//! The game loop and the scene stack.

use std::collections::{BTreeMap, BTreeSet, HashSet};
use std::io;
use std::path::PathBuf;
use std::time::{Duration, Instant};

use ratatui::DefaultTerminal;
use ratatui::crossterm::event::{self, Event, KeyCode, KeyEvent, KeyEventKind, KeyModifiers};

use crate::dungeon::Pos;
use crate::dungeon::arms::Dmg;
use crate::dungeon::crawl::SavedCrawl;
use crate::items::{self, Gear, Item, Stack};
use crate::save::{self, Character, Record};
use crate::scenes::inventory::Sort;
use crate::scenes::{Scene, Transition, title::Title};
use crate::seed;
use crate::space::galaxy::{self, Galaxy};
use crate::space::system::{System, Wreck};
use crate::term::{self, KeyboardCaps};
use crate::trade::Rack;

/// Simulation rate. Real-time scenes (flight) move by this many steps a
/// second; turn-based scenes (dungeons) can ignore ticks and react to keys.
pub const TICKS_PER_SECOND: u32 = 30;
const TICK: Duration = Duration::from_nanos(1_000_000_000 / TICKS_PER_SECOND as u64);
/// After a stall (suspended with ^Z, a slow terminal), run at most this many
/// missed ticks, then carry on from now instead of fast-forwarding.
const MAX_CATCH_UP: u32 = 5;
/// Without key releases, a held key's auto-repeats look like presses. After
/// the scene changes, presses are dropped for as long as they keep coming
/// closer together than this, as auto-repeats do.
const REPEAT_GAP: Duration = Duration::from_millis(150);

/// State every scene can see.
pub struct Ctx {
    /// The universe seed. Everything procedural derives from it (see `seed`).
    pub seed: u64,
    /// Who you're playing.
    pub character: Character,
    /// What they've done.
    pub record: Record,
    /// Ticks since the game started.
    pub ticks: u64,
    pub keyboard: KeyboardCaps,
    /// How many derelicts you've boarded. Each boarding is a different ship,
    /// `derive(seed, "derelict", n)`.
    pub boarded: u64,
    pub hold: Hold,
    /// Wrecks you've boarded, by seed. There's nothing left aboard them.
    pub stripped: HashSet<u64>,
    /// Every star system, and the lanes between them.
    pub galaxy: Galaxy,
    /// Which of the galaxy's systems you're in: an index into `galaxy.sites`.
    pub star: usize,
    /// The systems you've been to. They, and the systems a lane joins to
    /// them, are charted: you can plot a route through them.
    pub visited: BTreeSet<usize>,
    /// The star system you're in, generated whole.
    pub system: System,
    /// What to tell you when you next take the controls, after a journey
    /// the map can describe better than the flight can.
    pub arrival_note: Option<String>,
    /// Days since the game began. It moves on only when you travel, and
    /// everything in the system moves with it.
    pub day: f64,
    /// The day you set out for where you are now, while you're still
    /// there. Wrecks that were calling then are still here, even if their
    /// beacons have failed on the way: you came by their last fix. `None`
    /// after a jump or a tow, which bring you somewhere you didn't choose.
    pub departed: Option<f64>,
    /// Where in the system you are: an index into `system.places`.
    pub location: usize,
    /// Whether your ship is set down at `location`, rather than flying.
    pub landed: bool,
    /// Better lenses fitted to the mining laser.
    pub lenses: u32,
    /// How each kind of monster takes each kind of damage, as far as you've
    /// found out. Unlike what you carry, you keep this whatever happens.
    pub bestiary: BTreeSet<(&'static str, Dmg)>,
    /// The wreck you're aboard, as it stood after your last move, so a save
    /// can bring you back to it. `None` when you're not in one.
    pub crawl: Option<SavedCrawl>,
    /// Armourers' racks you've traded at this fortnight, as you left them.
    pub racks: Vec<Rack>,
    /// How your inventory's lists are sorted.
    pub inventory_sort: Sort,
    /// The folder saves go in. Without one, nothing is saved.
    pub saves: Option<PathBuf>,
    /// This character's save file. There's none until you've made or
    /// loaded a character, and nothing is saved until there is.
    pub slot: Option<PathBuf>,
    /// Why the last save failed, if it did.
    pub save_error: Option<String>,
    /// Keys held down right now. Only kept on terminals that report key
    /// releases (`keyboard.key_release`); elsewhere there's no telling when
    /// a key is let go, and this stays empty.
    held: HashSet<KeyCode>,
    /// Keys that were down when the scene last changed. They don't count as
    /// held, and their auto-repeats are dropped, until they're let go: the
    /// step that takes you out through an airlock shouldn't carry on
    /// walking you about on the other side.
    carried: HashSet<KeyCode>,
    /// The same for terminals that don't report releases: while the scene
    /// has only just changed, when the last key came.
    settling: Option<Instant>,
}

impl Ctx {
    pub fn new(seed: u64, keyboard: KeyboardCaps) -> Ctx {
        let galaxy = galaxy::generate(seed);
        let star = galaxy.home;
        let system = galaxy.system(star);
        // Someone to be until you make a character of your own.
        let culture = system.culture;
        let character = Character {
            name: culture.person(&mut seed::rng(seed::derive(seed, "you", 0))),
            origin: culture,
            ship: culture.word(&mut seed::rng(seed::derive(seed, "your ship", 0))),
        };
        Ctx {
            character,
            record: Record::default(),
            landed: false,
            crawl: None,
            racks: Vec::new(),
            inventory_sort: Sort::default(),
            saves: None,
            slot: None,
            save_error: None,
            location: system.home_place(),
            system,
            galaxy,
            star,
            visited: BTreeSet::from([star]),
            arrival_note: None,
            day: 0.0,
            departed: None,
            lenses: 0,
            bestiary: BTreeSet::new(),
            seed,
            ticks: 0,
            keyboard,
            boarded: 0,
            hold: Hold::default(),
            stripped: HashSet::new(),
            held: HashSet::new(),
            carried: HashSet::new(),
            settling: None,
        }
    }

    /// Starts a new game for `character` in universe `seed`, keeping only
    /// what belongs to the terminal: the clock, the keyboard, where saves go.
    /// The slot is cleared; whoever calls this decides where the new game
    /// saves.
    /// You start at the seat of your own people, on their homeworld.
    pub fn begin(&mut self, seed: u64, character: Character) {
        let mut fresh = Ctx::new(seed, self.keyboard);
        let seat = fresh.galaxy.seat(character.origin);
        if seat != fresh.star {
            fresh.visited.clear();
            fresh.enter_system(seat);
            fresh.location = fresh.system.home_place();
        }
        fresh.character = character;
        fresh.ticks = self.ticks;
        fresh.saves = self.saves.take();
        fresh.held = std::mem::take(&mut self.held);
        fresh.carried = std::mem::take(&mut self.carried);
        fresh.settling = self.settling;
        *self = fresh;
    }

    /// Arrives in another system, at its edge, in flight.
    pub fn enter_system(&mut self, star: usize) {
        self.star = star;
        self.system = self.galaxy.system(star);
        self.visited.insert(star);
        self.location = self.system.edge_place();
        self.landed = false;
        self.departed = None;
    }

    /// Flies to `place` in this system, `days` away.
    pub fn travel(&mut self, place: usize, days: f64) {
        self.departed = Some(self.day);
        self.day += days;
        self.location = place;
    }

    /// The wrecks you know of in this system that you haven't stripped:
    /// those whose beacons are calling, and those here you came by a
    /// failed beacon's last fix. Oldest first.
    pub fn wrecks(&self) -> Vec<Wreck> {
        let s = &self.system;
        let mut wrecks = s.beacons(self.day, &self.stripped);
        wrecks.retain(|w| w.place != self.location);
        wrecks.extend(s.wrecks_at(self.location, self.day, self.departed, &self.stripped));
        wrecks.sort_by(|a, b| a.arrived.total_cmp(&b.arrived));
        wrecks
    }

    /// Whether you're out of fuel somewhere no one sells any.
    pub fn stranded(&self) -> bool {
        self.hold.fuel == 0 && !self.system.sells_fuel()
    }

    /// Saves the game, if there's a character to save.
    pub fn autosave(&mut self) {
        self.save_error = save::write(self).err().map(|e| format!("couldn't save: {e}"));
    }

    pub fn is_held(&self, code: KeyCode) -> bool {
        let code = normalise(code);
        self.held.contains(&code) && !self.carried.contains(&code)
    }

    /// Whether the top scene should get this key event. Keeps track of
    /// which keys are held, too.
    fn admit(&mut self, key: &KeyEvent, now: Instant) -> bool {
        let code = normalise(key.code);
        if self.keyboard.key_release {
            // Scenes get presses and auto-repeats; releases only update
            // which keys are held.
            return match key.kind {
                KeyEventKind::Release => {
                    self.held.remove(&code);
                    self.carried.remove(&code);
                    false
                }
                KeyEventKind::Repeat if self.carried.contains(&code) => false,
                _ => {
                    self.held.insert(code);
                    self.carried.remove(&code);
                    true
                }
            };
        }
        match self.settling {
            _ if key.kind == KeyEventKind::Release => false,
            Some(last) if now.saturating_duration_since(last) < REPEAT_GAP => {
                self.settling = Some(now);
                false
            }
            _ => {
                self.settling = None;
                true
            }
        }
    }

    /// What's on screen changed under keys that are still down, without
    /// the scene changing (a summary popped up over it): treat them as the
    /// scene changing would, so a held key doesn't dismiss it unread.
    pub fn settle(&mut self) {
        self.scene_changed(Instant::now());
    }

    /// The top scene changed: keys still down were for the old one.
    fn scene_changed(&mut self, now: Instant) {
        self.carried.clone_from(&self.held);
        if !self.keyboard.key_release {
            self.settling = Some(now);
        }
    }
}

/// Letters count as the same key whatever the shift state, so releasing
/// shift mid-hold doesn't leave a key stuck down.
fn normalise(code: KeyCode) -> KeyCode {
    match code {
        KeyCode::Char(c) => KeyCode::Char(c.to_ascii_lowercase()),
        other => other,
    }
}

/// Everything you own: money, ore and fuel, what you carry, and what's
/// stowed aboard your ship.
pub struct Hold {
    /// Money, in ¤.
    pub scrip: u32,
    /// Tons of each kind of ore.
    pub ore: BTreeMap<&'static str, u32>,
    /// Tons of ore the hold can carry; cargo racks add more.
    pub ore_capacity: u32,
    /// What's on you: worn, ready and in your pack. It goes everywhere you
    /// go, wrecks too, and if you don't get out of one, all but your own
    /// torch and rivet gun stays there.
    pub gear: Gear,
    /// The ship's lockers, safe aboard whatever happens to you. Shops can
    /// reach them, and send what you buy to them.
    pub lockers: Vec<Stack>,
    /// What you've put down on your ship's deck, and where.
    pub deck: Vec<(Pos, Stack)>,
    /// Jumps' worth of fuel in the tank. Each jump burns one, however long.
    pub fuel: u32,
    /// How many jumps' worth the tank holds; extra tanks add more.
    pub fuel_capacity: u32,
    /// What you owe, in ¤: a tow you couldn't pay for. What you earn pays it
    /// off first.
    pub debt: u32,
}

/// Where something you own is kept, for a shop.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Kept {
    Pack(usize),
    Lockers(usize),
}

impl Kept {
    /// "", or " (in your ship)".
    pub fn note(self) -> &'static str {
        match self {
            Kept::Pack(_) => "",
            Kept::Lockers(_) => " (in your ship)",
        }
    }
}

impl Default for Hold {
    fn default() -> Hold {
        Hold {
            scrip: 0,
            ore: BTreeMap::new(),
            ore_capacity: Hold::BASE_ORE_CAPACITY,
            gear: Gear::default(),
            lockers: Vec::new(),
            deck: Vec::new(),
            fuel: Hold::BASE_FUEL,
            fuel_capacity: Hold::BASE_FUEL,
            debt: 0,
        }
    }
}

impl Hold {
    /// Tons of ore the hold carries before any racks are fitted.
    pub const BASE_ORE_CAPACITY: u32 = 40;
    /// Jumps the tank holds before any extra tanks are fitted.
    pub const BASE_FUEL: u32 = 4;

    /// Takes in money, paying off any debt first. Returns how much went to
    /// the debt.
    pub fn earn(&mut self, amount: u32) -> u32 {
        let paid = amount.min(self.debt);
        self.debt -= paid;
        self.scrip += amount - paid;
        paid
    }

    /// Pays a fee from what you have, and owes the rest. Returns how much
    /// is owed.
    pub fn charge(&mut self, fee: u32) -> u32 {
        let paid = fee.min(self.scrip);
        self.scrip -= paid;
        self.debt += fee - paid;
        fee - paid
    }

    pub fn ore_tons(&self) -> u32 {
        self.ore.values().sum()
    }

    /// Everything a shop can reach: what's in your pack, then what's in
    /// your lockers.
    pub fn kept(&self) -> impl Iterator<Item = (Kept, &Stack)> {
        let pack = self.gear.pack.iter().enumerate().map(|(i, s)| (Kept::Pack(i), s));
        pack.chain(self.lockers.iter().enumerate().map(|(i, s)| (Kept::Lockers(i), s)))
    }

    pub fn kept_mut(&mut self, at: Kept) -> Option<&mut Stack> {
        match at {
            Kept::Pack(i) => self.gear.pack.get_mut(i),
            Kept::Lockers(i) => self.lockers.get_mut(i),
        }
    }

    /// Takes up to `count` of what's kept `at`.
    pub fn take_kept(&mut self, at: Kept, count: u32) -> Stack {
        match at {
            Kept::Pack(i) => items::take(&mut self.gear.pack, i, count),
            Kept::Lockers(i) => items::take(&mut self.lockers, i, count),
        }
    }

    /// You lose everything you were `carrying` but your own torch and rivet
    /// gun. If you'd left one in the lockers, you take it out again.
    pub fn lose_carried(&mut self, carrying: &Gear) {
        let lockers = &mut self.lockers;
        self.gear = carrying.stripped(|gun| {
            let own = |s: &Stack| matches!(&s.item, Item::Weapon(w) if w.kit && w.is_gun() == gun);
            let i = lockers.iter().position(own)?;
            match items::take(lockers, i, 1).item {
                Item::Weapon(w) => Some(w),
                _ => None,
            }
        });
    }

    /// How many artifacts you have, on you and aboard.
    pub fn artifacts(&self) -> u32 {
        self.kept().filter(|(_, s)| matches!(s.item, Item::Artifact(_))).map(|(_, s)| s.count).sum()
    }

    /// How many medpatches you have, on you and aboard.
    pub fn medpatches(&self) -> u32 {
        self.kept().filter(|(_, s)| s.item == Item::Medpatch).map(|(_, s)| s.count).sum()
    }

    /// Puts something you've bought in your pack if there's room, and in
    /// your lockers if not. Says whether it's on you.
    pub fn deliver(&mut self, stack: Stack) -> bool {
        if self.gear.fits(&stack.item) >= stack.count {
            self.gear.add(stack);
            true
        } else {
            items::stow(&mut self.lockers, stack);
            false
        }
    }

    pub fn locker_mass(&self) -> u32 {
        items::pile_mass(&self.lockers)
    }

    pub fn ore_room(&self) -> u32 {
        self.ore_capacity.saturating_sub(self.ore_tons())
    }
}

/// Plays. Given a universe, starts a new character in it; otherwise picks up
/// the character you last played, if there is one.
pub fn run(universe: Option<u64>) -> io::Result<()> {
    let (mut terminal, keyboard) = term::init()?;
    let mut ctx = Ctx::new(universe.unwrap_or_else(seed::from_clock), keyboard);
    ctx.saves = save::default_dir();
    if universe.is_none()
        && let Some(dir) = &ctx.saves
    {
        let last = save::list(dir).into_iter().find(|s| s.summary.is_ok());
        if let Some(slot) = last {
            let _ = save::load(&slot.path, &mut ctx);
        }
    }
    let result = run_loop(&mut terminal, &mut ctx);
    ctx.autosave();
    term::restore(keyboard);
    result
}

/// After the stack changes: the new top scene catches up, and the game is
/// saved.
fn changed(stack: &mut [Box<dyn Scene>], ctx: &mut Ctx) {
    ctx.scene_changed(Instant::now());
    if let Some(top) = stack.last_mut() {
        top.on_top(ctx);
    }
    ctx.autosave();
}

fn run_loop(terminal: &mut DefaultTerminal, ctx: &mut Ctx) -> io::Result<()> {
    let mut stack: Vec<Box<dyn Scene>> = vec![Box::new(Title::new(ctx))];
    let mut next_tick = Instant::now() + TICK;

    while let Some(top) = stack.last() {
        terminal.draw(|frame| top.render(frame, ctx))?;

        // Wait for input until the next tick is due, then take whatever else
        // is already queued without waiting again.
        let mut timeout = next_tick.saturating_duration_since(Instant::now());
        while event::poll(timeout)? {
            timeout = Duration::ZERO;
            let Event::Key(key) = event::read()? else {
                continue;
            };
            if key.code == KeyCode::Char('c') && key.modifiers.contains(KeyModifiers::CONTROL) {
                return Ok(());
            }
            if !ctx.admit(&key, Instant::now()) {
                continue;
            }
            let Some(top) = stack.last_mut() else { break };
            let transition = top.key(key, ctx);
            if apply(&mut stack, transition) {
                changed(&mut stack, ctx);
            }
        }

        let mut caught_up = 0;
        while Instant::now() >= next_tick {
            let Some(top) = stack.last_mut() else { break };
            ctx.ticks += 1;
            let transition = top.tick(ctx);
            if apply(&mut stack, transition) {
                changed(&mut stack, ctx);
            }
            next_tick += TICK;
            caught_up += 1;
            if caught_up == MAX_CATCH_UP {
                next_tick = Instant::now() + TICK;
            }
        }
    }
    Ok(())
}

/// Changes the scene stack, and says whether it did.
fn apply(stack: &mut Vec<Box<dyn Scene>>, transition: Transition) -> bool {
    match transition {
        Transition::None => return false,
        Transition::Push(scene) => stack.push(scene),
        Transition::Open(scenes) => stack.extend(scenes),
        Transition::Pop => {
            stack.pop();
        }
        Transition::Replace(scenes) => {
            stack.pop();
            stack.extend(scenes);
        }
        Transition::Title => stack.truncate(1),
        Transition::Quit => stack.clear(),
    }
    true
}

#[cfg(test)]
mod tests {
    use super::*;

    fn event(code: KeyCode, kind: KeyEventKind) -> KeyEvent {
        KeyEvent::new_with_kind(code, KeyModifiers::NONE, kind)
    }

    #[test]
    fn going_to_the_title_closes_everything_above_it() {
        let ctx = Ctx::new(1, KeyboardCaps { key_release: false });
        let mut stack: Vec<Box<dyn Scene>> = vec![Box::new(Title::new(&ctx))];
        assert!(apply(&mut stack, Transition::Open(crate::scenes::flight::resume(&ctx))));
        assert!(stack.len() > 1);
        assert!(apply(&mut stack, Transition::Title));
        assert_eq!(stack.len(), 1);
    }

    #[test]
    fn keys_held_through_a_change_of_scene_stay_behind() {
        let mut ctx = Ctx::new(1, KeyboardCaps { key_release: true });
        let now = Instant::now();
        assert!(ctx.admit(&event(KeyCode::Left, KeyEventKind::Press), now));
        assert!(ctx.is_held(KeyCode::Left));
        ctx.scene_changed(now);
        assert!(!ctx.is_held(KeyCode::Left));
        assert!(!ctx.admit(&event(KeyCode::Left, KeyEventKind::Repeat), now));
        assert!(ctx.admit(&event(KeyCode::Right, KeyEventKind::Press), now), "others get through");
        assert!(!ctx.admit(&event(KeyCode::Left, KeyEventKind::Release), now));
        assert!(ctx.admit(&event(KeyCode::Left, KeyEventKind::Press), now));
        assert!(ctx.is_held(KeyCode::Left));
    }

    #[test]
    fn without_key_releases_auto_repeats_stay_behind() {
        let mut ctx = Ctx::new(1, KeyboardCaps { key_release: false });
        let start = Instant::now();
        let at = |ms| start + Duration::from_millis(ms);
        let left = event(KeyCode::Left, KeyEventKind::Press);
        ctx.scene_changed(start);
        assert!(!ctx.admit(&left, at(30)));
        assert!(!ctx.admit(&left, at(60)));
        assert!(!ctx.admit(&left, at(150)));
        assert!(ctx.admit(&left, at(400)), "a press after a pause is a new one");
        assert!(ctx.admit(&left, at(420)), "and from then on they all count");
    }
}