import { createHmac, randomBytes } from 'node:crypto'
import { createError, deleteCookie, getCookie, getRequestURL, setCookie } from 'h3'
import { getRuntimeEnvValue } from './runtime-env.js'
import { shouldUseSecureSessionCookie } from './session-cookie.js'

const googleAuthorizationUrl = 'https://accounts.google.com/o/oauth2/v2/auth'
const googleTokenUrl = 'https://oauth2.googleapis.com/token'
const googleUserInfoUrl = 'https://openidconnect.googleapis.com/v1/userinfo'
const googleOAuthStateCookieName = 'sori_google_oauth_nonce'
const googleOAuthStateMaxAge = 60 * 10
const googleOAuthCallbackPath = '/api/auth/google/callback'

/**
 * Google OAuth 클라이언트 설정을 조회한다.
 * @returns {{ clientId: string, clientSecret: string }} 클라이언트 설정
 */
export const getGoogleOAuthClientConfig = () => {
  const clientId = getRuntimeEnvValue('GOOGLE_OAUTH_CLIENT_ID', 'googleOAuthClientId', getRuntimeEnvValue('GOOGLE_ADSENSE_CLIENT_ID', 'googleOAuthClientId')).trim()
  const clientSecret = getRuntimeEnvValue('GOOGLE_OAUTH_CLIENT_SECRET', 'googleOAuthClientSecret', getRuntimeEnvValue('GOOGLE_ADSENSE_CLIENT_SECRET', 'googleOAuthClientSecret')).trim()

  if (!clientId || !clientSecret) {
    throw createError({
      statusCode: 500,
      message: 'Google 로그인 환경 변수가 없습니다. GOOGLE_OAUTH_CLIENT_ID와 GOOGLE_OAUTH_CLIENT_SECRET을 설정해 주세요.'
    })
  }

  return {
    clientId,
    clientSecret
  }
}

/**
 * Google OAuth callback URL을 만든다.
 * @param {import('h3').H3Event} event - 요청 이벤트
 * @returns {string} callback URL
 */
export const getGoogleOAuthRedirectUri = (event) => {
  const configuredUri = getRuntimeEnvValue('GOOGLE_OAUTH_REDIRECT_URI', 'googleOAuthRedirectUri').trim()
  if (configuredUri) {
    return configuredUri
  }

  return `${getRequestURL(event).origin}${googleOAuthCallbackPath}`
}

/**
 * OAuth state 서명 비밀값을 조회한다.
 * @returns {string} 서명 비밀값
 */
const getGoogleOAuthStateSecret = () => {
  const secret = getRuntimeEnvValue('MEMBER_SESSION_SECRET', 'memberSessionSecret').trim()
  if (!secret) {
    throw createError({
      statusCode: 500,
      message: '회원 세션 비밀값 환경 변수가 없습니다. MEMBER_SESSION_SECRET을 설정해 주세요.'
    })
  }

  return secret
}

/**
 * OAuth state payload를 서명한다.
 * @param {string} payload - base64url payload
 * @returns {string} 서명
 */
const signGoogleOAuthStatePayload = (payload) => createHmac('sha256', getGoogleOAuthStateSecret())
  .update(payload)
  .digest('base64url')

/**
 * 내부 경로 redirect만 허용한다.
 * @param {unknown} redirectTo - 요청 redirect 값
 * @param {string} fallback - 기본 경로
 * @returns {string} 안전한 redirect 경로
 */
export const normalizeGoogleOAuthRedirect = (redirectTo, fallback = '/') => {
  const value = String(redirectTo || '').trim()
  if (!value || !value.startsWith('/') || value.startsWith('//') || value.includes('\\')) {
    return fallback
  }

  return value
}

/**
 * Google OAuth state를 만들고 nonce 쿠키를 저장한다.
 * @param {import('h3').H3Event} event - 요청 이벤트
 * @param {{ mode: 'member' | 'admin' | 'link', redirectTo: string, userId?: string }} input - state 입력
 * @returns {string} state 문자열
 */
export const createGoogleOAuthState = (event, input) => {
  const nonce = randomBytes(24).toString('base64url')
  const payload = Buffer.from(JSON.stringify({
    mode: input.mode,
    redirectTo: input.redirectTo,
    userId: input.userId || '',
    nonce,
    createdAt: Date.now()
  })).toString('base64url')
  const state = `${payload}.${signGoogleOAuthStatePayload(payload)}`

  setCookie(event, googleOAuthStateCookieName, nonce, {
    httpOnly: true,
    sameSite: 'lax',
    secure: shouldUseSecureSessionCookie(event),
    path: '/',
    maxAge: googleOAuthStateMaxAge
  })

  return state
}

/**
 * Google OAuth state를 검증한다.
 * @param {import('h3').H3Event} event - 요청 이벤트
 * @param {string} state - state 문자열
 * @returns {{ mode: 'member' | 'admin' | 'link', redirectTo: string, userId: string }} state payload
 */
export const verifyGoogleOAuthState = (event, state) => {
  const [payload, signature] = String(state || '').split('.')
  const expectedNonce = getCookie(event, googleOAuthStateCookieName)

  deleteCookie(event, googleOAuthStateCookieName, {
    path: '/'
  })

  if (!payload || !signature || signature !== signGoogleOAuthStatePayload(payload)) {
    throw createError({
      statusCode: 400,
      message: 'Google 로그인 상태값이 올바르지 않습니다.'
    })
  }

  let parsed = null
  try {
    parsed = JSON.parse(Buffer.from(payload, 'base64url').toString('utf8'))
  } catch {
    throw createError({
      statusCode: 400,
      message: 'Google 로그인 상태값을 읽을 수 없습니다.'
    })
  }

  if (!expectedNonce || parsed.nonce !== expectedNonce || Date.now() - Number(parsed.createdAt || 0) > googleOAuthStateMaxAge * 1000) {
    throw createError({
      statusCode: 400,
      message: 'Google 로그인 요청이 만료되었습니다. 다시 시도해 주세요.'
    })
  }

  if (!['member', 'admin', 'link'].includes(parsed.mode)) {
    throw createError({
      statusCode: 400,
      message: 'Google 로그인 모드가 올바르지 않습니다.'
    })
  }

  return {
    mode: parsed.mode,
    redirectTo: normalizeGoogleOAuthRedirect(parsed.redirectTo, parsed.mode === 'admin' ? '/admin' : '/'),
    userId: String(parsed.userId || '')
  }
}

/**
 * Google OAuth 인증 URL을 만든다.
 * @param {import('h3').H3Event} event - 요청 이벤트
 * @param {string} state - state 문자열
 * @returns {string} Google 인증 URL
 */
export const createGoogleAuthorizationUrl = (event, state) => {
  const { clientId } = getGoogleOAuthClientConfig()
  const url = new URL(googleAuthorizationUrl)
  url.searchParams.set('client_id', clientId)
  url.searchParams.set('redirect_uri', getGoogleOAuthRedirectUri(event))
  url.searchParams.set('response_type', 'code')
  url.searchParams.set('scope', 'openid email profile')
  url.searchParams.set('state', state)
  url.searchParams.set('prompt', 'select_account')
  return url.toString()
}

/**
 * Google OAuth code를 사용자 정보로 교환한다.
 * @param {import('h3').H3Event} event - 요청 이벤트
 * @param {string} code - OAuth code
 * @returns {Promise<{ sub: string, email: string, emailVerified: boolean, name: string, picture: string }>} Google 사용자 정보
 */
export const exchangeGoogleOAuthCode = async (event, code) => {
  const { clientId, clientSecret } = getGoogleOAuthClientConfig()
  const tokenResponse = await fetch(googleTokenUrl, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/x-www-form-urlencoded'
    },
    body: new URLSearchParams({
      code,
      client_id: clientId,
      client_secret: clientSecret,
      redirect_uri: getGoogleOAuthRedirectUri(event),
      grant_type: 'authorization_code'
    })
  })

  if (!tokenResponse.ok) {
    throw createError({
      statusCode: 502,
      message: 'Google 로그인 토큰을 발급받지 못했습니다.'
    })
  }

  const tokenData = await tokenResponse.json()
  const accessToken = tokenData?.access_token
  if (!accessToken) {
    throw createError({
      statusCode: 502,
      message: 'Google access token이 없습니다.'
    })
  }

  const profileResponse = await fetch(googleUserInfoUrl, {
    headers: {
      Authorization: `Bearer ${accessToken}`
    }
  })

  if (!profileResponse.ok) {
    throw createError({
      statusCode: 502,
      message: 'Google 사용자 정보를 조회하지 못했습니다.'
    })
  }

  const profile = await profileResponse.json()
  return {
    sub: String(profile?.sub || ''),
    email: String(profile?.email || '').trim().toLowerCase(),
    emailVerified: Boolean(profile?.email_verified),
    name: String(profile?.name || '').trim(),
    picture: String(profile?.picture || '').trim()
  }
}