//! Per-board map-file load/save and the small serde types that orchestrate it.
//!
//! A board in a `.toml` world file is a `[map]` header plus an ordered array of
//! `[[layers]]` (see [`crate::layer`]). This module owns the [`MapFile`]/
//! [`MapHeader`] serde shells and the conversions to and from a runtime
//! [`Board`]; the per-layer grid/palette work lives in [`crate::layer`].
//!
//! Loading is **best-effort/nonfatal**: only a layer grid-dimension mismatch is a
//! hard error. Every other problem (unknown archetype/char → `ErrorBlock`, missing
//! or duplicate player cell, two solids stacked on a cell, duplicate object/portal
//! names) is recovered and recorded on [`Board::load_errors`].

use color::Rgba8;
use serde::{Deserialize, Serialize};
use std::collections::hash_map::Entry;
use std::collections::{BTreeMap, HashMap, HashSet};
use std::convert::TryFrom;
use std::path::Path;
use crate::api::queue::ObjQueue;
use crate::archetype::Archetype;
use crate::board::{Board, Decoration};
use crate::builtin_scripts::archetype_from_builtin_tag;
use crate::floor::{Floor, FloorGenerator};
use crate::glyph::Glyph;
use crate::layer::{GridData, PaletteEntry, Placement, build_grid};
use crate::log::LogLine;
use crate::object_def::ObjectDef;
use crate::utils::{ObjectId, PlayerPos, PortalDef};

/// The serde shell for one board in a `.toml` file: a header, the single grid, and
/// the off-grid trigger/decoration lists.
///
/// On load this is converted into a [`Board`] via [`TryFrom`] and discarded; on
/// save a [`Board`] is converted back via [`From<&Board>`]. See `maps/start.toml`
/// for a complete example of the format.
#[derive(Deserialize, Serialize)]
pub struct MapFile {
    /// The `[map]` header: name, dimensions, floor, optional board script.
    pub map: MapHeader,
    /// The single `[grid]`: palette + char map for all solids and most non-solids.
    #[serde(default)]
    pub(crate) grid: GridData,
    /// Invisible, non-solid, script-only objects (`[[triggers]]`).
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub(crate) triggers: Vec<TriggerSpec>,
    /// Non-solid `(glyph, archetype)` cells drawn only where the grid is empty
    /// (`[[decorations]]`). Normally absent; used by save files.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub(crate) decorations: Vec<DecorationSpec>,
}

/// The `[map]` header section of a board.
#[derive(Deserialize, Serialize)]
pub struct MapHeader {
    /// Human-readable name for this board, e.g. `"Opening Room"`.
    pub name: String,
    /// Width of the board in cells. Must match the grid row length.
    pub width: usize,
    /// Height of the board in cells. Must match the grid row count.
    pub height: usize,
    /// The board's optional cosmetic floor. Absent ⇒ blank; see [`FloorSpec`].
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub floor: Option<FloorSpec>,
    /// Name of the board-level script in the `[scripts]` table, if any.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub board_script_name: Option<String>,
    /// When `true`, this is a "dark" board: front-ends reveal only cells within
    /// the player's field of view. Absent ⇒ `false` (fully lit); omitted from
    /// the saved TOML when `false`. See [`Board::dark`](crate::board::Board::dark).
    #[serde(default, skip_serializing_if = "is_false")]
    pub dark: bool,
}

/// serde `skip_serializing_if` predicate: omit a `bool` field when it is `false`
/// (so the common non-dark board doesn't emit a `dark = false` line).
fn is_false(b: &bool) -> bool {
    !*b
}

/// Serde form of the board floor attribute (`floor = { … }` in `[map]`).
///
/// Resolves (in [`FloorSpec::resolve`]) to a [`Floor`]: a `generator` name gives a
/// biome, otherwise any of `tile`/`fg`/`bg` gives a single fixed glyph, and an
/// empty spec is blank.
#[derive(Deserialize, Serialize, Clone)]
pub struct FloorSpec {
    /// Procedural biome name (`"grass"`/`"dirt"`/`"stone"`).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub generator: Option<String>,
    /// Fixed-glyph tile index (int or single-char string).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub tile: Option<TileIndex>,
    /// Fixed-glyph foreground `"#RRGGBB"`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub fg: Option<String>,
    /// Fixed-glyph background `"#RRGGBB"`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub bg: Option<String>,
}

impl FloorSpec {
    /// Resolves this spec to a [`Floor`] for a `width × height` board, recording a
    /// nonfatal error (and falling back to [`Floor::Blank`]) for an unknown generator.
    fn resolve(&self, width: usize, height: usize, errors: &mut Vec<LogLine>) -> Floor {
        if let Some(name) = &self.generator {
            return match FloorGenerator::from_name(name) {
                Some(g) => Floor::biome(g, width, height),
                None => {
                    errors.push(LogLine::error(format!(
                        "floor names unknown generator '{name}'; using blank floor"
                    )));
                    Floor::Blank
                }
            };
        }
        // A fixed glyph if any visual field is given, else a blank floor.
        if self.tile.is_some() || self.fg.is_some() || self.bg.is_some() {
            Floor::Fixed(Glyph {
                tile: self.tile.map(TileIndex::into_u32).unwrap_or(32),
                fg: self.fg.as_deref().map(parse_color).unwrap_or(Rgba8 { r: 0, g: 0, b: 0, a: 255 }),
                bg: self.bg.as_deref().map(parse_color).unwrap_or(Rgba8 { r: 0, g: 0, b: 0, a: 255 }),
            })
        } else {
            Floor::Blank
        }
    }
}

/// Serde form of one `[[triggers]]` entry: an invisible, non-solid, script-only
/// object at `(x, y)`. Triggers are folded into [`Board::objects`] at load; they
/// are re-emitted here on save (recognised as scripted, non-solid, glyphless).
#[derive(Deserialize, Serialize, Clone)]
pub(crate) struct TriggerSpec {
    /// Column (0-indexed).
    pub x: usize,
    /// Row (0-indexed).
    pub y: usize,
    /// Name of the Rhai script (in `[scripts]`) this trigger runs.
    pub script_name: String,
    /// Optional board-unique name.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub name: Option<String>,
    /// Optional open-ended labels.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub tags: Option<Vec<String>>,
}

/// Serde form of one `[[decorations]]` entry: a non-solid `(glyph, archetype)` at
/// `(x, y)`, drawn only where the grid cell is empty. A solid archetype is rejected.
#[derive(Deserialize, Serialize, Clone)]
pub(crate) struct DecorationSpec {
    /// Column (0-indexed).
    pub x: usize,
    /// Row (0-indexed).
    pub y: usize,
    /// Archetype name (or `"empty"`); must be non-solid.
    pub kind: String,
    /// Tile index (int or single-char string).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub tile: Option<TileIndex>,
    /// Foreground `"#RRGGBB"`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub fg: Option<String>,
    /// Background `"#RRGGBB"`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub bg: Option<String>,
}

/// A tile index in a palette entry: either a plain integer or a character literal.
///
/// Accepting both forms lets map files write `tile = 35` or `tile = "#"` (the char
/// is converted to its Unicode scalar) interchangeably.
#[derive(Deserialize, Serialize, Clone, Copy)]
#[serde(untagged)]
pub enum TileIndex {
    /// A direct tile index (e.g. `tile = 35`).
    Num(u32),
    /// A single-character shorthand (e.g. `tile = "#"`); converted to its Unicode scalar.
    Chr(char),
}

impl TileIndex {
    /// Returns the tile index as a `u32`, converting a char to its scalar value.
    pub(crate) fn into_u32(self) -> u32 {
        match self {
            TileIndex::Num(n) => n,
            TileIndex::Chr(c) => c as u32,
        }
    }
}

/// Parses an `"#RRGGBB"` hex color string into an [`Rgba8`].
/// Returns opaque black on any parse failure.
pub(crate) fn parse_color(hex: &str) -> Rgba8 {
    let hex = hex.trim_start_matches('#');
    if hex.len() != 6 {
        return Rgba8 {
            r: 0,
            g: 0,
            b: 0,
            a: 255,
        };
    }
    let r = u8::from_str_radix(&hex[0..2], 16).unwrap_or(0);
    let g = u8::from_str_radix(&hex[2..4], 16).unwrap_or(0);
    let b = u8::from_str_radix(&hex[4..6], 16).unwrap_or(0);
    Rgba8 { r, g, b, a: 255 }
}

/// Converts an [`Rgba8`] to an `"#RRGGBB"` hex string (alpha is ignored).
pub(crate) fn color_to_hex(color: Rgba8) -> String {
    format!("#{:02X}{:02X}{:02X}", color.r, color.g, color.b)
}

/// Converts a parsed map file into a runtime [`Board`].
///
/// Builds the single grid (collecting object/portal/player placements), resolves
/// the floor, then runs the cross-cell validations that span the whole board:
/// - the player must appear exactly once (missing → `(0, 0)`; multiple → the first), and wins its cell;
/// - at most one solid may occupy a cell (a conflicting solid object is dropped);
/// - object names must be board-unique (a duplicate is cleared) and portal names unique (a duplicate is dropped).
///
/// Finally the `[[triggers]]` load as non-solid glyphless objects and the
/// `[[decorations]]` as off-grid non-solid cells.
///
/// Returns `Err` only when the grid dimensions disagree with the header.
impl TryFrom<MapFile> for Board {
    type Error = String;

    fn try_from(mf: MapFile) -> Result<Self, Self::Error> {
        let w = mf.map.width;
        let h = mf.map.height;
        let mut load_errors: Vec<LogLine> = Vec::new();

        // Build the single grid, collecting non-terrain placements.
        let (mut grid, placements) = build_grid(&mf.grid, w, h, &mut load_errors)?;
        let mut object_specs: Vec<(crate::layer::ObjectTemplate, usize, usize)> = Vec::new();
        let mut portal_specs: Vec<(crate::layer::PortalTemplate, usize, usize)> = Vec::new();
        let mut player_positions: Vec<(usize, usize)> = Vec::new();
        for p in placements {
            match p {
                Placement::Object(t, x, y) => object_specs.push((t, x, y)),
                Placement::Portal(t, x, y) => portal_specs.push((t, x, y)),
                Placement::Player(x, y) => player_positions.push((x, y)),
            }
        }

        // Resolve the cosmetic floor attribute (blank / fixed glyph / biome).
        let floor = mf
            .map
            .floor
            .as_ref()
            .map(|f| f.resolve(w, h, &mut load_errors))
            .unwrap_or(Floor::Blank);

        // The player must be placed exactly once.
        let (px, py) = match player_positions.len() {
            1 => player_positions[0],
            0 => {
                load_errors.push(LogLine::error(
                    "no player cell (kind = \"player\") found; placing player at (0, 0)",
                ));
                (0, 0)
            }
            n => {
                load_errors.push(LogLine::error(format!(
                    "player cell appears {n} times; using the first"
                )));
                player_positions[0]
            }
        };
        let pidx = py * w + px;

        // Track which cells hold a solid (the grid's own solids seed the map).
        let mut solid_occupied = vec![false; w * h];
        for (idx, cell) in grid.iter().enumerate() {
            if cell.1.behavior().solid {
                solid_occupied[idx] = true;
            }
        }

        // The player wins its cell: clear any solid terrain under it and claim the
        // cell so a solid object placed here is dropped below.
        if grid[pidx].1.behavior().solid {
            grid[pidx] = (Glyph::transparent(), Archetype::Empty);
        }
        solid_occupied[pidx] = true;

        // Spawn objects in reading order, so ids are deterministic and "lowest id
        // wins a collision" / "first claimant keeps the name" hold.
        let mut objects: BTreeMap<ObjectId, ObjectDef> = BTreeMap::new();
        let mut next_object_id: ObjectId = 1;
        let mut seen_names: HashMap<String, ObjectId> = HashMap::new();
        for (t, x, y) in object_specs {
            let idx = y * w + x;
            // A solid object may not share a cell with another solid.
            if t.solid && solid_occupied[idx] {
                // The player silently wins its cell; any other conflict is reported.
                if idx != pidx {
                    load_errors.push(LogLine::error(format!(
                        "solid object at ({x}, {y}) conflicts with an existing solid; skipping object"
                    )));
                }
                continue;
            }
            let id = next_object_id;
            // Name uniqueness: first claimant keeps it; later duplicates are cleared.
            let name = t.name.and_then(|n| claim_name(n, id, &mut seen_names, &mut load_errors));
            if t.solid {
                solid_occupied[idx] = true;
            }
            objects.insert(
                id,
                ObjectDef {
                    id,
                    x,
                    y,
                    glyph: t.glyph,
                    solid: t.solid,
                    opaque: t.opaque,
                    pushable: t.pushable,
                    light: t.light,
                    // Hand-placed objects are never grab targets; only expanded
                    // grab archetypes (e.g. gems) set this (see expand_builtin_archetypes).
                    grab: false,
                    script_name: t.script_name,
                    // Script-backed archetypes are expanded after the board is built
                    // (see `expand_builtin_archetypes` below), not via templates.
                    builtin_script: None,
                    tags: t.tags.into_iter().collect(),
                    queue: ObjQueue::new(),
                    name,
                },
            );
            next_object_id += 1;
        }

        // Triggers: invisible, non-solid, script-only objects. They join the same
        // `objects` map (so ids/name-uniqueness/script dispatch all apply), after the
        // hand-placed grid objects.
        for t in mf.triggers {
            if !t.x.lt(&w) || !t.y.lt(&h) {
                load_errors.push(LogLine::error(format!(
                    "trigger at ({}, {}) is out of bounds; skipping",
                    t.x, t.y
                )));
                continue;
            }
            let id = next_object_id;
            let name = t.name.and_then(|n| claim_name(n, id, &mut seen_names, &mut load_errors));
            objects.insert(
                id,
                ObjectDef {
                    id,
                    x: t.x,
                    y: t.y,
                    glyph: Glyph::transparent(),
                    solid: false,
                    opaque: false,
                    pushable: false,
                    light: 0,
                    grab: false,
                    script_name: Some(t.script_name),
                    builtin_script: None,
                    tags: t.tags.unwrap_or_default().into_iter().collect(),
                    queue: ObjQueue::new(),
                    name,
                },
            );
            next_object_id += 1;
        }

        // Build the portal list, dropping duplicate names (first claimant wins).
        let mut seen_portal_names: HashSet<String> = HashSet::new();
        let mut portals: Vec<PortalDef> = Vec::new();
        for (t, x, y) in portal_specs {
            if !seen_portal_names.insert(t.name.clone()) {
                load_errors.push(LogLine::error(format!(
                    "portal name {:?} already used by another portal; skipping portal",
                    t.name
                )));
                continue;
            }
            portals.push(PortalDef {
                name: t.name,
                x,
                y,
                target_map: t.target_map,
                target_entry: t.target_entry,
            });
        }

        // Decorations: non-solid off-grid cells (a solid archetype is rejected).
        let mut decorations: Vec<Decoration> = Vec::new();
        for d in mf.decorations {
            match resolve_decoration(&d) {
                Ok(dec) => decorations.push(dec),
                Err(msg) => load_errors.push(LogLine::error(msg)),
            }
        }

        let mut board = Board {
            name: mf.map.name,
            width: w,
            height: h,
            grid,
            floor,
            decorations,
            player: PlayerPos {
                x: px as i64,
                y: py as i64,
            },
            objects,
            next_object_id,
            portals,
            board_script_name: mf.map.board_script_name,
            dark: mf.map.dark,
            load_errors,
            registry: HashMap::new(),
        };
        // Turn script-backed archetype cells (pushers/spinners) into their scripted
        // objects. Runs after the cross-cell validation above, so board invariants
        // hold; the same call also fixes editor-placed machines before a playtest.
        board.expand_builtin_archetypes();
        Ok(board)
    }
}

/// Claims `name` for object `id` in `seen_names`, returning `Some(name)` for the
/// first claimant and `None` (with a logged error) for any later duplicate.
fn claim_name(
    n: String,
    id: ObjectId,
    seen_names: &mut HashMap<String, ObjectId>,
    errors: &mut Vec<LogLine>,
) -> Option<String> {
    match seen_names.entry(n.clone()) {
        Entry::Vacant(v) => {
            v.insert(id);
            Some(n)
        }
        Entry::Occupied(o) => {
            errors.push(LogLine::error(format!(
                "object name {n:?} already used by object {}; clearing name",
                o.get()
            )));
            None
        }
    }
}

/// Resolves a [`DecorationSpec`] into a [`Decoration`], erroring if its archetype is
/// unknown or solid (decorations must be non-solid).
fn resolve_decoration(d: &DecorationSpec) -> Result<Decoration, String> {
    let arch = if d.kind == "empty" {
        Archetype::Empty
    } else {
        Archetype::try_from(d.kind.as_str())
            .map_err(|msg| format!("decoration at ({}, {}): {msg}; skipping", d.x, d.y))?
    };
    if arch.behavior().solid {
        return Err(format!(
            "decoration at ({}, {}) has solid archetype {:?}; skipping",
            d.x, d.y, d.kind
        ));
    }
    let default = arch.default_glyph();
    Ok(Decoration {
        x: d.x,
        y: d.y,
        glyph: Glyph {
            tile: d.tile.map(TileIndex::into_u32).unwrap_or(default.tile),
            fg: d.fg.as_deref().map(parse_color).unwrap_or(default.fg),
            bg: d.bg.as_deref().map(parse_color).unwrap_or(default.bg),
        },
        archetype: arch,
    })
}

/// Pool of palette characters for save: printable ASCII (plus a leading space for
/// the common transparent-empty cell), excluding `"` and `\` which would need
/// escaping inside a TOML string.
fn char_pool() -> Vec<char> {
    let mut pool = vec![' '];
    pool.extend(
        (33u8..=126u8)
            .filter(|&b| b != b'"' && b != b'\\')
            .map(|b| b as char),
    );
    pool
}

/// Builds the [`PaletteEntry`] for a grid terrain cell `(glyph, arch)`.
///
/// A grid `Empty` cell is always transparent now (floors are a board attribute),
/// so it maps to `kind = "empty"`; anything else is its archetype keyword.
fn cell_entry(glyph: Glyph, arch: Archetype) -> PaletteEntry {
    if arch == Archetype::Empty {
        PaletteEntry {
            kind: "empty".into(),
            ..Default::default()
        }
    } else {
        PaletteEntry {
            kind: arch.name().into(),
            tile: Some(TileIndex::Num(glyph.tile)),
            fg: Some(color_to_hex(glyph.fg)),
            bg: Some(color_to_hex(glyph.bg)),
            ..Default::default()
        }
    }
}

/// Whether an object is a **trigger** — an invisible, non-solid, script-only object
/// authored/serialized in `[[triggers]]` rather than the grid palette.
fn is_trigger(o: &ObjectDef) -> bool {
    !o.solid && o.glyph.tile == 0 && o.script_name.is_some() && o.builtin_script.is_none()
}

/// Serializes `board`'s single grid (terrain + non-trigger objects + portals +
/// player) into a [`GridData`].
fn grid_to_data(board: &Board) -> GridData {
    let (w, h) = (board.width, board.height);
    let mut pool = char_pool().into_iter();
    let mut palette: HashMap<String, PaletteEntry> = HashMap::new();
    let mut cell_to_key: HashMap<(Glyph, Archetype), char> = HashMap::new();
    let mut grid: Vec<Vec<char>> = vec![vec![' '; w]; h];

    // Terrain cells: dedup each unique (glyph, archetype) to one palette char.
    for (y, row) in grid.iter_mut().enumerate() {
        for (x, slot) in row.iter_mut().enumerate() {
            let (glyph, arch) = *board.get(x, y);
            *slot = *cell_to_key.entry((glyph, arch)).or_insert_with(|| {
                let ch = pool.next().expect("ran out of palette characters");
                palette.insert(ch.to_string(), cell_entry(glyph, arch));
                ch
            });
        }
    }

    // Objects overwrite their (transparent) grid cell with an object char. Triggers
    // are written to `[[triggers]]` instead (see `From<&Board>`), so skip them here.
    for o in board.objects.values().filter(|o| !is_trigger(o)) {
        // A built-in archetype object (e.g. a pusher) round-trips back to its
        // archetype keyword: emit it as a terrain cell (deduped with real terrain),
        // using the object's current glyph, rather than a `kind = "object"` entry.
        if let Some(arch) = o.tags.iter().find_map(|t| archetype_from_builtin_tag(t)) {
            let ch = *cell_to_key.entry((o.glyph, arch)).or_insert_with(|| {
                let ch = pool.next().expect("ran out of palette characters");
                palette.insert(ch.to_string(), cell_entry(o.glyph, arch));
                ch
            });
            grid[o.y][o.x] = ch;
            continue;
        }
        let ch = pool.next().expect("ran out of palette characters");
        let mut tags: Vec<String> = o.tags.iter().cloned().collect();
        tags.sort();
        palette.insert(
            ch.to_string(),
            PaletteEntry {
                kind: "object".into(),
                tile: Some(TileIndex::Num(o.glyph.tile)),
                fg: Some(color_to_hex(o.glyph.fg)),
                bg: Some(color_to_hex(o.glyph.bg)),
                solid: Some(o.solid),
                opaque: Some(o.opaque),
                pushable: Some(o.pushable),
                light: (o.light > 0).then_some(o.light),
                script_name: o.script_name.clone(),
                tags: (!tags.is_empty()).then_some(tags),
                name: o.name.clone(),
                ..Default::default()
            },
        );
        grid[o.y][o.x] = ch;
    }

    // Portals.
    for p in board.portals.iter() {
        let ch = pool.next().expect("ran out of palette characters");
        palette.insert(
            ch.to_string(),
            PaletteEntry {
                kind: "portal".into(),
                name: Some(p.name.clone()),
                target_map: Some(p.target_map.clone()),
                target_entry: Some(p.target_entry.clone()),
                ..Default::default()
            },
        );
        grid[p.y][p.x] = ch;
    }

    // The player.
    {
        let ch = pool.next().expect("ran out of palette characters");
        palette.insert(
            ch.to_string(),
            PaletteEntry {
                kind: "player".into(),
                ..Default::default()
            },
        );
        grid[board.player.y as usize][board.player.x as usize] = ch;
    }

    let content = grid
        .into_iter()
        .map(|row| row.into_iter().collect::<String>())
        .collect::<Vec<_>>()
        .join("\n")
        + "\n";
    // Save always emits an explicit grid; `fill`/`sparse` are load-time conveniences.
    GridData {
        content: Some(content),
        fill: None,
        sparse: None,
        palette,
    }
}

/// Builds the [`FloorSpec`] for `board`'s floor, or `None` for a blank floor. A
/// biome re-emits its generator name (so the procedural floor round-trips); a fixed
/// glyph re-emits its tile/fg/bg.
fn floor_to_spec(floor: &Floor) -> Option<FloorSpec> {
    match floor {
        Floor::Blank => None,
        Floor::Fixed(g) => Some(FloorSpec {
            generator: None,
            tile: Some(TileIndex::Num(g.tile)),
            fg: Some(color_to_hex(g.fg)),
            bg: Some(color_to_hex(g.bg)),
        }),
        Floor::Biome { generator, .. } => Some(FloorSpec {
            generator: Some(generator.name().into()),
            tile: None,
            fg: None,
            bg: None,
        }),
    }
}

/// Converts a runtime [`Board`] back into a serializable [`MapFile`].
///
/// Emits the single `[grid]`, the `[[triggers]]` (invisible script objects) and
/// `[[decorations]]` lists, and the `floor` attribute (a biome re-emits its
/// generator name, so procedural floors round-trip).
impl From<&Board> for MapFile {
    fn from(board: &Board) -> Self {
        let grid = grid_to_data(board);
        // Trigger objects → `[[triggers]]`.
        let triggers = board
            .objects
            .values()
            .filter(|o| is_trigger(o))
            .map(|o| {
                let mut tags: Vec<String> = o.tags.iter().cloned().collect();
                tags.sort();
                TriggerSpec {
                    x: o.x,
                    y: o.y,
                    script_name: o.script_name.clone().unwrap_or_default(),
                    name: o.name.clone(),
                    tags: (!tags.is_empty()).then_some(tags),
                }
            })
            .collect();
        // Decorations → `[[decorations]]`.
        let decorations = board
            .decorations
            .iter()
            .map(|d| DecorationSpec {
                x: d.x,
                y: d.y,
                kind: d.archetype.name().into(),
                tile: Some(TileIndex::Num(d.glyph.tile)),
                fg: Some(color_to_hex(d.glyph.fg)),
                bg: Some(color_to_hex(d.glyph.bg)),
            })
            .collect();
        MapFile {
            map: MapHeader {
                name: board.name.clone(),
                width: board.width,
                height: board.height,
                floor: floor_to_spec(&board.floor),
                board_script_name: board.board_script_name.clone(),
                dark: board.dark,
            },
            grid,
            triggers,
            decorations,
        }
    }
}

/// Loads a map file from disk and returns a ready-to-use [`Board`].
///
/// Reads the file at `path`, deserializes it as a single-board [`MapFile`], then
/// converts it via [`TryFrom`]. Production code uses [`crate::world::load`] for
/// multi-board world files instead.
pub fn load(path: &str) -> Result<Board, Box<dyn std::error::Error>> {
    let content = std::fs::read_to_string(path)?;
    let map_file: MapFile = toml::from_str(&content)?;
    Board::try_from(map_file).map_err(|e| e.into())
}

/// Serializes a [`Board`] to a `.toml` map file at `path`.
pub fn save(board: &Board, path: &Path) -> Result<(), Box<dyn std::error::Error>> {
    let map_file = MapFile::from(board);
    let toml_str = toml::to_string_pretty(&map_file)?;
    std::fs::write(path, toml_str)?;
    Ok(())
}