/**
 * A tilemap is a grid of cells, and every cell names the tile lying there. Which of that tile's
 * quarters a cell shows is *not* stored: it follows from the neighbours and is worked out
 * while drawing (#128), so painting one cell fixes the edges of the ones around it by itself.
 *
 * Cells are sparse – a map from `"x,y"` to a tile id – rather than one entry per grid square.
 * A map is what painting, erasing and reading a neighbour all want, and changing the grid size then
 * moves nothing: what falls outside is simply not drawn and comes back when the grid grows again.
 * The project file stores them more compactly (#134, `store/tilemapCells.ts`).
 */
import type { TileAsset, TilemapLayer } from './Asset';
import { type Neighbours, type TileQuadrants, tileQuadrants } from './autotile';
import { type TileKind, tileKind } from './tile';
import type { PropertyBag } from './Properties';
import { findAssetOf, type Project } from './Project';
import { cellsTileIds, cellsVersion, KeyedMemo } from './tilemapMemo';

export const TILEMAP_COLUMNS_KEY = 'columns';
export const TILEMAP_ROWS_KEY = 'rows';
export const TILEMAP_TILE_KEY = 'tileSize';
/** The most columns or rows a grid may have – the schema's limit, and the edge buttons' too. */
export const TILEMAP_MAX_CELLS = 1000;

/**
 * The grid is read from a property bag rather than from the asset: a placed tilemap may override
 * its size like any other row, and the footprint the scene view picks and frames by has nothing
 * but the bag (see `properties/bounds.ts`).
 */
export function tilemapColumns(props: PropertyBag): number {
  return wholeAbove(props[TILEMAP_COLUMNS_KEY], 20);
}

export function tilemapRows(props: PropertyBag): number {
  return wholeAbove(props[TILEMAP_ROWS_KEY], 15);
}

/** Side of one cell in world units; the tile's own pictures are scaled onto it. */
export function tilemapTileSize(props: PropertyBag): number {
  const size = Number(props[TILEMAP_TILE_KEY]);
  return Number.isFinite(size) && size > 0 ? size : 48;
}

function wholeAbove(value: unknown, fallback: number): number {
  const count = Math.floor(Number(value));
  return Number.isFinite(count) && count >= 1 ? count : fallback;
}

export function tilemapSize(props: PropertyBag): { w: number; h: number } {
  const tile = tilemapTileSize(props);
  return { w: tilemapColumns(props) * tile, h: tilemapRows(props) * tile };
}

/** A cell of the grid by column and row; `0,0` is the top-left corner. */
export interface Cell {
  x: number;
  y: number;
}

export function cellKey(x: number, y: number): string {
  return `${x},${y}`;
}

/** Read without `split`: a map reads every key of a layer again after each painted cell (#347). */
export function parseCellKey(key: string): Cell | null {
  const comma = key.indexOf(',');
  if (comma < 0) return null;
  const end = key.indexOf(',', comma + 1);
  const x = Number(key.slice(0, comma));
  const y = Number(end < 0 ? key.slice(comma + 1) : key.slice(comma + 1, end));
  return Number.isInteger(x) && Number.isInteger(y) ? { x, y } : null;
}

export function cellAt(layer: TilemapLayer, x: number, y: number): string {
  return layer.cells[cellKey(x, y)] ?? '';
}

/**
 * The tile a cell holds as far as anything but the file is concerned: `''` for an empty cell and for
 * one naming a tile the project does not have (#268). Such a cell draws and blocks nothing, so it
 * reads and fills as empty too.
 */
export function presentTile(project: Project, tileId: string): string {
  return tileId !== '' && findAssetOf(project, tileId, 'tile') ? tileId : '';
}

/** The cells without those naming `tileId`, or null when none does. */
export function cellsWithout(cells: Record<string, string>, tileId: string): Record<string, string> | null {
  if (!Object.values(cells).includes(tileId)) return null;
  return Object.fromEntries(Object.entries(cells).filter(([, id]) => id !== tileId));
}

export function isLayerVisible(layer: TilemapLayer): boolean {
  return layer.hidden !== true;
}

/** How far a layer is drawn above its tilemap's own `z` (#174); a layer never given one sits on it. */
export function layerZ(layer: TilemapLayer): number {
  return layer.z ?? 0;
}

export function findLayer(asset: { layers: TilemapLayer[] }, layerId: string): TilemapLayer | undefined {
  return asset.layers.find((layer) => layer.id === layerId);
}

export function inGrid(props: PropertyBag, x: number, y: number): boolean {
  return x >= 0 && y >= 0 && x < tilemapColumns(props) && y < tilemapRows(props);
}

/**
 * Which neighbours a cell is joined to. Only the *same* tile joins: a different one counts as
 * empty, so every autotile draws its own border against everything else – what the RPG-Maker sheets
 * are drawn for. Outside the grid counts as empty too, so a map ends with a proper edge.
 */
export function neighboursOf(
  props: PropertyBag,
  layer: TilemapLayer,
  x: number,
  y: number,
  tileId: string,
): Neighbours {
  const same = (dx: number, dy: number): boolean =>
    inGrid(props, x + dx, y + dy) && cellAt(layer, x + dx, y + dy) === tileId;
  return {
    n: same(0, -1),
    e: same(1, 0),
    s: same(0, 1),
    w: same(-1, 0),
    ne: same(1, -1),
    se: same(1, 1),
    sw: same(-1, 1),
    nw: same(-1, -1),
  };
}

/**
 * A layer's painted cells inside the grid, read once per content and grid size: in reading order,
 * and by place. Reading the `x,y` keys again for every cell and each of its neighbours was most of
 * what one painted cell cost a big map (#347).
 */
export interface LayerCells {
  columns: number;
  rows: number;
  list: readonly { x: number; y: number; tileId: string }[];
  /** Tile id by `y * columns + x`. */
  at: ReadonlyMap<number, string>;
}

const indexed = new WeakMap<Record<string, string>, LayerCells & { version: number }>();

export function layerCells(props: PropertyBag, layer: TilemapLayer): LayerCells {
  const columns = tilemapColumns(props);
  const rows = tilemapRows(props);
  const version = cellsVersion(layer.cells);
  const held = indexed.get(layer.cells);
  if (held && held.version === version && held.columns === columns && held.rows === rows) return held;
  const at = new Map<number, string>();
  for (const [key, tileId] of Object.entries(layer.cells)) {
    const cell = parseCellKey(key);
    if (!tileId || !cell || cell.x < 0 || cell.y < 0 || cell.x >= columns || cell.y >= rows) continue;
    at.set(cell.y * columns + cell.x, tileId);
  }
  const list = [...at.keys()]
    .sort((a, b) => a - b)
    .map((i) => ({ x: i % columns, y: Math.floor(i / columns), tileId: at.get(i)! }));
  const fresh = { columns, rows, list, at, version };
  indexed.set(layer.cells, fresh);
  return fresh;
}

/** `neighboursOf`, read from the index. */
export function neighboursIn(cells: LayerCells, x: number, y: number, tileId: string): Neighbours {
  const { columns, rows, at } = cells;
  const same = (dx: number, dy: number): boolean => {
    const nx = x + dx;
    const ny = y + dy;
    return nx >= 0 && ny >= 0 && nx < columns && ny < rows && at.get(ny * columns + nx) === tileId;
  };
  return {
    n: same(0, -1),
    e: same(1, 0),
    s: same(0, 1),
    w: same(-1, 0),
    ne: same(1, -1),
    se: same(1, 1),
    sw: same(-1, 1),
    nw: same(-1, -1),
  };
}

/** One cell as it is drawn: where it sits, which tile it is and which quarters build it. */
export interface TileDraw {
  x: number;
  y: number;
  tileId: string;
  quadrants: TileQuadrants;
}

/**
 * Every cell of one layer that is inside the grid and names a tile that exists, in reading order
 * so the result is the same list twice. A cell naming a tile the project does not have is skipped
 * (see `presentTile`).
 */
export function layerTiles(project: Project, props: PropertyBag, layer: TilemapLayer): readonly TileDraw[] {
  const kinds = new Map<string, TileKind>();
  for (const id of cellsTileIds(layer.cells)) {
    const tile: TileAsset | undefined = findAssetOf(project, id, 'tile');
    if (tile) kinds.set(id, tileKind(tile));
  }
  const key = [
    tilemapColumns(props),
    tilemapRows(props),
    cellsVersion(layer.cells),
    [...kinds].map(([id, kind]) => `${id}:${kind}`).join(','),
  ].join('|');
  return drawn.get(key, () => workOutLayerTiles(props, layer, kinds));
}

const drawn = new KeyedMemo<readonly TileDraw[]>();

function workOutLayerTiles(
  props: PropertyBag,
  layer: TilemapLayer,
  kinds: Map<string, TileKind>,
): TileDraw[] {
  const cells = layerCells(props, layer);
  const tiles: TileDraw[] = [];
  for (const { x, y, tileId } of cells.list) {
    const kind = kinds.get(tileId);
    if (!kind) continue;
    tiles.push({ x, y, tileId, quadrants: tileQuadrants(kind, neighboursIn(cells, x, y, tileId)) });
  }
  return tiles;
}

/**
 * The layer names of every tilemap in the project, each once, in asset and layer order. A node
 * picks a layer by name before it knows which map it will be given (#135), so it is offered them all.
 */
export function tilemapLayerNames(project: Project): string[] {
  const names = project.assets.flatMap((asset) =>
    asset.type === 'tilemap' ? asset.layers.map((layer) => layer.name) : [],
  );
  return [...new Set(names)];
}

/**
 * The cell a point in the tilemap's own frame falls into. The grid is centred on the object's
 * position, as every footprint is, so the top-left corner lies half a map up and to the left.
 */
export function cellAtPoint(props: PropertyBag, x: number, y: number): Cell {
  const tile = tilemapTileSize(props);
  const { w, h } = tilemapSize(props);
  return { x: Math.floor((x + w / 2) / tile), y: Math.floor((y + h / 2) / tile) };
}

/** Where the top-left corner of a cell sits in the tilemap's own frame, in world units. */
export function cellOrigin(props: PropertyBag, x: number, y: number): { x: number; y: number } {
  const tile = tilemapTileSize(props);
  const { w, h } = tilemapSize(props);
  return { x: x * tile - w / 2, y: y * tile - h / 2 };
}

/** A side of the grid that grows or shrinks (#136). */
export type TilemapEdge = 'left' | 'top' | 'right' | 'bottom';

export const TILEMAP_EDGES: readonly TilemapEdge[] = ['left', 'top', 'right', 'bottom'];

/** Left and right change the columns, top and bottom the rows. */
export function edgeSizeKey(edge: TilemapEdge): string {
  return edge === 'left' || edge === 'right' ? TILEMAP_COLUMNS_KEY : TILEMAP_ROWS_KEY;
}

/**
 * One layer's cells moved by whole cells. Growing at the left or top edge is this: cell `0,0` is
 * always the top-left corner, so what was painted moves one column or row further in. Nothing is
 * dropped – a cell pushed below zero lies outside the grid and comes back when the edge grows again.
 */
export function shiftedCells(cells: Record<string, string>, dx: number, dy: number): Record<string, string> {
  const moved: Record<string, string> = {};
  for (const [key, tileId] of Object.entries(cells)) {
    const at = parseCellKey(key);
    if (at) moved[cellKey(at.x + dx, at.y + dy)] = tileId;
  }
  return moved;
}

/**
 * How far the origin moves, in the tilemap's own frame, for the painted cells to stay where they are
 * when `edge` gains `count` cells (negative removes them). The grid is centred on the origin, so
 * every added column pushes the content half a cell away from that edge; the origin follows by as
 * much the other way.
 */
export function edgeCompensation(
  edge: TilemapEdge,
  count: number,
  tileSize: number,
): { x: number; y: number } {
  const half = (count * tileSize) / 2;
  switch (edge) {
    case 'left':
      return { x: -half, y: 0 };
    case 'right':
      return { x: half, y: 0 };
    case 'top':
      return { x: 0, y: -half };
    case 'bottom':
      return { x: 0, y: half };
  }
}

/** The cells of the rectangle between two corners, both included and clipped to the grid. */
export function cellsInRect(props: PropertyBag, a: Cell, b: Cell): Cell[] {
  const cells: Cell[] = [];
  const x0 = Math.max(0, Math.min(a.x, b.x));
  const x1 = Math.min(tilemapColumns(props) - 1, Math.max(a.x, b.x));
  const y0 = Math.max(0, Math.min(a.y, b.y));
  const y1 = Math.min(tilemapRows(props) - 1, Math.max(a.y, b.y));
  for (let y = y0; y <= y1; y++) for (let x = x0; x <= x1; x++) cells.push({ x, y });
  return cells;
}

/**
 * The cells a fill from `start` changes (#133): every cell reached through its four edge
 * neighbours that holds what `start` holds – empty included – clipped to the grid. Diagonals do not
 * count, or a fill would leak through the gap between two corners. Filling with the tile already
 * there changes nothing, so that returns no cells. A cell naming a missing tile is empty here.
 */
export function floodFill(
  project: Project,
  props: PropertyBag,
  layer: TilemapLayer,
  start: Cell,
  tileId: string,
): Cell[] {
  if (!inGrid(props, start.x, start.y)) return [];
  const present = new Map<string, string>();
  const tileAt = (x: number, y: number): string => {
    const id = cellAt(layer, x, y);
    let shown = present.get(id);
    if (shown === undefined) present.set(id, (shown = presentTile(project, id)));
    return shown;
  };
  const from = tileAt(start.x, start.y);
  if (from === tileId) return [];
  // The list is its own queue: everything in it is filled, and it is walked while it grows.
  const cells = [{ x: start.x, y: start.y }];
  const seen = new Set([cellKey(start.x, start.y)]);
  for (let index = 0; index < cells.length; index++) {
    const cell = cells[index]!;
    for (const [dx, dy] of [
      [0, -1],
      [1, 0],
      [0, 1],
      [-1, 0],
    ] as const) {
      const x = cell.x + dx;
      const y = cell.y + dy;
      const key = cellKey(x, y);
      if (seen.has(key) || !inGrid(props, x, y) || tileAt(x, y) !== from) continue;
      seen.add(key);
      cells.push({ x, y });
    }
  }
  return cells;
}

/**
 * The cells a stroke from one cell to another covers. A pointer jumps between events, so without
 * this a fast drag would paint dots instead of a line.
 */
export function cellsAlong(from: Cell, to: Cell): Cell[] {
  const steps = Math.max(Math.abs(to.x - from.x), Math.abs(to.y - from.y));
  if (steps === 0) return [{ ...to }];
  const cells: Cell[] = [];
  for (let i = 1; i <= steps; i++)
    cells.push({
      x: Math.round(from.x + ((to.x - from.x) * i) / steps),
      y: Math.round(from.y + ((to.y - from.y) * i) / steps),
    });
  return cells;
}