import { createRng, shuffle } from "../rng";

// Legacy export — board still imports it but we no longer use it for hints
export type ShapeHint = "free";

export interface Region {
  id: number;
  cells: [number, number][];     // all cells in grid
  hintCell: [number, number];    // topmost-leftmost cell (always in solution)
  relCells: [number, number][];  // shape normalised to (0,0) origin
  previewRows: number;
  previewCols: number;
  size: number;
  color: string;
}

export interface PatchesPuzzle {
  size: number; // 6
  regions: Region[];
  grid: number[][];  // grid[r][c] = regionId
}

export const PATCH_COLORS = [
  "#e8b040", // gold
  "#4db86e", // green
  "#4a9fd4", // blue
  "#e05050", // red
  "#e07830", // orange
  "#30b8b0", // teal
  "#9060c8", // purple
  "#d06898", // pink
];

/** Place N seeds spread across the grid (no two adjacent). */
function placeSeeds(size: number, n: number, rng: () => number): [number, number][] {
  const all: [number, number][] = [];
  for (let r = 0; r < size; r++)
    for (let c = 0; c < size; c++)
      all.push([r, c]);
  const pool = shuffle(all, rng);

  const seeds: [number, number][] = [];
  const banned = new Set<string>();

  for (const [r, c] of pool) {
    if (seeds.length >= n) break;
    if (banned.has(`${r},${c}`)) continue;
    seeds.push([r, c]);
    // Ban cell + its orthogonal neighbours (avoid touching seeds)
    for (const [dr, dc] of [[0,0],[-1,0],[1,0],[0,-1],[0,1]])
      banned.add(`${r+dr},${c+dc}`);
  }
  return seeds;
}

/**
 * Grow N polyomino regions from seeds, then flood-fill any remaining cells.
 * Returns a size×size grid where grid[r][c] = regionId.
 */
function growPolyominos(size: number, seeds: [number, number][], rng: () => number): number[][] {
  const grid: number[][] = Array.from({ length: size }, () => Array(size).fill(-1));
  const sizes: number[] = Array(seeds.length).fill(0);
  const n = seeds.length;
  const target = Math.round((size * size) / n);

  // Place seeds
  for (let i = 0; i < n; i++) {
    grid[seeds[i][0]][seeds[i][1]] = i;
    sizes[i] = 1;
  }

  // BFS frontier per region
  const ADJ: [number, number][] = [[-1,0],[1,0],[0,-1],[0,1]];

  // Build initial frontiers
  const frontiers: Set<string>[] = Array.from({ length: n }, (_, id) => {
    const s = new Set<string>();
    const [sr, sc] = seeds[id];
    for (const [dr, dc] of ADJ) {
      const nr = sr+dr, nc = sc+dc;
      if (nr>=0 && nr<size && nc>=0 && nc<size && grid[nr][nc] === -1)
        s.add(`${nr},${nc}`);
    }
    return s;
  });

  // Grow until each region hits its target (randomised round-robin)
  let anyGrew = true;
  while (anyGrew) {
    anyGrew = false;
    const order = shuffle(Array.from({ length: n }, (_, i) => i), rng);
    for (const id of order) {
      if (sizes[id] >= target) continue;
      // Pick a random free frontier cell
      const candidates = [...frontiers[id]].filter(k => {
        const [r, c] = k.split(",").map(Number);
        return grid[r][c] === -1;
      });
      if (!candidates.length) continue;
      const k = candidates[Math.floor(rng() * candidates.length)];
      const [nr, nc] = k.split(",").map(Number);
      if (grid[nr][nc] !== -1) { frontiers[id].delete(k); continue; } // race condition
      grid[nr][nc] = id;
      sizes[id]++;
      frontiers[id].delete(k);
      anyGrew = true;
      // Expand frontier
      for (const [dr, dc] of ADJ) {
        const nnr = nr+dr, nnc = nc+dc;
        if (nnr>=0 && nnr<size && nnc>=0 && nnc<size && grid[nnr][nnc] === -1)
          frontiers[id].add(`${nnr},${nnc}`);
      }
    }
  }

  // Flood-fill unassigned cells → smallest adjacent region
  let changed = true;
  while (changed) {
    changed = false;
    for (let r = 0; r < size; r++)
      for (let c = 0; c < size; c++) {
        if (grid[r][c] !== -1) continue;
        let best = -1, bestSz = Infinity;
        for (const [dr, dc] of ADJ) {
          const nr = r+dr, nc = c+dc;
          if (nr<0 || nr>=size || nc<0 || nc>=size) continue;
          const id = grid[nr][nc];
          if (id === -1) continue;
          if (sizes[id] < bestSz) { bestSz = sizes[id]; best = id; }
        }
        if (best !== -1) { grid[r][c] = best; sizes[best]++; changed = true; }
      }
  }

  return grid;
}

export function generatePatches(date: string): PatchesPuzzle {
  const seed = date.split("-").reduce((a, n) => a * 1000 + parseInt(n), 0) + 333;
  const rng = createRng(seed);
  const size = 6;

  // 7 or 8 regions → avg 4.5–5 cells each, with interesting shapes
  const n = 7 + Math.floor(rng() * 2);

  const seeds = placeSeeds(size, n, rng);
  const grid = growPolyominos(size, seeds, rng);

  const numRegions = Math.max(...grid.flat()) + 1;

  // Collect cells per region
  const regionCells = new Map<number, [number, number][]>();
  for (let r = 0; r < size; r++)
    for (let c = 0; c < size; c++) {
      const id = grid[r][c];
      if (!regionCells.has(id)) regionCells.set(id, []);
      regionCells.get(id)!.push([r, c]);
    }

  const colors = shuffle([...PATCH_COLORS], rng);

  const regions: Region[] = [];
  for (let id = 0; id < numRegions; id++) {
    const cells = regionCells.get(id) ?? [];
    if (!cells.length) continue;

    // Hint cell = topmost row, then leftmost col
    const hintCell = cells.reduce((best, cur) =>
      cur[0] < best[0] || (cur[0] === best[0] && cur[1] < best[1]) ? cur : best
    );

    // Normalised shape (origin at 0,0)
    const minR = Math.min(...cells.map(([r]) => r));
    const minC = Math.min(...cells.map(([, c]) => c));
    const relCells: [number, number][] = cells.map(([r, c]) => [r - minR, c - minC]);
    const previewRows = Math.max(...relCells.map(([r]) => r)) + 1;
    const previewCols = Math.max(...relCells.map(([, c]) => c)) + 1;

    regions.push({
      id,
      cells,
      hintCell,
      relCells,
      previewRows,
      previewCols,
      size: cells.length,
      color: colors[id % colors.length],
    });
  }

  return { size, regions, grid };
}