package http

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"math"
	"math/rand"
	"net"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/debridmediamanager/zurg/pkg/logutil"
	http_dialer "github.com/mwitkow/go-http-dialer"
	"golang.org/x/net/proxy"

	cmap "github.com/orcaman/concurrent-map/v2"
)

type HTTPClient struct {
	token              string
	client             *http.Client
	maxRetries         int
	timeoutSecs        int
	rateLimitSleepSecs int
	backoff            func(int, int) time.Duration
	dnsCache           cmap.ConcurrentMap[string, string]
	hosts              []string
	log                *logutil.Logger
}

type ApiErrorResponse struct {
	Message string `json:"error"`
	Code    int    `json:"error_code"`
}

func (e *ApiErrorResponse) Error() string {
	return fmt.Sprintf("api response error: %s (code: %d)", e.Message, e.Code)
}

type DownloadErrorResponse struct {
	Message string
	Code    int
}

func (e *DownloadErrorResponse) Error() string {
	return fmt.Sprintf("download response error: %s (code: %d)", e.Message, e.Code)
}

func NewHTTPClient(
	token string,
	maxRetries int,
	timeoutSecs int,
	forceIPv6 bool,
	hosts []string,
	proxyURL string,
	log *logutil.Logger,
) *HTTPClient {
	client := HTTPClient{
		token:              token,
		client:             &http.Client{},
		maxRetries:         maxRetries,
		timeoutSecs:        timeoutSecs,
		rateLimitSleepSecs: 2,
		backoff:            backoffFunc,
		dnsCache:           cmap.New[string](),
		hosts:              hosts,
		log:                log,
	}

	var dialer proxy.Dialer = &net.Dialer{
		Timeout: time.Duration(timeoutSecs) * time.Second, // timeout for dns resolution, tcp handshake
	}

	if proxyURLString := proxyURL; proxyURLString != "" {
		proxyURL, err := url.Parse(proxyURLString)
		if err != nil {
			log.Errorf("Failed to parse proxy URL: %v", err)
			return nil
		}
		dialer, err = client.proxyDialer(proxyURL)
		if err != nil {
			log.Errorf("Failed to create proxy dialer: %v", err)
			return nil
		}
	}

	client.client.Transport = &http.Transport{
		ResponseHeaderTimeout: time.Duration(timeoutSecs) * time.Second,
		MaxIdleConnsPerHost:   32,
		MaxConnsPerHost:       32,
		IdleConnTimeout:       90 * time.Second,
	}

	if forceIPv6 {
		// replace the default dialer with a custom one that resolves hostnames to IPv6 addresses
		client.client.Transport.(*http.Transport).DialContext = func(ctx context.Context, network, address string) (net.Conn, error) {
			// if address is already cached, use it
			if ipv6Address, ok := client.dnsCache.Get(address); ok {
				return dialer.Dial(network, ipv6Address)
			}

			host, port, err := net.SplitHostPort(address)
			if err != nil {
				return nil, err
			}
			ips, err := net.DefaultResolver.LookupIPAddr(ctx, host)
			if err != nil {
				return nil, err
			}

			for _, ip := range ips {
				if ip.IP.To4() == nil { // IPv6 address found
					ipv6Address := net.JoinHostPort(ip.IP.String(), port)
					client.dnsCache.Set(address, ipv6Address)
					return dialer.Dial(network, ipv6Address)
				}
			}

			return nil, fmt.Errorf("no ipv6 address found")
		}
	}

	return &client
}

func (r *HTTPClient) Do(req *http.Request) (*http.Response, error) {
	if r.token != "" && req.Header.Get("Authorization") == "" {
		req.Header.Set("Authorization", "Bearer "+r.token)
	}

	var resp *http.Response
	var err error

	attempt := 0
	var origBody []byte
	if req.Method == "POST" || req.Method == "PUT" || req.Method == "PATCH" {
		origBody, _ = io.ReadAll(req.Body)
	}

	for {
		if origBody != nil {
			req.Body = io.NopCloser(bytes.NewReader(origBody))
		}
		if resp != nil && resp.Body != nil {
			resp.Body.Close()
		}

		if len(r.hosts) > 0 {
			r.ensureReachableHost(req)
		}

		resp, err = r.client.Do(req)

		// http 4xx and 5xx errors
		if resp != nil && resp.StatusCode >= http.StatusBadRequest {
			body, _ := io.ReadAll(resp.Body)
			if req.Host == "api.real-debrid.com" {
				// api servers
				if body != nil {
					var errResp ApiErrorResponse
					jsonErr := json.Unmarshal(body, &errResp)
					if jsonErr == nil {
						errResp.Message += fmt.Sprintf(" (status code: %d)", resp.StatusCode)
					} else {
						errResp.Message = string(body)
						errResp.Code = resp.StatusCode
					}
					err = &errResp
				}
			} else {
				// download servers
				err = &DownloadErrorResponse{
					Message: resp.Header.Get("X-Error"),
					Code:    resp.StatusCode,
				}
			}
		}

		incr := r.shouldRetry(req, resp, err, attempt, r.rateLimitSleepSecs)
		if incr == -1 {
			break
		} else if incr == 0 {
			continue
		}
		attempt += incr
	}
	return resp, err
}

func (r *HTTPClient) ensureReachableHost(req *http.Request) {
	if !strings.Contains(req.Host, ".download.real-debrid.") {
		return
	}
	if req.Host[0] >= 'a' && req.Host[0] <= 'z' {
		return
	}

	// check if req.Host is in r.hosts
	if r.CheckIfHostIsReachable(req.Host) {
		return
	}
	// replace prefix of req.Host from .com to .cloud or vice versa
	var newHost string
	if strings.HasSuffix(req.Host, ".com") {
		newHost = strings.Replace(req.Host, ".com", ".cloud", 1)
	} else if strings.HasSuffix(req.Host, ".cloud") {
		newHost = strings.Replace(req.Host, ".cloud", ".com", 1)
	}
	if r.CheckIfHostIsReachable(newHost) {
		req.Host = newHost
		req.URL.Host = req.Host
		return
	}

	req.Host = r.hosts[rand.Intn(len(r.hosts))]
	req.URL.Host = req.Host
}

func (r *HTTPClient) CheckIfHostIsReachable(reqHost string) bool {
	for _, host := range r.hosts {
		if reqHost == host {
			return true
		}
	}
	return false
}

func (r *HTTPClient) proxyDialer(proxyURL *url.URL) (proxy.Dialer, error) {
	if proxyURL.Scheme == "http" || proxyURL.Scheme == "https" {
		httpProxyDialer := http_dialer.New(proxyURL, http_dialer.WithConnectionTimeout(time.Duration(r.timeoutSecs)*time.Second))
		return httpProxyDialer, nil
	} else if proxyURL.Scheme == "socks5" {
		return proxy.FromURL(proxyURL, proxy.Direct)
	}
	return nil, fmt.Errorf("unsupported proxy scheme: %s", proxyURL.Scheme)
}

// shouldRetry returns a number indicating whether the request should be retried
// -1: don't retry
// 0: retry indefinitely
// 1: retry until maxRetries
func (r *HTTPClient) shouldRetry(req *http.Request, resp *http.Response, err error, attempts, rateLimitSleep int) int {
	if attempts >= r.maxRetries {
		return -1
	}

	// assume that all addMagnet requests are always successful;
	// don't retry to prevent duplicate torrents
	if req.Host == "api.real-debrid.com" && strings.HasSuffix(req.URL.Path, "torrents/addMagnet") {
		return -1
	}

	if apiErr, ok := err.(*ApiErrorResponse); ok {
		switch apiErr.Code {
		case 5: // Slow down (retry infinitely)
		case 34: // Too many requests (retry infinitely)
			secs := r.backoff(attempts, rateLimitSleep)
			r.log.Debugf("API rate limit reached, retrying in %d seconds", secs/time.Second)
			time.Sleep(secs)
			return 0
		case 36: // Fair Usage Limit
			secs := r.backoff(attempts, rateLimitSleep)
			r.log.Debugf("Fair usage limit reached, retrying in %d seconds", secs/time.Second)
			time.Sleep(secs)
			return 0
		case -1: // Internal error
			r.log.Debugf("RD Internal error, attempt #%d, retrying", attempts+1)
			return 1
		default:
			return -1
		}
	} else if downloadErr, ok := err.(*DownloadErrorResponse); ok {
		switch downloadErr.Message {
		case "invalid_download_code": // 404
			secs := r.backoff(attempts, rateLimitSleep)
			r.log.Debugf("Invalid download code, attempt #%d, retrying in %d seconds", attempts+1, secs/time.Second)
			time.Sleep(r.backoff(attempts, rateLimitSleep))
			return 1
		default:
			return -1
		}
	}

	// succesful requests
	if resp != nil {
		okResponseCode := resp.StatusCode == http.StatusOK || resp.StatusCode == http.StatusPartialContent
		// if the request has a Range header but the server doesn't respond with a Content-Range header
		hasRangeHeader := req.Header.Get("Range") != "" && !strings.HasPrefix(req.Header.Get("Range"), "bytes=0-")
		if okResponseCode && hasRangeHeader && resp.Header.Get("Content-Range") == "" {
			return 0
		}
		return -1
	}

	r.log.Debugf("Request failed, attempt #%d, retrying (error=%v)", attempts+1, err)
	return 1
}

func backoffFunc(attempt, base int) time.Duration {
	maxDuration := 60
	backoff := int(math.Pow(float64(base), float64(attempt+1)))
	if backoff > maxDuration {
		backoff = maxDuration
	}
	return time.Duration(backoff) * time.Second
}

func (r *HTTPClient) VerifyLink(link string) error {
	req, err := http.NewRequest(http.MethodHead, link, nil)
	if err != nil {
		return err
	}
	timeout := time.Duration(r.timeoutSecs) * time.Second
	ctx, cancel := context.WithTimeout(context.Background(), timeout)
	defer cancel()
	req = req.WithContext(ctx)
	resp, err := r.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("unexpected status code: %d", resp.StatusCode)
	}
	return nil
}