package ocm

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"io"
	"mime"
	"net"
	"net/http"
	"strings"
	"sync"
	"time"

	"github.com/sagernet/sing-box/adapter"
	boxService "github.com/sagernet/sing-box/adapter/service"
	"github.com/sagernet/sing-box/common/dialer"
	"github.com/sagernet/sing-box/common/listener"
	"github.com/sagernet/sing-box/common/tls"
	C "github.com/sagernet/sing-box/constant"
	"github.com/sagernet/sing-box/log"
	"github.com/sagernet/sing-box/option"
	"github.com/sagernet/sing/common"
	"github.com/sagernet/sing/common/buf"
	E "github.com/sagernet/sing/common/exceptions"
	M "github.com/sagernet/sing/common/metadata"
	N "github.com/sagernet/sing/common/network"
	aTLS "github.com/sagernet/sing/common/tls"

	"github.com/go-chi/chi/v5"
	"github.com/openai/openai-go/v3"
	"github.com/openai/openai-go/v3/responses"
	"golang.org/x/net/http2"
)

func RegisterService(registry *boxService.Registry) {
	boxService.Register[option.OCMServiceOptions](registry, C.TypeOCM, NewService)
}

type errorResponse struct {
	Error errorDetails `json:"error"`
}

type errorDetails struct {
	Type    string `json:"type"`
	Code    string `json:"code,omitempty"`
	Message string `json:"message"`
}

func writeJSONError(w http.ResponseWriter, r *http.Request, statusCode int, errorType string, message string) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(statusCode)

	json.NewEncoder(w).Encode(errorResponse{
		Error: errorDetails{
			Type:    errorType,
			Message: message,
		},
	})
}

func isHopByHopHeader(header string) bool {
	switch strings.ToLower(header) {
	case "connection", "keep-alive", "proxy-authenticate", "proxy-authorization", "te", "trailers", "transfer-encoding", "upgrade", "host":
		return true
	default:
		return false
	}
}

type Service struct {
	boxService.Adapter
	ctx            context.Context
	logger         log.ContextLogger
	credentialPath string
	credentials    *oauthCredentials
	users          []option.OCMUser
	httpClient     *http.Client
	httpHeaders    http.Header
	listener       *listener.Listener
	tlsConfig      tls.ServerConfig
	httpServer     *http.Server
	userManager    *UserManager
	accessMutex    sync.RWMutex
	usageTracker   *AggregatedUsage
	trackingGroup  sync.WaitGroup
	shuttingDown   bool
}

func NewService(ctx context.Context, logger log.ContextLogger, tag string, options option.OCMServiceOptions) (adapter.Service, error) {
	serviceDialer, err := dialer.NewWithOptions(dialer.Options{
		Context: ctx,
		Options: option.DialerOptions{
			Detour: options.Detour,
		},
		RemoteIsDomain: true,
	})
	if err != nil {
		return nil, E.Cause(err, "create dialer")
	}

	httpClient := &http.Client{
		Transport: &http.Transport{
			ForceAttemptHTTP2: true,
			DialContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
				return serviceDialer.DialContext(ctx, network, M.ParseSocksaddr(addr))
			},
		},
	}

	userManager := &UserManager{
		tokenMap: make(map[string]string),
	}

	var usageTracker *AggregatedUsage
	if options.UsagesPath != "" {
		usageTracker = &AggregatedUsage{
			LastUpdated:  time.Now(),
			Combinations: make([]CostCombination, 0),
			filePath:     options.UsagesPath,
			logger:       logger,
		}
	}

	service := &Service{
		Adapter:        boxService.NewAdapter(C.TypeOCM, tag),
		ctx:            ctx,
		logger:         logger,
		credentialPath: options.CredentialPath,
		users:          options.Users,
		httpClient:     httpClient,
		httpHeaders:    options.Headers.Build(),
		listener: listener.New(listener.Options{
			Context: ctx,
			Logger:  logger,
			Network: []string{N.NetworkTCP},
			Listen:  options.ListenOptions,
		}),
		userManager:  userManager,
		usageTracker: usageTracker,
	}

	if options.TLS != nil {
		tlsConfig, err := tls.NewServer(ctx, logger, common.PtrValueOrDefault(options.TLS))
		if err != nil {
			return nil, err
		}
		service.tlsConfig = tlsConfig
	}

	return service, nil
}

func (s *Service) Start(stage adapter.StartStage) error {
	if stage != adapter.StartStateStart {
		return nil
	}

	s.userManager.UpdateUsers(s.users)

	credentials, err := platformReadCredentials(s.credentialPath)
	if err != nil {
		return E.Cause(err, "read credentials")
	}
	s.credentials = credentials

	if s.usageTracker != nil {
		err = s.usageTracker.Load()
		if err != nil {
			s.logger.Warn("load usage statistics: ", err)
		}
	}

	router := chi.NewRouter()
	router.Mount("/", s)

	s.httpServer = &http.Server{Handler: router}

	if s.tlsConfig != nil {
		err = s.tlsConfig.Start()
		if err != nil {
			return E.Cause(err, "create TLS config")
		}
	}

	tcpListener, err := s.listener.ListenTCP()
	if err != nil {
		return err
	}

	if s.tlsConfig != nil {
		if !common.Contains(s.tlsConfig.NextProtos(), http2.NextProtoTLS) {
			s.tlsConfig.SetNextProtos(append([]string{"h2"}, s.tlsConfig.NextProtos()...))
		}
		tcpListener = aTLS.NewListener(tcpListener, s.tlsConfig)
	}

	go func() {
		serveErr := s.httpServer.Serve(tcpListener)
		if serveErr != nil && !errors.Is(serveErr, http.ErrServerClosed) {
			s.logger.Error("serve error: ", serveErr)
		}
	}()

	return nil
}

func (s *Service) getAccessToken() (string, error) {
	s.accessMutex.RLock()
	if !s.credentials.needsRefresh() {
		token := s.credentials.getAccessToken()
		s.accessMutex.RUnlock()
		return token, nil
	}
	s.accessMutex.RUnlock()

	s.accessMutex.Lock()
	defer s.accessMutex.Unlock()

	if !s.credentials.needsRefresh() {
		return s.credentials.getAccessToken(), nil
	}

	newCredentials, err := refreshToken(s.httpClient, s.credentials)
	if err != nil {
		return "", err
	}

	s.credentials = newCredentials

	err = platformWriteCredentials(newCredentials, s.credentialPath)
	if err != nil {
		s.logger.Warn("persist refreshed token: ", err)
	}

	return newCredentials.getAccessToken(), nil
}

func (s *Service) getAccountID() string {
	s.accessMutex.RLock()
	defer s.accessMutex.RUnlock()
	return s.credentials.getAccountID()
}

func (s *Service) isAPIKeyMode() bool {
	s.accessMutex.RLock()
	defer s.accessMutex.RUnlock()
	return s.credentials.isAPIKeyMode()
}

func (s *Service) getBaseURL() string {
	if s.isAPIKeyMode() {
		return openaiAPIBaseURL
	}
	return chatGPTBackendURL
}

func (s *Service) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	path := r.URL.Path
	if !strings.HasPrefix(path, "/v1/") {
		writeJSONError(w, r, http.StatusNotFound, "invalid_request_error", "path must start with /v1/")
		return
	}

	var proxyPath string
	if s.isAPIKeyMode() {
		proxyPath = path
	} else {
		if path == "/v1/chat/completions" {
			writeJSONError(w, r, http.StatusBadRequest, "invalid_request_error",
				"chat completions endpoint is only available in API key mode")
			return
		}
		proxyPath = strings.TrimPrefix(path, "/v1")
	}

	var username string
	if len(s.users) > 0 {
		authHeader := r.Header.Get("Authorization")
		if authHeader == "" {
			s.logger.Warn("authentication failed for request from ", r.RemoteAddr, ": missing Authorization header")
			writeJSONError(w, r, http.StatusUnauthorized, "authentication_error", "missing api key")
			return
		}
		clientToken := strings.TrimPrefix(authHeader, "Bearer ")
		if clientToken == authHeader {
			s.logger.Warn("authentication failed for request from ", r.RemoteAddr, ": invalid Authorization format")
			writeJSONError(w, r, http.StatusUnauthorized, "authentication_error", "invalid api key format")
			return
		}
		var ok bool
		username, ok = s.userManager.Authenticate(clientToken)
		if !ok {
			s.logger.Warn("authentication failed for request from ", r.RemoteAddr, ": unknown key: ", clientToken)
			writeJSONError(w, r, http.StatusUnauthorized, "authentication_error", "invalid api key")
			return
		}
	}

	var requestModel string

	if s.usageTracker != nil && r.Body != nil {
		bodyBytes, err := io.ReadAll(r.Body)
		if err == nil {
			var request struct {
				Model string `json:"model"`
			}
			err := json.Unmarshal(bodyBytes, &request)
			if err == nil {
				requestModel = request.Model
			}
			r.Body = io.NopCloser(bytes.NewBuffer(bodyBytes))
		}
	}

	accessToken, err := s.getAccessToken()
	if err != nil {
		s.logger.Error("get access token: ", err)
		writeJSONError(w, r, http.StatusUnauthorized, "authentication_error", "Authentication failed")
		return
	}

	proxyURL := s.getBaseURL() + proxyPath
	if r.URL.RawQuery != "" {
		proxyURL += "?" + r.URL.RawQuery
	}
	proxyRequest, err := http.NewRequestWithContext(r.Context(), r.Method, proxyURL, r.Body)
	if err != nil {
		s.logger.Error("create proxy request: ", err)
		writeJSONError(w, r, http.StatusInternalServerError, "api_error", "Internal server error")
		return
	}

	for key, values := range r.Header {
		if !isHopByHopHeader(key) && key != "Authorization" {
			proxyRequest.Header[key] = values
		}
	}

	for key, values := range s.httpHeaders {
		proxyRequest.Header.Del(key)
		proxyRequest.Header[key] = values
	}

	proxyRequest.Header.Set("Authorization", "Bearer "+accessToken)

	if accountID := s.getAccountID(); accountID != "" {
		proxyRequest.Header.Set("ChatGPT-Account-Id", accountID)
	}

	response, err := s.httpClient.Do(proxyRequest)
	if err != nil {
		writeJSONError(w, r, http.StatusBadGateway, "api_error", err.Error())
		return
	}
	defer response.Body.Close()

	for key, values := range response.Header {
		if !isHopByHopHeader(key) {
			w.Header()[key] = values
		}
	}
	w.WriteHeader(response.StatusCode)

	trackUsage := s.usageTracker != nil && response.StatusCode == http.StatusOK &&
		(path == "/v1/chat/completions" || strings.HasPrefix(path, "/v1/responses"))
	if trackUsage {
		s.handleResponseWithTracking(w, response, path, requestModel, username)
	} else {
		mediaType, _, err := mime.ParseMediaType(response.Header.Get("Content-Type"))
		if err == nil && mediaType != "text/event-stream" {
			_, _ = io.Copy(w, response.Body)
			return
		}
		flusher, ok := w.(http.Flusher)
		if !ok {
			s.logger.Error("streaming not supported")
			return
		}
		buffer := make([]byte, buf.BufferSize)
		for {
			n, err := response.Body.Read(buffer)
			if n > 0 {
				_, writeError := w.Write(buffer[:n])
				if writeError != nil {
					s.logger.Error("write streaming response: ", writeError)
					return
				}
				flusher.Flush()
			}
			if err != nil {
				return
			}
		}
	}
}

func (s *Service) handleResponseWithTracking(writer http.ResponseWriter, response *http.Response, path string, requestModel string, username string) {
	isChatCompletions := path == "/v1/chat/completions"
	mediaType, _, err := mime.ParseMediaType(response.Header.Get("Content-Type"))
	isStreaming := err == nil && mediaType == "text/event-stream"

	if !isStreaming {
		bodyBytes, err := io.ReadAll(response.Body)
		if err != nil {
			s.logger.Error("read response body: ", err)
			return
		}

		var responseModel string
		var inputTokens, outputTokens, cachedTokens int64

		if isChatCompletions {
			var chatCompletion openai.ChatCompletion
			if json.Unmarshal(bodyBytes, &chatCompletion) == nil {
				responseModel = chatCompletion.Model
				inputTokens = chatCompletion.Usage.PromptTokens
				outputTokens = chatCompletion.Usage.CompletionTokens
				cachedTokens = chatCompletion.Usage.PromptTokensDetails.CachedTokens
			}
		} else {
			var responsesResponse responses.Response
			if json.Unmarshal(bodyBytes, &responsesResponse) == nil {
				responseModel = string(responsesResponse.Model)
				inputTokens = responsesResponse.Usage.InputTokens
				outputTokens = responsesResponse.Usage.OutputTokens
				cachedTokens = responsesResponse.Usage.InputTokensDetails.CachedTokens
			}
		}

		if inputTokens > 0 || outputTokens > 0 {
			if responseModel == "" {
				responseModel = requestModel
			}
			if responseModel != "" {
				s.usageTracker.AddUsage(responseModel, inputTokens, outputTokens, cachedTokens, username)
			}
		}

		_, _ = writer.Write(bodyBytes)
		return
	}

	flusher, ok := writer.(http.Flusher)
	if !ok {
		s.logger.Error("streaming not supported")
		return
	}

	var inputTokens, outputTokens, cachedTokens int64
	var responseModel string
	buffer := make([]byte, buf.BufferSize)
	var leftover []byte

	for {
		n, err := response.Body.Read(buffer)
		if n > 0 {
			data := append(leftover, buffer[:n]...)
			lines := bytes.Split(data, []byte("\n"))

			if err == nil {
				leftover = lines[len(lines)-1]
				lines = lines[:len(lines)-1]
			} else {
				leftover = nil
			}

			for _, line := range lines {
				line = bytes.TrimSpace(line)
				if len(line) == 0 {
					continue
				}

				if bytes.HasPrefix(line, []byte("data: ")) {
					eventData := bytes.TrimPrefix(line, []byte("data: "))
					if bytes.Equal(eventData, []byte("[DONE]")) {
						continue
					}

					if isChatCompletions {
						var chatChunk openai.ChatCompletionChunk
						if json.Unmarshal(eventData, &chatChunk) == nil {
							if chatChunk.Model != "" {
								responseModel = chatChunk.Model
							}
							if chatChunk.Usage.PromptTokens > 0 {
								inputTokens = chatChunk.Usage.PromptTokens
								cachedTokens = chatChunk.Usage.PromptTokensDetails.CachedTokens
							}
							if chatChunk.Usage.CompletionTokens > 0 {
								outputTokens = chatChunk.Usage.CompletionTokens
							}
						}
					} else {
						var streamEvent responses.ResponseStreamEventUnion
						if json.Unmarshal(eventData, &streamEvent) == nil {
							if streamEvent.Type == "response.completed" {
								completedEvent := streamEvent.AsResponseCompleted()
								if string(completedEvent.Response.Model) != "" {
									responseModel = string(completedEvent.Response.Model)
								}
								if completedEvent.Response.Usage.InputTokens > 0 {
									inputTokens = completedEvent.Response.Usage.InputTokens
									cachedTokens = completedEvent.Response.Usage.InputTokensDetails.CachedTokens
								}
								if completedEvent.Response.Usage.OutputTokens > 0 {
									outputTokens = completedEvent.Response.Usage.OutputTokens
								}
							}
						}
					}
				}
			}

			_, writeError := writer.Write(buffer[:n])
			if writeError != nil {
				s.logger.Error("write streaming response: ", writeError)
				return
			}
			flusher.Flush()
		}

		if err != nil {
			if responseModel == "" {
				responseModel = requestModel
			}

			if inputTokens > 0 || outputTokens > 0 {
				if responseModel != "" {
					s.usageTracker.AddUsage(responseModel, inputTokens, outputTokens, cachedTokens, username)
				}
			}
			return
		}
	}
}

func (s *Service) Close() error {
	err := common.Close(
		common.PtrOrNil(s.httpServer),
		common.PtrOrNil(s.listener),
		s.tlsConfig,
	)

	if s.usageTracker != nil {
		s.usageTracker.cancelPendingSave()
		saveErr := s.usageTracker.Save()
		if saveErr != nil {
			s.logger.Error("save usage statistics: ", saveErr)
		}
	}

	return err
}