const API_BASE_URL = import.meta.env.VITE_API_BASE_URL ?? '/api'

export function apiUrl(path: string) {
  return `${API_BASE_URL}${path}`
}

let csrfToken: string | null = null

export class ApiError extends Error {
  status: number
  payload: unknown

  constructor(status: number, message: string, payload: unknown) {
    super(message)
    this.name = 'ApiError'
    this.status = status
    this.payload = payload
  }
}

async function readError(response: Response) {
  let payload: unknown
  try {
    payload = await response.json()
  } catch {
    payload = null
  }
  const detail = payload && typeof payload === 'object' && 'detail' in payload
    ? String((payload as { detail: unknown }).detail)
    : `API 请求失败（${response.status}）`
  return new ApiError(response.status, detail, payload)
}

async function getCsrfToken() {
  if (!csrfToken) {
    const response = await fetch(apiUrl('/accounts/auth/csrf'), {
      credentials: 'include'
    })
    if (!response.ok) {
      throw await readError(response)
    }
    const data = (await response.json()) as { csrfToken: string }
    csrfToken = data.csrfToken
  }
  return csrfToken
}

export async function apiRequest<T>(path: string, init?: RequestInit): Promise<T> {
  const headers = new Headers(init?.headers)
  if (init?.body && !(init.body instanceof FormData) && !headers.has('content-type')) {
    headers.set('content-type', 'application/json')
  }
  const method = init?.method?.toUpperCase() ?? 'GET'
  if (!['GET', 'HEAD', 'OPTIONS'].includes(method) && !headers.has('x-csrftoken')) {
    headers.set('x-csrftoken', await getCsrfToken())
  }

  const response = await fetch(apiUrl(path), {
    ...init,
    credentials: 'include',
    headers
  })

  if (!response.ok) {
    throw await readError(response)
  }

  if (response.status === 204) {
    return undefined as T
  }

  return response.json() as Promise<T>
}