// Draft (client-side composition) serialization, kept pure for unit tests. The server stores
// the JSON opaquely; only the client interprets {rack_order, board_tiles}. The rack
// order is a comma-joined permutation of the server rack's indices, in the player's visual
// order; the board tiles are the tiles laid but not yet submitted.

import type { Tile } from './model';
import type { PendingTile } from './placement';

interface DraftData {
  rack_order: string;
  board_tiles: Tile[];
}

/** serializeDraft builds the JSON to persist: the rack order and the pending board tiles. */
export function serializeDraft(rackOrder: number[], pending: PendingTile[]): string {
  const data: DraftData = {
    rack_order: rackOrder.join(','),
    board_tiles: pending.map((p) => ({ row: p.row, col: p.col, letter: p.letter, blank: p.blank })),
  };
  return JSON.stringify(data);
}

/** parseDraft decodes a stored draft, or null when empty or malformed. */
export function parseDraft(json: string): { rackOrder: number[]; tiles: Tile[] } | null {
  if (!json) return null;
  try {
    const d = JSON.parse(json) as Partial<DraftData>;
    const rackOrder = String(d.rack_order ?? '')
      .split(',')
      .filter((s) => s !== '')
      .map(Number);
    const tiles = Array.isArray(d.board_tiles) ? d.board_tiles : [];
    return { rackOrder, tiles };
  } catch {
    return null;
  }
}

/**
 * validRackOrder returns order when it is a permutation of [0, len), else null — so a stale
 * order (the rack changed since the draft was saved) is ignored and the server order is kept.
 */
export function validRackOrder(order: number[], len: number): number[] | null {
  if (order.length !== len) return null;
  const seen = new Set<number>();
  for (const i of order) {
    if (!Number.isInteger(i) || i < 0 || i >= len || seen.has(i)) return null;
    seen.add(i);
  }
  return order;
}

/**
 * liveDraftTiles drops saved tiles whose cell is now occupied on the committed board (the
 * opponent has since played there) — the position-only reconcile after a refresh.
 */
export function liveDraftTiles(tiles: Tile[], occupied: (row: number, col: number) => boolean): Tile[] {
  return tiles.filter((t) => !occupied(t.row, t.col));
}