//! The board grid: the palette+char map-file unit and its load-time conversion.
//!
//! A board is a single **grid** — a character grid plus a palette mapping each
//! character to one *kind* of thing: an archetype (terrain), a scripted object, a
//! portal, or the player. (The board's cosmetic floor is a separate `[map]`
//! attribute, not a grid cell; see [`crate::floor`].)
//!
//! This module owns the grid serde type ([`GridData`], [`PaletteEntry`]) and the
//! load-time conversion ([`build_grid`]) that turns one `GridData` into the board's
//! `Vec<(Glyph, Archetype)>` cells plus a list of [`Placement`]s (objects/portals/
//! player) for the map loader to resolve. Cross-cell validation (one solid per
//! cell, unique names, the player winning its cell) lives in [`crate::map_file`].

use crate::archetype::Archetype;
use crate::glyph::Glyph;
use crate::log::LogLine;
use crate::map_file::{TileIndex, parse_color};
use crate::object_def::ObjectDef;
use serde::{Deserialize, Serialize};
use std::collections::HashMap;

/// Serde representation of the board `[grid]`: a char grid plus its palette.
///
/// The grid is given in exactly one of three ways (precedence: `content`, then
/// `fill`, then `sparse`; none of them ⇒ an all-spaces grid):
/// - `content` — a multi-line grid string, one char per cell (`width × height`).
/// - `fill` — a single character; the whole grid is filled with it.
/// - `sparse` — a list of `{ x, y, ch }` cells over an otherwise all-spaces grid
///   (handy for a grid holding just a few things).
///
/// A space (`' '`) is always a transparent empty cell and is never a palette key
/// (any `" "` entry in `palette` is ignored).
#[derive(Deserialize, Serialize, Default)]
pub(crate) struct GridData {
    /// Multi-line grid string; one char per cell, looked up in `palette`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub content: Option<String>,
    /// Single character to fill the whole `width × height` grid with.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub fill: Option<String>,
    /// Individual cells over an otherwise all-spaces grid.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub sparse: Option<Vec<SparseCell>>,
    /// Char (as a one-character string key) → palette entry.
    #[serde(default)]
    pub palette: HashMap<String, PaletteEntry>,
}

/// One cell in a [`GridData::sparse`] list: a single character at `(x, y)`.
#[derive(Deserialize, Serialize, Clone)]
pub(crate) struct SparseCell {
    /// Column (0-indexed).
    pub x: usize,
    /// Row (0-indexed).
    pub y: usize,
    /// The grid character at this cell (a one-character string).
    pub ch: String,
}

/// One palette entry, discriminated by [`kind`](PaletteEntry::kind).
///
/// A single flat struct (rather than an enum) because `kind` is open-ended: it is
/// any archetype name (`"wall"`, `"crate"`, `"pusher_east"`, …) *or* one of the
/// meta-kinds `empty`, `object`, `portal`, `player`. Only the fields relevant to a
/// given kind are read; the rest stay `None`. See [`resolve_entry`].
#[derive(Deserialize, Serialize, Default, Clone)]
pub(crate) struct PaletteEntry {
    /// What this entry is: an archetype name, or `empty`/`object`/`portal`/`player`.
    pub kind: String,
    /// Tile index (int or single-char string). Used by archetype/object kinds.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub tile: Option<TileIndex>,
    /// Foreground `"#RRGGBB"`. Used by archetype/object kinds.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub fg: Option<String>,
    /// Background `"#RRGGBB"`. Used by archetype/object kinds.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub bg: Option<String>,
    /// Object solidity (defaults `true`). Only for `kind = "object"`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub solid: Option<bool>,
    /// Object opacity (defaults `true`). Only for `kind = "object"`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub opaque: Option<bool>,
    /// Object pushability (defaults `false`). Only for `kind = "object"`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub pushable: Option<bool>,
    /// Light radius in cells emitted on a dark board (defaults `0` = none).
    /// Only for `kind = "object"`. See [`ObjectDef::light`].
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub light: Option<u32>,
    /// Rhai script name. Only for `kind = "object"`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub script_name: Option<String>,
    /// Open-ended labels. Only for `kind = "object"`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub tags: Option<Vec<String>>,
    /// Unique name. For `kind = "object"` (optional) or `kind = "portal"` (required).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub name: Option<String>,
    /// Target board key. Required for `kind = "portal"`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub target_map: Option<String>,
    /// Target portal name on the destination board. Required for `kind = "portal"`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub target_entry: Option<String>,
}

/// A single grid cell: its visual and its behavioral class.
pub(crate) type GridCell = (Glyph, Archetype);

/// A non-terrain thing the grid places at a cell, resolved by the map loader.
///
/// Terrain goes straight into the grid cells; these need cross-cell handling (ids,
/// name uniqueness, the single player), so [`build_grid`] returns them separately
/// with their `(x, y)` for [`crate::map_file`] to finish.
pub(crate) enum Placement {
    /// A scripted object to spawn at `(x, y)`.
    Object(ObjectTemplate, usize, usize),
    /// A portal at `(x, y)`.
    Portal(PortalTemplate, usize, usize),
    /// The player's start cell `(x, y)`.
    Player(usize, usize),
}

/// A resolved object definition minus board-assigned fields (`id`).
#[derive(Clone)]
pub(crate) struct ObjectTemplate {
    pub glyph: Glyph,
    pub solid: bool,
    pub opaque: bool,
    pub pushable: bool,
    /// Light radius in cells (0 = none); see [`ObjectDef::light`].
    pub light: u32,
    pub script_name: Option<String>,
    pub tags: Vec<String>,
    pub name: Option<String>,
}

/// A resolved portal definition minus `(x, y)`.
#[derive(Clone)]
pub(crate) struct PortalTemplate {
    pub name: String,
    pub target_map: String,
    pub target_entry: String,
}

/// What a palette character resolves to during the grid walk.
#[derive(Clone)]
enum Resolved {
    /// A fixed cell written straight into the grid (terrain, empty, error block).
    Cell(Glyph, Archetype),
    /// A scripted object placed per occurrence.
    Object(ObjectTemplate),
    /// A portal placed per occurrence.
    Portal(PortalTemplate),
    /// The player's start cell.
    Player,
}

/// Resolves one palette entry to a [`Resolved`], recording any nonfatal problem.
///
/// Unknown archetype names become a visible [`Archetype::ErrorBlock`]; a `portal`
/// missing required fields falls back to a transparent cell (the grid char is
/// still consumed). Object/archetype glyphs fall back to the relevant default for
/// any absent visual field.
fn resolve_entry(ch: char, e: &PaletteEntry, errors: &mut Vec<LogLine>) -> Resolved {
    // Builds a glyph from the entry's tile/fg/bg, each falling back to `default`.
    let glyph_with_default = |default: Glyph| Glyph {
        tile: e.tile.map(TileIndex::into_u32).unwrap_or(default.tile),
        fg: e.fg.as_deref().map(parse_color).unwrap_or(default.fg),
        bg: e.bg.as_deref().map(parse_color).unwrap_or(default.bg),
    };

    match e.kind.as_str() {
        // Transparent: the floor / a lower thing shows through here.
        "empty" => Resolved::Cell(Glyph::transparent(), Archetype::Empty),
        "object" => Resolved::Object(ObjectTemplate {
            glyph: glyph_with_default(ObjectDef::default_glyph()),
            solid: e.solid.unwrap_or(true),
            opaque: e.opaque.unwrap_or(true),
            pushable: e.pushable.unwrap_or(false),
            light: e.light.unwrap_or(0),
            script_name: e.script_name.clone(),
            tags: e.tags.clone().unwrap_or_default(),
            name: e.name.clone(),
        }),
        "portal" => match (e.name.clone(), e.target_map.clone(), e.target_entry.clone()) {
            (Some(name), Some(target_map), Some(target_entry)) => {
                Resolved::Portal(PortalTemplate {
                    name,
                    target_map,
                    target_entry,
                })
            }
            _ => {
                errors.push(LogLine::error(format!(
                    "portal palette '{ch}' needs name, target_map and target_entry; skipping"
                )));
                Resolved::Cell(Glyph::transparent(), Archetype::Empty)
            }
        },
        "player" => Resolved::Player,
        // Any other kind must be an archetype name. Script-backed archetypes (e.g.
        // pushers/spinners) load as a plain terrain cell here and are turned into
        // their scripted objects afterward by `Board::expand_builtin_archetypes`
        // (called from `TryFrom<MapFile>`), so the expansion lives in one place.
        other => match Archetype::try_from(other) {
            Ok(a) => Resolved::Cell(glyph_with_default(a.default_glyph()), a),
            Err(msg) => {
                errors.push(LogLine::error(format!(
                    "palette '{ch}': {msg}; using error block"
                )));
                Resolved::Cell(Archetype::ErrorBlock.default_glyph(), Archetype::ErrorBlock)
            }
        },
    }
}

/// Resolves the grid to a `height × width` matrix of chars from whichever of
/// `content` / `fill` / `sparse` is supplied (in that precedence; none ⇒ all spaces).
///
/// Only an explicit `content` can mismatch the board dimensions — the single hard
/// error. `fill`/`sparse` always produce an exactly-sized grid; a non-single-char
/// `fill`/`ch` or an out-of-bounds `sparse` cell is recorded on `errors` and the
/// offending cell falls back to (or stays) a space.
fn grid_chars(
    data: &GridData,
    width: usize,
    height: usize,
    errors: &mut Vec<LogLine>,
) -> Result<Vec<Vec<char>>, String> {
    // Reads a one-character string field, recording `context` and returning `None`
    // when it is empty or longer than one char.
    let single_char = |s: &str, context: String, errors: &mut Vec<LogLine>| {
        let mut chs = s.chars();
        match (chs.next(), chs.next()) {
            (Some(c), None) => Some(c),
            _ => {
                errors.push(LogLine::error(context));
                None
            }
        }
    };

    if let Some(content) = &data.content {
        // Explicit grid: validate it matches the declared dimensions.
        let rows: Vec<&str> = content.lines().collect();
        if rows.len() != height {
            return Err(format!(
                "grid has {} rows but the board is {height} tall",
                rows.len()
            ));
        }
        let mut grid = Vec::with_capacity(height);
        for (i, line) in rows.iter().enumerate() {
            let row: Vec<char> = line.chars().collect();
            if row.len() != width {
                return Err(format!(
                    "grid row {i} has {} characters but the board is {width} wide",
                    row.len()
                ));
            }
            grid.push(row);
        }
        return Ok(grid);
    }

    if let Some(fill) = &data.fill {
        // A whole grid of one character.
        let ch = single_char(
            fill,
            format!("grid fill must be a single character (got {fill:?}); using a space"),
            errors,
        )
        .unwrap_or(' ');
        return Ok(vec![vec![ch; width]; height]);
    }

    // `sparse` (or nothing): an all-spaces grid with the listed cells stamped in.
    let mut grid = vec![vec![' '; width]; height];
    for cell in data.sparse.iter().flatten() {
        let Some(ch) = single_char(
            &cell.ch,
            format!(
                "sparse cell ch must be a single character (got {:?}); skipping",
                cell.ch
            ),
            errors,
        ) else {
            continue;
        };
        if cell.x >= width || cell.y >= height {
            errors.push(LogLine::error(format!(
                "sparse cell ({}, {}) is out of bounds; skipping",
                cell.x, cell.y
            )));
            continue;
        }
        grid[cell.y][cell.x] = ch;
    }
    Ok(grid)
}

/// Builds the board's grid cells from its [`GridData`], plus the non-terrain
/// placements it contains (with their `(x, y)`).
///
/// Returns `Err` only on a grid-dimension mismatch (the single hard error);
/// every other problem is recorded on `errors`.
pub(crate) fn build_grid(
    data: &GridData,
    width: usize,
    height: usize,
    errors: &mut Vec<LogLine>,
) -> Result<(Vec<GridCell>, Vec<Placement>), String> {
    // Resolve each palette entry once. Space is always a transparent empty cell, so
    // it is never a palette key — any `" "` entry is ignored.
    let resolved: HashMap<char, Resolved> = data
        .palette
        .iter()
        .filter_map(|(key, entry)| {
            let ch = key.chars().next().unwrap_or(' ');
            (ch != ' ').then(|| (ch, resolve_entry(ch, entry, errors)))
        })
        .collect();

    // Resolve the grid (content / fill / sparse) before walking it.
    let grid = grid_chars(data, width, height, errors)?;

    // Walk the grid, filling cells and collecting placements.
    let mut cells: Vec<GridCell> = Vec::with_capacity(width * height);
    let mut placements: Vec<Placement> = Vec::new();
    for (y, row) in grid.iter().enumerate() {
        for (x, &ch) in row.iter().enumerate() {
            // A space is always a transparent empty cell, palette or not.
            if ch == ' ' {
                cells.push((Glyph::transparent(), Archetype::Empty));
                continue;
            }
            match resolved.get(&ch) {
                Some(Resolved::Cell(g, a)) => cells.push((*g, *a)),
                Some(Resolved::Object(t)) => {
                    cells.push((Glyph::transparent(), Archetype::Empty));
                    placements.push(Placement::Object(t.clone(), x, y));
                }
                Some(Resolved::Portal(t)) => {
                    cells.push((Glyph::transparent(), Archetype::Empty));
                    placements.push(Placement::Portal(t.clone(), x, y));
                }
                Some(Resolved::Player) => {
                    cells.push((Glyph::transparent(), Archetype::Empty));
                    placements.push(Placement::Player(x, y));
                }
                None => {
                    errors.push(LogLine::error(format!(
                        "unknown grid character '{ch}' at ({x}, {y}); using error block"
                    )));
                    cells.push((Archetype::ErrorBlock.default_glyph(), Archetype::ErrorBlock));
                }
            }
        }
    }

    Ok((cells, placements))
}