//! Entities, zones, order of play, stats and the event log: the game's state.
//! The rules for resolving actions live in `queue.rs`.

use super::card::{Aura, Card, CardDef, CardLibrary};
use super::event::Event;

/// A handle to an entity. Ids are never reused and stay valid when the entity changes zone.
pub type EntityId = u32;
pub type PlayerId = u8;

/// Starting Health of each hero.
pub const HERO_HEALTH: i32 = 30;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Zone {
    Deck,
    Hand,
    Board,
    Graveyard,
}

#[derive(Debug)]
struct Entity {
    card: String,
    owner: PlayerId,
    zone: Zone,
    /// Stamped each time the entity enters the board; `None` until it first does.
    order_of_play: Option<u32>,
    attack: i32,
    /// Current Health. At 0 or below the entity is mortally wounded: still in play until the
    /// Death Creation Step.
    health: i32,
    /// Hit by a destroy effect: still in play until the Death Creation Step.
    pending_destroy: bool,
}

/// An aura in force: which player's minion has it.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct ActiveAura {
    pub owner: PlayerId,
    pub aura: Aura,
}

/// One player's zones. Each is an ordered list of ids (the board is left to right).
#[derive(Debug, Default)]
struct Side {
    deck: Vec<EntityId>,
    hand: Vec<EntityId>,
    board: Vec<EntityId>,
    graveyard: Vec<EntityId>,
    hero: EntityId,
    armor: i32,
}

impl Side {
    fn zone(&self, zone: Zone) -> &Vec<EntityId> {
        match zone {
            Zone::Deck => &self.deck,
            Zone::Hand => &self.hand,
            Zone::Board => &self.board,
            Zone::Graveyard => &self.graveyard,
        }
    }

    fn zone_mut(&mut self, zone: Zone) -> &mut Vec<EntityId> {
        match zone {
            Zone::Deck => &mut self.deck,
            Zone::Hand => &mut self.hand,
            Zone::Board => &mut self.board,
            Zone::Graveyard => &mut self.graveyard,
        }
    }
}

/// Makes a player's choices: called with what is being chosen and the options, it
/// returns one of the options. Hearthstone would ask the player or pick at random.
pub type Chooser = Box<dyn FnMut(&str, &[String]) -> String>;

pub struct World {
    library: CardLibrary,
    chooser: Chooser,
    /// Indexed by `EntityId`.
    entities: Vec<Entity>,
    sides: [Side; 2],
    next_order_of_play: u32,
    log: Vec<Event>,
    /// The auras in force as of the last Aura Update. Changes only there (see `aura.rs`).
    auras: Vec<ActiveAura>,
}

impl World {
    /// A new game: both heroes are in play from the start, so they are the oldest entities.
    pub fn new(library: CardLibrary) -> World {
        let mut world = World {
            library,
            // Until a chooser is set, take the first option.
            chooser: Box::new(|_, options| options[0].clone()),
            entities: Vec::new(),
            sides: Default::default(),
            next_order_of_play: 0,
            log: Vec::new(),
            auras: Vec::new(),
        };
        for owner in 0..2 {
            let id = world.entities.len() as EntityId;
            world.next_order_of_play += 1;
            world.entities.push(Entity {
                card: "Hero".to_string(),
                owner,
                zone: Zone::Board,
                order_of_play: Some(world.next_order_of_play),
                attack: 0,
                health: HERO_HEALTH,
                pending_destroy: false,
            });
            // In play, but not on the board list: the board holds minions only.
            world.sides[owner as usize].hero = id;
        }
        world
    }

    /// Create an entity of `card` for `owner` at the end of `zone` (the right end for the board).
    pub fn create(&mut self, card: &str, owner: PlayerId, zone: Zone) -> EntityId {
        self.create_at(card, owner, zone, None)
    }

    /// Create an entity of `card` for `owner` in `zone` at index `at` (clamped to the
    /// zone's length), or at the end if `at` is `None`.
    pub fn create_at(
        &mut self,
        card: &str,
        owner: PlayerId,
        zone: Zone,
        at: Option<usize>,
    ) -> EntityId {
        assert!(owner < 2, "no player {owner}");
        let def = &self.library.get(card).def;
        let entity = Entity {
            card: def.name.clone(),
            owner,
            zone,
            order_of_play: None,
            attack: def.attack,
            health: def.health,
            pending_destroy: false,
        };
        let id = self.entities.len() as EntityId;
        self.entities.push(entity);
        self.enter(id, zone, at);
        id
    }

    /// Move an entity to the end of `zone` on its owner's side, keeping its id.
    pub fn move_to(&mut self, id: EntityId, zone: Zone) {
        let (owner, from) = (self.entity(id).owner, self.entity(id).zone);
        self.sides[owner as usize]
            .zone_mut(from)
            .retain(|&e| e != id);
        self.enter(id, zone, None);
    }

    /// The single place an entity arrives in a zone. Entering the board starts a new order of play.
    fn enter(&mut self, id: EntityId, zone: Zone, at: Option<usize>) {
        let owner = self.entity(id).owner;
        let list = self.sides[owner as usize].zone_mut(zone);
        list.insert(at.map_or(list.len(), |i| i.min(list.len())), id);
        let entity = &mut self.entities[id as usize];
        entity.zone = zone;
        if zone == Zone::Board {
            self.next_order_of_play += 1;
            entity.order_of_play = Some(self.next_order_of_play);
            self.record(Event::Summoned { id });
        }
    }

    fn entity(&self, id: EntityId) -> &Entity {
        self.entities
            .get(id as usize)
            .unwrap_or_else(|| panic!("unknown entity id {id}"))
    }

    fn entity_mut(&mut self, id: EntityId) -> &mut Entity {
        self.entities
            .get_mut(id as usize)
            .unwrap_or_else(|| panic!("unknown entity id {id}"))
    }

    // ---- Queries -------------------------------------------------------

    pub fn card(&self, name: &str) -> &Card {
        self.library.get(name)
    }

    pub fn has_card(&self, name: &str) -> bool {
        self.library.contains(name)
    }

    /// The cards an Assemble may offer, sorted by name.
    pub fn pool(&self) -> Vec<&Card> {
        self.library.pool()
    }

    pub fn zone_of(&self, id: EntityId) -> Zone {
        self.entity(id).zone
    }

    pub fn card_name(&self, id: EntityId) -> &str {
        &self.entity(id).card
    }

    pub fn owner_of(&self, id: EntityId) -> PlayerId {
        self.entity(id).owner
    }

    /// When the entity last entered the board (larger is later); `None` if it never has.
    pub fn order_of_play(&self, id: EntityId) -> Option<u32> {
        self.entity(id).order_of_play
    }

    /// The ids in one player's zone, in zone order (left to right for the board).
    pub fn zone(&self, owner: PlayerId, zone: Zone) -> &[EntityId] {
        assert!(owner < 2, "no player {owner}");
        self.sides[owner as usize].zone(zone)
    }

    pub fn hero(&self, owner: PlayerId) -> EntityId {
        assert!(owner < 2, "no player {owner}");
        self.sides[owner as usize].hero
    }

    pub fn is_hero(&self, id: EntityId) -> bool {
        self.sides.iter().any(|s| s.hero == id)
    }

    /// Every minion on either board, oldest first (order of play).
    pub fn minions_in_play(&self) -> Vec<EntityId> {
        let mut ids: Vec<EntityId> = self.sides.iter().flat_map(|s| s.board.clone()).collect();
        ids.sort_by_key(|&id| self.order_of_play(id));
        ids
    }

    pub fn attack(&self, id: EntityId) -> i32 {
        self.entity(id).attack
    }

    pub fn health(&self, id: EntityId) -> i32 {
        self.entity(id).health
    }

    /// The cost printed on the entity's card.
    pub fn cost(&self, id: EntityId) -> i32 {
        self.card(self.card_name(id)).def.cost
    }

    /// The minions in a player's hand, in hand order.
    pub fn minions_in_hand(&self, owner: PlayerId) -> Vec<EntityId> {
        self.zone(owner, Zone::Hand)
            .iter()
            .copied()
            .filter(|&id| !self.card(self.card_name(id)).is_spell())
            .collect()
    }

    /// Mortally wounded (0 or less Health) or pending destroy: it leaves play at the next
    /// Death Creation Step.
    pub fn is_doomed(&self, id: EntityId) -> bool {
        let entity = self.entity(id);
        entity.health <= 0 || entity.pending_destroy
    }

    /// Index of a minion on its owner's board, left to right; `None` if it is not on the board.
    pub fn board_index(&self, id: EntityId) -> Option<usize> {
        self.zone(self.owner_of(id), Zone::Board)
            .iter()
            .position(|&e| e == id)
    }

    pub fn armor(&self, owner: PlayerId) -> i32 {
        self.sides[owner as usize].armor
    }

    pub fn active_auras(&self) -> &[ActiveAura] {
        &self.auras
    }

    pub fn log(&self) -> &[Event] {
        &self.log
    }

    // ---- Changes: each one records its event ----------------------------

    pub fn record(&mut self, event: Event) {
        self.log.push(event);
    }

    /// Add a card to the library, or replace the card with the same name.
    pub fn register(&mut self, def: CardDef) {
        self.library.register(def);
    }

    /// Add a card made by Assemble (see `assemble.rs`).
    pub fn register_assembled(&mut self, def: CardDef) {
        self.library.register_assembled(def);
    }

    pub fn set_chooser(&mut self, chooser: Chooser) {
        self.chooser = chooser;
    }

    /// Ask the chooser to pick one of `options` (not empty). Panics if it answers
    /// something that isn't an option.
    pub fn choose(&mut self, kind: &str, options: &[String]) -> String {
        let answer = (self.chooser)(kind, options);
        assert!(
            options.contains(&answer),
            "chooser answered {answer:?} for {kind:?}; the options were {options:?}"
        );
        answer
    }

    /// Only an Aura Update calls this.
    pub fn set_active_auras(&mut self, auras: Vec<ActiveAura>) {
        self.auras = auras;
    }

    pub fn clear_log(&mut self) {
        self.log.clear();
    }

    pub fn damage(&mut self, target: EntityId, amount: i32) {
        self.entity_mut(target).health -= amount;
        self.record(Event::Damaged { target, amount });
    }

    /// Draw the top card of `player`'s deck (the first in the list). An empty deck
    /// records `Fatigue` and changes nothing else.
    pub fn draw(&mut self, player: PlayerId) {
        match self.zone(player, Zone::Deck).first() {
            Some(&id) => {
                self.move_to(id, Zone::Hand);
                self.record(Event::Drew { player, id });
            }
            None => self.record(Event::Fatigue { player }),
        }
    }

    /// Mark for destruction. Nothing leaves play until the Death Creation Step.
    pub fn mark_destroyed(&mut self, id: EntityId) {
        self.entity_mut(id).pending_destroy = true;
    }

    /// Move a minion from play to its owner's graveyard, recording its Death Event.
    pub fn kill(&mut self, id: EntityId, position: usize) {
        self.entity_mut(id).pending_destroy = false;
        self.move_to(id, Zone::Graveyard);
        self.record(Event::Destroyed { id, position });
    }

    pub fn gain_armor(&mut self, player: PlayerId, amount: i32) {
        self.sides[player as usize].armor += amount;
        self.record(Event::ArmorGained { player, amount });
    }

    pub fn buff(&mut self, id: EntityId, attack: i32, health: i32) {
        let entity = self.entity_mut(id);
        entity.attack += attack;
        entity.health += health;
        let (attack, health) = (entity.attack, entity.health);
        self.record(Event::StatsChanged { id, attack, health });
    }

    pub fn gain_attack(&mut self, id: EntityId, amount: i32) {
        let entity = self.entity_mut(id);
        entity.attack += amount;
        let (attack, health) = (entity.attack, entity.health);
        self.record(Event::StatsChanged { id, attack, health });
    }
}