stay;
        }
        let ctrl = key.modifiers.contains(KeyModifiers::CONTROL);
        if let Some(choice) = self.menu {
            let Some(row) = self.picked(view) else {
                self.menu = None;
                return Reply::Stay;
            };
            let acts = Self::acts(view, row, self.count.unwrap_or(1));
            let last = acts.len().saturating_sub(1);
            let chosen = match key.code {
                KeyCode::Down | KeyCode::Char('j') => {
                    self.menu = Some((choice + 1).min(last));
                    None
                }
                KeyCode::Up | KeyCode::Char('k') => {
                    self.menu = Some(choice.saturating_sub(1));
                    None
                }
                KeyCode::Enter | KeyCode::Char('l') => acts.get(choice),
                KeyCode::Esc | KeyCode::Char('q' | 'h') => {
                    self.menu = None;
                    None
                }
                KeyCode::Char(c) => acts.iter().find(|a| a.key == c),
                _ => None,
            };
            return match chosen {
                Some(act) => {
                    self.menu = None;
                    self.count = None;
                    Reply::Do(act.command)
                }
                None => Reply::Stay,
            };
        }
        if let KeyCode::Char(c @ '0'..='9') = key.code
            && !ctrl
            && (c != '0' || self.count.is_some())
        {
            let digit = c.to_digit(10).unwrap_or(0);
            self.count = Some((self.count.unwrap_or(0) * 10 + digit).min(9999));
            return Reply::Stay;
        }
        let count = self.count.take();
        let n = count.unwrap_or(1);
        let twice = std::mem::take(&mut self.g);
        let half = (self.page.get() / 2).max(1) as isize;
        let side = self.side(view);
        match key.code {
            KeyCode::Char('d') if ctrl => self.move_by(view, half),
            KeyCode::Char('u') if ctrl => self.move_by(view, -half),
            KeyCode::Char('f') if ctrl => self.move_by(view, half * 2),
            KeyCode::Char('b') if ctrl => self.move_by(view, -half * 2),
            KeyCode::PageDown => self.move_by(view, half * 2),
            KeyCode::PageUp => self.move_by(view, -half * 2),
            KeyCode::Down | KeyCode::Char('j') => self.move_by(view, n as isize),
            KeyCode::Up | KeyCode::Char('k') => self.move_by(view, -(n as isize)),
            KeyCode::Home => self.cursor[usize::from(side)] = 0,
            KeyCode::Char('g') if twice => self.cursor[usize::from(side)] = 0,
            KeyCode::Char('g') => self.g = true,
            KeyCode::End | KeyCode::Char('G') => {
                let last = self.picks(view, side).len().saturating_sub(1);
                let to = count.map_or(last, |n| (n as usize).saturating_sub(1).min(last));
                self.cursor[usize::from(side)] = to;
            }
            KeyCode::Left | KeyCode::Char('h') => self.on_beside = false,
            KeyCode::Right | KeyCode::Char('l') => self.on_beside = view.beside.is_some(),
            KeyCode::Tab | KeyCode::BackTab => self.on_beside = !side && view.beside.is_some(),
            KeyCode::Char('/') => {
                self.finding = true;
                self.filter.clear();
                self.cursor = [0, 0];
            }
            KeyCode::Esc if !self.filter.is_empty() => {
                self.filter.clear();
                self.cursor = [0, 0];
            }
            KeyCode::Esc | KeyCode::Char('q' | 'i') => return Reply::Close,
            KeyCode::Char('o') => {
                return self.sort(view, Sort { by: view.sort.by.next(), reversed: false });
            }
            KeyCode::Char('O') => {
                return self.sort(view, Sort { reversed: !view.sort.reversed, ..view.sort });
            }
            KeyCode::Enter => {
                if let Some(row) = self.picked(view)
                    && !Self::acts(view, row, n).is_empty()
                {
                    self.menu = Some(0);
                    self.count = count;
                }
            }
            KeyCode::Char(c) => {
                if let Some(row) = self.picked(view)
                    && let Some(act) = Self::acts(view, row, n).into_iter().find(|a| a.key == c)
                {
                    return Reply::Do(act.command);
                }
                // Wherever the cursor is, at an armourer's.
                if c == 'R' && view.shop.is_some() {
                    return Reply::Do(Command::MendAll);
                }
            }
            _ => {}
        }
        Reply::Stay
    }

    /// Sorts the lists another way, keeping the cursor on what it was on.
    fn sort(&mut self, view: &View, sort: Sort) -> Reply {
        let sorted = View { sort, ..*view };
        for side in [false, true] {
            let picks = self.picks(view, side);
            let at = self.cursor[usize::from(side)].min(picks.len().saturating_sub(1));
            if let Some(row) = picks.get(at) {
                let now = self.picks(&sorted, side).iter().position(|r| r == row);
                self.cursor[usize::from(side)] = now.unwrap_or(0);
            }
        }
        Reply::Sort(sort)
    }

    /// Draws the inventory over the whole of `area`.
    pub fn render(&self, frame: &mut Frame, area: Rect, view: &View) {
        frame.render_widget(Clear, area);
        let [body, foot] =
            Layout::vertical([Constraint::Fill(1), Constraint::Length(2)]).areas(area);
        let wide = body.width >= WIDE;
        // Below the lists, on a short screen the details give up room first.
        let details_height = (body.height * 2 / 5).clamp(6, DETAILS_HEIGHT);
        let (you, beside, details) = match view.beside {
            Some(_) if wide => {
                let [a, b, c] = Layout::horizontal([Constraint::Fill(1); 3]).areas(body);
                (a, Some(b), c)
            }
            Some(_) => {
                let [lists, details] =
                    Layout::vertical([Constraint::Fill(1), Constraint::Length(details_height)])
                        .areas(body);
                let [a, b] = Layout::horizontal([Constraint::Fill(1); 2]).areas(lists);
                (a, Some(b), details)
            }
            None if body.width >= 72 => {
                let [a, c] =
                    Layout::horizontal([Constraint::Fill(3), Constraint::Fill(2)]).areas(body);
                (a, None, c)
            }
            None => {
                let [a, c] =
                    Layout::vertical([Constraint::Fill(1), Constraint::Length(details_height)])
                        .areas(body);
                (a, None, c)
            }
        };
        self.draw_list(frame, you, view, false);
        if let Some(beside) = beside {
            self.draw_list(frame, beside, view, true);
        }
        self.draw_details(frame, details, view);
        self.draw_foot(frame, foot, view.shop.is_some());
    }

    fn draw_list(&self, frame: &mut Frame, area: Rect, view: &View, beside: bool) {
        let focused = self.side(view) == beside;
        let title = if beside {
            match view.beside {
                Some((Beside::Lockers, stacks)) => format!(
                    " LOCKERS · {} / {} kg ",
                    items::kg(items::pile_mass(stacks)),
                    items::kg(LOCKER_CAPACITY)
                ),
                Some((Beside::Floor(here), _)) => format!(" {} ", here.to_uppercase()),
                Some((Beside::Rack, _)) => {
                    format!(" FOR SALE · you have {} ¤ ", view.shop.as_ref().map_or(0, |s| s.scrip))
                }
                None => String::new(),
            }
        } else {
            let g = view.gear;
            format!(
                " YOU · {} / {} kg · {} ",
                items::kg(g.carried()),
                items::kg(g.capacity),
                view.sort.says()
            )
        };
        let colour = if focused { ACCENT } else { DIM };
        let block = Block::bordered()
            .border_style(Style::new().fg(colour))
            .title(Line::from(title).fg(colour).bold());
        let inner = block.inner(area);
        frame.render_widget(block, area);

        let rows = self.rows(view, beside);
        let picked = self.picked(view);
        let height = usize::from(inner.height);
        if focused {
            self.page.set(height);
        }
        let at = rows.iter().position(|r| Some(*r) == picked && focused).unwrap_or(0);
        // Keep the picked row in view, with its heading if there's room.
        let first =
            at.saturating_sub(height.saturating_sub(1) / 2).min(rows.len().saturating_sub(height));
        let width = usize::from(inner.width);
        // Which column is which, over the first heading in sight.
        let mut labelled = false;
        let mut lines: Vec<Line> = rows
            .iter()
            .skip(first)
            .take(height)
            .map(|&row| {
                let line = match row {
                    Row::Heading(text) => {
                        heading(text, width, !std::mem::replace(&mut labelled, true))
                    }
                    _ => self.row_line(view, row, width),
                };
                if Some(row) == picked && focused {
                    line.patch_style(Style::new().add_modifier(Modifier::REVERSED))
                } else {
                    line
                }
            })
            .collect();
        if rows.is_empty() {
            let rack = matches!(view.beside, Some((Beside::Rack, _)));
            let empty = match (beside, self.filter.is_empty()) {
                (_, false) => "Nothing like that.",
                (true, true) if rack => "The rack's bare.",
                (true, true) => "Nothing here.",
                (false, true) => "Nothing on you.",
            };
            lines.push(Line::from(format!(" {empty}")).fg(DIM));
        }
        frame.render_widget(Paragraph::new(lines), inner);
    }

    fn row_line(&self, view: &View, row: Row, width: usize) -> Line<'static> {
        let weighed = width >= NARROW;
        let label = match row {
            Row::Heading(text) => return heading(text, width, true),
            Row::You(Spot::Worn(slot)) => format!("{:<6}", slot.name()),
            Row::You(Spot::Melee) => "melee ".into(),
            Row::You(Spot::Gun) => "gun   ".into(),
            _ => String::new(),
        };
        let Some(stack) = Self::stack(view, row) else {
            return Line::from(vec![
                Span::raw(format!("{INDENT}  {label}")).fg(DIM),
                Span::raw("—").fg(DIM),
            ]);
        };
        let (glyph, colour) = look(&stack.item);
        let mut name = stack.item.label();
        if stack.count > 1 {
            name = format!("{name} ×{}", stack.count);
        }
        if let Item::Weapon(w) = &stack.item
            && let Some(g) = w.gun
        {
            name = format!("{name} {}/{}", w.loaded, g.magazine);
        }
        if let Item::Armor(a) = &stack.item
            && a.durability < a.max_durability
        {
            name = format!("{name} {}/{}", a.durability, a.max_durability);
        }
        let (price, price_colour) = match price(view, row, &stack) {
            Price::Here(n, true) => (n.to_string(), ACCENT),
            Price::Here(n, false) => (n.to_string(), DIM),
            Price::About(n) => (format!("~{n}"), GUESS),
            Price::Unknown => ("?".into(), DIM),
            Price::Nothing => (String::new(), DIM),
        };
        let kg = items::kg(stack.mass());
        let right = columns(width, &kg, &price);
        let used = INDENT.len() + 2 + label.chars().count() + 1 + right.chars().count();
        let room = width.saturating_sub(used);
        let shown: String = name.chars().take(room).collect();
        let pad = room.saturating_sub(shown.chars().count());
        let named = match &stack.item {
            Item::Weapon(w) => w.named,
            Item::Armor(a) => a.named,
            _ => false,
        };
        let name_style = Style::new().fg(rgb(colour));
        let mut spans = vec![
            Span::raw(INDENT),
            Span::raw(glyph.to_string()).fg(rgb(colour)),
            Span::raw(" "),
            Span::raw(label).fg(DIM),
            Span::styled(shown, if named { name_style.bold() } else { name_style }),
            Span::raw(format!("{:pad$} ", "")),
        ];
        if weighed {
            spans.push(Span::raw(format!("{kg:>5}  ")).fg(DIM));
        }
        spans.push(Span::raw(format!("{price:>5} ")).fg(price_colour));
        Line::from(spans)
    }

    fn draw_details(&self, frame: &mut Frame, area: Rect, view: &View) {
        let picked = self.picked(view);
        let stack = picked.and_then(|row| Self::stack(view, row));
        let title = stack.as_ref().map_or(String::new(), |s| format!(" {} ", s.item.label()));
        let block = Block::bordered()
            .border_style(Style::new().fg(DIM))
            .title(Line::from(title).fg(ACCENT).bold())
            .padding(Padding::horizontal(1));
        let inner = block.inner(area);
        frame.render_widget(block, area);
        let Some(row) = picked else { return };
        let mut lines = about(view, row, stack.as_ref());
        let acts = Self::acts(view, row, self.count.unwrap_or(1));
        if !acts.is_empty() {
            lines.push(Line::default());
            match self.menu {
                Some(choice) => {
                    for (i, act) in acts.iter().enumerate() {
                        let line = Line::from(vec![
                            Span::raw(format!(" {} ", act.key)).fg(ACCENT).bold(),
                            Span::raw(format!(" {} ", act.what)),
                        ]);
                        let chosen = i == choice.min(acts.len() - 1);
                        lines.push(if chosen {
                            line.patch_style(Style::new().add_modifier(Modifier::REVERSED))
                        } else {
                            line
                        });
                    }
                }
                None => {
                    let mut spans = Vec::new();
                    for act in &acts {
                        spans.push(Span::raw(act.key.to_string()).fg(ACCENT).bold());
                        spans.push(Span::raw(format!(" {}   ", act.what)).fg(DIM));
                    }
                    lines.push(Line::from(spans));
                }
            }
        }
        frame.render_widget(Paragraph::new(lines).wrap(Wrap { trim: false }), inner);
    }

    fn draw_foot(&self, frame: &mut Frame, area: Rect, shop: bool) {
        let keys: Vec<Span> = if self.finding {
            let mut spans = vec![
                Span::raw(format!("/{}", self.filter)).fg(ACCENT),
                Span::raw("█  ").fg(ACCENT),
            ];
            spans.extend(keys::line(&[("enter", "keep"), ("esc", "clear")]).spans);
            spans
        } else if self.menu.is_some() {
            keys::line(&[("j/k", "choose"), ("enter", "do it"), ("esc", "back")]).spans
        } else {
            let mut hints = vec![
                ("j/k", "move"),
                ("gg/G", "top/end"),
                ("^d/^u", "page"),
                ("h/l", "lists"),
                ("/", "find"),
                ("o/O", "sort"),
                ("enter", "act"),
            ];
            if shop {
                hints.push(("b/s", "buy/sell"));
                hints.push(("r/R", "mend"));
            }
            hints.push(("esc", if shop { "step away" } else { "close" }));
            keys::line(&hints).spans
        };
        // What you're finding, a count you've typed and what just happened,
        // above the keys.
        let mut top = Vec::new();
        if !self.filter.is_empty() && !self.finding {
            top.push(Span::raw(format!(" /{}", self.filter)).fg(ACCENT));
        }
        if let Some(n) = self.count {
            top.push(Span::raw(format!(" {n}…")).fg(ACCENT).bold());
        }
        if let Some(note) = &self.note {
            top.push(Span::raw(format!(" {note}")).fg(ACCENT));
        }
        let lines = vec![Line::from(top), Line::from(keys)];
        frame.render_widget(Paragraph::new(lines), area);
    }
}

/// What's on the right of a row: what it weighs, in kg, and what it would
/// fetch; too narrow for both, only what it'd fetch.
fn columns(width: usize, kg: &str, price: &str) -> String {
    if width >= NARROW { format!("{kg:>5}  {price:>5} ") } else { format!("{price:>5} ") }
}

/// A heading over a kind of thing: "WEAPONS", with which column is which
/// on the right if `units`.
fn heading(text: &str, width: usize, units: bool) -> Line<'static> {
    let mut spans = vec![Span::raw(format!(" {text}")).fg(HEADING).bold()];
    if units {
        let units = columns(width, "kg", "¤");
        let pad = width.saturating_sub(1 + text.chars().count() + units.chars().count());
        spans.push(Span::raw(format!("{:pad$}{units}", "")).fg(DIM));
    }
    Line::from(spans)
}

/// A description as a sentence: "Dense and faintly sweet."
fn sentence(text: &str) -> String {
    capitalise(&format!("{}.", text.trim_end_matches('.')))
}

/// All about what's picked out.
fn about(view: &View, row: Row, stack: Option<&Stack>) -> Vec<Line<'static>> {
    let dim = |text: String| Line::from(text).fg(DIM);
    let Some(stack) = stack else {
        return match row {
            Row::You(Spot::Worn(slot)) => vec![dim(format!("Nothing on your {}.", slot.name()))],
            _ => Vec::new(),
        };
    };
    let mut lines = vec![Line::from(capitalise(&stack.name())).fg(rgb(look(&stack.item).1)).bold()];
    match &stack.item {
        Item::Weapon(w) => weapon_lines(view, w, row, &mut lines),
        Item::Armor(a) => armour_lines(view, a, row, &mut lines),
        Item::Food(f) => {
            lines.push(Line::from(sentence(&f.description)).italic().fg(DIM));
            lines.push(dim("Nothing gets hungry yet.".into()));
        }
        Item::Medpatch => {
            lines.push(Line::from(format!(
                "Stings, then numbs: heals {MEDPATCH_HEAL} and stops bleeding."
            )));
            lines.push(dim("Aboard a wreck, m uses one (or a, here).".into()));
        }
        Item::Artifact(a) if a.identified => {
            lines.push(Line::from(format!("A scholar has told you what it is: {}.", a.true_name)));
            let value = trade::artifact_value(a);
            lines.push(dim(format!("A scholar would give you about {value} ¤ for it.")));
        }
        Item::Artifact(_) => {
            lines.push(Line::from("Something strange, from a wreck."));
            lines.push(dim("A scholar can tell you what it is, and buy it.".into()));
        }
        Item::Salvage(s) => {
            lines.push(Line::from(format!("Worth about {} ¤ to a broker or a station.", s.value)));
        }
    }
    if let Some(shop) = &view.shop {
        match row {
            Row::Beside(_) => {
                if let Some(asking) = shop.terms.asking(&stack.item) {
                    let have = shop.scrip;
                    lines.push(if asking <= have {
                        Line::from(format!("{asking} ¤. You have {have} ¤."))
                    } else {
                        Line::from(format!("{asking} ¤: {} ¤ more than you have.", asking - have))
                            .yellow()
                    });
                }
            }
            _ => {
                if let Some(offer) = shop.terms.offer(&stack.item) {
                    lines.push(Line::from(format!("They'd give you {offer} ¤ for it.")));
                    let alone = match row {
                        Row::You(Spot::Melee) => view.gear.spare(false).is_none(),
                        Row::You(Spot::Gun) => view.gear.spare(true).is_none(),
                        _ => false,
                    };
                    if alone {
                        lines.push(dim("Have another of its sort to ready first.".into()));
                    }
                }
            }
        }
    }
    if let Row::Aboard(_) = row {
        lines.push(dim("In your ship's lockers.".into()));
    }
    let each = items::kg(stack.item.mass());
    let mut weighs = if stack.count > 1 {
        format!("{each} kg each, {} kg in all.", items::kg(stack.mass()))
    } else {
        format!("{each} kg.")
    };
    // Salvage and artifacts say what they're worth already.
    if view.shop.is_none()
        && matches!(stack.item, Item::Weapon(_) | Item::Armor(_))
        && let Some(offer) = trade::typical_offer(&stack.item)
    {
        weighs.push_str(&format!(" An armourer would give you about {offer} ¤ for it."));
    }
    lines.push(dim(weighs));
    lines
}

/// What a row's stack would fetch, or cost: at an armourer's, their price
/// for what they deal in; anywhere else, or for anything else, about what a
/// buyer would give.
fn price(view: &View, row: Row, stack: &Stack) -> Price {
    if let Some(shop) = &view.shop {
        let here = match row {
            Row::Beside(_) => {
                shop.terms.asking(&stack.item).map(|n| Price::Here(n, n <= shop.scrip))
            }
            _ => shop.terms.offer(&stack.item).map(|n| Price::Here(n, true)),
        };
        if let Some(here) = here {
            return here;
        }
    }
    match (&stack.item, trade::typical_offer(&stack.item)) {
        (_, Some(n)) => Price::About(n.saturating_mul(stack.count)),
        (Item::Artifact(_), None) => Price::Unknown,
        _ => Price::Nothing,
    }
}

/// Which of two rows of a pile comes first, within their kind, by the
/// view's sort. Things the sort says nothing about (no price, no
/// durability) go last whichever way round; ties go by name.
fn order(view: &View, a: &(Row, &Stack), b: &(Row, &Stack)) -> std::cmp::Ordering {
    let name = |(_, s): &(Row, &Stack)| s.item.label().to_lowercase();
    let by_name = name(a).cmp(&name(b));
    let sort = view.sort;
    if sort.by == SortBy::Name {
        return if sort.reversed { by_name.reverse() } else { by_name };
    }
    let key = |&(row, s): &(Row, &Stack)| -> Option<f64> {
        let grams = f64::from(s.mass());
        match sort.by {
            SortBy::Name => None,
            SortBy::Weight => Some(grams),
            SortBy::Price => price(view, row, s).amount().map(f64::from),
            SortBy::Density => {
                let n = price(view, row, s).amount()?;
                (grams > 0.0).then(|| f64::from(n) / grams)
            }
            // Most worn first: least left, as a share of whole.
            SortBy::Durability => match &s.item {
                Item::Armor(a) if a.max_durability > 0 => {
                    Some(-f64::from(a.durability) / f64::from(a.max_durability))
                }
                _ => None,
            },
            SortBy::Strength => match &s.item {
                Item::Weapon(w) => {
                    let pellets = w.gun.map_or(1, |g| g.pellets);
                    Some(f64::from(w.damage.0 + w.damage.1) / 2.0 * f64::from(pellets))
                }
                Item::Armor(a) => {
                    Some(f64::from(Dmg::ALL.iter().map(|&d| a.guard(d)).sum::<i32>()))
                }
                _ => None,
            },
            SortBy::Newest => match row {
                Row::You(Spot::Pack(i)) | Row::Beside(i) | Row::Aboard(i) => Some(i as f64),
                _ => None,
            },
        }
    };
    let first = match (key(a), key(b)) {
        (Some(x), Some(y)) => {
            // Highest first, unless turned round.
            let o = y.total_cmp(&x);
            if sort.reversed { o.reverse() } else { o }
        }
        (Some(_), None) => std::cmp::Ordering::Less,
        (None, Some(_)) => std::cmp::Ordering::Greater,
        (None, None) => std::cmp::Ordering::Equal,
    };
    first.then(by_name)
}

/// What the armourer you're at wants to mend `item`, if it's armour that
/// needs it.
fn mend_cost(view: &View, item: &Item) -> Option<u32> {
    let shop = view.shop.as_ref()?;
    let Item::Armor(a) = item else { return None };
    Some(shop.terms.mending(a)).filter(|&cost| cost > 0)
}

/// How many pieces of yours want mending, on you and aboard, and what the
/// armourer you're at wants for all of them.
fn mend_all_cost(view: &View) -> Option<(usize, u32)> {
    let shop = view.shop.as_ref()?;
    let g = view.gear;
    let packed = g.pack.iter().chain(shop.aboard).filter_map(|s| match &s.item {
        Item::Armor(a) => Some(a),
        _ => None,
    });
    let costs: Vec<u32> =
        g.worn.values().chain(packed).map(|a| shop.terms.mending(a)).filter(|&c| c > 0).collect();
    (!costs.is_empty()).then(|| (costs.len(), costs.iter().sum()))
}

fn armour_lines(view: &View, a: &Armor, row: Row, lines: &mut Vec<Line<'static>>) {
    let what = capitalise(&a.description);
    let what = match a.condition {
        Condition::Worn => Some(format!("{what}, worn: it won't last as long.")),
        Condition::Sound if a.named => Some(format!("{what}.")),
        Condition::Sound => None,
        Condition::Fine => Some(format!("{what}, finely made.")),
        Condition::Relic => Some(format!("{what}: a relic, and stronger for it.")),
    };
    lines.extend(what.map(|what| Line::from(what).italic().fg(DIM)));
    let on = match row {
        Row::You(Spot::Worn(_)) => "You wear it",
        _ => "Worn",
    };
    lines.push(Line::from(format!("{on} on your {}. Guards {}.", a.slot.name(), a.guards_text())));
    let mut durability = capitalise(&a.durability_text());
    if a.ruined() {
        durability.push_str(": worn out, it guards nothing until it's mended.");
    } else if a.thin() {
        durability.push_str(": below half, it guards 1 less.");
    } else {
        durability.push('.');
    }
    let line = match mend_cost(view, &Item::Armor(a.clone())) {
        Some(cost) if !matches!(row, Row::Beside(_)) => Line::from(vec![
            Span::raw(durability),
            Span::raw(format!(" Mending it whole: {cost} ¤.")).fg(ACCENT),
        ]),
        _ => Line::from(durability),
    };
    lines.push(match () {
        _ if a.ruined() => line.red(),
        _ if a.thin() => line.yellow(),
        _ => line,
    });
    if !matches!(row, Row::You(Spot::Worn(_))) {
        lines.push(versus_armour(a, view.gear.worn.get(&a.slot)));
    }
    if view.shop.is_none() {
        lines.push(dim_line("Each blow it softens wears it 1. An armourer mends it."));
    }
}

fn dim_line(text: &str) -> Line<'static> {
    Line::from(text.to_string()).fg(DIM)
}

/// How `a` measures up against what you wear in its place, as it is now:
/// "Against your vac-helmet: +1 cut, -1 pierce." Better in green, worse in
/// yellow.
fn versus_armour(a: &Armor, worn: Option<&Armor>) -> Line<'static> {
    let Some(worn) = worn else {
        return dim_line(&format!("You wear nothing on your {} now.", a.slot.name()));
    };
    let mut diffs: Vec<(i32, String)> = Vec::new();
    for dmg in Dmg::ALL {
        let d = a.guard(dmg) - worn.guard(dmg);
        if d != 0 {
            diffs.push((d, format!("{d:+} {}", dmg.name())));
        }
    }
    match (a.stanching(), worn.stanching()) {
        (true, false) => diffs.push((1, "stops bleeding".into())),
        (false, true) => diffs.push((-1, "lets wounds bleed".into())),
        _ => {}
    }
    let kg = |grams: u32| f64::from(grams) / 1000.0;
    let heavier = kg(a.mass) - kg(worn.mass);
    if heavier.abs() >= 0.1 {
        diffs.push((if heavier < 0.0 { 1 } else { -1 }, format!("{heavier:+.1} kg")));
    }
    let mut spans = vec![Span::raw(format!("Against {}: ", worn.yours())).fg(DIM)];
    if diffs.is_empty() {
        spans.push(Span::raw("much the same.").fg(DIM));
    }
    let last = diffs.len().saturating_sub(1);
    for (i, (sign, text)) in diffs.into_iter().enumerate() {
        let span = Span::raw(text);
        spans.push(match sign {
            s if s > 0 => span.green(),
            s if s < 0 => span.yellow(),
            _ => span,
        });
        spans.push(Span::raw(if i == last { "." } else { ", " }).fg(DIM));
    }
    Line::from(spans)
}

fn weapon_lines(view: &View, w: &Weapon, row: Row, lines: &mut Vec<Line<'static>>) {
    let what = match w.condition {
        _ if w.kit => {
            "Your own. Lose everything else aboard a wreck and you keep this.".to_string()
        }
        Condition::Worn => format!("{}, worn: it hits softer.", capitalise(&w.description)),
        Condition::Sound => format!("{}.", capitalise(&w.description)),
        Condition::Fine => format!("{}, finely made.", capitalise(&w.description)),
        Condition::Relic => {
            format!("{}: a relic, and stronger for it.", capitalise(&w.description))
        }
    };
    lines.push(Line::from(what).italic().fg(DIM));
    match row {
        Row::You(Spot::Melee) => lines.push(Line::from("Ready: you hit things with it.")),
        Row::You(Spot::Gun) => lines.push(Line::from("Ready: you fire it.")),
        _ => {}
    }
    lines.extend(w.stats().into_iter().map(Line::from));
    if !matches!(row, Row::You(Spot::Melee | Spot::Gun)) {
        let ready = if w.is_gun() { &view.gear.gun } else { &view.gear.melee };
        lines.push(versus(w, ready));
    }
    lines.push(Line::from(w.dmg.about()).fg(DIM));
    let against = |pick: fn(Affinity) -> bool| {
        let names: Vec<&str> = MONSTERS
            .iter()
            .filter(|k| view.known.contains(&(k.name, w.dmg)) && pick(k.affinity(w.dmg)))
            .map(|k| k.name)
            .collect();
        names.join(", ")
    };
    let good = against(|a| a == Affinity::Weak);
    if !good.is_empty() {
        lines.push(Line::from(vec!["good against ".green(), Span::from(good)]));
    }
    let poor = against(|a| matches!(a, Affinity::Resists | Affinity::Immune));
    if !poor.is_empty() {
        lines.push(Line::from(vec!["poor against ".yellow(), Span::from(poor)]));
    }
}

/// How `w` measures up against the weapon you have ready in its place:
/// "Against your needler: +3 damage, +5 range." Better in green, worse in
/// yellow.
fn versus(w: &Weapon, ready: &Weapon) -> Line<'static> {
    let damage = |w: &Weapon| {
        let (lo, hi) = w.damage;
        f64::from(lo + hi) / 2.0 * f64::from(w.gun.map_or(1, |g| g.pellets))
    };
    let pct = |p: f64| (p * 100.0).round() as i32;
    let mut diffs: Vec<(f64, String)> = Vec::new();
    let d = damage(w) - damage(ready);
    if d.abs() >= 0.25 {
        let d = (d * 2.0).round() / 2.0;
        let shown = if d.fract() == 0.0 { format!("{d:+.0}") } else { format!("{d:+.1}") };
        diffs.push((d, format!("{shown} damage")));
    }
    match (w.gun, ready.gun) {
        (Some(g), Some(r)) => {
            if g.range != r.range {
                diffs
                    .push((f64::from(g.range - r.range), format!("{:+} range", g.range - r.range)));
            }
            if g.magazine != r.magazine {
                let n = i64::from(g.magazine) - i64::from(r.magazine);
                let rounds = if n.abs() == 1 { "round" } else { "rounds" };
                diffs.push((n as f64, format!("{n:+} {rounds}")));
            }
        }
        _ => {
            let hit = pct(w.accuracy) - pct(ready.accuracy);
            if hit != 0 {
                diffs.push((f64::from(hit), format!("{hit:+}% to hit")));
            }
        }
    }
    let crit = pct(w.crit) - pct(ready.crit);
    if crit != 0 {
        diffs.push((f64::from(crit), format!("{crit:+}% crit")));
    }
    if w.dmg != ready.dmg {
        diffs.push((0.0, format!("{} not {}", w.dmg.name(), ready.dmg.name())));
    }
    let mut spans = vec![Span::raw(format!("Against {}: ", ready.yours())).fg(DIM)];
    if diffs.is_empty() {
        spans.push(Span::raw("much the same.").fg(DIM));
    }
    let last = diffs.len().saturating_sub(1);
    for (i, (sign, text)) in diffs.into_iter().enumerate() {
        let span = Span::raw(text);
        spans.push(match sign {
            s if s > 0.0 => span.green(),
            s if s < 0.0 => span.yellow(),
            _ => span,
        });
        spans.push(Span::raw(if i == last { "." } else { ", " }).fg(DIM));
    }
    Line::from(spans)
}

fn capitalise(s: &str) -> String {
    let mut chars = s.chars();
    chars.next().map_or(String::new(), |c| c.to_uppercase().chain(chars).collect())
}

/// Carries out a command that takes no time, outside a wreck: on what you
/// carry, the lockers if they're beside you, and the pile on the floor
/// where you stand. Says how it went.
pub fn carry_out(
    command: Command,
    gear: &mut Gear,
    lockers: Option<&mut Vec<Stack>>,
    floor: &mut Vec<Stack>,
    beside: Option<Beside>,
) -> String {
    let said = |result: Result<String, String>| result.unwrap_or_else(|e| e);
    match command {
        Command::Ready(i) => said(gear.ready(i)),
        Command::Wear(i) => said(gear.wear(i)),
        Command::TakeOff(slot) => said(gear.take_off(slot)),
        Command::Eat(i) => said(gear.eat(i)),
        Command::UseMedpatch => "You're not hurt.".into(),
        Command::Drop(spot, n) => match gear.remove(spot, n) {
            Ok(stack) => {
                let said = format!("You put down {}.", stack.name());
                items::stow(floor, stack);
                said
            }
            Err(said) => said,
        },
        Command::Stow(spot, n) => {
            let Some(lockers) = lockers else { return "There are no lockers here.".into() };
            let Some(stack) = gear.get(spot) else { return "There's nothing there.".into() };
            let n = n.min(stack.count);
            let room = LOCKER_CAPACITY.saturating_sub(items::pile_mass(lockers));
            if stack.item.mass().saturating_mul(n) > room {
                return "The lockers are full.".into();
            }
            match gear.remove(spot, n) {
                Ok(stack) => {
                    let said = format!("You stow {} in the lockers.", stack.name());
                    items::stow(lockers, stack);
                    said
                }
                Err(said) => said,
            }
        }
        Command::Fetch(i, n) => {
            let (pile, from) = match (beside, lockers) {
                (Some(Beside::Lockers), Some(lockers)) => (lockers, " from the lockers"),
                _ => (floor, ""),
            };
            let Some(stack) = pile.get(i) else { return "There's nothing there.".into() };
            let n = n.min(stack.count).min(gear.fits(&stack.item));
            if n == 0 {
                let room = items::kg(gear.room());
                return format!("You've no room for {}: only {room} kg to spare.", stack.name());
            }
            let stack = items::take(pile, i, n);
            let said = format!("You take {}{from}.", stack.name());
            gear.add(stack);
            said
        }
        Command::Buy(_) | Command::Sell(_) | Command::SellAboard(_) => {
            "There's no one here to trade with.".into()
        }
        Command::Mend(_) | Command::MendAboard(_) | Command::MendAll => {
            "There's no armourer here to mend it.".into()
        }
    }
}

/// Takes the stacks lying at `at` out of a list of piles, to work on.
pub fn gather<K: PartialEq + Copy>(piles: &mut Vec<(K, Stack)>, at: K) -> Vec<Stack> {
    let mut here = Vec::new();
    let mut i = 0;
    while i < piles.len() {
        if piles[i].0 == at {
            here.push(piles.remove(i).1);
        } else {
            i += 1;
        }
    }
    here
}

/// Puts back what `gather` took, after.
pub fn scatter<K: Copy>(piles: &mut Vec<(K, Stack)>, at: K, here: Vec<Stack>) {
    piles.extend(here.into_iter().map(|s| (at, s)));
}

/// What's lying at `at` in a list of piles, for showing.
pub fn lying<K: PartialEq>(piles: &[(K, Stack)], at: K) -> Vec<Stack> {
    piles.iter().filter(|(k, _)| *k == at).map(|(_, s)| s.clone()).collect()
}

/// What to say when you step onto things: "There's a cleaver here (g)."
pub fn underfoot(here: &[Stack]) -> Option<String> {
    match here {
        [] => None,
        [one] => Some(format!("There's {} here (g picks it up).", one.name())),
        _ => Some(format!("There are {} things here (g to look).", here.len())),
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::dungeon::{Pos, arms};
    use crate::names::Culture;
    use crate::seed;

    fn press(inv: &mut Inventory, view: &View, code: KeyCode) -> Reply {
        inv.key(KeyEvent::new(code, KeyModifiers::NONE), view)
    }

    fn typed(inv: &mut Inventory, view: &View, keys: &str) -> Vec<Reply> {
        keys.chars().map(|c| press(inv, view, KeyCode::Char(c))).collect()
    }

    fn gear() -> Gear {
        let mut gear = Gear::default();
        gear.add(Stack { item: Item::Medpatch, count: 5 });
        let mut rng = seed::rng(2);
        gear.add(Stack::one(Item::Weapon(arms::find(&mut rng, arms::Source::Crew, false))));
        gear
    }

    #[test]
    fn vim_keys_move_and_counts_count() {
        let gear = gear();
        let known = BTreeSet::new();
        let view = View {
            gear: &gear,
            beside: None,
            known: &known,
            hurt: false,
            shop: None,
            sort: Sort::default(),
        };
        let mut inv = Inventory::new();
        // Worn ×4, ready ×2, then the pack: the torch is ready, so the pack
        // has the found weapon and the medpatches.
        assert_eq!(inv.picks(&view, false).len(), 8);
        typed(&mut inv, &view, "G");
        assert_eq!(inv.picked(&view), Some(Row::You(Spot::Pack(0))), "medpatches come last");
        typed(&mut inv, &view, "gg");
        assert_eq!(inv.picked(&view), Some(Row::You(Spot::Worn(Slot::Head))));
        typed(&mut inv, &view, "5j");
        assert_eq!(inv.picked(&view), Some(Row::You(Spot::Gun)));
        typed(&mut inv, &view, "G");
        let replies = typed(&mut inv, &view, "3d");
        assert_eq!(replies[1], Reply::Do(Command::Drop(Spot::Pack(0), 3)));
        assert_eq!(typed(&mut inv, &view, "D")[0], Reply::Do(Command::Drop(Spot::Pack(0), 5)));
        assert_eq!(typed(&mut inv, &view, "a")[0], Reply::Stay, "no use for one here");
        assert_eq!(press(&mut inv, &view, KeyCode::Esc), Reply::Close);
    }

    #[test]
    fn at_an_armourers_you_buy_off_the_rack_and_sell_what_you_can_spare() {
        // The torch and rivet gun ready, a found weapon and medpatches packed.
        let gear = gear();
        let found = gear.pack.iter().position(|s| matches!(s.item, Item::Weapon(_))).unwrap();
        let mut rng = seed::rng(4);
        let rack: Vec<Stack> = (0..3)
            .map(|_| Stack::one(Item::Weapon(arms::stocked(&mut rng, Culture::Cant, false))))
            .collect();
        let aboard = [Stack::one(Item::Medpatch), rack[0].clone()];
        let terms = trade::armoury_terms(&crate::space::system::generate(1), 0);
        let known = BTreeSet::new();
        let view = View {
            gear: &gear,
            beside: Some((Beside::Rack, &rack)),
            known: &known,
            hurt: false,
            shop: Some(Counter { terms, aboard: &aboard, scrip: 40 }),
            sort: Sort::default(),
        };
        let mut inv = Inventory::beside();
        let Some(Row::Beside(i)) = inv.picked(&view) else { panic!("starts on the rack") };
        assert_eq!(typed(&mut inv, &view, "b")[0], Reply::Do(Command::Buy(i)));
        assert_eq!(typed(&mut inv, &view, "m")[0], Reply::Stay, "you can't just take it");
        press(&mut inv, &view, KeyCode::Char('h'));
        // Only what they'd buy from your lockers, under its own heading.
        let rows = inv.rows(&view, false);
        let heading = rows.iter().position(|r| *r == Row::Heading("IN YOUR SHIP")).unwrap();
        assert_eq!(rows[heading + 1..], [Row::Aboard(1)]);
        typed(&mut inv, &view, "G");
        assert_eq!(typed(&mut inv, &view, "s")[0], Reply::Do(Command::SellAboard(1)));
        let acts = |row| Inventory::acts(&view, row, 1);
        let sells = |row| acts(row).iter().any(|a| a.key == 's');
        assert!(sells(Row::You(Spot::Pack(found))));
        let Item::Weapon(w) = &gear.pack[found].item else { unreachable!() };
        let (spared, alone) =
            if w.is_gun() { (Spot::Gun, Spot::Melee) } else { (Spot::Melee, Spot::Gun) };
        assert!(sells(Row::You(spared)), "ready, with a spare to take its place");
        assert!(!sells(Row::You(alone)), "not with nothing else to fight with");
        assert!(!sells(Row::You(Spot::Pack(1 - found))), "they don't buy medpatches");
        // What they'd pay here, beside what it weighs.
        let item = &gear.pack[found].item;
        let price = terms.offer(item).unwrap();
        let line = inv.row_line(&view, Row::You(Spot::Pack(found)), 40).to_string();
        let kg = items::kg(item.mass());
        assert!(line.ends_with(&format!("{kg:>5}  {price:>5} ")), "{line}");
        assert!(line.starts_with("   ) "), "indented under its heading: {line}");
    }

    #[test]
    fn rows_show_what_things_weigh_and_about_what_theyd_fetch() {
        let mut gear = gear();
        let mut rng = seed::rng(3);
        let scrap = items::Salvage { title: "hull plate".into(), value: 20, mass: 12_000 };
        gear.add(Stack { item: Item::Salvage(scrap), count: 3 });
        gear.add(Stack::one(Item::Artifact(crate::names::artifact(&mut rng))));
        let known = BTreeSet::new();
        let view = View {
            gear: &gear,
            beside: None,
            known: &known,
            hurt: false,
            shop: None,
            sort: Sort::default(),
        };
        let inv = Inventory::new();
        let line = |row| inv.row_line(&view, row, 50).to_string();
        let at = |pick: fn(&Item) -> bool| {
            Row::You(Spot::Pack(gear.pack.iter().position(|s| pick(&s.item)).unwrap()))
        };
        // A whole stack's worth, and its weight.
        assert!(line(at(|i| matches!(i, Item::Salvage(_)))).ends_with(" 36.0    ~60 "));
        assert!(line(at(|i| matches!(i, Item::Artifact(_)))).ends_with("    ? "), "not named yet");
        assert!(line(at(|i| *i == Item::Medpatch)).ends_with("      "), "no one buys them");
        let weapon = at(|i| matches!(i, Item::Weapon(_)));
        let Row::You(Spot::Pack(w)) = weapon else { unreachable!() };
        let about = trade::typical_offer(&gear.pack[w].item).unwrap();
        assert!(line(weapon).ends_with(&format!("~{about} ")));
        // The headings say which column is which.
        let heading = inv.row_line(&view, Row::Heading("WEAPONS"), 50).to_string();
        assert!(heading.starts_with(" WEAPONS") && heading.ends_with("   kg      ¤ "), "{heading}");
        // Too narrow for both, just the price.
        assert!(inv.row_line(&view, weapon, 24).to_string().ends_with(&format!("~{about} ")));
        assert!(!inv.row_line(&view, weapon, 24).to_string().contains(" kg"));
    }

    #[test]
    fn o_sorts_both_lists_within_each_kind_and_o_turns_it_round() {
        let mut gear = Gear::default();
        let scrap = |title: &str, value, mass| {
            Stack::one(Item::Salvage(items::Salvage { title: title.into(), value, mass }))
        };
        gear.add(scrap("brass fitting", 30, 1000));
        gear.add(scrap("hull plate", 20, 12_000));
        gear.add(scrap("coil", 50, 4000));
        gear.add(Stack { item: Item::Medpatch, count: 2 });
        let floor = [scrap("valve", 5, 500), scrap("anchor", 90, 30_000)];
        let known = BTreeSet::new();
        let mut view = View {
            gear: &gear,
            beside: Some((Beside::Floor("on the floor"), &floor)),
            known: &known,
            hurt: false,
            shop: None,
            sort: Sort::default(),
        };
        let mut inv = Inventory::new();
        let salvage = |inv: &Inventory, view: &View, beside: bool| -> Vec<String> {
            inv.rows(view, beside)
                .into_iter()
                .filter_map(|r| Inventory::stack(view, r))
                .filter(|s| matches!(s.item, Item::Salvage(_)))
                .map(|s| s.item.label())
                .collect()
        };
        assert_eq!(salvage(&inv, &view, false), ["brass fitting", "coil", "hull plate"]);
        // On the coil, then sorted heaviest first: the cursor stays on it.
        inv.cursor[0] =
            inv.picks(&view, false).iter().position(|r| *r == Row::You(Spot::Pack(2))).unwrap();
        let Reply::Sort(sort) = press(&mut inv, &view, KeyCode::Char('o')) else { panic!() };
        assert_eq!(sort, Sort { by: SortBy::Weight, reversed: false });
        view.sort = sort;
        assert_eq!(salvage(&inv, &view, false), ["hull plate", "coil", "brass fitting"]);
        assert_eq!(salvage(&inv, &view, true), ["anchor", "valve"], "the floor too");
        assert_eq!(inv.picked(&view), Some(Row::You(Spot::Pack(2))));
        let rows = inv.rows(&view, false);
        let medical = rows.iter().position(|r| *r == Row::Heading("MEDICAL")).unwrap();
        let salvage_at = rows.iter().position(|r| *r == Row::Heading("SALVAGE")).unwrap();
        assert!(medical < salvage_at, "still grouped by kind");

        let Reply::Sort(sort) = press(&mut inv, &view, KeyCode::Char('O')) else { panic!() };
        view.sort = sort;
        assert_eq!(salvage(&inv, &view, false), ["brass fitting", "coil", "hull plate"]);
        assert_eq!(sort.says(), "lightest first");

        view.sort = Sort { by: SortBy::Density, reversed: false };
        assert_eq!(salvage(&inv, &view, false), ["brass fitting", "coil", "hull plate"]);
        view.sort = Sort { by: SortBy::Newest, reversed: false };
        assert_eq!(salvage(&inv, &view, false), ["coil", "hull plate", "brass fitting"]);
        // Round they go, back to names.
        let mut by = SortBy::Name;
        for _ in 0..SortBy::ALL.len() {
            by = by.next();
        }
        assert_eq!(by, SortBy::Name);
    }

    #[test]
    fn worn_armour_sorts_first_by_durability_and_the_rest_after() {
        let mut rng = seed::rng(9);
        let mut gear = Gear::default();
        for left in [10, 2, 6] {
            let mut a = crate::dungeon::armour::stocked(&mut rng, Culture::Cant, false);
            (a.title, a.max_durability, a.durability) = (format!("piece {left}"), 10, left);
            gear.add(Stack::one(Item::Armor(a)));
        }
        let known = BTreeSet::new();
        let mut view = View {
            gear: &gear,
            beside: None,
            known: &known,
            hurt: false,
            shop: None,
            sort: Sort { by: SortBy::Durability, reversed: false },
        };
        let inv = Inventory::new();
        let armour = |view: &View| -> Vec<String> {
            inv.rows(view, false)
                .into_iter()
                .filter_map(|r| match r {
                    Row::You(Spot::Pack(_)) => Inventory::stack(view, r),
                    _ => None,
                })
                .map(|s| s.item.label())
                .collect()
        };
        assert_eq!(armour(&view), ["piece 2", "piece 6", "piece 10"]);
        view.sort.reversed = true;
        assert_eq!(armour(&view), ["piece 10", "piece 6", "piece 2"]);
    }

    #[test]
    fn at_an_armourers_worn_armour_can_be_mended() {
        let mut rng = seed::rng(6);
        let mut piece = crate::dungeon::armour::stocked(&mut rng, Culture::Drift, false);
        let mut gear = Gear::default();
        piece.durability = 1;
        gear.worn.insert(piece.slot, piece.clone());
        let mut spare = piece.clone();
        spare.slot = piece.slot;
        gear.add(Stack::one(Item::Armor(spare)));
        let whole = {
            let mut p = piece.clone();
            p.repair();
            p
        };
        let aboard = [Stack::one(Item::Armor(whole))];
        let terms = trade::armoury_terms(&crate::space::system::generate(1), 0);
        let known = BTreeSet::new();
        let rack = Vec::new();
        let view = View {
            gear: &gear,
            beside: Some((Beside::Rack, &rack)),
            known: &known,
            hurt: false,
            shop: Some(Counter { terms, aboard: &aboard, scrip: 40 }),
            sort: Sort::default(),
        };
        let cost = terms.mending(&piece);
        let acts = Inventory::acts(&view, Row::You(Spot::Worn(piece.slot)), 1);
        let mend = acts.iter().find(|a| a.key == 'r').expect("an act to mend it");
        assert_eq!(mend.what, format!("mend it for {cost} ¤"));
        let all = acts.iter().find(|a| a.key == 'R').expect("and to mend them all");
        assert_eq!(all.what, format!("mend all 2 for {} ¤", cost * 2));
        let whole_acts = Inventory::acts(&view, Row::Aboard(0), 1);
        assert!(!whole_acts.iter().any(|a| a.key == 'r'), "nothing to mend in a whole one");
        // R mends everything from wherever the cursor is.
        let mut inv = Inventory::beside();
        assert_eq!(typed(&mut inv, &view, "R")[0], Reply::Do(Command::MendAll));
        // The list shows how worn it is.
        let line = inv.row_line(&view, Row::You(Spot::Worn(piece.slot)), 60).to_string();
        assert!(line.contains(&format!(" 1/{}", piece.max_durability)), "{line}");
    }

    #[test]
    fn armour_says_how_it_measures_up_to_what_you_wear() {
        let mut rng = seed::rng(6);
        let mut worn = crate::dungeon::armour::stocked(&mut rng, Culture::Drift, false);
        worn.title = "vac-helmet".into();
        worn.guards = [(Dmg::Pierce, 1), (Dmg::Blunt, 1)].into_iter().collect();
        worn.mass = 1800;
        let mut other = worn.clone();
        other.guards = [(Dmg::Cut, 1), (Dmg::Blunt, 1)].into_iter().collect();
        other.mass = 1300;
        assert_eq!(
            versus_armour(&other, Some(&worn)).to_string(),
            "Against your vac-helmet: +1 cut, -1 pierce, -0.5 kg."
        );
        assert!(versus_armour(&other, None).to_string().starts_with("You wear nothing on your"));
    }

    #[test]
    fn a_weapon_says_how_it_measures_up_to_the_one_you_have_ready() {
        let torch = arms::cutting_torch();
        let mut better = torch.clone();
        better.damage = (4, 7);
        better.accuracy = 0.75;
        assert_eq!(
            versus(&better, &torch).to_string(),
            "Against your cutting torch: +2 damage, -5% to hit."
        );
        assert_eq!(
            versus(&torch, &torch).to_string(),
            "Against your cutting torch: much the same."
        );
        let gun = arms::rivet_gun();
        let mut longer = gun.clone();
        longer.gun.as_mut().unwrap().range += 4;
        longer.dmg = Dmg::Shock;
        assert_eq!(
            versus(&longer, &gun).to_string(),
            "Against your rivet gun: +4 range, shock not pierce."
        );
    }

    #[test]
    fn finding_narrows_the_list() {
        let gear = gear();
        let known = BTreeSet::new();
        let view = View {
            gear: &gear,
            beside: None,
            known: &known,
            hurt: true,
            shop: None,
            sort: Sort::default(),
        };
        let mut inv = Inventory::new();
        press(&mut inv, &view, KeyCode::Char('/'));
        typed(&mut inv, &view, "medp");
        press(&mut inv, &view, KeyCode::Enter);
        assert_eq!(inv.picks(&view, false), [Row::You(Spot::Pack(0))]);
        assert_eq!(typed(&mut inv, &view, "a")[0], Reply::Do(Command::UseMedpatch));
        press(&mut inv, &view, KeyCode::Esc);
        assert_eq!(inv.picks(&view, false).len(), 8, "esc clears it");
    }

    #[test]
    fn the_menu_lists_what_you_can_do() {
        let gear = gear();
        let known = BTreeSet::new();
        let lockers = vec![Stack { item: Item::Medpatch, count: 2 }];
        let view = View {
            gear: &gear,
            beside: Some((Beside::Lockers, &lockers)),
            known: &known,
            hurt: false,
            shop: None,
            sort: Sort::default(),
        };
        let mut inv = Inventory::new();
        typed(&mut inv, &view, "G");
        press(&mut inv, &view, KeyCode::Enter);
        assert_eq!(inv.menu, Some(0));
        typed(&mut inv, &view, "jj");
        // drop one, drop them all, stow one, stow them all.
        assert_eq!(
            press(&mut inv, &view, KeyCode::Enter),
            Reply::Do(Command::Stow(Spot::Pack(0), 1))
        );
        typed(&mut inv, &view, "l");
        assert_eq!(typed(&mut inv, &view, "M")[0], Reply::Do(Command::Fetch(0, 2)));
    }

    #[test]
    fn carrying_out_moves_things_about() {
        let mut gear = gear();
        let mut lockers = Vec::new();
        let mut floor = Vec::new();
        let lockers_beside = Some(Beside::Lockers);
        let said = carry_out(
            Command::Stow(Spot::Pack(0), 2),
            &mut gear,
            Some(&mut lockers),
            &mut floor,
            lockers_beside,
        );
        assert_eq!(said, "You stow 2 medpatches in the lockers.");
        assert_eq!((gear.medpatches(), lockers[0].count), (3, 2));
        carry_out(Command::Fetch(0, 9), &mut gear, Some(&mut lockers), &mut floor, lockers_beside);
        assert_eq!((gear.medpatches(), lockers.len()), (5, 0));
        // Your own torch can go, and the blade in your pack takes its place;
        // but not the blade too, with nothing left to hit things with.
        let said = carry_out(Command::Drop(Spot::Melee, 1), &mut gear, None, &mut floor, None);
        assert_eq!(said, "You put down your cutting torch.");
        assert!(!gear.melee.kit);
        let said = carry_out(Command::Drop(Spot::Melee, 1), &mut gear, None, &mut floor, None);
        assert!(said.contains("nothing to hit things with"), "{said}");
        assert_eq!(floor.len(), 1);
        let said = carry_out(
            Command::Fetch(0, 1),
            &mut gear,
            None,
            &mut floor,
            Some(Beside::Floor("on the deck")),
        );
        assert!(said.starts_with("You take"), "{said}");
        assert!(floor.is_empty());
    }

    #[test]
    fn piles_gather_and_scatter() {
        let mut piles = vec![
            (Pos::new(1, 1), Stack::one(Item::Medpatch)),
            (Pos::new(2, 2), Stack::one(Item::Medpatch)),
            (Pos::new(1, 1), Stack { item: Item::Medpatch, count: 3 }),
        ];
        let here = gather(&mut piles, Pos::new(1, 1));
        assert_eq!((here.len(), piles.len()), (2, 1));
        scatter(&mut piles, Pos::new(1, 1), here);
        assert_eq!(lying(&piles, Pos::new(1, 1)).len(), 2);
        assert!(underfoot(&lying(&piles, Pos::new(2, 2))).unwrap().contains("a medpatch"));
    }
}