package server

import (
	"bufio"
	"bytes"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
	"github.com/google/uuid"
	"github.com/rs/zerolog/log"

	"gitlab.com/technofab/go-copilot-proxy/internal/auth"
	"gitlab.com/technofab/go-copilot-proxy/internal/config"
)

func NewRouter(accessToken string, copilotAuth *auth.CopilotAuth) chi.Router {
	r := chi.NewRouter()
	r.Use(middleware.Recoverer)
	r.Use(middleware.RealIP)
	r.Use(middleware.RequestID)
	r.Use(middleware.Heartbeat("/healthz"))
	r.Use(corsHandler)

	r.Route("/v1", func(r chi.Router) {
		r.Use(authMiddleware(accessToken))
		r.Post("/chat/completions", createChatHandler(copilotAuth))
		r.Post("/embeddings", createProxyHandler("https://api.githubcopilot.com/embeddings", copilotAuth))
		r.Get("/models", createProxyHandler("https://api.githubcopilot.com/models", copilotAuth))
	})

	return r
}

func authMiddleware(accessToken string) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			authHeader := r.Header.Get("Authorization")
			token := strings.TrimPrefix(authHeader, "Bearer ")
			if token != accessToken {
				http.Error(w, "Invalid access token", http.StatusForbidden)
				return
			}
			next.ServeHTTP(w, r)
		})
	}
}

func corsHandler(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Access-Control-Allow-Origin", "*")
		w.Header().Set("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE")
		w.Header().Set("Access-Control-Allow-Headers", "Accept, Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, Authorization")
		w.Header().Set("Access-Control-Expose-Headers", "Content-Type, Content-Length, Transfer-Encoding")
		if r.Method == "OPTIONS" {
			w.WriteHeader(http.StatusOK)
			return
		}
		next.ServeHTTP(w, r)
	})
}

func createChatHandler(copilotAuth *auth.CopilotAuth) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		log.Debug().
			Str("method", r.Method).
			Str("path", r.URL.Path).
			Msg("Handling chat completions request")

		token := copilotAuth.GetToken()
		if token == "" {
			http.Error(w, "No Copilot token available", http.StatusServiceUnavailable)
			return
		}

		body, err := io.ReadAll(r.Body)
		if err != nil {
			http.Error(w, "Failed to read request body", http.StatusBadRequest)
			return
		}
		r.Body.Close()

		req, err := http.NewRequest("POST", "https://api.githubcopilot.com/chat/completions", bytes.NewBuffer(body))
		if err != nil {
			http.Error(w, "Failed to create request", http.StatusInternalServerError)
			return
		}

		headers := createRequestHeaders(token, "api.githubcopilot.com")
		for key, value := range headers {
			req.Header.Set(key, value)
		}

		client := &http.Client{}
		resp, err := client.Do(req)
		if err != nil {
			log.Error().Err(err).Msg("Failed to make request to GitHub Copilot API")
			http.Error(w, "Failed to proxy request", http.StatusBadGateway)
			return
		}
		defer resp.Body.Close()

		copyHeaders(w.Header(), resp.Header)
		w.Header().Set("Access-Control-Allow-Origin", "*")

		isStreaming := resp.Header.Get("Transfer-Encoding") == "chunked" ||
			strings.Contains(resp.Header.Get("Content-Type"), "text/event-stream")

		if resp.StatusCode == http.StatusOK && isStreaming {
			handleStreamingResponse(w, resp, r)
		} else if resp.StatusCode == http.StatusOK {
			handleNonStreamingResponse(w, resp, r)
		} else {
			w.WriteHeader(resp.StatusCode)
			io.Copy(w, resp.Body)
		}
	}
}

func createRequestHeaders(token, host string) map[string]string {
	hash := sha256.Sum256([]byte(token))
	machineID := hex.EncodeToString(hash[:])

	return map[string]string{
		"Authorization":          "Bearer " + token,
		"Host":                   host,
		"X-Request-Id":           uuid.New().String(),
		"X-Github-Api-Version":   "2025-04-01",
		"Vscode-Sessionid":       uuid.New().String() + fmt.Sprintf("%d", time.Now().Unix()),
		"Vscode-Machineid":       machineID,
		"Editor-Version":         config.EditorVersion,
		"Editor-Plugin-Version":  config.EditorPluginVersion,
		"Openai-Organization":    "github-copilot",
		"Copilot-Integration-Id": config.CopilotIntegrationID,
		"Openai-Intent":          "conversation-panel",
		"Content-Type":           "application/json",
		"User-Agent":             config.UserAgent,
		"Accept":                 "*/*",
		"Accept-Encoding":        "gzip, deflate, br",
	}
}

func copyHeaders(dst, src http.Header) {
	for key, values := range src {
		for _, value := range values {
			dst.Add(key, value)
		}
	}
}

func handleStreamingResponse(w http.ResponseWriter, resp *http.Response, r *http.Request) {
	w.Header().Set("Content-Type", "text/event-stream")
	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("Connection", "keep-alive")

	flusher, ok := w.(http.Flusher)
	if !ok {
		log.Error().Msg("Response writer does not support flushing")
		http.Error(w, "Streaming not supported", http.StatusInternalServerError)
		return
	}

	scanner := bufio.NewScanner(resp.Body)
	buffer := ""
	delimiter := "\n\n"

	for scanner.Scan() {
		line := scanner.Text()
		buffer += line + "\n"

		if strings.HasSuffix(buffer, delimiter) {
			lines := strings.Split(strings.TrimSuffix(buffer, delimiter), delimiter)
			for _, chunk := range lines {
				if cleanedChunk := cleanStreamLine(chunk); cleanedChunk != "" {
					fmt.Fprint(w, cleanedChunk+delimiter)
					flusher.Flush()
				}
			}
			buffer = ""
		}
	}

	if buffer != "" {
		if cleanedChunk := cleanStreamLine(strings.TrimSuffix(buffer, "\n")); cleanedChunk != "" {
			fmt.Fprint(w, cleanedChunk+"\n")
			flusher.Flush()
		}
	}

	if err := scanner.Err(); err != nil {
		log.Error().Err(err).Msg("Error reading streaming response")
	}
}

func handleNonStreamingResponse(w http.ResponseWriter, resp *http.Response, r *http.Request) {
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		log.Error().Err(err).Msg("Failed to read response body")
		http.Error(w, "Failed to read response", http.StatusInternalServerError)
		return
	}

	cleanedBody := cleanResponse(string(body))
	w.WriteHeader(resp.StatusCode)
	fmt.Fprint(w, cleanedBody)
}

func cleanResponse(responseBody string) string {
	var data map[string]interface{}
	if err := json.Unmarshal([]byte(responseBody), &data); err != nil {
		log.Error().Err(err).Msg("Failed to parse response JSON")
		return responseBody
	}

	data["object"] = "chat.completion"
	delete(data, "prompt_filter_results")

	if choices, ok := data["choices"].([]interface{}); ok {
		for _, choice := range choices {
			if choiceMap, ok := choice.(map[string]interface{}); ok {
				delete(choiceMap, "content_filter_results")
			}
		}
	}

	cleanedBytes, err := json.Marshal(data)
	if err != nil {
		log.Error().Err(err).Msg("Failed to marshal cleaned response")
		return responseBody
	}

	return string(cleanedBytes)
}

func cleanStreamLine(line string) string {
	if !strings.HasPrefix(line, "data: ") {
		return line
	}

	dataContent := strings.TrimPrefix(line, "data: ")
	if dataContent == "[DONE]" {
		return line
	}

	var data map[string]interface{}
	if err := json.Unmarshal([]byte(dataContent), &data); err != nil {
		log.Debug().Err(err).Msg("Failed to parse stream line JSON")
		return line
	}

	if choices, ok := data["choices"].([]interface{}); ok {
		if len(choices) == 0 {
			return ""
		}

		data["object"] = "chat.completion.chunk"

		for _, choice := range choices {
			if choiceMap, ok := choice.(map[string]interface{}); ok {
				delete(choiceMap, "content_filter_offsets")
				delete(choiceMap, "content_filter_results")

				if delta, ok := choiceMap["delta"].(map[string]interface{}); ok {
					for key, value := range delta {
						if value == nil {
							delete(delta, key)
						}
					}
				}
			}
		}
	}

	cleanedBytes, err := json.Marshal(data)
	if err != nil {
		log.Error().Err(err).Msg("Failed to marshal cleaned stream data")
		return line
	}

	return "data: " + string(cleanedBytes)
}

func createProxyHandler(targetURL string, copilotAuth *auth.CopilotAuth) http.HandlerFunc {
	target, err := url.Parse(targetURL)
	if err != nil {
		log.Fatal().Err(err).Str("url", targetURL).Msg("Invalid target URL")
	}

	return func(w http.ResponseWriter, r *http.Request) {
		log.Debug().
			Str("method", r.Method).
			Str("path", r.URL.Path).
			Str("target", targetURL).
			Msg("Proxying request")

		token := copilotAuth.GetToken()
		if token == "" {
			http.Error(w, "No Copilot token available", http.StatusServiceUnavailable)
			return
		}

		body, err := io.ReadAll(r.Body)
		if err != nil {
			http.Error(w, "Failed to read request body", http.StatusBadRequest)
			return
		}
		r.Body.Close()

		req, err := http.NewRequest(r.Method, target.String(), bytes.NewBuffer(body))
		if err != nil {
			http.Error(w, "Failed to create request", http.StatusInternalServerError)
			return
		}

		headers := createRequestHeaders(token, target.Host)
		for key, value := range headers {
			req.Header.Set(key, value)
		}

		client := &http.Client{}
		resp, err := client.Do(req)
		if err != nil {
			log.Error().Err(err).Msg("Failed to make request")
			http.Error(w, "Failed to proxy request", http.StatusBadGateway)
			return
		}
		defer resp.Body.Close()

		copyHeaders(w.Header(), resp.Header)
		w.Header().Set("Access-Control-Allow-Origin", "*")
		w.WriteHeader(resp.StatusCode)
		io.Copy(w, resp.Body)
	}
}