package assets

import (
	"XProxy/next/logger"
	"bytes"
	"errors"
	"github.com/andybalholm/brotli"
	"github.com/avast/retry-go"
	"github.com/go-http-utils/headers"
	"github.com/klauspost/compress/flate"
	"github.com/klauspost/compress/gzip"
	"io"
	"net/http"
	"net/url"
	"time"
)

const DownloadRetry = 3     // max retry times
const DownloadTimeout = 480 // max request seconds

// broltiDecode handles brolti encoding in http responses.
func broltiDecode(stream io.Reader) ([]byte, error) {
	var buffer bytes.Buffer
	_, err := io.Copy(&buffer, brotli.NewReader(stream))
	if err != nil {
		logger.Errorf("Failed to decode http responses with brolti encoding -> %v", err)
		return nil, err
	}
	return buffer.Bytes(), nil
}

// gzipDecode handles gzip encoding in http responses.
func gzipDecode(stream io.Reader) ([]byte, error) {
	reader, err := gzip.NewReader(stream)
	if err != nil {
		logger.Errorf("Failed to decode http responses with gzip encoding -> %v", err)
		return nil, err
	}

	var buffer bytes.Buffer
	_, err = io.Copy(&buffer, reader)
	if err != nil {
		logger.Errorf("Failed to handle gzip reader -> %v", err)
		return nil, err
	}
	return buffer.Bytes(), nil
}

// deflateDecode handles deflate encoding in http responses.
func deflateDecode(stream io.Reader) ([]byte, error) {
	var buffer bytes.Buffer
	_, err := io.Copy(&buffer, flate.NewReader(stream))
	if err != nil {
		logger.Errorf("Failed to decode http responses with deflate encoding -> %v", err)
		return nil, err
	}
	return buffer.Bytes(), nil
}

// nonDecode handles plain encoding in http responses.
func nonDecode(stream io.Reader) ([]byte, error) {
	var buffer bytes.Buffer
	_, err := io.Copy(&buffer, stream)
	if err != nil {
		logger.Errorf("Failed to read http responses -> %v", err)
		return nil, err
	}
	return buffer.Bytes(), nil
}

// createClient build http client based on http or socks proxy url.
func createClient(remoteUrl string, proxyUrl string) (http.Client, error) {
	if proxyUrl == "" {
		logger.Infof("Downloading `%s` without proxy", remoteUrl)
		return http.Client{
			Timeout: DownloadTimeout * time.Second,
		}, nil
	}
	logger.Infof("Downloading `%s` via `%s`", remoteUrl, proxyUrl)
	proxy, err := url.Parse(proxyUrl)
	if err != nil {
		logger.Errorf("Invalid proxy url `%s` -> %v", proxyUrl, err)
		return http.Client{}, err
	}
	return http.Client{
		Transport: &http.Transport{
			Proxy: http.ProxyURL(proxy),
		},
		Timeout: DownloadTimeout * time.Second,
	}, nil
}

// doRequest initiates http request and allows retries.
func doRequest(client http.Client, req *http.Request) (*http.Response, error) {
	maxRetry := retry.Attempts(DownloadRetry)
	maxDelay := retry.MaxDelay(DownloadTimeout * time.Second)
	onRetry := retry.OnRetry(func(n uint, err error) {
		logger.Errorf("Failed to execute http request -> %v", err)
		if DownloadRetry != n+1 {
			logger.Infof("Download retry on the %d times, remain %d times...", n+1, DownloadRetry-n-1)
		}
	})
	delay := retry.Delay(4 * time.Second) // backoff start at 4s

	var resp *http.Response
	retryFunc := func() error {
		var err error
		if resp, err = client.Do(req); err != nil {
			return err
		}
		return nil
	}
	if err := retry.Do(retryFunc, delay, maxDelay, onRetry, maxRetry); err != nil {
		return nil, err
	}
	return resp, nil
}

// assetDate attempts to obtain the last modification time of the remote
// file and returns nil if it does not exist or is invalid.
func assetDate(resp *http.Response) *time.Time {
	date, err := http.ParseTime(resp.Header.Get(headers.LastModified))
	if err != nil {
		logger.Warnf("Unable to get remote data modification time")
		return nil
	}
	logger.Debugf("Remote data modification time -> `%v`", date)
	return &date
}

// downloadAsset obtains resource file from the remote server, gets its
// modification time, and supports proxy acquisition.
func downloadAsset(url string, proxy string) ([]byte, *time.Time, error) {
	client, err := createClient(url, proxy)
	if err != nil {
		return nil, nil, err
	}

	req, err := http.NewRequest("GET", url, nil)
	if err != nil {
		logger.Errorf("Failed to create http request -> %v", err)
		return nil, nil, err
	}
	req.Header.Set(headers.AcceptEncoding, "gzip, deflate, br")

	resp, err := doRequest(client, req)
	if err != nil {
		return nil, nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		logger.Errorf("Download `%s` with http status code -> %d", url, resp.StatusCode)
		return nil, nil, errors.New("http status code non-2xx")
	}
	logger.Debugf("Remote data downloaded successfully")

	var content []byte
	switch resp.Header.Get(headers.ContentEncoding) {
	case "br":
		logger.Debugf("Downloaded content using brolti encoding")
		content, err = broltiDecode(resp.Body)
	case "gzip":
		logger.Debugf("Downloaded content using gzip encoding")
		content, err = gzipDecode(resp.Body)
	case "deflate":
		logger.Debugf("Downloaded content using deflate encoding")
		content, err = deflateDecode(resp.Body)
	default:
		content, err = nonDecode(resp.Body)
	}
	if err != nil {
		return nil, nil, err
	}
	logger.Debugf("Download `%s` successfully -> %d bytes", url, len(content))
	return content, assetDate(resp), nil
}