const initSqlJs = require('sql.js');
const path = require('path');
const fs = require('fs');

const DATA_DIR = path.join(__dirname, '..', 'data');
const DB_PATH = path.join(DATA_DIR, 'exams.db');

let db = null;

async function initDb() {
  if (!fs.existsSync(DATA_DIR)) {
    fs.mkdirSync(DATA_DIR, { recursive: true });
  }

  const SQL = await initSqlJs();

  if (fs.existsSync(DB_PATH)) {
    const buffer = fs.readFileSync(DB_PATH);
    db = new SQL.Database(buffer);
  } else {
    db = new SQL.Database();
  }

  db.run('PRAGMA foreign_keys = ON');

  db.run(`
    CREATE TABLE IF NOT EXISTS users (
      id INTEGER PRIMARY KEY AUTOINCREMENT,
      login TEXT UNIQUE NOT NULL,
      password TEXT,
      name TEXT NOT NULL,
      email TEXT,
      role TEXT DEFAULT 'teacher',
      auth_type TEXT DEFAULT 'local',
      groups TEXT,
      created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
      last_login DATETIME
    )
  `);

  db.run(`
    CREATE TABLE IF NOT EXISTS students (
      id INTEGER PRIMARY KEY AUTOINCREMENT,
      last_name TEXT NOT NULL,
      first_name TEXT NOT NULL,
      patronymic TEXT DEFAULT '',
      class TEXT DEFAULT '',
      school_code TEXT DEFAULT '',
      passport_series TEXT DEFAULT '',
      passport_number TEXT DEFAULT '',
      created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
      UNIQUE(last_name, first_name, patronymic, class)
    )
  `);

  db.run(`
    CREATE TABLE IF NOT EXISTS subjects (
      code TEXT PRIMARY KEY,
      name TEXT NOT NULL,
      exam_date TEXT DEFAULT '',
      is_mandatory INTEGER DEFAULT 0
    )
  `);

  db.run(`
    CREATE TABLE IF NOT EXISTS exam_results (
      id INTEGER PRIMARY KEY AUTOINCREMENT,
      student_id INTEGER NOT NULL,
      subject_code TEXT NOT NULL,
      primary_score INTEGER,
      grade INTEGER,
      FOREIGN KEY (student_id) REFERENCES students(id) ON DELETE CASCADE,
      FOREIGN KEY (subject_code) REFERENCES subjects(code),
      UNIQUE(student_id, subject_code)
    )
  `);

  db.run('INSERT OR IGNORE INTO subjects (code, name, is_mandatory) VALUES (?, ?, 1)', ['01', 'Русский язык']);
  db.run('INSERT OR IGNORE INTO subjects (code, name, is_mandatory) VALUES (?, ?, 1)', ['02', 'Математика']);

  saveDb();

  // Миграция: перенос Русского/Математики в обязательные слоты 01/02, если они пусты
  migrateMandatorySubjects();

  console.log('БД инициализирована');
  return db;
}

function saveDb() {
  if (!db) return;
  const data = db.export();
  const buffer = Buffer.from(data);
  fs.writeFileSync(DB_PATH, buffer);
}

function migrateMandatorySubjects() {
  if (!db) return;

  // Найти русский язык с кодом ≠ 01, где слот 01 пуст (нет grade)
  const rusRows = dbAll(`
    SELECT DISTINCT er.student_id, er.subject_code, er.primary_score, er.grade
    FROM exam_results er
    JOIN subjects s ON s.code = er.subject_code
    WHERE s.name = 'Русский язык' AND er.subject_code != '01'
    AND NOT EXISTS (
      SELECT 1 FROM exam_results er2
      WHERE er2.student_id = er.student_id AND er2.subject_code = '01' AND er2.grade IS NOT NULL
    )
  `);
  for (const row of rusRows) {
    dbRun('INSERT OR REPLACE INTO exam_results (student_id, subject_code, primary_score, grade) VALUES (?, ?, ?, ?)', [row.student_id, '01', row.primary_score, row.grade]);
    dbRun('DELETE FROM exam_results WHERE student_id = ? AND subject_code = ?', [row.student_id, row.subject_code]);
  }

  // Найти математику с кодом ≠ 02, где слот 02 пуст
  const mathRows = dbAll(`
    SELECT DISTINCT er.student_id, er.subject_code, er.primary_score, er.grade
    FROM exam_results er
    JOIN subjects s ON s.code = er.subject_code
    WHERE s.name = 'Математика' AND er.subject_code != '02'
    AND NOT EXISTS (
      SELECT 1 FROM exam_results er2
      WHERE er2.student_id = er.student_id AND er2.subject_code = '02' AND er2.grade IS NOT NULL
    )
  `);
  for (const row of mathRows) {
    dbRun('INSERT OR REPLACE INTO exam_results (student_id, subject_code, primary_score, grade) VALUES (?, ?, ?, ?)', [row.student_id, '02', row.primary_score, row.grade]);
    dbRun('DELETE FROM exam_results WHERE student_id = ? AND subject_code = ?', [row.student_id, row.subject_code]);
  }

  // Удалить лишние subjects (не 01/02) для русского и математики, если они без результатов
  dbRun(`DELETE FROM subjects WHERE (name = 'Русский язык' AND code != '01') OR (name = 'Математика' AND code != '02')`);

  if (rusRows.length > 0 || mathRows.length > 0) {
    console.log(`Миграция: перенесено в обязательные — русский: ${rusRows.length}, математика: ${mathRows.length}`);
    saveDb();
  }
}

function getDb() {
  if (!db) throw new Error('БД не инициализирована.');
  return db;
}

// Wrappers emulating better-sqlite3 API
function dbGet(sql, params = []) {
  const st = db.prepare(sql);
  st.bind(params);
  const hasRow = st.step();
  const row = hasRow ? st.getAsObject() : null;
  st.free();
  return row;
}

function dbAll(sql, params = []) {
  const st = db.prepare(sql);
  st.bind(params);
  const rows = [];
  while (st.step()) {
    rows.push(st.getAsObject());
  }
  st.free();
  return rows;
}

function dbRun(sql, params = []) {
  const before = db.getRowsModified();
  db.run(sql, params);
  const after = db.getRowsModified();
  return { changes: after - before };
}

function dbLastInsertId() {
  const r = db.exec('SELECT last_insert_rowid() as id');
  return r.length ? r[0].values[0][0] : null;
}

function dbExec(sql) {
  db.run(sql);
}

function dbBegin() { db.run('BEGIN'); }
function dbCommit() { db.run('COMMIT'); }
function dbRollback() { try { db.run('ROLLBACK'); } catch (e) {} }

module.exports = { initDb, getDb, saveDb, dbGet, dbAll, dbRun, dbLastInsertId, dbExec, dbBegin, dbCommit, dbRollback };