//! The rules of a crawl: moving, fighting, picking things up, and what the
//! derelict's inhabitants do each turn. Nothing here draws; the scene turns
//! keys into `Action`s and draws whatever state results.

use rand::RngExt;

use super::fov::{self, Fov};
use super::ship;
use super::{Map, Pos, Tile};
use crate::names::Artifact;
use crate::seed::{self, Rng};

/// How far your lamp reaches, in cells.
pub const SIGHT_RADIUS: i32 = 8;
const PLAYER_HP: i32 = 20;
/// Your cutting torch.
const PLAYER_DAMAGE: (i32, i32) = (2, 5);
const PLAYER_HIT: f64 = 0.8;
const MONSTER_HIT: f64 = 0.7;
const MEDPATCH_HEAL: i32 = 8;
const LOG_LENGTH: usize = 50;

pub struct MonsterKind {
    pub name: &'static str,
    pub glyph: char,
    pub rgb: (u8, u8, u8),
    pub hp: i32,
    pub damage: (i32, i32),
    /// As in "the rust-mite bites you".
    pub verb: &'static str,
    /// How common it is, relative to the others.
    pub weight: u32,
    /// At most one aboard any ship.
    pub unique: bool,
}

#[rustfmt::skip]
pub const MONSTERS: &[MonsterKind] = &[
    MonsterKind { name: "rust-mite", glyph: 'm', rgb: (196, 112, 60), hp: 3, damage: (1, 2), verb: "bites", weight: 5, unique: false },
    MonsterKind { name: "maintenance drone", glyph: 'd', rgb: (150, 175, 200), hp: 6, damage: (1, 3), verb: "zaps", weight: 3, unique: false },
    MonsterKind { name: "hollow crewman", glyph: 'h', rgb: (160, 200, 150), hp: 9, damage: (2, 4), verb: "claws at", weight: 2, unique: false },
    MonsterKind { name: "choir-wraith", glyph: 'W', rgb: (200, 150, 255), hp: 14, damage: (3, 6), verb: "sings into", weight: 1, unique: true },
];

pub struct Monster {
    pub kind: &'static MonsterKind,
    pub pos: Pos,
    pub hp: i32,
    /// Dormant until it comes into view; then it hunts you.
    pub awake: bool,
}

pub enum Item {
    Artifact(Artifact),
    Salvage { name: &'static str, value: u32 },
    Medpatch,
}

pub struct Loot {
    pub pos: Pos,
    pub item: Item,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Outcome {
    /// Back through the airlock, with everything carried.
    Escaped,
    Died {
        killer: &'static str,
    },
}

#[derive(Clone, Copy, Debug)]
pub enum Action {
    Move(i32, i32),
    Wait,
    UseMedpatch,
}

pub struct Crawl {
    /// "the Vexant".
    pub name: String,
    /// "Cant hauler".
    pub description: String,
    pub map: Map,
    pub player: Pos,
    pub hp: i32,
    pub max_hp: i32,
    pub monsters: Vec<Monster>,
    pub loot: Vec<Loot>,
    /// What you're carrying. It's only yours once you're back through the airlock.
    pub artifacts: Vec<Artifact>,
    pub scrip: u32,
    pub medpatches: u32,
    pub fov: Fov,
    /// Cells you've seen at some point, drawn from memory when out of sight.
    seen: Vec<bool>,
    /// Messages, oldest first.
    pub log: Vec<String>,
    pub turns: u32,
    pub outcome: Option<Outcome>,
    /// Dice for fights. Separate from the ship's seed, so the same ship and
    /// the same moves always play out the same way.
    rng: Rng,
}

impl Crawl {
    pub fn new(seed: u64) -> Crawl {
        let ship = ship::generate(seed::derive(seed, "ship", 0));
        let cells = (ship.map.width * ship.map.height) as usize;
        let mut crawl = Crawl {
            fov: fov::compute(&ship.map, ship.start, SIGHT_RADIUS),
            name: ship.name,
            description: ship.description,
            map: ship.map,
            player: ship.start,
            hp: PLAYER_HP,
            max_hp: PLAYER_HP,
            monsters: ship.monsters,
            loot: ship.loot,
            artifacts: Vec::new(),
            scrip: 0,
            medpatches: 0,
            seen: vec![false; cells],
            log: Vec::new(),
            turns: 0,
            outcome: None,
            rng: seed::rng(seed::derive(seed, "dice", 0)),
        };
        crawl.say(format!("You board {}, a derelict {}.", crawl.name, crawl.description));
        crawl.look();
        crawl
    }

    pub fn seen(&self, p: Pos) -> bool {
        self.map.contains(p) && self.seen[self.map.index(p)]
    }

    pub fn monster_at(&self, p: Pos) -> Option<&Monster> {
        self.monsters.iter().find(|m| m.pos == p)
    }

    pub fn loot_at(&self, p: Pos) -> Option<&Loot> {
        self.loot.iter().find(|l| l.pos == p)
    }

    /// The name of where you're standing.
    pub fn location(&self) -> &'static str {
        self.map.room_at(self.player).map_or("a dark passage", |r| r.name)
    }

    /// Takes your turn, then everything else's. Does nothing once the crawl
    /// is over, or if the action wouldn't take any time (walking into a wall).
    pub fn act(&mut self, action: Action) {
        if self.outcome.is_some() {
            return;
        }
        let took_time = match action {
            Action::Wait => true,
            Action::Move(dx, dy) => self.step(dx, dy),
            Action::UseMedpatch => self.use_medpatch(),
        };
        if !took_time || self.outcome.is_some() {
            return;
        }
        self.turns += 1;
        self.monsters_act();
        self.look();
    }

    fn say(&mut self, message: String) {
        self.log.push(message);
        if self.log.len() > LOG_LENGTH {
            self.log.remove(0);
        }
    }

    /// Recomputes what you can see, remembers it, and wakes anything that's
    /// now in view (and so, by symmetry, can see you).
    fn look(&mut self) {
        self.fov = fov::compute(&self.map, self.player, SIGHT_RADIUS);
        for p in self.map.positions() {
            if self.fov.contains(p) {
                let i = self.map.index(p);
                self.seen[i] = true;
            }
        }
        let mut woken = Vec::new();
        for m in &mut self.monsters {
            if !m.awake && self.fov.contains(m.pos) {
                m.awake = true;
                woken.push(m.kind.name);
            }
        }
        for name in woken {
            self.say(format!("A {name} stirs and turns toward you."));
        }
    }

    fn step(&mut self, dx: i32, dy: i32) -> bool {
        let target = self.player.offset(dx, dy);
        if let Some(i) = self.monsters.iter().position(|m| m.pos == target) {
            self.attack(i);
            return true;
        }
        match self.map.tile(target) {
            Tile::Door { open: false } => {
                self.map.set(target, Tile::Door { open: true });
                self.say("The door grinds open.".into());
                true
            }
            Tile::Airlock => {
                self.outcome = Some(Outcome::Escaped);
                self.say("You cycle the airlock and cast off.".into());
                true
            }
            tile if tile.walkable() => {
                self.player = target;
                self.pick_up();
                true
            }
            _ => false,
        }
    }

    fn pick_up(&mut self) {
        while let Some(i) = self.loot.iter().position(|l| l.pos == self.player) {
            match self.loot.remove(i).item {
                Item::Artifact(artifact) => {
                    self.say(format!("You find {}.", artifact.unidentified));
                    self.artifacts.push(artifact);
                }
                Item::Salvage { name, value } => {
                    self.scrip += value;
                    self.say(format!("You salvage {name} ({value} ¤)."));
                }
                Item::Medpatch => {
                    self.medpatches += 1;
                    self.say("You pocket a medpatch.".into());
                }
            }
        }
    }

    fn use_medpatch(&mut self) -> bool {
        if self.medpatches == 0 {
            self.say("You have no medpatches.".into());
            return false;
        }
        if self.hp == self.max_hp {
            self.say("You're not hurt.".into());
            return false;
        }
        self.medpatches -= 1;
        let healed = MEDPATCH_HEAL.min(self.max_hp - self.hp);
        self.hp += healed;
        self.say(format!("The medpatch stings, then numbs (+{healed})."));
        true
    }

    fn attack(&mut self, i: usize) {
        let name = self.monsters[i].kind.name;
        self.monsters[i].awake = true;
        if !self.rng.random_bool(PLAYER_HIT) {
            self.say(format!("Your torch misses the {name}."));
            return;
        }
        let damage = self.rng.random_range(PLAYER_DAMAGE.0..=PLAYER_DAMAGE.1);
        self.monsters[i].hp -= damage;
        if self.monsters[i].hp <= 0 {
            self.monsters.remove(i);
            self.say(format!("You burn the {name} down to slag."));
        } else {
            self.say(format!("You burn the {name} ({damage})."));
        }
    }

    /// Each awake monster attacks if it's next to you, or else takes one
    /// step along the shortest path toward you, opening doors on the way.
    fn monsters_act(&mut self) {
        let dist = self.map.distances_from(self.player);
        for i in 0..self.monsters.len() {
            if self.outcome.is_some() {
                return;
            }
            let monster = &self.monsters[i];
            if !monster.awake {
                continue;
            }
            if monster.pos.steps_to(self.player) == 1 {
                self.monster_attacks(i);
                continue;
            }
            let here = dist[self.map.index(monster.pos)].unwrap_or(u32::MAX);
            let next = monster
                .pos
                .neighbours()
                .filter(|&n| self.map.contains(n) && self.monster_at(n).is_none())
                .filter_map(|n| dist[self.map.index(n)].map(|d| (d, n)))
                .filter(|&(d, _)| d < here)
                .min_by_key(|&(d, n)| (d, n.y, n.x));
            if let Some((_, n)) = next {
                if self.map.tile(n) == (Tile::Door { open: false }) {
                    self.map.set(n, Tile::Door { open: true });
                } else {
                    self.monsters[i].pos = n;
                }
            }
        }
    }

    fn monster_attacks(&mut self, i: usize) {
        let kind = self.monsters[i].kind;
        if !self.rng.random_bool(MONSTER_HIT) {
            self.say(format!("The {} misses you.", kind.name));
            return;
        }
        let damage = self.rng.random_range(kind.damage.0..=kind.damage.1);
        self.hp = (self.hp - damage).max(0);
        self.say(format!("The {} {} you ({damage}).", kind.name, kind.verb));
        if self.hp == 0 {
            self.outcome = Some(Outcome::Died { killer: kind.name });
            self.say(format!("You die aboard {}.", self.name));
        }
    }
}

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

    /// A bot that wanders at random, for shaking out panics and broken rules.
    fn wander(crawl: &mut Crawl, rng: &mut Rng, turns: usize) {
        const ACTIONS: [Action; 10] = [
            Action::Move(-1, -1),
            Action::Move(0, -1),
            Action::Move(1, -1),
            Action::Move(-1, 0),
            Action::Move(1, 0),
            Action::Move(-1, 1),
            Action::Move(0, 1),
            Action::Move(1, 1),
            Action::Wait,
            Action::UseMedpatch,
        ];
        for _ in 0..turns {
            crawl.act(ACTIONS[rng.random_range(..ACTIONS.len())]);
        }
    }

    #[test]
    fn random_play_keeps_the_rules() {
        for seed in 0..40 {
            let mut crawl = Crawl::new(seed);
            wander(&mut crawl, &mut seed::rng(seed), 600);
            assert!(crawl.hp >= 0 && crawl.hp <= crawl.max_hp);
            assert!(crawl.map.tile(crawl.player).walkable(), "seed {seed}: player in a wall");
            for m in &crawl.monsters {
                assert!(crawl.map.tile(m.pos).walkable(), "seed {seed}: {} in a wall", m.kind.name);
                assert_ne!(m.pos, crawl.player);
            }
            if crawl.outcome.is_none() {
                assert!(crawl.fov.contains(crawl.player));
            }
        }
    }

    #[test]
    fn same_seed_same_moves_same_story() {
        let play = || {
            let mut crawl = Crawl::new(7);
            wander(&mut crawl, &mut seed::rng(70), 300);
            crawl.log
        };
        assert_eq!(play(), play());
    }

    #[test]
    fn the_airlock_takes_you_home() {
        let mut crawl = Crawl::new(3);
        let airlock = crawl.player.neighbours().find(|&n| crawl.map.tile(n) == Tile::Airlock);
        let airlock = airlock.expect("the start is beside the airlock");
        let (dx, dy) = (airlock.x - crawl.player.x, airlock.y - crawl.player.y);
        crawl.act(Action::Move(dx, dy));
        assert_eq!(crawl.outcome, Some(Outcome::Escaped));
    }

    #[test]
    fn fighting_kills_things() {
        let mut crawl = Crawl::new(5);
        let next_to_player = crawl.player.neighbours().find(|&n| crawl.map.tile(n).walkable());
        let pos = next_to_player.unwrap();
        crawl.monsters = vec![Monster { kind: &MONSTERS[0], pos, hp: 3, awake: true }];
        let (dx, dy) = (pos.x - crawl.player.x, pos.y - crawl.player.y);
        for _ in 0..50 {
            crawl.act(Action::Move(dx, dy));
            if crawl.monsters.is_empty() {
                break;
            }
        }
        assert!(crawl.monsters.is_empty(), "a rust-mite survived 50 swings");
        assert!(crawl.log.iter().any(|m| m.contains("slag")));
    }

    #[test]
    fn walking_into_walls_takes_no_time() {
        let mut crawl = Crawl::new(11);
        let wall = crawl
            .player
            .neighbours()
            .find(|&n| matches!(crawl.map.tile(n), Tile::Wall | Tile::Hull));
        let wall = wall.unwrap();
        crawl.act(Action::Move(wall.x - crawl.player.x, wall.y - crawl.player.y));
        assert_eq!(crawl.turns, 0);
    }
}