import {BskyAgent, stringifyLex, jsonToLex} from '@atproto/api'
import {cacheDirectory, copyAsync, moveAsync} from 'expo-file-system'

const GET_TIMEOUT = 15e3 // 15s
const POST_TIMEOUT = 60e3 // 60s

export function doPolyfill() {
  BskyAgent.configure({fetch: fetchHandler})
}

interface FetchHandlerResponse {
  status: number
  headers: Record<string, string>
  body: any
}

async function fetchHandler(
  reqUri: string,
  reqMethod: string,
  reqHeaders: Record<string, string>,
  reqBody: any,
): Promise<FetchHandlerResponse> {
  const reqMimeType = reqHeaders['Content-Type'] || reqHeaders['content-type']
  if (reqMimeType && reqMimeType.startsWith('application/json')) {
    reqBody = stringifyLex(reqBody)
  } else if (
    typeof reqBody === 'string' &&
    (reqBody.startsWith('/') || reqBody.startsWith('file:'))
  ) {
    if (reqBody.endsWith('.jpeg') || reqBody.endsWith('.jpg')) {
      // HACK
      // React native has a bug that inflates the size of jpegs on upload
      // we get around that by renaming the file ext to .bin
      // see https://github.com/facebook/react-native/issues/27099
      // -prf

      // On some platforms, moving this file is not possible. We will attempt to move it (this is optimal, since
      // we don't create duplicates) and if there is an error, we will instead copy the file to the cache directory
      const fileName = reqBody.split('/').pop() ?? ''
      const newPath = `${cacheDirectory ?? ''}${fileName.replace(
        /\.jpe?g$/,
        '.bin',
      )}`
      try {
        await moveAsync({
          from: reqBody,
          to: newPath,
        })
        reqBody = newPath
      } catch (e) {
        await copyAsync({
          from: reqBody,
          to: newPath,
        })
      }
    }
    // NOTE
    // React native treats bodies with {uri: string} as file uploads to pull from cache
    // -prf
    reqBody = {uri: reqBody}
  }

  const controller = new AbortController()
  const to = setTimeout(
    () => controller.abort(),
    reqMethod === 'post' ? POST_TIMEOUT : GET_TIMEOUT,
  )

  const res = await fetch(reqUri, {
    method: reqMethod,
    headers: reqHeaders,
    body: reqBody,
    signal: controller.signal,
  })

  const resStatus = res.status
  const resHeaders: Record<string, string> = {}
  res.headers.forEach((value: string, key: string) => {
    resHeaders[key] = value
  })
  const resMimeType = resHeaders['Content-Type'] || resHeaders['content-type']
  let resBody
  if (resMimeType) {
    if (resMimeType.startsWith('application/json')) {
      resBody = jsonToLex(await res.json())
    } else if (resMimeType.startsWith('text/')) {
      resBody = await res.text()
    } else {
      throw new Error('TODO: non-textual response body')
    }
  }

  clearTimeout(to)

  return {
    status: resStatus,
    headers: resHeaders,
    body: resBody,
  }
}