export interface FetchRequestContext {
  url: string
  init: RequestInit
}

export interface FetchRequestInterceptor {
  onRequest?(
    context: FetchRequestContext,
  ): Promise<FetchRequestContext> | FetchRequestContext
  onResponse?(
    context: FetchRequestContext,
    response: Response,
  ): Promise<Response> | Response
  onError?(context: FetchRequestContext, error: unknown): Promise<void> | void
}

function mergeHeaders(
  currentHeaders: HeadersInit | undefined,
  newHeaders: HeadersInit,
): Headers {
  const mergedHeaders = new Headers(currentHeaders)
  const incomingHeaders = new Headers(newHeaders)

  incomingHeaders.forEach((value, key) => {
    mergedHeaders.set(key, value)
  })

  return mergedHeaders
}

export function createHeaderRequestInterceptor(
  headers: HeadersInit,
): FetchRequestInterceptor {
  return {
    onRequest(context) {
      return {
        ...context,
        init: {
          ...context.init,
          headers: mergeHeaders(context.init.headers, headers),
        },
      }
    },
  }
}

export function createEnsureSuccessResponseInterceptor(): FetchRequestInterceptor {
  return {
    async onResponse(_, response) {
      if (response.ok) {
        return response
      }

      const errorBody = await response.text().catch(() => '')
      const normalizedBody = errorBody
      return Promise.reject({
        status: response.status,
        statusText: response.statusText,
        body: normalizedBody,
      })
    },
  }
}