const AUTH_SESSION_KEY = 'teaching-feedback-auth-session-v1'
const EXPIRY_SKEW_MS = 60_000

interface RawLoginResponse {
  access_token: string
  expires_at: string
  user_id: string
}

interface ErrorBody {
  error?: string
}

export interface AuthSession {
  apiBaseUrl: string
  accessToken: string
  expiresAt: number
  userId: string
}

export class AuthenticationError extends Error {
  constructor(message: string) {
    super(message)
    this.name = 'AuthenticationError'
  }
}

let pendingLogin: { apiBaseUrl: string; promise: Promise<AuthSession> } | null = null

export function getStoredAuthSession(apiBaseUrl: string): AuthSession | null {
  const value = wx.getStorageSync(AUTH_SESSION_KEY) as Partial<AuthSession> | string
  if (!value || typeof value !== 'object') return null
  if (
    value.apiBaseUrl !== apiBaseUrl ||
    typeof value.accessToken !== 'string' ||
    !value.accessToken ||
    typeof value.expiresAt !== 'number' ||
    typeof value.userId !== 'string' ||
    !value.userId
  ) {
    return null
  }
  return value as AuthSession
}

export function clearAuthSession(): void {
  wx.removeStorageSync(AUTH_SESSION_KEY)
}

export async function getAccessToken(apiBaseUrl: string, forceRefresh = false): Promise<string> {
  if (!forceRefresh) {
    const stored = getStoredAuthSession(apiBaseUrl)
    if (stored && stored.expiresAt > Date.now() + EXPIRY_SKEW_MS) return stored.accessToken
  }
  return (await login(apiBaseUrl)).accessToken
}

export async function ensureAuthSession(apiBaseUrl: string): Promise<AuthSession> {
  const accessToken = await getAccessToken(apiBaseUrl)
  const session = getStoredAuthSession(apiBaseUrl)
  if (!session || session.accessToken !== accessToken) {
    throw new AuthenticationError('登录状态保存失败，请重试')
  }
  return session
}

async function login(apiBaseUrl: string): Promise<AuthSession> {
  if (pendingLogin?.apiBaseUrl === apiBaseUrl) return pendingLogin.promise

  const promise = loginWithWechat(apiBaseUrl).finally(() => {
    if (pendingLogin?.promise === promise) pendingLogin = null
  })
  pendingLogin = { apiBaseUrl, promise }
  return promise
}

async function loginWithWechat(apiBaseUrl: string): Promise<AuthSession> {
  const code = await getWechatLoginCode()
  const response = await exchangeCode(apiBaseUrl, code)
  const expiresAt = Date.parse(response.expires_at)
  if (
    !response.access_token ||
    !response.user_id ||
    Number.isNaN(expiresAt) ||
    expiresAt <= Date.now()
  ) {
    throw new AuthenticationError('登录服务返回了无效会话')
  }
  const session: AuthSession = {
    apiBaseUrl,
    accessToken: response.access_token,
    expiresAt,
    userId: response.user_id
  }
  wx.setStorageSync(AUTH_SESSION_KEY, session)
  return session
}

function getWechatLoginCode(): Promise<string> {
  return new Promise((resolve, reject) => {
    wx.login({
      success(result) {
        if (result.code) {
          resolve(result.code)
          return
        }
        reject(new AuthenticationError('微信未返回登录凭证'))
      },
      fail(error) {
        reject(new AuthenticationError(`微信登录失败：${error.errMsg}`))
      }
    })
  })
}

function exchangeCode(apiBaseUrl: string, code: string): Promise<RawLoginResponse> {
  return new Promise((resolve, reject) => {
    wx.request({
      url: `${apiBaseUrl}/api/v1/auth/wechat/login`,
      method: 'POST',
      data: { code },
      timeout: 15_000,
      header: { 'Content-Type': 'application/json' },
      success(response) {
        if (response.statusCode >= 200 && response.statusCode < 300) {
          resolve(response.data as RawLoginResponse)
          return
        }
        const body = response.data as ErrorBody
        reject(new AuthenticationError(body?.error || `登录服务返回 HTTP ${response.statusCode}`))
      },
      fail(error) {
        reject(new AuthenticationError(`无法连接登录服务：${error.errMsg}`))
      }
    })
  })
}