use std::collections::{BTreeMap, HashMap};
use crate::archetype::Archetype;
use crate::archetype::Archetype::Empty;
use crate::font::FontSpec;
use crate::glyph::Glyph;
use crate::log::LogLine;
use crate::object_def::ObjectDef;
use crate::script::Direction;
use crate::utils::{ObjectId, Player, PortalDef, Solid};

/// The complete state of one game board (a single room or screen).
///
/// `Board` is the central data structure of the engine, equivalent to a
/// "board" in ZZT. It contains everything needed to represent and run one
/// self-contained area of the game world:
///
/// - A grid of cells, each with a visual representation ([`Glyph`]) and an [`Archetype`]
/// - The current player position
/// - Scripted objects and portals (loaded but not yet active)
///
/// ## Cell storage
///
/// Cells are stored as `(Glyph, Archetype)` tuples in a row-major `Vec`.
/// Each cell directly owns its visual and behavioral class — there is no
/// separate element palette or index indirection. Access cells with
/// [`Board::get`] and [`Board::get_mut`] using `(x, y)` coordinates.
/// Use [`Board::is_passable`] for collision checks.
pub struct Board {
    /// Human-readable name for this board, loaded from the map file and round-tripped on save.
    pub name: String,
    /// Width of the board in cells.
    pub width: usize,
    /// Height of the board in cells.
    pub height: usize,
    /// Row-major grid of `(Glyph, Archetype)` pairs. Use [`Board::get`] to
    /// access by `(x, y)` coordinates.
    pub(crate) cells: Vec<(Glyph, Archetype)>,
    /// Row-major cache of the visual floor layer: the glyph drawn for a cell when
    /// it would otherwise render as [`Archetype::Empty`]. Computed once at load
    /// from [`floor_spec`](Board::floor_spec) (see [`crate::floor::build_floor`]).
    /// When a map declares no `[floor]`, every entry is black-on-black space (the
    /// historical look of an empty cell). Read it via [`Board::glyph_at`].
    pub(crate) floor: Vec<Glyph>,
    /// The raw `[floor]` declaration, kept so [`crate::map_file::save`] can
    /// round-trip it. `None` when the map declared no floor. (Generators
    /// re-randomize on reload; literal glyph grids are preserved exactly.)
    pub(crate) floor_spec: Option<crate::floor::FloorSpec>,
    /// Current player position. See [`Player`] for caveats about its future.
    pub player: Player,
    /// Scripted objects on this board, keyed by stable [`ObjectId`]. A `BTreeMap`
    /// (not a `Vec`) so an object can be removed without invalidating other
    /// objects' ids; iteration is in ascending-id order, which equals load order
    /// (ids are assigned sequentially as the map loads).
    pub objects: BTreeMap<ObjectId, ObjectDef>,
    /// The next [`ObjectId`] to hand out (starts at 1, monotonically increasing).
    /// See [`Board::add_object`].
    pub next_object_id: ObjectId,
    /// Portals on this board. Parsed from the map file; not yet active.
    pub portals: Vec<PortalDef>,
    /// Optional font override for this board. When `None`, the app default is used.
    pub font: Option<FontSpec>,
    /// Integer scale factor applied to tiles when rendering this board. 1 = natural size.
    pub zoom: u32,
    /// Named Rhai scripts available on this board: script name → source text.
    ///
    /// All script source lives here; [`ObjectDef`]s and [`Board::board_script_name`]
    /// reference entries by name. This means multiple objects can share the same
    /// source while each running instance gets its own Rhai scope at runtime.
    pub scripts: HashMap<String, String>,
    /// Name of the board-level script in [`Board::scripts`], if any.
    ///
    /// A board script runs on the board as a whole (e.g. `on_enter`, `on_tick`)
    /// rather than being tied to a specific object cell.
    pub board_script_name: Option<String>,
    /// Nonfatal problems collected while loading this map (e.g. unknown
    /// archetypes, dropped objects, recovered placement chars), as red-on-black
    /// [`LogLine`]s. Empty for a clean load; see [`Board::is_valid`]. Not part of
    /// the map file (purely a load diagnostic).
    pub(crate) load_errors: Vec<LogLine>,
}

impl Board {
    /// Returns a reference to the cell at `(x, y)`.
    ///
    /// The cell is a `(Glyph, Archetype)` tuple. Panics if `x` or `y` are
    /// out of bounds.
    pub fn get(&self, x: usize, y: usize) -> &(Glyph, Archetype) {
        &self.cells[y * self.width + x]
    }

    /// Returns a mutable reference to the cell at `(x, y)`.
    ///
    /// Panics if `x` or `y` are out of bounds.
    pub fn get_mut(&mut self, x: usize, y: usize) -> &mut (Glyph, Archetype) {
        &mut self.cells[y * self.width + x]
    }

    /// Returns the glyph we should display for a given coordinate:
    ///
    /// - If the coord contains a [`Solid`], use the appropriate glyph for that
    /// - If it contains at least one non-solid object with a glyph other than 0, use one (arbitrarily)
    /// - If it contains any non-Empty archetype, use that glyph
    /// - Fall back to the [`floor`](Board::floor) glyph.
    ///
    /// An `Empty` cell's *own* glyph is intentionally ignored — the floor layer
    /// supersedes it (so a cell vacated by a pushed crate reveals the floor, not
    /// black). Panics if out of bounds.
    pub fn glyph_at(&self, x: usize, y: usize) -> Glyph {
        if let Some(solid) = self.solid_at(x, y) {
            // Use the solid
            return match solid {
                Solid::Player => Glyph::player(),
                Solid::Cell(_) => self.get(x, y).0,
                Solid::Object(id) => self.objects[&id].glyph
            }
        }

        let (glyph, arch) = *self.get(x, y);
        let ids = self.object_ids_at(x, y); // IDs of non-solid (ethereal?) objects

        // Objects with nonzero (nonblank) glyphs take precedence. This allows us to use invisible
        // nonsolid objects on the board.
        if let Some(glyph) = ids.iter().find(|id| self.objects[id].glyph.tile != 0 ).map(|id| self.objects[id].glyph) {
            return glyph
        }

        // Is there a normal archetype?
        if arch != Empty {
            return glyph
        }

        self.floor[y * self.width + x]
    }

    /// Returns `true` if `(x, y)` is a valid cell coordinate on this board.
    ///
    /// Takes signed coords so callers can pass a raw `pos + delta` without first
    /// checking for negatives.
    pub fn in_bounds(&self, pos: (i32, i32)) -> bool {
        let (x, y) = pos;
        x >= 0 && y >= 0 && (x as usize) < self.width && (y as usize) < self.height
    }

    /// Records a nonfatal error: appends `message` as a red-on-black line to the
    /// board's [`load_errors`](Board::load_errors). Used by the map loader (and
    /// available at runtime) to surface recoverable problems.
    pub fn report_error(&mut self, message: impl Into<String>) {
        self.load_errors.push(LogLine::error(message));
    }

    /// Returns `true` if the map loaded with no nonfatal errors (the error list
    /// is empty).
    pub fn is_valid(&self) -> bool {
        self.load_errors.is_empty()
    }
    
    /// Returns the single solid entity occupying `(x, y)`, if any.
    ///
    /// Checks player first, then objects, then the grid archetype. Because at most one solid
    /// may occupy a cell (an invariant enforced when the board is loaded — see
    /// [`crate::map_file`]), this returns that one occupant or `None`.
    /// Panics if `x` or `y` are out of bounds.
    pub fn solid_at(&self, x: usize, y: usize) -> Option<Solid> {
        // The player wins its cell (load-time invariant), so it is the solid there.
        if self.player.x == x as i32 && self.player.y == y as i32 {
            return Some(Solid::Player);
        }
        // A solid object shadows the grid cell it sits on.
        if let Some(id) = self.solid_object_id_at(x, y)
        {
            return Some(Solid::Object(id));
        }
        // Otherwise the grid archetype itself may be solid (e.g. a wall).
        let arch = self.get(x, y).1;
        if arch.behavior().solid {
            return Some(Solid::Cell(arch));
        }
        None
    }

    /// Returns `true` if a mover can enter `(x, y)` — i.e. no solid occupies it.
    ///
    /// Convenience inverse of [`solid_at`](Board::solid_at).
    /// Panics if `x` or `y` are out of bounds.
    pub fn is_passable(&self, x: usize, y: usize) -> bool {
        self.solid_at(x, y).is_none()
    }

    /// Whether the cell's single solid occupant (if any) can be pushed in `dir`.
    ///
    /// Non-solid things are never pushable: `pushable` only matters for solids.
    /// Grid archetypes may restrict the axis (see [`Pushable`]); pushable objects
    /// can be shoved in any direction.
    fn is_pushable(&self, x: usize, y: usize, dir: Direction) -> bool {
        match self.solid_at(x, y) {
            Some(Solid::Player) => true, // the player is pushable in any direction
            Some(Solid::Cell(a)) => a.behavior().pushable.allows(dir),
            Some(Solid::Object(id)) => self.objects[&id].pushable,
            None => false,
        }
    }

    /// Whether the chain of pushable solids starting at `(x, y)` can be shoved one
    /// step in `dir` — i.e. the chain ends at a passable cell rather than the board
    /// edge or a non-pushable solid.
    ///
    /// Read-only (`&self`); pairs with [`push`](Board::push). Returns `false` when
    /// `(x, y)` itself holds no pushable solid, so it doubles as the "is the cell
    /// ahead shovable?" half of a "can I move here?" query.
    pub fn can_push(&self, x: usize, y: usize, dir: Direction) -> bool {
        let (dx, dy): (i32, i32) = dir.into();
        let (mut cx, mut cy) = (x, y);
        loop {
            // This cell must hold a solid pushable in `dir` to advance the chain.
            if !self.is_pushable(cx, cy, dir) {
                return false;
            }
            let next = (cx as i32 + dx, cy as i32 + dy);
            if !self.in_bounds(next) {
                return false; // chain runs off the board
            }
            let (nx, ny) = (next.0 as usize, next.1 as usize);
            if self.is_passable(nx, ny) {
                return true; // open space at the end: the whole chain can move
            }
            // Next cell holds a solid too; continue (it must itself be pushable).
            cx = nx;
            cy = ny;
        }
    }

    /// Shoves the chain of pushable solids starting at `(x, y)` one step in `dir`,
    /// leaving `Empty` floor behind each moved cell.
    ///
    /// No-op when the chain can't move (it self-checks via [`can_push`](Board::can_push)),
    /// so it is safe to call unconditionally.
    pub fn push(&mut self, x: usize, y: usize, dir: Direction) {
        if !self.can_push(x, y, dir) {
            return;
        }
        let (dx, dy): (i32, i32) = dir.into();
        // can_push guaranteed the chain ends at an in-bounds passable cell, so
        // re-walk it (no bounds checks needed) and shift the far end first, which
        // keeps each destination cell vacated before its occupant arrives.
        let mut chain: Vec<(usize, usize)> = Vec::new();
        let (mut cx, mut cy) = (x, y);
        while !self.is_passable(cx, cy) {
            chain.push((cx, cy));
            cx = (cx as i32 + dx) as usize;
            cy = (cy as i32 + dy) as usize;
        }
        for &(px, py) in chain.iter().rev() {
            self.shift_solid(px, py, dx, dy);
        }
    }

    /// Moves the single solid occupant of `(x, y)` one step by `(dx, dy)`.
    ///
    /// A solid object is relocated; otherwise the grid archetype (a crate) is
    /// moved, leaving `Empty` floor behind (the grid has no separate floor layer).
    /// The caller guarantees the destination is already clear.
    fn shift_solid(&mut self, x: usize, y: usize, dx: i32, dy: i32) {
        let (tx, ty) = ((x as i32 + dx) as usize, (y as i32 + dy) as usize);
        // The player owns its cell, so move it before considering objects/grid.
        if self.player.x == x as i32 && self.player.y == y as i32 {
            self.player.x = tx as i32;
            self.player.y = ty as i32;
        } else if let Some(id) = self.solid_object_id_at(x, y)
        {
            let obj = self.objects.get_mut(&id).expect("id from object_id_at");
            obj.x = tx;
            obj.y = ty;
        } else {
            let moved = *self.get(x, y);
            *self.get_mut(tx, ty) = moved;
            *self.get_mut(x, y) = (Archetype::Empty.default_glyph(), Archetype::Empty);
        }
    }

    /// Returns the [`ObjectId`]s of the objects at `(x, y)`, if any.
    pub fn object_ids_at(&self, x: usize, y: usize) -> Vec<ObjectId> {
        self.objects
            .iter()
            .filter(|(_, o)| o.x == x && o.y == y)
            .map(|(&id, _)| id).collect()
    }

    /// Returns a borrow of the actual object at `(x, y)` if any
    pub fn solid_object_id_at(&self, x: usize, y: usize) -> Option<ObjectId> {
        self.objects
            .iter()
            .find_map(|(&id, o)| {
                if o.x == x && o.y == y && o.solid {
                    Some(id)
                } else {
                    None
                }
            })
    }

    /// Inserts `object`, assigning it the next free [`ObjectId`], and returns that id.
    ///
    /// Ids start at 1 and increase monotonically; an id is never reused, so it
    /// stays a valid handle to this object for the board's lifetime.
    pub fn add_object(&mut self, object: ObjectDef) -> ObjectId {
        let id = self.next_object_id;
        self.next_object_id += 1;
        self.objects.insert(id, object);
        id
    }
}

#[cfg(test)]
pub(crate) mod tests {
    use std::collections::{BTreeMap, HashMap};
    use color::Rgba8;
    use crate::archetype::Archetype;
    use crate::glyph::Glyph;
    use crate::object_def::ObjectDef;
    use crate::script::Direction;
    use crate::utils::{ObjectId, Player, Solid};
    use super::Board;

    /// Builds an all-empty `w×h` board with the given player position, objects,
    /// and `(name, source)` scripts. Assigns sequential ids (1..=n) to objects.
    pub(crate) fn open_board(
        w: usize,
        h: usize,
        player: (i32, i32),
        objects: Vec<ObjectDef>,
        scripts: &[(&str, &str)],
    ) -> Board {
        let mut object_map: BTreeMap<ObjectId, ObjectDef> = BTreeMap::new();
        let mut next_object_id: ObjectId = 1;
        for o in objects {
            object_map.insert(next_object_id, o);
            next_object_id += 1;
        }
        Board {
            name: "test".into(),
            width: w,
            height: h,
            cells: vec![(Archetype::Empty.default_glyph(), Archetype::Empty); w * h],
            floor: vec![Archetype::Empty.default_glyph(); w * h],
            floor_spec: None,
            player: Player { x: player.0, y: player.1 },
            objects: object_map,
            next_object_id,
            portals: Vec::new(),
            font: None,
            zoom: 1,
            scripts: scripts.iter().map(|(k, v)| (k.to_string(), v.to_string())).collect::<HashMap<_,_>>(),
            board_script_name: None,
            load_errors: Vec::new(),
        }
    }

    /// Stamps a crate cell onto a board.
    pub(crate) fn crate_at(board: &mut Board, x: usize, y: usize) {
        *board.get_mut(x, y) = (Archetype::Crate.default_glyph(), Archetype::Crate);
    }

    /// Stamps a wall cell onto a board.
    pub(crate) fn wall_at(board: &mut Board, x: usize, y: usize) {
        *board.get_mut(x, y) = (Archetype::Wall.default_glyph(), Archetype::Wall);
    }

    /// Stamps an arbitrary archetype cell onto a board.
    pub(crate) fn stamp(board: &mut Board, x: usize, y: usize, arch: Archetype) {
        *board.get_mut(x, y) = (arch.default_glyph(), arch);
    }

    #[test]
    fn solid_at_reports_wall_object_and_empty() {
        let mut board = open_board(4, 1, (3, 0), vec![], &[]);
        board.cells[1] = (Archetype::Wall.default_glyph(), Archetype::Wall);
        board.add_object(ObjectDef::new(2, 0));

        assert!(board.solid_at(0, 0).is_none());
        assert!(board.is_passable(0, 0));

        match board.solid_at(1, 0) {
            Some(Solid::Cell(Archetype::Wall)) => {}
            other => panic!("expected Solid::Cell(Wall), got {:?}", other.is_some()),
        }
        assert!(!board.is_passable(1, 0));

        match board.solid_at(2, 0) {
            Some(Solid::Object(id)) => assert_eq!((board.objects[&id].x, board.objects[&id].y), (2, 0)),
            _ => panic!("expected Solid::Object"),
        }
        assert!(!board.is_passable(2, 0));
    }

    #[test]
    fn non_solid_object_does_not_block() {
        let mut obj = ObjectDef::new(1, 0);
        obj.solid = false;
        let board = open_board(3, 1, (0, 0), vec![obj], &[]);
        assert!(board.solid_at(1, 0).is_none());
        assert!(board.is_passable(1, 0));
    }

    #[test]
    fn solid_at_reports_player() {
        let board = open_board(3, 1, (1, 0), vec![], &[]);
        match board.solid_at(1, 0) {
            Some(Solid::Player) => {}
            _ => panic!("expected Solid::Player at the player's cell"),
        }
        assert!(!board.is_passable(1, 0));
    }

    #[test]
    fn in_bounds_checks_grid_boundaries() {
        let board = open_board(3, 2, (0, 0), vec![], &[]);
        assert!(board.in_bounds((0, 0)));
        assert!(board.in_bounds((2, 1)));
        assert!(!board.in_bounds((-1, 0)));
        assert!(!board.in_bounds((0, -1)));
        assert!(!board.in_bounds((3, 0)));
        assert!(!board.in_bounds((0, 2)));
    }

    #[test]
    fn can_push_is_read_only_and_correct() {
        let mut board = open_board(3, 1, (0, 0), vec![], &[]);
        crate_at(&mut board, 1, 0);
        assert!(board.can_push(1, 0, Direction::East));
        assert_eq!(board.get(1, 0).1, Archetype::Crate); // no mutation
        assert_eq!(board.get(2, 0).1, Archetype::Empty);

        let mut board = open_board(3, 1, (0, 0), vec![], &[]);
        crate_at(&mut board, 1, 0);
        wall_at(&mut board, 2, 0);
        assert!(!board.can_push(1, 0, Direction::East));
    }

    #[test]
    fn push_into_player_pushes_player() {
        // Crate shoved east into the player slides the player along into open space.
        let mut board = open_board(4, 1, (2, 0), vec![], &[]);
        crate_at(&mut board, 1, 0);
        assert!(board.can_push(1, 0, Direction::East));
        board.push(1, 0, Direction::East);
        assert_eq!(board.get(1, 0).1, Archetype::Empty);
        assert_eq!(board.get(2, 0).1, Archetype::Crate);
        assert_eq!((board.player.x, board.player.y), (3, 0));
    }

    #[test]
    fn push_into_player_blocked_by_wall() {
        // Player backed against a wall: push has nowhere to go, nothing moves.
        let mut board = open_board(4, 1, (2, 0), vec![], &[]);
        crate_at(&mut board, 1, 0);
        wall_at(&mut board, 3, 0);
        assert!(!board.can_push(1, 0, Direction::East));
        board.push(1, 0, Direction::East); // no-op
        assert_eq!(board.get(1, 0).1, Archetype::Crate);
        assert_eq!((board.player.x, board.player.y), (2, 0));
    }

    #[test]
    fn glyph_at_uses_floor_for_empty_and_grid_for_solid() {
        // Player parked at (2,0) so it doesn't overlap either asserted cell.
        let mut board = open_board(3, 1, (2, 0), vec![], &[]);
        let floor_glyph = Glyph {
            tile: '.' as u32,
            fg: Rgba8 { r: 10, g: 20, b: 30, a: 255 },
            bg: Rgba8 { r: 1, g: 2, b: 3, a: 255 },
        };
        board.floor = vec![floor_glyph; 3];
        wall_at(&mut board, 0, 0);
        assert_eq!(board.glyph_at(0, 0), Archetype::Wall.default_glyph());
        assert_eq!(board.glyph_at(1, 0), floor_glyph);
    }

    #[test]
    fn fresh_board_is_valid_and_reports_errors() {
        let mut board = open_board(1, 1, (0, 0), vec![], &[]);
        assert!(board.is_valid());
        board.report_error("something went wrong");
        assert!(!board.is_valid());
        assert_eq!(board.load_errors.len(), 1);
    }
}