use crate::floor::Floor;
use crate::fov::{color_to_rgb, FovCaster, Lighting};
use crate::glyph::Glyph;
use crate::utils::{Direction, Point};
use crate::utils::{ObjectId, RegistryValue};
use std::collections::{HashMap, HashSet};
use crate::portal::Portal;
use crate::tile::{DrawLayer, Hookable, IntoTile, LocatedObject, ScriptAttributes, Sensor, Tile, TileSpec};

/// 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.
///
/// `Board` derives [`Clone`] to support deep-copying a whole [`World`](crate::world::World)
/// (see [`World::deep_clone`](crate::world::World::deep_clone)) — e.g. the editor's
/// playtest runs a game against an isolated copy so play mutations never touch the
/// boards being edited.
#[derive(Clone)]
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,
    /// The single row-major grid of `Option<Tile>` cells (`width * height`),
    /// holding every solid. A transparent cell (glyph tile 0)
    /// draws nothing, revealing a `Sensor` or the
    /// [`floor`](Board::floor) beneath. Access a cell with [`Board::get`]/
    /// [`Board::get_mut`] by `(x, y)`.
    pub(crate) grid: Vec<Option<Tile>>,
    /// The board's cosmetic floor (blank / one fixed glyph / a biome), drawn beneath
    /// everything.
    pub(crate) floor: Floor,
    /// Non-solid things placed off the main grid, can't affect movement but see other hooks
    pub sensors: Vec<Sensor>,
    /// The portals aren't really a kind of sensor, and they can't be on the grid because the player
    /// can share a space with them:
    pub portals: Vec<Portal>,
    /// The next [`ObjectId`] to hand out (starts at 1, monotonically increasing).
    /// See [`Board::add_object`].
    pub next_object_id: ObjectId,
    /// When `true`, this board is "dark": front-ends reveal only the cells the
    /// player can see and that receive light (see [`Board::lighting`]) and draw
    /// everything else as unlit darkness. Sight and light are blocked by opaque cells.
    /// Loaded from / saved to the `dark` key in the map file's `[map]` header;
    /// defaults to `false` (fully lit).
    pub dark: bool,
    /// Per-board key→value store written and read by Rhai scripts via the
    /// `Registry` scope constant. Persists automatically across board transitions
    /// because all boards live as `Rc<RefCell<Board>>` in `World::boards` and are
    /// never evicted. Not saved to disk in v1.
    pub registry: HashMap<String, RegistryValue>,
}

impl Board {
    /// Return a list of all `ObjectId`s currently on the board.
    pub fn all_ids(&self) -> Vec<ObjectId> {
        let mut grid_ids = self.grid.iter().filter_map(|cell| {
            if let Some(Tile::Object(def)) = cell {
                Some(def.scripting.id)
            } else {
                None
            }
        }).collect::<Vec<_>>();
        grid_ids.extend(self.sensors.iter().map(|s| s.scripting.id));
        grid_ids.sort();
        grid_ids
    }

    /// Returns a reference to the `(Glyph, Archetype)` cell at `(x, y)`.
    ///
    /// Panics if `x` or `y` are out of bounds.
    pub fn get<P: Into<Point>>(&self, p: P) -> &Option<Tile> {
        let p = p.into();
        &self.grid[p.uy() * self.width + p.ux()]
    }

    /// Returns a mutable reference to the cell at `(x, y)`.
    ///
    /// Panics if `x` or `y` are out of bounds.
    pub fn get_mut<P: Into<Point>>(&mut self, p: P) -> &mut Option<Tile> {
        let p = p.into();
        let w = self.width;
        &mut self.grid[p.uy() * w + p.ux()]
    }

    /// Replace the solid terrain (if any) at `(x, y)` with a transparent `Empty`
    /// cell, revealing the floor beneath.
    pub fn clear_cell<P: Into<Point>>(&mut self, p: P) {
        let p = p.into();
        if self.in_bounds(p) {
            *self.get_mut(p) = None;
        }
    }

    /// Returns the glyph to display at `(x, y)`.
    ///
    /// With a single grid the draw order is a fixed precedence (no layer walk):
    ///
    /// 1. a sensor `Above` the grid whose glyph is visible (drawn on top of the
    ///    player too);
    /// 2. the grid cell's tile — the player or an object — when its glyph is
    ///    visible (`tile != 0`, so invisible objects exist);
    /// 3. a sensor `Below` the grid whose glyph is visible (only reachable
    ///    because the grid cell drew nothing);
    /// 4. a portal at the cell (portals sit on a transparent grid cell), when
    ///    its glyph is visible;
    /// 5. the [`floor`](Board::floor) glyph, if any;
    /// 6. the canonical black `Empty` glyph.
    ///
    /// Panics if out of bounds.
    pub fn glyph_at<P: Into<Point>>(&self, p: P) -> Glyph {
        let p = p.into();
        let grid_glyph = self.get(p).as_ref().map(Tile::glyph);

        let sensors = self.sensors.iter().filter(|&s| s.location == p);

        // Is there a sensor above the grid?
        if let Some(above) = sensors.clone().find(|s| s.draw_layer == DrawLayer::Above && s.scripting.glyph.is_visible()) {
            return above.scripting.glyph;
        }

        // Does the grid have a good glyph?
        if let Some(glyph) = grid_glyph && glyph.is_visible() {
            return glyph;
        }

        // Is there a sensor below the grid?
        if let Some(below) = sensors.clone().find(|s| s.draw_layer == DrawLayer::Below && s.scripting.glyph.is_visible()) {
            return below.scripting.glyph;
        }

        // A portal at the cell, if its glyph is visible (a `tile = 0` portal is
        // deliberately invisible, so the floor shows through instead).
        if let Some(portal) = self.portal_at(p) && portal.glyph.is_visible() {
            return portal.glyph;
        }

        // Otherwise the floor, or the canonical black empty cell.
        self.floor.glyph_at(p, self.width).unwrap_or_else(Glyph::transparent)
    }

    /// 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<P: Into<Point>>(&self, pos: P) -> bool {
        let p = pos.into();
        p.x >= 0 && p.y >= 0 && p.ux() < self.width && p.uy() < self.height
    }

    /// Returns `true` if cell `(x, y)` blocks line of sight (and light).
    ///
    /// A cell is sight-blocking if its grid terrain is opaque (e.g. a `Wall`)
    /// **or** any object on it is opaque. This is the input to lighting on
    /// [`dark`](Board::dark) boards; see [`Board::lighting`].
    /// Panics if `x` or `y` are out of bounds.
    pub fn is_opaque_at<P: Into<Point>>(&self, p: P) -> bool {
        let p = p.into();
        if self.sensors.iter().any(|s| s.location == p && s.scripting.optics.opaque) {
            true
        } else {
            match self.get(p) {
                None => false,
                Some(Tile::Player) => false,
                Some(Tile::Object(def)) => {
                    def.scripting.optics.opaque
                }
            }
        }
    }

    /// Computes lighting + line-of-sight for the player on this board.
    ///
    /// Returns `None` unless the board is [`dark`](Board::dark) — a lit board
    /// needs no lighting and front-ends draw every cell at full color. On a dark
    /// board it (a) casts an unbounded line-of-sight field from the player, then
    /// (b) accumulates colored light from every source — the player's torch
    /// (radius `player_torch`, white), each object with `light > 0`, and each
    /// terrain cell with [`Archetype::light`] `> 0` — each source colored by its
    /// own glyph fg and falling off linearly to its radius. Opaque cells (via
    /// [`is_opaque_at`](Board::is_opaque_at)) block both sight and light.
    pub fn lighting(&self, player_torch: u32) -> Option<Lighting> {
        if !self.dark {
            return None;
        }
        let (w, h) = (self.width, self.height);
        let mut lighting = Lighting::new(w, h);
        // One caster whose transparency is seeded once from the opaque cells;
        // reused for the LOS pass and every light source (its FOV is cleared per cast).
        let mut caster = FovCaster::new(w, h, |x, y| !self.is_opaque_at((x, y)));

        let (px, py) = {
            let p = self.player_pos();
            (p.ux(), p.uy())
        };

        // (a) Player line of sight — unbounded (radius 0), pure geometry.
        caster.cast(px, py, 0, |x, y| lighting.set_los(x, y));

        // (b) Accumulate each light source into the per-cell color buffer. A
        // source paints every cell it can see within its radius, tinted by its
        // glyph fg and dimmed by a linear falloff (full at the source, 0 at the edge).
        let mut add_source = |lighting: &mut Lighting, sx: usize, sy: usize, radius: u32, color: [f32; 3]| {
            let r = radius as f32;
            caster.cast(sx, sy, radius as usize, |x, y| {
                let d = ((x as f32 - sx as f32).powi(2) + (y as f32 - sy as f32).powi(2)).sqrt();
                let falloff = (1.0 - d / r).max(0.0);
                lighting.add_light(x, y, [color[0] * falloff, color[1] * falloff, color[2] * falloff]);
            });
        };

        // The player's torch: a white light centered on the player.
        if player_torch > 0 {
            add_source(&mut lighting, px, py, player_torch, [1.0, 1.0, 1.0]);
        }
        // Glowing terrain (e.g. a `Torch` cell): color = the cell's glyph foreground.
        for y in 0..h {
            for x in 0..w {
                if let Some(Tile::Object(obj)) = self.get((x, y)) {
                    let radius = obj.scripting.optics.glow;
                    if radius > 0 {
                        add_source(&mut lighting, x, y, radius, color_to_rgb(obj.scripting.glyph.fg));
                    }
                }
            }
        }
        // Glowing sensors
        for s in self.sensors.iter() {
            if s.optics().glow > 0 {
                add_source(&mut lighting, s.location.ux(), s.location.uy(), s.optics().glow, color_to_rgb(s.scripting.glyph.fg));
            }
        }

        Some(lighting)
    }

    /// Returns the [`ObjectId`]s of the **non-solid** objects at `(x, y)`.
    ///
    /// These are the targets of an `enter` hook when a solid relocates onto the
    /// cell (terrain is always solid, so only objects can be non-solid). Mirrors
    /// [`object_ids_at`](Board::object_ids_at) / [`solid_object_id_at`](Board::solid_object_id_at).
    pub fn sensor_ids_at<P: Into<Point>>(&self, p: P) -> Vec<ObjectId> {
        let p = p.into();
        self.sensors
            .iter()
            .filter(|s| s.location == p)
            .map(|s| s.scripting.id)
            .collect()
    }

    /// Find and return the portal at the given location
    pub fn portal_at<P: Into<Point>>(&self, p: P) -> Option<&Portal> {
        let p = p.into();
        self.portals.iter().find(|&portal| portal.location == p)
    }

    /// Editor primitive: stamps `arch` (with visual `glyph`) into the cell at
    /// `(x, y)`, applying the editor's placement/removal rules.
    ///
    /// Two cases, keyed only on the archetype (the floor is **never** touched — the
    /// drawing tools cannot place, remove, or alter a floor):
    ///
    /// - **Terrain** (`arch != Empty`, always solid today): removes any solid object
    ///   already in the cell, then writes `(glyph, arch)` into the grid cell.
    /// - **Erase** (`arch == Empty`): removes the grid cell's terrain *and* every
    ///   object in it, leaving the floor beneath in place.
    ///
    /// A vacated grid cell becomes a transparent `Empty` so the floor shows through.
    /// Panics if `(x, y)` is out of bounds.
    pub fn place<P: Into<Point>>(&mut self, p: P, spec: Option<TileSpec>) -> Result<(), String> {
        if let Some(spec) = spec {
            let tile = spec.into_tile(&mut self.next_object_id)?;
            *self.get_mut(p) = Some(tile);
        } else {
            *self.get_mut(p) = None;
        }
        Ok(())
    }

    /// Shifts a set of cells, given as `(x, y)` coordinates. Backs the script
    /// `shift()` fn. Returns a [`ShiftOutcome`] carrying any error [`LogLine`]s for
    /// the caller to log plus the `(from, to)` relocations it performed (so the
    /// caller can fire `enter` on non-solids each moved solid landed on).
    pub fn apply_shift(&mut self, cells: &[Point]) -> Result<Vec<(Point, Point)>, String> {
        // Validate all the cells are in bounds, error if not:
        if cells.iter().any(|&c| !self.in_bounds(c)) {
            return Err("Called shift() with a cell out of bounds".to_string())
        }

        // Get all the Solids at these cells:
        let solids: Vec<_> = cells.iter().map(|&c| self.get_mut(c).take()).collect();

        // Find which ones are blockers
        let mut immobile = HashSet::new();
        for (curr_idx, curr) in solids.iter().enumerate() {
            let pushable = curr.as_ref().is_none_or(Tile::shiftable);
            if !pushable {
                immobile.insert(curr_idx);
            }
        }

        // Trace back from each immobile until we find an empty:
        let mut blocked = HashSet::new();
        for curr_idx in immobile {
            let mut prev_idx = curr_idx;
            loop {
                if solids[prev_idx].is_some() && !blocked.contains(&prev_idx) {
                    blocked.insert(prev_idx);
                    prev_idx = (prev_idx + cells.len() - 1) % cells.len();
                } else {
                    break
                }
            }
        }

        // Now, move anything that we've decided is not blocked, recording each
        // relocation so the caller can fire `enter` at every destination.
        let mut moves = Vec::new();
        for (curr_idx, curr) in solids.into_iter().enumerate() {
            if let Some(solid) = curr {
                if !blocked.contains(&curr_idx) {
                    // Not blocked, write it to target
                    let origin = cells[curr_idx];
                    let target = cells[(curr_idx + 1) % cells.len()];
                    *self.get_mut(target) = Some(solid);
                    moves.push((origin, target));
                } else {
                    // it was blocked so just write it back where it was
                    let origin = cells[curr_idx];
                    *self.get_mut(origin) = Some(solid);
                }
            }
        }

        Ok(moves)
    }

    /// Clear the queues of all objects on this board: called when entering a board, objects
    /// don't retain their state across board visits (they get initialized again, but can
    /// store things in the board registry)
    pub fn clear_all_queues(&mut self) {
        for cell in self.grid.iter_mut() {
            if let Some(Tile::Object(obj)) = cell {
                obj.scripting.queue.clear()
            }
        }
    }

    pub fn player_pos(&self) -> Point {
        self.grid.iter().enumerate().find_map(|(i, cell)| {
            if matches!(cell, Some(Tile::Player)) {
                Some((i % self.width, i / self.width).into())
            } else { None }
        }).expect("No player found!") // This should never happen, player presence is validated when building a board
    }

    pub fn get_hookable(&self, id: ObjectId) -> Option<Box<dyn Hookable + '_>> {
        // Search sensors first because it's probably shorter
        for sensor in self.sensors.iter() {
            if sensor.scripting.id == id {
                return Some(Box::new(sensor))
            }
        }

        for (i, tile) in self.grid.iter().enumerate() {
            if let Some(Tile::Object(obj)) = tile && obj.scripting.id == id {
                return Some(Box::new(LocatedObject(obj, (i % self.width, i / self.width).into())))
            }
        }

        None
    }

    pub fn get_named(&self, name: &str) -> Option<Box<dyn Hookable + '_>> {
        // Search sensors first because it's probably shorter
        for sensor in self.sensors.iter() {
            if let Some(n) = sensor.scripting.name.as_ref() &&
                n.as_str() == name {
                return Some(Box::new(sensor))
            }
        }

        for (i, tile) in self.grid.iter().enumerate() {
            if let Some(Tile::Object(obj)) = tile &&
                let Some(n) = obj.scripting.name.as_ref() &&
                n.as_str() == name {
                return Some(Box::new(LocatedObject(obj, (i % self.width, i / self.width).into())))
            }
        }

        None
    }

    pub fn get_tagged(&self, tag: &str) -> Vec<Box<dyn Hookable + '_>> {
        self.sorted_hookables().into_iter().filter(|hookable| {
            hookable.scriptable().tags.contains(tag)
        }).collect()
    }

    pub fn scripting_mut(&mut self, id: ObjectId) -> Option<&mut ScriptAttributes> {
        for sensor in self.sensors.iter_mut() {
            if sensor.scripting.id == id {
                return Some(&mut sensor.scripting)
            }
        }

        for tile in self.grid.iter_mut() {
            if let Some(Tile::Object(obj)) = tile && obj.scripting.id == id {
                return Some(&mut obj.scripting)
            }
        }

        None
    }

    pub fn sorted_hookables(&self) -> Vec<Box<dyn Hookable + '_>> {
        // Collect all the sensors
        let mut hookables = self.sensors.iter().map(|s| Box::new(s) as Box<dyn Hookable>).collect::<Vec<_>>();

        // Add the objects into it
        for (i, tile) in self.grid.iter().enumerate() {
            if let Some(Tile::Object(obj)) = tile {
                hookables.push(Box::new(LocatedObject(obj, (i % self.width, i / self.width).into())))
            }
        }

        // Sort by id
        hookables.sort_by_key(|a| a.id());
        hookables
    }

    pub fn remove_object(&mut self, id: ObjectId) {
        if let Some(tile) = self.grid.iter_mut().find(|cell| { matches!(cell, Some(Tile::Object(obj)) if obj.scripting.id == id) }) {
            tile.take();
        } else {
            self.sensors.retain(|s| s.id() != id);
        }
    }

    pub fn named_portal(&self, name: &str) -> Option<&Portal> {
        self.portals.iter().find(|p| p.name == name)
    }

    pub fn move_sensor(&mut self, id: ObjectId, dir: Direction) {
        if let Some(sensor_idx) = self.sensors.iter().position(|s| s.scripting.id == id) {
            let new_loc = self.sensors[sensor_idx].location.in_dir(dir);
            if self.in_bounds(new_loc) {
                self.sensors[sensor_idx].location = new_loc
            }
        }
    }

    /// Moves whatever is in `from` to `to`, leaving an empty cell behind. Silent no-op if either
    /// `from` or `to` is out of bounds, or if they're the same cell.
    pub fn move_cell<P1: Into<Point>, P2: Into<Point>>(&mut self, from: P1, to: P2) {
        let from = from.into();
        let to = to.into();
        if from != to && self.in_bounds(from) && self.in_bounds(to) {
            let thing = self.get_mut(from).take();
            *self.get_mut(to) = thing;
        }
    }

    /// Return whether the given point is empty
    pub fn is_empty<P: Into<Point>>(&self, p: P) -> bool {
        self.get(p).is_none()
    }

    /// Return whether the given point contains the player
    pub fn is_player<P: Into<Point>>(&self, p: P) -> bool {
        matches!(self.get(p), Some(Tile::Player))
    }

    /// Return whether the given point contains an object
    pub fn is_object<P: Into<Point>>(&self, p: P) -> bool {
        matches!(self.get(p), Some(Tile::Object(_)))
    }

    /// Return if there's an object at the given point and if it's mobile
    pub fn is_mobile<P: Into<Point>>(&self, p: P) -> bool {
        if let Some(Tile::Object(o)) = self.get(p) {
            o.mobile
        } else {
            false
        }
    }
}

#[cfg(test)]
pub(crate) mod tests {
    use super::Board;
    use crate::builtin::Builtin;
    use crate::floor::Floor;
    use crate::glyph::Glyph;
    use crate::utils::ObjectId;
    use color::Rgba8;
    use std::collections::HashMap;
    use crate::object_def::ObjectDef;
    use crate::tile::{
        DrawLayer, IntoTile, Optics, ScriptAttributes, Sensor, SensorSpec, Tile,
        TileSpec,
    };

    /// Builds an all-empty `w×h` board.
    ///
    /// The grid is fully transparent (a blank floor), so terrain stamped via
    /// [`crate_at`] etc. lands on the single grid. Use [`add_floor`] to give the
    /// board a visible fixed floor underneath.
    pub(crate) fn open_board(
        w: usize,
        h: usize,
        player_pos: (usize, usize)
    ) -> Board {
        let mut board = Board {
            name: "test".into(),
            width: w,
            height: h,
            grid: vec![None; w * h],
            floor: Floor::Blank,
            sensors: Vec::new(),
            portals: Vec::new(),
            next_object_id: 1,
            dark: false,
            registry: HashMap::new(),
        };
        player_at(&mut board, player_pos.0, player_pos.1);
        board
    }

    /// Gives the board a uniform fixed floor glyph (the single-grid replacement for
    /// the old separate floor layer).
    pub(crate) fn add_floor(board: &mut Board, glyph: Glyph) {
        board.floor = Floor::Fixed(glyph);
    }

    /// Stamps a crate cell onto the grid.
    pub(crate) fn crate_at(board: &mut Board, x: usize, y: usize) {
        *board.get_mut((x, y)) = Some(TileSpec::krate().into_tile(&mut board.next_object_id).unwrap());
    }

    /// Stamps a wall cell onto the grid.
    pub(crate) fn wall_at(board: &mut Board, x: usize, y: usize) {
        *board.get_mut((x, y)) = Some(TileSpec::wall().into_tile(&mut board.next_object_id).unwrap());
    }

    /// Stamps a gem cell onto the grid.
    pub(crate) fn gem_at(board: &mut Board, x: usize, y: usize) {
        *board.get_mut((x, y)) = Some(TileSpec::gem().into_tile(&mut board.next_object_id).unwrap());
    }

    /// Stamps the builtin named `kind` (any alias accepted by [`Builtin::from_name`],
    /// e.g. `"spinner_cw"`, `"pusher_east"`) onto the grid, returning its id.
    ///
    /// The generic counterpart to [`crate_at`]/[`wall_at`]/[`gem_at`]: `into_tile`
    /// attaches the family's [`ScriptKey`](crate::tile::ScriptKey) and the
    /// `BUILTIN_<kind>` tag, so the object is fully live with no world script pool.
    /// Panics on an unknown `kind`.
    pub(crate) fn builtin_at(board: &mut Board, x: usize, y: usize, kind: &str) -> ObjectId {
        let tile = TileSpec::Builtin { kind: kind.to_string(), glyph: None }
            .into_tile(&mut board.next_object_id)
            .unwrap_or_else(|e| panic!("{e}"));
        let id = match &tile {
            Tile::Object(obj) => obj.scripting.id,
            Tile::Player => unreachable!("a builtin never resolves to the player"),
        };
        *board.get_mut((x, y)) = Some(tile);
        id
    }

    /// Stamps a scripted object at `(x, y)` running the world script named `script`,
    /// answering entry attempts with `enter`, and returns its id.
    ///
    /// The on-grid counterpart to [`sensor_at`]: this object occupies its cell and
    /// takes part in collision, so `enter` decides how it responds to something
    /// moving into it (`Block` for an ordinary solid, `Push(..)` for a shovable one).
    pub(crate) fn object_at(
        board: &mut Board,
        x: usize,
        y: usize,
        script: &str,
        mobile: bool,
    ) -> ObjectId {
        let tile = TileSpec::Object {
            script: Some(script.to_string()),
            mobile,
            glyph: ObjectDef::default_glyph(),
            optics: Optics { opaque: true, glow: 0 },
            name: None,
            tags: Vec::new(),
        }
        .into_tile(&mut board.next_object_id)
        .expect("an object spec always resolves");
        let id = match &tile {
            Tile::Object(obj) => obj.scripting.id,
            Tile::Player => unreachable!("an object spec never resolves to the player"),
        };
        *board.get_mut((x, y)) = Some(tile);
        id
    }

    /// Stamps an object at `(x, y)` with **no script attached**, returning its id.
    ///
    /// For the "an object without a script is inert" path, and for plain physical
    /// props (a pushable block with no behavior of its own). Everything scripted
    /// should use [`object_at`].
    pub(crate) fn plain_object_at(
        board: &mut Board,
        x: usize,
        y: usize,
        mobile: bool,
    ) -> ObjectId {
        let tile = TileSpec::Object {
            script: None,
            mobile,
            glyph: ObjectDef::default_glyph(),
            optics: Optics { opaque: true, glow: 0 },
            name: None,
            tags: Vec::new(),
        }
        .into_tile(&mut board.next_object_id)
        .expect("an object spec always resolves");
        let id = match &tile {
            Tile::Object(obj) => obj.scripting.id,
            Tile::Player => unreachable!("an object spec never resolves to the player"),
        };
        *board.get_mut((x, y)) = Some(tile);
        id
    }

    /// Adds an invisible, script-only [`Sensor`] at `(x, y)` running the world script
    /// named `script`, returning its id.
    ///
    /// This is how a test gets "a scripted thing that doesn't get in the way": every
    /// object on the grid is solid now, so a script host that must not block movement
    /// (or must share a cell) has to live off-grid in [`Board::sensors`].
    pub(crate) fn sensor_at(board: &mut Board, x: usize, y: usize, script: &str) -> ObjectId {
        let sensor = SensorSpec {
            location: (x, y).into(),
            script: Some(script.to_string()),
            glyph: Glyph::transparent(),
            optics: Optics::default(),
            name: None,
            tags: Vec::new(),
            draw_layer: DrawLayer::Below,
        }
        .into_sensor(&mut board.next_object_id);
        let id = sensor.scripting.id;
        board.sensors.push(sensor);
        id
    }

    /// Stamps a player cell onto the grid.
    pub(crate) fn player_at(board: &mut Board, x: usize, y: usize) {
        *board.get_mut((x, y)) = Some(TileSpec::player().into_tile(&mut board.next_object_id).unwrap());
    }

    pub(crate) fn lamp_at(board: &mut Board, x: usize, y: usize) {
        let lamp = Sensor {
            location: (x, y).into(),
            draw_layer: DrawLayer::Above,
            scripting: ScriptAttributes {
                id: board.next_object_id,
                glyph: Glyph { tile: '☺', fg: Rgba8 { r: 255, g: 0, b: 0, a: 255 }, bg: Rgba8 { r: 0, g: 0, b: 0, a: 255 } },
                optics: Optics {
                    glow: 4,
                    opaque: false
                },
                ..Default::default()
            }
        };
        board.next_object_id += 1;
        board.sensors.push(lamp);
    }

    pub(crate) fn is_builtin(board: &Board, x: usize, y: usize, tag: &str) -> bool {
        if let Some(Tile::Object(obj)) = board.get((x, y)) {
            obj.scripting.tags.contains(&format!("BUILTIN_{tag}"))
        } else { false }
    }

    #[test]
    fn in_bounds_checks_grid_boundaries() {
        let board = open_board(3, 2, (0, 0));
        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 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));
        let floor_glyph = Glyph {
            tile: '.',
            fg: Rgba8 {
                r: 10,
                g: 20,
                b: 30,
                a: 255,
            },
            bg: Rgba8 {
                r: 1,
                g: 2,
                b: 3,
                a: 255,
            },
        };
        // A fixed floor attribute, a wall on the grid at (0,0).
        add_floor(&mut board, floor_glyph);
        wall_at(&mut board, 0, 0);
        // The wall (solid) draws over the floor; the empty cell reveals the floor.
        assert_eq!(board.glyph_at((0, 0)), Builtin::Wall.default_glyph_for("wall"));
        assert_eq!(board.glyph_at((1, 0)), floor_glyph);
    }

    #[test]
    fn apply_shift_out_of_bounds_rejects_immediately() {
        // apply_shift validates all cells upfront; any out-of-bounds cell causes immediate failure.
        let mut board = open_board(3, 1, (2, 0));
        crate_at(&mut board, 0, 0);
        let errs = board.apply_shift(&[(0, 0).into(), (9, 0).into()]);
        assert!(errs.is_err());
        assert!(is_builtin(&board, 0, 0, "crate")); // unchanged
    }

    #[test]
    fn apply_shift_wall_stops_cascade_but_empty_limits_it() {
        // A wall is immobile (`mobile = false`). Backward cascade from the wall traces
        // through preceding solids until it hits empty, marking those as blocked.
        // Solids on the *other* side of the empty (outside the blocked region) still move.
        let mut board = open_board(6, 1, (5, 0));
        crate_at(&mut board, 0, 0);
        // (1,0) stays empty
        wall_at(&mut board, 2, 0);
        crate_at(&mut board, 3, 0);
        crate_at(&mut board, 4, 0);

        // Cycle: idx 0 → idx 1 → idx 2 → idx 3 → idx 4 → idx 0 (wrap)
        // immobile = {2} (the wall: Tile::shiftable() is false)
        // Backward trace from idx 2: solids[2]=Some → blocked.insert(2), prev=1
        //   solids[1]=None (empty) → break
        // blocked = {2}; Crate at (0,0) is NOT blocked
        // Result: Crate(0,0)→(1,0), empty→no-op, Wall stays at (2,0),
        //         Crate(3,0)→(4,0), Crate(4,0)→(0,0) wrap
        let _errs = board.apply_shift(&[(0, 0), (1, 0), (2, 0), (3, 0), (4, 0)].map(Into::into));

        assert!(is_builtin(&board, 0, 0, "crate")); // wrapped from (4,0)
        assert!(is_builtin(&board, 1, 0, "crate")); // moved from (0,0)
        assert!(is_builtin(&board, 2, 0, "wall")); // blocked, immobile
        assert!(board.get((3, 0)).is_none()); // cleared, crate moved
        assert!(is_builtin(&board, 4, 0, "crate")); // moved from (3,0)
    }

    #[test]
    fn lighting_none_when_not_dark() {
        // A lit board needs no lighting; front-ends draw every cell.
        let board = open_board(5, 1, (0, 0));
        assert!(!board.dark);
        assert!(board.lighting(10).is_none());
    }

    #[test]
    fn wall_is_opaque_empty_is_not() {
        let mut board = open_board(3, 1, (0, 0));
        wall_at(&mut board, 1, 0);
        assert!(board.is_opaque_at((1, 0))); // wall blocks sight
        assert!(!board.is_opaque_at((2, 0))); // empty cell is transparent
    }

    #[test]
    fn dark_board_hides_cells_behind_a_wall() {
        // Player at the left end of a 1-wide corridor; a wall at x=2 occludes
        // everything past it. The player's torch lights cells before the wall
        // (and the wall itself); the cells behind the wall are neither lit nor
        // in line of sight, so they are not visible.
        let mut board = open_board(5, 1, (0, 0));
        board.dark = true;
        wall_at(&mut board, 2, 0);

        let lit = board.lighting(10).expect("dark board yields Lighting");
        assert!(lit.is_visible(0, 0)); // the player's own cell
        assert!(lit.is_visible(1, 0)); // open cell before the wall
        assert!(lit.is_visible(2, 0)); // the wall itself (light_walls = true)
        assert!(!lit.is_visible(3, 0)); // occluded behind the wall
        assert!(!lit.is_visible(4, 0)); // occluded behind the wall
    }

    #[test]
    fn unlit_cell_in_sight_is_not_visible() {
        // A long lit-free corridor: with a tiny torch, far cells are in line of
        // sight but receive no light, so they are not visible (LOS ∩ lit).
        let mut board = open_board(10, 1, (0, 0));
        board.dark = true;
        let lit = board.lighting(2).expect("dark board yields Lighting");
        assert!(lit.is_visible(0, 0)); // at the torch
        assert!(lit.is_visible(1, 0)); // within the torch radius
        assert!(!lit.is_visible(8, 0)); // in sight but unlit → dark
    }

    #[test]
    fn object_light_tints_toward_its_color() {
        // A dark board with no player torch and one red-glyph light object: the
        // object's cell is lit red, so a white base tints red (green/blue killed).
        let mut board = open_board(3, 1, (1, 0));
        board.dark = true;
        lamp_at(&mut board, 1, 0);

        let lit = board.lighting(0).expect("dark board yields Lighting"); // no player torch
        let white = Rgba8 { r: 255, g: 255, b: 255, a: 255 };
        let t = lit.tint(1, 0, white);
        assert!(t.r > 0, "red channel survives");
        assert_eq!(t.g, 0, "green killed by red light");
        assert_eq!(t.b, 0, "blue killed by red light");
    }
}