nextjs-app/src/lib/http.ts

export type HttpMethod = 'GET' | 'POST' | 'PUT' | 'PATCH' | 'DELETE' | 'HEAD'

export type JsonRecord = Record<string, unknown>

export class ApiError extends Error {
  name = 'ApiError'
  url: string
  status?: number
  details?: unknown

  constructor(message: string, opts: { url: string; status?: number; details?: unknown }) {
    super(message)
    this.url = opts.url
    this.status = opts.status
    this.details = opts.details
  }
}

function sleep(ms: number) {
  return new Promise((resolve) => setTimeout(resolve, ms))
}

function isRetryableStatus(status?: number) {
  if (!status) return true
  return status === 408 || status === 425 || status === 429 || (status >= 500 && status <= 599)
}

export type FetchJsonOptions = {
  timeoutMs?: number
  retries?: number
  retryDelayMs?: number
  retryMethods?: HttpMethod[]
  headers?: HeadersInit
  /** If provided, body will be JSON-stringified and content-type set. */
  jsonBody?: unknown
  /** If true, sends cookies/credentials (only for same-site or allowed CORS). */
  credentials?: RequestCredentials
}

export async function fetchJson<T>(url: string, init?: RequestInit, opts?: FetchJsonOptions): Promise<T> {
  const timeoutMs = opts?.timeoutMs ?? 12000
  const retries = opts?.retries ?? 1
  const retryDelayMs = opts?.retryDelayMs ?? 600
  const retryMethods = opts?.retryMethods ?? ['GET', 'HEAD']

  const method = ((init?.method ?? 'GET').toUpperCase() as HttpMethod) || 'GET'
  const shouldRetryMethod = retryMethods.includes(method)

  const controller = new AbortController()
  const timeout = setTimeout(() => controller.abort(), timeoutMs)

  const headers: HeadersInit = {
    ...(opts?.jsonBody !== undefined ? { 'Content-Type': 'application/json' } : null),
    ...(opts?.headers ?? null),
    ...(init?.headers ?? null),
  }

  const requestInit: RequestInit = {
    ...init,
    headers,
    signal: controller.signal,
    credentials: opts?.credentials ?? init?.credentials,
    body:
      opts?.jsonBody !== undefined
        ? JSON.stringify(opts.jsonBody)
        : init?.body,
  }

  let lastError: unknown

  try {
    for (let attempt = 0; attempt <= retries; attempt++) {
      try {
        const res = await fetch(url, requestInit)

        if (!res.ok) {
          let details: unknown = undefined
          const contentType = res.headers.get('content-type') || ''
          try {
            details = contentType.includes('application/json') ? await res.json() : await res.text()
          } catch {
            // ignore
          }

          const detailMessage =
            details && typeof details === 'object' && 'error' in (details as Record<string, unknown>)
              ? String((details as Record<string, unknown>).error)
              : undefined

          const err = new ApiError(detailMessage || `API Error: ${res.status}`, { url, status: res.status, details })
          if (attempt < retries && shouldRetryMethod && isRetryableStatus(res.status)) {
            await sleep(retryDelayMs * (attempt + 1))
            continue
          }
          throw err
        }

        const contentType = res.headers.get('content-type') || ''
        if (contentType.includes('application/json')) {
          return (await res.json()) as T
        }

        // Allow endpoints returning plain text
        return (await res.text()) as unknown as T
      } catch (error) {
        lastError = error

        const isAbort = error instanceof DOMException && error.name === 'AbortError'
        if (attempt < retries && shouldRetryMethod && !isAbort) {
          await sleep(retryDelayMs * (attempt + 1))
          continue
        }

        if (isAbort) {
          throw new ApiError(`API Timeout after ${timeoutMs}ms`, { url })
        }

        throw error
      }
    }

    throw lastError instanceof Error
      ? lastError
      : new ApiError('Unknown API error', { url })
  } finally {
    clearTimeout(timeout)
  }
}