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package main

import (
	"bufio"
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"sync"
	"time"

	"path/filepath"
	"strings"

	varlinklib "codeberg.org/Profpatsch/Profpatsch/users/Profpatsch/varlink-lib"
	"github.com/varlink/go/varlink/idl"
)

var (
	varlinkAddress = flag.String("varlink-address", "", "Varlink service address (e.g., unix:/run/user/1000/service.sock)")
	interfaceName  = flag.String("interface", "", "Varlink interface name (e.g., de.profpatsch.ClaudeLastPosition)")
	debugLog       = flag.Bool("debug", false, "Enable debug logging to stderr")
	httpMode       = flag.Bool("http-mode", false, "Run as HTTP server instead of stdio")
	httpPort       = flag.Int("http-port", 3000, "HTTP port to listen on (only with --http-mode)")
)

type Bridge struct {
	varlinkClient *varlinklib.VarlinkClient
	tools         []Tool
	lastID        int64
	cache         *Cache
	cacheDir      string     // Base cache directory
	sessionDir    string     // Directory for this session's files
	sessionID     string     // MCP session ID for HTTP mode
	expiresAt     int64      // Session expiration timestamp
	sessionMu     sync.Mutex // Protects lastID and session state in HTTP mode
}

func main() {
	flag.Parse()

	if *varlinkAddress == "" || *interfaceName == "" {
		fmt.Fprintf(os.Stderr, "Usage: %s --varlink-address=<address> --interface=<name>\n", os.Args[0])
		fmt.Fprintf(os.Stderr, "Example: %s --varlink-address=unix:/run/user/1000/service.sock --interface=de.profpatsch.Service\n", os.Args[0])
		os.Exit(1)
	}

	// Setup logging to stderr
	if !*debugLog {
		log.SetOutput(os.Stderr)
		log.SetFlags(0)
		log.SetPrefix("")
	} else {
		log.SetOutput(os.Stderr)
		log.SetFlags(log.Ltime | log.Lshortfile)
	}

	ctx := context.Background()

	// Connect to varlink service and introspect
	log.Printf("Connecting to varlink service at %s...\n", *varlinkAddress)
	varlinkClient, err := varlinklib.NewVarlinkClient(ctx, *varlinkAddress, *interfaceName)
	if err != nil {
		log.Fatalf("Failed to initialize varlink client: %v\n", err)
	}
	defer varlinkClient.Close()

	log.Printf("Successfully connected and introspected interface %s\n", *interfaceName)

	// Build MCP tools from varlink interface
	tools, err := buildTools(varlinkClient.GetIDL(), *interfaceName)
	if err != nil {
		log.Fatalf("Failed to build MCP tools: %v\n", err)
	}

	log.Printf("Discovered %d methods as MCP tools\n", len(tools))
	if *debugLog {
		for _, tool := range tools {
			log.Printf("  - %s\n", tool.Name)
		}
	}

	// Initialize cache (use XDG_CACHE_HOME or default to ~/.cache)
	xdgCache := os.Getenv("XDG_CACHE_HOME")
	if xdgCache == "" {
		xdgCache = filepath.Join(os.Getenv("HOME"), ".cache")
	}
	cacheDir := filepath.Join(xdgCache, "varlink-mcp-bridge")
	cache, err := InitCache(cacheDir)
	if err != nil {
		log.Fatalf("Failed to initialize cache: %v\n", err)
	}
	defer cache.Close()

	// In HTTP mode, session directory will be created per-session
	// In stdio mode, create a one-time session directory
	var sessionDir string
	if !*httpMode {
		// Create session directory in ~/.cache/varlink-mcp-bridge/sessions/<session-id>/
		sessionID := generateSessionID()
		sessionDir = filepath.Join(cacheDir, "sessions", sessionID)
		if err := os.MkdirAll(sessionDir, 0755); err != nil {
			log.Fatalf("Failed to create session directory: %v\n", err)
		}
		log.Printf("Session directory: %s\n", sessionDir)
	}

	bridge := &Bridge{
		varlinkClient: varlinkClient,
		tools:         tools,
		lastID:        -1,
		cache:         cache,
		cacheDir:      cacheDir,
		sessionDir:    sessionDir,
	}

	// Start in appropriate mode
	if *httpMode {
		log.Printf("Starting MCP bridge (HTTP mode on port %d)...\n", *httpPort)
		bridge.runHTTP(ctx)
	} else {
		log.Println("Starting MCP bridge (stdio mode)...")
		bridge.runStdio(ctx)
	}
}

func (b *Bridge) runStdio(ctx context.Context) {
	scanner := bufio.NewScanner(os.Stdin)
	encoder := json.NewEncoder(os.Stdout)

	for scanner.Scan() {
		line := scanner.Bytes()
		if *debugLog {
			log.Printf("Received: %s\n", string(line))
		}

		// Parse request
		var req JSONRPCRequest
		if err := json.Unmarshal(line, &req); err != nil {
			b.sendError(encoder, 0, ErrCodeParseError, "Parse error", err.Error())
			continue
		}

		// Validate JSON-RPC version
		if req.JSONRPC != "2.0" {
			if req.ID != nil {
				b.sendError(encoder, *req.ID, ErrCodeInvalidRequest, "Invalid request", "jsonrpc must be '2.0'")
			}
			continue
		}

		// Validate monotonic ID (only for requests, not notifications)
		if req.ID != nil {
			if *req.ID <= b.lastID {
				b.sendError(encoder, *req.ID, ErrCodeInvalidRequest, "Invalid request", "ID must be monotonically increasing")
				continue
			}
			b.lastID = *req.ID
		}

		// Handle request
		resp := b.handleRequest(ctx, req)

		// Only send response for requests, not notifications
		if req.ID != nil {
			// Send response
			if err := encoder.Encode(resp); err != nil {
				log.Printf("Failed to encode response: %v\n", err)
				return
			}

			if *debugLog {
				respBytes, _ := json.Marshal(resp)
				log.Printf("Sent: %s\n", string(respBytes))
			}
		} else if *debugLog {
			log.Printf("Notification handled: %s\n", req.Method)
		}
	}

	if err := scanner.Err(); err != nil {
		log.Printf("Scanner error: %v\n", err)
	}
}

func (b *Bridge) runHTTP(ctx context.Context) {
	http.HandleFunc("/mcp", func(w http.ResponseWriter, r *http.Request) {
		b.handleMCPEndpoint(ctx, w, r)
	})

	addr := fmt.Sprintf("127.0.0.1:%d", *httpPort)
	log.Printf("Listening on http://%s/mcp\n", addr)

	if err := http.ListenAndServe(addr, nil); err != nil {
		log.Fatalf("HTTP server error: %v\n", err)
	}
}

func (b *Bridge) handleMCPEndpoint(ctx context.Context, w http.ResponseWriter, r *http.Request) {
	// Security: Validate Origin header to prevent DNS rebinding attacks
	origin := r.Header.Get("Origin")
	if origin != "" && !isAllowedOrigin(origin) {
		http.Error(w, "Forbidden origin", http.StatusForbidden)
		log.Printf("Rejected request from origin: %s\n", origin)
		return
	}

	switch r.Method {
	case http.MethodPost:
		b.handleMCPPost(ctx, w, r)
	case http.MethodGet:
		b.handleMCPGet(ctx, w, r)
	case http.MethodDelete:
		b.handleMCPDelete(ctx, w, r)
	default:
		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
	}
}

func (b *Bridge) handleMCPPost(ctx context.Context, w http.ResponseWriter, r *http.Request) {
	// Read request body
	body, err := io.ReadAll(r.Body)
	if err != nil {
		http.Error(w, "Failed to read request body", http.StatusBadRequest)
		return
	}
	defer r.Body.Close()

	if *debugLog {
		log.Printf("POST /mcp: %s\n", string(body))
	}

	// Parse JSON-RPC request
	var req JSONRPCRequest
	if err := json.Unmarshal(body, &req); err != nil {
		http.Error(w, "Invalid JSON-RPC request", http.StatusBadRequest)
		return
	}

	// Load existing session if header present
	existingSessionID := r.Header.Get("Mcp-Session-Id")
	if existingSessionID != "" && req.Method != "initialize" {
		b.sessionMu.Lock()
		session, err := b.cache.LoadSession(existingSessionID)
		if err != nil {
			b.sessionMu.Unlock()
			log.Printf("Error loading session %s: %v\n", existingSessionID, err)
			http.Error(w, "Failed to load session", http.StatusInternalServerError)
			return
		}
		if session == nil {
			b.sessionMu.Unlock()
			// Session expired or not found
			http.Error(w, "Session not found or expired", http.StatusNotFound)
			return
		}
		// Restore session state
		b.sessionID = session.SessionID
		b.lastID = session.LastID
		b.sessionDir = session.SessionDir
		b.expiresAt = session.ExpiresAt
		b.sessionMu.Unlock()
	}

	// Validate monotonic ID (only for requests, not notifications)
	// Notifications have ID == nil
	if req.ID != nil {
		b.sessionMu.Lock()
		if *req.ID <= b.lastID {
			b.sessionMu.Unlock()
			errorResp := b.makeErrorResponse(*req.ID, ErrCodeInvalidRequest, "Invalid request", "ID must be monotonically increasing")
			b.sendJSONResponse(w, r, errorResp)
			return
		}
		b.lastID = *req.ID
		b.sessionMu.Unlock()
	}

	// Handle request
	resp := b.handleRequest(ctx, req)

	// For initialize request, create new session
	if req.Method == "initialize" && resp.Error == nil {
		b.sessionMu.Lock()
		if b.sessionID == "" {
			b.sessionID = generateSessionID()
			b.expiresAt = time.Now().Add(2 * time.Hour).Unix() // 2 hour expiration
			b.sessionDir = filepath.Join(b.cacheDir, "sessions", b.sessionID)

			// Create session directory
			if err := os.MkdirAll(b.sessionDir, 0755); err != nil {
				b.sessionMu.Unlock()
				log.Printf("Failed to create session directory: %v\n", err)
				http.Error(w, "Failed to create session", http.StatusInternalServerError)
				return
			}

			w.Header().Set("Mcp-Session-Id", b.sessionID)
			log.Printf("Created new session: %s (expires: %s)\n", b.sessionID, time.Unix(b.expiresAt, 0).Format(time.RFC3339))
		}
		b.sessionMu.Unlock()
	}

	// Save session state after processing request (if we have a session and it's not a notification)
	if b.sessionID != "" && req.ID != nil {
		b.sessionMu.Lock()
		if err := b.cache.SaveSession(b.sessionID, b.lastID, b.sessionDir, b.expiresAt); err != nil {
			log.Printf("Warning: failed to save session state: %v\n", err)
		}
		b.sessionMu.Unlock()
	}

	// Notifications (ID == nil) don't get a response
	if req.ID == nil {
		w.WriteHeader(http.StatusAccepted)
		if *debugLog {
			log.Printf("Notification handled: %s\n", req.Method)
		}
		return
	}

	// Send JSON response for requests
	b.sendJSONResponse(w, r, resp)
}

func (b *Bridge) handleMCPGet(ctx context.Context, w http.ResponseWriter, r *http.Request) {
	// GET is used for SSE streaming - we don't support it yet
	// Return 405 Method Not Allowed to indicate no SSE support
	http.Error(w, "SSE streaming not implemented", http.StatusMethodNotAllowed)
}

func (b *Bridge) handleMCPDelete(ctx context.Context, w http.ResponseWriter, r *http.Request) {
	// DELETE is used to terminate sessions
	sessionID := r.Header.Get("Mcp-Session-Id")
	if sessionID == "" {
		http.Error(w, "No session ID provided", http.StatusBadRequest)
		return
	}

	b.sessionMu.Lock()
	if b.sessionID == sessionID {
		log.Printf("Session terminated by client: %s\n", sessionID)
		b.sessionID = ""
		b.lastID = -1
	}
	b.sessionMu.Unlock()

	w.WriteHeader(http.StatusOK)
}

func (b *Bridge) sendJSONResponse(w http.ResponseWriter, r *http.Request, resp JSONRPCResponse) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusOK)

	respBytes, err := json.Marshal(resp)
	if err != nil {
		log.Printf("Failed to marshal response: %v\n", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	if *debugLog {
		log.Printf("Response: %s\n", string(respBytes))
	}

	w.Write(respBytes)
}

func isAllowedOrigin(origin string) bool {
	// Allow localhost and 127.0.0.1
	return strings.HasPrefix(origin, "http://localhost") ||
		strings.HasPrefix(origin, "http://127.0.0.1") ||
		strings.HasPrefix(origin, "https://localhost") ||
		strings.HasPrefix(origin, "https://127.0.0.1")
}

func (b *Bridge) handleRequest(ctx context.Context, req JSONRPCRequest) JSONRPCResponse {
	// Get request ID (0 for notifications, though they shouldn't reach here)
	reqID := int64(0)
	if req.ID != nil {
		reqID = *req.ID
	}

	switch req.Method {
	case "initialize":
		return b.handleInitialize(req)
	case "tools/list":
		return b.handleToolsList(req)
	case "tools/call":
		return b.handleToolsCall(ctx, req)
	default:
		return b.makeErrorResponse(reqID, ErrCodeMethodNotFound, "Method not found", req.Method)
	}
}

func (b *Bridge) handleInitialize(req JSONRPCRequest) JSONRPCResponse {
	result := InitializeResult{
		ProtocolVersion: "2024-11-05",
		Capabilities: map[string]any{
			"tools": map[string]any{},
		},
		ServerInfo: map[string]any{
			"name":    "varlink-mcp-bridge",
			"version": "0.1.0",
		},
	}

	reqID := int64(0)
	if req.ID != nil {
		reqID = *req.ID
	}

	return JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      reqID,
		Result:  result,
	}
}

func (b *Bridge) handleToolsList(req JSONRPCRequest) JSONRPCResponse {
	result := ToolsListResult{
		Tools: b.tools,
	}

	reqID := int64(0)
	if req.ID != nil {
		reqID = *req.ID
	}

	return JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      reqID,
		Result:  result,
	}
}

func (b *Bridge) handleToolsCall(ctx context.Context, req JSONRPCRequest) JSONRPCResponse {
	reqID := int64(0)
	if req.ID != nil {
		reqID = *req.ID
	}

	var params ToolsCallParams
	if err := json.Unmarshal(req.Params, &params); err != nil {
		return b.makeErrorResponse(reqID, ErrCodeInvalidParams, "Invalid params", err.Error())
	}

	// Find the tool and get its original Varlink method name
	var methodName string
	for _, tool := range b.tools {
		if tool.Name == params.Name {
			methodName = tool.VarlinkMethod
			break
		}
	}

	if methodName == "" {
		return b.makeErrorResponse(reqID, ErrCodeInvalidParams, "Unknown tool", params.Name)
	}

	// Call varlink method
	result, err := b.varlinkClient.Call(ctx, methodName, params.Arguments)
	if err != nil {
		return b.makeErrorResponse(reqID, ErrCodeInternal, fmt.Sprintf("Varlink call failed: %v", err), "")
	}

	// Check if result contains HTTP resources (can be at top level or under parameters)
	var resourceParams map[string]any
	if resourceType, ok := result["resource_type"].(string); ok && resourceType == "http_listing" {
		// Resource type at top level (maildir style)
		resourceParams = result
	} else if resultParams, ok := result["parameters"].(map[string]any); ok {
		if resourceType, ok := resultParams["resource_type"].(string); ok && resourceType == "http_listing" {
			// Resource type under parameters
			resourceParams = resultParams
		}
	}

	if resourceParams != nil {
		// Handle binary resources
		return b.handleResourceResponse(ctx, reqID, methodName, params.Arguments, resourceParams)
	}

	// Format normal result as MCP content
	resultJSON, _ := json.Marshal(result)
	callResult := ToolsCallResult{
		Content: []ContentItem{
			{
				Type: "text",
				Text: string(resultJSON),
			},
		},
	}

	return JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      reqID,
		Result:  callResult,
	}
}

// handleResourceResponse handles responses containing binary resources
func (b *Bridge) handleResourceResponse(ctx context.Context, id int64, methodName string, originalParams map[string]any, resultParams map[string]any) JSONRPCResponse {
	// Clean old resources (older than 1 hour)
	if err := b.cache.CleanOldResources(3600); err != nil {
		log.Printf("Warning: failed to clean old resources: %v\n", err)
	}

	// Extract resources array
	resourcesRaw, ok := resultParams["resources"].([]any)
	if !ok || len(resourcesRaw) == 0 {
		return b.makeErrorResponse(id, ErrCodeInternal, "No resources found in http_listing", "")
	}

	// Extract resource paths and filenames
	type ResourceInfo struct {
		Path     string
		Filename string
		Size     int64
	}

	var resourceInfos []ResourceInfo
	var resourcePaths []string

	for _, resRaw := range resourcesRaw {
		resMap, ok := resRaw.(map[string]any)
		if !ok {
			continue
		}

		path, _ := resMap["path"].(string)
		if path == "" {
			continue
		}

		// Extract filename (prefer explicit filename field, fall back to path)
		filename := ""
		if fn, ok := resMap["filename"].(string); ok && fn != "" {
			filename = fn
		} else {
			// Extract from path
			parts := strings.Split(path, "/")
			if len(parts) > 0 && parts[len(parts)-1] != "" {
				filename = parts[len(parts)-1]
			} else {
				filename = fmt.Sprintf("resource-%d", len(resourcePaths))
			}
		}

		size, _ := resMap["size"].(float64) // JSON numbers are float64

		resourceInfos = append(resourceInfos, ResourceInfo{
			Path:     path,
			Filename: filename,
			Size:     int64(size),
		})
		resourcePaths = append(resourcePaths, path)
	}

	// Fetch all resources at once
	log.Printf("Fetching %d resources from varlink...\n", len(resourcePaths))
	resourceData, err := b.varlinkClient.FetchResources(ctx, methodName, originalParams, resourcePaths)
	if err != nil {
		return b.makeErrorResponse(id, ErrCodeInternal, fmt.Sprintf("Failed to fetch resources: %v", err), "")
	}

	// Write files to session directory and collect file paths
	var filePaths []string
	for i, info := range resourceInfos {
		data, ok := resourceData[info.Path]
		if !ok {
			log.Printf("Warning: resource %s not found in fetched data\n", info.Path)
			continue
		}

		// Write to session directory
		filePath := filepath.Join(b.sessionDir, info.Filename)
		if err := os.WriteFile(filePath, data, 0644); err != nil {
			log.Printf("Warning: failed to write file %s: %v\n", filePath, err)
			continue
		}

		filePaths = append(filePaths, filePath)
		log.Printf("Wrote resource %d/%d: %s (%d bytes)\n", i+1, len(resourceInfos), filePath, len(data))

		// Also store in cache for future reference
		_, err = b.cache.StoreResource(info.Filename, "", data, *varlinkAddress, methodName)
		if err != nil {
			log.Printf("Warning: failed to cache resource: %v\n", err)
		}
	}

	if len(filePaths) == 0 {
		return b.makeErrorResponse(id, ErrCodeInternal, "No files were successfully written", "")
	}

	// Return text content with file paths
	var responseText strings.Builder
	responseText.WriteString(fmt.Sprintf("Downloaded %d file(s) to session directory:\n\n", len(filePaths)))
	for _, path := range filePaths {
		responseText.WriteString(fmt.Sprintf("%s\n", path))
	}

	callResult := ToolsCallResult{
		Content: []ContentItem{
			{
				Type: "text",
				Text: responseText.String(),
			},
		},
	}

	return JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      id,
		Result:  callResult,
	}
}

func (b *Bridge) sendError(encoder *json.Encoder, id int64, code int, message, data string) {
	resp := b.makeErrorResponse(id, code, message, data)
	encoder.Encode(resp)
}

func (b *Bridge) makeErrorResponse(id int64, code int, message, data string) JSONRPCResponse {
	return JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      id,
		Error: &RPCError{
			Code:    code,
			Message: message,
			Data:    data,
		},
	}
}

func generateSessionID() string {
	// Generate session ID using timestamp + random bytes
	timestamp := time.Now().Unix()

	// Generate 4 random bytes
	randomBytes := make([]byte, 4)
	if _, err := rand.Read(randomBytes); err != nil {
		// Fallback to timestamp only if random fails
		return fmt.Sprintf("%d", timestamp)
	}

	randomHex := hex.EncodeToString(randomBytes)
	return fmt.Sprintf("%d-%s", timestamp, randomHex)
}

func buildTools(parsedIDL *idl.IDL, interfaceName string) ([]Tool, error) {
	var tools []Tool

	for _, method := range parsedIDL.Methods {
		// Build input schema
		inputSchema, err := buildInputSchemaForMethod(method)
		if err != nil {
			return nil, fmt.Errorf("failed to build schema for %s: %w", method.Name, err)
		}

		tool := Tool{
			Name:          sanitizeToolName(interfaceName, method.Name),
			Description:   method.Doc, // ✨ Documentation from varlink comments!
			InputSchema:   inputSchema,
			VarlinkMethod: method.Name, // Store original Varlink method name
		}

		tools = append(tools, tool)
	}

	return tools, nil
}