import fs from 'node:fs/promises'
import path from 'node:path'
import { fileURLToPath } from 'node:url'
import crypto from 'node:crypto'
import { hashPassword } from './crypto.js'

export type SessionKind = 'full' | 'mfa_pending'

export type DbUser = {
  id: string
  email: string
  password_hash: string
  created_at: string
  login_failures?: number
  login_locked_until?: string | null
}

export type DbMfaSettings = {
  user_id: string
  totp_enabled: boolean
  totp_secret: string | null
  totp_secret_pending: string | null
  totp_verified_at: string | null
  backup_batch_id: string | null
  updated_at: string
  mfa_failures?: number
  mfa_locked_until?: string | null
}

export type DbBackupCode = {
  id: string
  user_id: string
  batch_id: string
  code_hash: string
  created_at: string
  used_at: string | null
}

export type DbRecoveryRequest = {
  id: string
  user_id: string
  method: 'backup_code' | 'password'
  status: 'pending' | 'completed' | 'cancelled'
  created_at: string
  resolved_at: string | null
}

export type DbAuditLog = {
  id: string
  user_id: string
  action: string
  result: 'success' | 'failure'
  ip: string | null
  user_agent: string | null
  meta: Record<string, unknown>
  created_at: string
}

export type DbSession = {
  id: string
  user_id: string
  kind: SessionKind
  created_at: string
  expires_at: string
}

export type DbSchema = {
  users: DbUser[]
  mfa_settings: DbMfaSettings[]
  backup_codes: DbBackupCode[]
  recovery_requests: DbRecoveryRequest[]
  audit_logs: DbAuditLog[]
  sessions: DbSession[]
}

const __filename = fileURLToPath(import.meta.url)
const __dirname = path.dirname(__filename)

let dataDir = process.env.DATA_DIR
  ? path.resolve(process.env.DATA_DIR)
  : path.resolve(__dirname, '../data')
let dbPath = path.resolve(dataDir, 'db.json')

function switchDataDir(nextDir: string) {
  dataDir = path.resolve(nextDir)
  dbPath = path.resolve(dataDir, 'db.json')
}

async function ensureDataDirWritable(): Promise<void> {
  try {
    await fs.mkdir(dataDir, { recursive: true })
    return
  } catch (e) {
    const err = e as NodeJS.ErrnoException
    if (err?.code === 'EACCES' || err?.code === 'EPERM' || err?.code === 'EROFS') {
      switchDataDir('/tmp/totp-2fa-closedloop')
      await fs.mkdir(dataDir, { recursive: true })
      return
    }
    throw e
  }
}

let queue: Promise<unknown> = Promise.resolve()

export function nowIso() {
  return new Date().toISOString()
}

export function newId() {
  return crypto.randomUUID()
}

function createEmptyDb(): DbSchema {
  return {
    users: [],
    mfa_settings: [],
    backup_codes: [],
    recovery_requests: [],
    audit_logs: [],
    sessions: [],
  }
}

async function readDbFile(): Promise<DbSchema> {
  await ensureDataDirWritable()
  try {
    const raw = await fs.readFile(dbPath, 'utf8')
    const parsed = JSON.parse(raw) as DbSchema
    const db = {
      ...createEmptyDb(),
      ...parsed,
    }
    await ensureDemoAccount(db)
    return db
  } catch (e) {
    const err = e as NodeJS.ErrnoException
    if (err?.code === 'ENOENT') {
      const empty = createEmptyDb()
      await ensureDemoAccount(empty)
      await fs.writeFile(dbPath, JSON.stringify(empty, null, 2), 'utf8')
      return empty
    }
    if (err?.code === 'EACCES' || err?.code === 'EPERM' || err?.code === 'EROFS') {
      switchDataDir('/tmp/totp-2fa-closedloop')
      await fs.mkdir(dataDir, { recursive: true })
      const empty = createEmptyDb()
      await ensureDemoAccount(empty)
      await fs.writeFile(dbPath, JSON.stringify(empty, null, 2), 'utf8')
      return empty
    }
    throw e
  }
}

async function ensureDemoAccount(db: DbSchema): Promise<void> {
  const email = 'demo@example.com'
  const password = 'Demo12345'

  let user = db.users.find((u) => u.email === email)
  if (!user) {
    const userId = newId()
    const passwordHash = await hashPassword(password)
    user = {
      id: userId,
      email,
      password_hash: passwordHash,
      created_at: nowIso(),
      login_failures: 0,
      login_locked_until: null,
    }
    db.users.push(user)
  }

  user.login_failures = 0
  user.login_locked_until = null

  let mfa = db.mfa_settings.find((x) => x.user_id === user.id)
  if (!mfa) {
    db.mfa_settings.push({
      user_id: user.id,
      totp_enabled: false,
      totp_secret: null,
      totp_secret_pending: null,
      totp_verified_at: null,
      backup_batch_id: null,
      updated_at: nowIso(),
      mfa_failures: 0,
      mfa_locked_until: null,
    })
    mfa = db.mfa_settings.find((x) => x.user_id === user.id) ?? null
  }

  if (mfa) {
    mfa.mfa_failures = 0
    mfa.mfa_locked_until = null
  }
}

async function writeDbFile(db: DbSchema): Promise<void> {
  await ensureDataDirWritable()
  try {
    await fs.writeFile(dbPath, JSON.stringify(db, null, 2), 'utf8')
  } catch (e) {
    const err = e as NodeJS.ErrnoException
    if (err?.code === 'EACCES' || err?.code === 'EPERM' || err?.code === 'EROFS') {
      switchDataDir('/tmp/totp-2fa-closedloop')
      await fs.mkdir(dataDir, { recursive: true })
      await fs.writeFile(dbPath, JSON.stringify(db, null, 2), 'utf8')
      return
    }
    throw e
  }
}

export async function withDb<T>(fn: (db: DbSchema) => Promise<T> | T): Promise<T> {
  const task = async () => {
    const db = await readDbFile()
    const result = await fn(db)
    await writeDbFile(db)
    return result
  }

  queue = queue.then(task, task)
  return queue as Promise<T>
}

export function pruneExpiredSessions(db: DbSchema) {
  const now = Date.now()
  db.sessions = db.sessions.filter((s) => {
    const exp = Date.parse(s.expires_at)
    return Number.isFinite(exp) && exp > now
  })
}