import crypto from 'crypto'
import { hashPassword, verifyPassword } from './auth'
import { getDb, ensureReady } from './db'

export type Role = 'admin' | 'user'

export interface User {
  id: string
  username: string
  passwordHash: string
  salt: string
  role: Role
  createdAt: string
}

/** User fields safe to expose to the client (no credentials). */
export type PublicUser = Omit<User, 'passwordHash' | 'salt'>

type DbRow = Record<string, unknown>

function rowToUser(row: DbRow): User {
  return {
    id: row.id as string,
    username: row.username as string,
    passwordHash: row.password_hash as string,
    salt: row.salt as string,
    role: row.role as Role,
    createdAt: row.created_at as string,
  }
}

function toPublic(user: User): PublicUser {
  const { passwordHash: _, salt: __, ...pub } = user
  return pub
}

export async function listUsers(): Promise<PublicUser[]> {
  await ensureReady()
  const { rows } = await getDb().execute(
    'SELECT * FROM users ORDER BY created_at ASC',
  )
  return rows.map((r) => toPublic(rowToUser(r)))
}

export async function findUserByUsername(username: string): Promise<User | undefined> {
  await ensureReady()
  const { rows } = await getDb().execute({
    sql: 'SELECT * FROM users WHERE username = ? COLLATE NOCASE',
    args: [username],
  })
  return rows[0] ? rowToUser(rows[0]) : undefined
}

export async function findUserById(id: string): Promise<User | undefined> {
  await ensureReady()
  const { rows } = await getDb().execute({
    sql: 'SELECT * FROM users WHERE id = ?',
    args: [id],
  })
  return rows[0] ? rowToUser(rows[0]) : undefined
}

export async function createUser(
  username: string,
  password: string,
  role: Role,
): Promise<PublicUser> {
  await ensureReady()
  if (!username.trim()) throw new Error('Username cannot be empty')
  if (password.length < 8) throw new Error('Password must be at least 8 characters')

  const { hash, salt } = await hashPassword(password)
  const user: User = {
    id: crypto.randomUUID(),
    username: username.trim(),
    passwordHash: hash,
    salt,
    role,
    createdAt: new Date().toISOString(),
  }

  try {
    await getDb().execute({
      sql: `INSERT INTO users (id,username,password_hash,salt,role,created_at)
            VALUES (?,?,?,?,?,?)`,
      args: [user.id, user.username, user.passwordHash, user.salt, user.role, user.createdAt],
    })
  } catch (e: unknown) {
    if (String(e).includes('UNIQUE')) {
      throw new Error(`Username "${username}" is already taken`)
    }
    throw e
  }

  return toPublic(user)
}

export async function deleteUser(id: string): Promise<void> {
  await ensureReady()
  const db = getDb()

  const { rows: userRows } = await db.execute({
    sql: 'SELECT * FROM users WHERE id = ?',
    args: [id],
  })
  if (!userRows[0]) throw new Error('User not found')
  const user = rowToUser(userRows[0])

  if (user.role === 'admin') {
    const { rows: adminRows } = await db.execute(
      "SELECT COUNT(*) as cnt FROM users WHERE role = 'admin'",
    )
    if ((adminRows[0].cnt as number) <= 1) {
      throw new Error('Cannot delete the last admin account')
    }
  }

  await db.execute({ sql: 'DELETE FROM users WHERE id = ?', args: [id] })
}

export async function updatePassword(id: string, newPassword: string): Promise<void> {
  await ensureReady()
  if (newPassword.length < 8) throw new Error('Password must be at least 8 characters')

  const { rows } = await getDb().execute({
    sql: 'SELECT id FROM users WHERE id = ?',
    args: [id],
  })
  if (!rows[0]) throw new Error('User not found')

  const { hash, salt } = await hashPassword(newPassword)
  await getDb().execute({
    sql: 'UPDATE users SET password_hash = ?, salt = ? WHERE id = ?',
    args: [hash, salt, id],
  })
}

export async function authenticateUser(username: string, password: string): Promise<User | null> {
  const user = await findUserByUsername(username)
  if (!user) {
    await hashPassword(password) // constant-time dummy to prevent enumeration
    return null
  }
  const valid = await verifyPassword(password, user.passwordHash, user.salt)
  return valid ? user : null
}

export async function countUsers(): Promise<number> {
  await ensureReady()
  const { rows } = await getDb().execute('SELECT COUNT(*) as cnt FROM users')
  return rows[0].cnt as number
}

/**
 * Seeds an initial admin user if no users exist yet.
 * Reads ADMIN_USERNAME (default "admin") and ADMIN_PASSWORD from environment.
 */
export async function seedAdminIfEmpty(): Promise<void> {
  const count = await countUsers()
  if (count > 0) return
  const password = process.env.ADMIN_PASSWORD
  if (!password) return
  const username = process.env.ADMIN_USERNAME ?? 'admin'
  try {
    await createUser(username, password, 'admin')
    console.log(`[auth] Seeded initial admin user: "${username}"`)
  } catch (e) {
    console.error('[auth] Failed to seed admin user:', e)
  }
}