// Instructor account CRUD + the small set of invariants that protect the platform from
// locking itself out (never zero active owners). Shared by the auth routes (login/session) and
// the admin instructor-management routes.

const { hashPassword } = require('./auth/password');

function publicInstructor(row) {
  if (!row) return null;
  const { password_hash, ...rest } = row;
  return rest;
}

async function getActiveInstructor(pool, instructorId) {
  const { rows } = await pool.query(
    `SELECT * FROM instructors WHERE instructor_id = $1 AND status = 'active'`, [instructorId]
  );
  return rows[0] || null;
}

// Returns the row regardless of status — the login flow needs to tell "wrong password" apart
// from "correct password, but account is deactivated" (see instructor-auth-routes.js), which
// requires seeing inactive accounts too.
async function getInstructorByEmail(pool, email) {
  const { rows } = await pool.query(`SELECT * FROM instructors WHERE email = $1`, [String(email).toLowerCase().trim()]);
  return rows[0] || null;
}

async function listInstructors(pool) {
  const { rows } = await pool.query(`SELECT * FROM instructors ORDER BY created_at`);
  return rows.map(publicInstructor);
}

async function countActiveOwners(pool, excludingId) {
  const { rows } = await pool.query(
    `SELECT count(*)::int AS n FROM instructors WHERE role = 'owner' AND status = 'active' AND instructor_id != $1`,
    [excludingId || '00000000-0000-0000-0000-000000000000']
  );
  return rows[0].n;
}

async function createInstructor(pool, { email, displayName, role, password }) {
  const emailLower = String(email).toLowerCase().trim();
  const passwordHash = hashPassword(password);
  const client = await pool.connect();
  try {
    await client.query('BEGIN');
    const { rows } = await client.query(
      `INSERT INTO instructors (email, display_name, password_hash, role) VALUES ($1, $2, $3, $4) RETURNING *`,
      [emailLower, displayName.trim(), passwordHash, role || 'instructor']
    );
    const instructor = rows[0];
    await client.query(
      `INSERT INTO auth_identities (instructor_id, provider, provider_subject, provider_email) VALUES ($1, 'local', $2, $3)`,
      [instructor.instructor_id, String(instructor.instructor_id), emailLower]
    );
    await client.query('COMMIT');
    return instructor;
  } catch (e) {
    await client.query('ROLLBACK');
    throw e;
  } finally {
    client.release();
  }
}

// Guards the one invariant that matters: never let the platform end up with zero active
// owners. Called before any update that would deactivate an owner or demote their role.
async function assertNotLastOwner(pool, instructorId) {
  const remaining = await countActiveOwners(pool, instructorId);
  if (remaining === 0) {
    const err = new Error('Cannot remove the last active owner.');
    err.code = 'LAST_OWNER';
    throw err;
  }
}

module.exports = { publicInstructor, getActiveInstructor, getInstructorByEmail, listInstructors, countActiveOwners, createInstructor, assertNotLastOwner };