/**
 * JSON file database — single source of truth for server-side state.
 *
 * All mutations are atomic (write entire file via fs.rename) so concurrent
 * requests won't produce half-written files.  On HF Spaces the /data directory
 * persists across container restarts.
 *
 * NEVER import this from client code — it uses Node.js fs and has the
 * server-side access_token.  Client code goes through /api/db instead.
 */

import { readFileSync, writeFileSync, existsSync, mkdirSync, renameSync } from "node:fs";
import { resolve } from "node:path";
import { tmpdir } from "node:os";

// ---------------------------------------------------------------------------
// Types
// ---------------------------------------------------------------------------

export interface PlayerRecord {
  id: string;
  display_name: string;
  anonymous_id: string | null;
  elo_rating: number;
  games_played: number;
  star_coins: number;
  claim_code: string | null;
  spectrum_position: number | null;
  created_at: string;
}

export interface GameSessionRecord {
  id: string;
  player_id: string;
  mode: string;
  score: number;
  accuracy: number;
  streak_max: number;
  duration_ms: number;
  questions_answered: number;
  questions_correct: number;
  created_at: string;
}

export interface LeaderboardEntryRecord {
  id: string;
  player_id: string;
  player_name: string;
  mode: string;
  score: number;
  accuracy: number;
  season_id: string | null;
  created_at: string;
}

export interface PlayerAchievementRecord {
  id: string;
  player_id: string;
  achievement_id: string;
  progress: number;
  unlocked: boolean;
  unlocked_at: string | null;
}

export interface PlayerCosmeticRecord {
  id: string;
  player_id: string;
  cosmetic_id: string;
  purchased_at: string;
}

export interface PlayerEquippedRecord {
  id: string;
  player_id: string;
  category: string;
  cosmetic_id: string;
}

export interface MatchRecord {
  id: string;
  player1_id: string;
  player2_id: string;
  player1_score: number;
  player2_score: number;
  winner_id: string | null;
  elo_change: number;
  question_ids: string[];
  created_at: string;
}

export interface DebateRecord {
  id: string;
  topic_id: string;
  player1_id: string | null;
  player2_id: string | null;
  duration_minutes: number;
  rounds: number;
  winner_id: string | null;
  player1_score: number | null;
  player2_score: number | null;
  verdict: string | null;
  elo_change: number | null;
  is_practice: boolean | null;
  created_at: string;
}

export interface DebateRoundRecord {
  id: string;
  debate_id: string;
  round_number: number;
  player1_argument: string | null;
  player2_argument: string | null;
  created_at: string;
}

export interface DbData {
  players: PlayerRecord[];
  game_sessions: GameSessionRecord[];
  leaderboard_entries: LeaderboardEntryRecord[];
  player_achievements: PlayerAchievementRecord[];
  player_cosmetics: PlayerCosmeticRecord[];
  player_equipped: PlayerEquippedRecord[];
  matches: MatchRecord[];
  debates: DebateRecord[];
  debate_rounds: DebateRoundRecord[];
  // Store the seed state for deterministic IDs
  _nextId: number;
}

// ---------------------------------------------------------------------------
// File paths
// ---------------------------------------------------------------------------

function getDbDir(): string {
  // HF Spaces /data persists; fall back to tmp during dev
  return process.env.HF_SPACE_STORAGE_PATH
    ? resolve(process.env.HF_SPACE_STORAGE_PATH, "triviaverse")
    : process.env.DATA_DIR
      ? process.env.DATA_DIR
      : resolve(process.cwd(), ".data");
}

const DB_PATH = () => resolve(getDbDir(), "db.json");

// ---------------------------------------------------------------------------
// Initial data
// ---------------------------------------------------------------------------

const EMPTY_DB: DbData = {
  players: [],
  game_sessions: [],
  leaderboard_entries: [],
  player_achievements: [],
  player_cosmetics: [],
  player_equipped: [],
  matches: [],
  debates: [],
  debate_rounds: [],
  _nextId: 1,
};

// ---------------------------------------------------------------------------
// Atomic read / write
// ---------------------------------------------------------------------------

let _cache: DbData | null = null;

export function readDb(): DbData {
  if (_cache) return _cache;
  const path = DB_PATH();
  if (!existsSync(path)) {
    // Ensure directory exists
    const dir = getDbDir();
    if (!existsSync(dir)) mkdirSync(dir, { recursive: true });
    writeSync(EMPTY_DB);
    _cache = { ...EMPTY_DB };
    return _cache;
  }
  try {
    const raw = readFileSync(path, "utf-8");
    _cache = JSON.parse(raw) as DbData;
    return _cache;
  } catch {
    _cache = { ...EMPTY_DB };
    return _cache;
  }
}

function writeSync(data: DbData): void {
  const path = DB_PATH();
  const tmp = resolve(tmpdir(), `db-${Date.now()}.json`);
  writeFileSync(tmp, JSON.stringify(data, null, 1), "utf-8");
  renameSync(tmp, path);
}

export function writeDb(data: DbData): void {
  _cache = data;
  writeSync(data);
}

// ---------------------------------------------------------------------------
// ID generation
// ---------------------------------------------------------------------------

export function nextId(): string {
  const db = readDb();
  const id = String(db._nextId);
  db._nextId++;
  writeDb(db);
  return id;
}

// ---------------------------------------------------------------------------
// Claim code generation
// ---------------------------------------------------------------------------

const CLAIM_CHARSET = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789";

export function generateClaimCode(): string {
  return Array.from(
    { length: 6 },
    () => CLAIM_CHARSET[Math.floor(Math.random() * CLAIM_CHARSET.length)]
  ).join("");
}

export function generateUniqueClaimCode(): string {
  const db = readDb();
  for (let attempt = 0; attempt < 100; attempt++) {
    const code = generateClaimCode();
    if (!db.players.some((p) => p.claim_code === code)) return code;
  }
  return `X${Date.now().toString(36).toUpperCase().slice(0, 5)}`;
}

// ---------------------------------------------------------------------------
// Read helpers
// ---------------------------------------------------------------------------

export function getTimestamp(): string {
  return new Date().toISOString();
}