package api

import (
	"context"
	"encoding/json"
	"errors"
	"net/http"
	"sync"

	"github.com/gin-gonic/gin"
	"github.com/gorilla/websocket"

	"monica-go-completion-backend/internal/completion"
)

var wsUpgrader = websocket.Upgrader{
	ReadBufferSize:  4096,
	WriteBufferSize: 4096,
	CheckOrigin: func(_ *http.Request) bool {
		return true
	},
}

type wsCompletionRequest struct {
	ID        string `json:"id"`
	Language  string `json:"language,omitempty"`
	SessionID string `json:"sessionId,omitempty"`
	URI       string `json:"uri"`
	Text      string `json:"text"`
	Line      int    `json:"line"`
	Character int    `json:"character"`
}

type wsCompletionResponse struct {
	ID           string            `json:"id"`
	Items        []completion.Item `json:"items,omitempty"`
	IsIncomplete bool              `json:"isIncomplete,omitempty"`
	RouteTo      string            `json:"routeTo,omitempty"`
	OwnerID      string            `json:"ownerId,omitempty"`
	Error        string            `json:"error,omitempty"`
}

type wsRPCRequest struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      json.RawMessage `json:"id"`
	Method  string          `json:"method"`
	Params  json.RawMessage `json:"params"`
}

type wsRPCResponse struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      json.RawMessage `json:"id"`
	Result  any             `json:"result,omitempty"`
	Error   any             `json:"error,omitempty"`
}

func registerWSRoutes(router *gin.Engine, service CompletionService, opts RouteOptions) {
	handler := func(c *gin.Context, defaultLanguage string) {
		conn, err := wsUpgrader.Upgrade(c.Writer, c.Request, nil)
		if err != nil {
			return
		}
		defer conn.Close()

		conn.SetReadLimit(opts.MaxBodyBytes)

		var writeMu sync.Mutex

		for {
			_, payload, err := conn.ReadMessage()
			if err != nil {
				break
			}
			handleWSMessage(conn, &writeMu, service, payload, defaultLanguage, opts)
		}
	}

	router.GET("/ws/completions", func(c *gin.Context) {
		handler(c, "")
	})
	router.GET("/ws/completions/:language", func(c *gin.Context) {
		handler(c, c.Param("language"))
	})
}

func handleWSMessage(
	conn *websocket.Conn,
	writeMu *sync.Mutex,
	service CompletionService,
	payload []byte,
	defaultLanguage string,
	opts RouteOptions,
) {
	if tryHandleRPCMessage(conn, writeMu, service, payload, defaultLanguage, opts) {
		return
	}

	var req wsCompletionRequest
	if err := json.Unmarshal(payload, &req); err != nil {
		sendWSResponse(conn, writeMu, wsCompletionResponse{
			ID:    "",
			Error: "invalid JSON payload",
		})
		return
	}
	if req.Language == "" {
		req.Language = defaultLanguage
	}

	processWSCompletion(conn, writeMu, service, req, opts)
}

func tryHandleRPCMessage(
	conn *websocket.Conn,
	writeMu *sync.Mutex,
	service CompletionService,
	payload []byte,
	defaultLanguage string,
	opts RouteOptions,
) bool {
	var rpcReq wsRPCRequest
	if err := json.Unmarshal(payload, &rpcReq); err != nil {
		return false
	}
	if rpcReq.JSONRPC != "2.0" || rpcReq.Method == "" {
		return false
	}

	if rpcReq.Method != "completion/complete" && rpcReq.Method != "completion.complete" {
		sendWSRPCResponse(conn, writeMu, wsRPCResponse{
			JSONRPC: "2.0",
			ID:      rpcReq.ID,
			Error: map[string]any{
				"code":    -32601,
				"message": "method not found",
			},
		})
		return true
	}

	var req wsCompletionRequest
	if err := json.Unmarshal(rpcReq.Params, &req); err != nil {
		sendWSRPCResponse(conn, writeMu, wsRPCResponse{
			JSONRPC: "2.0",
			ID:      rpcReq.ID,
			Error: map[string]any{
				"code":    -32602,
				"message": "invalid params",
			},
		})
		return true
	}
	if req.Language == "" {
		req.Language = defaultLanguage
	}
	if req.ID == "" {
		req.ID = string(rpcReq.ID)
	}

	ctx, cancel := context.WithTimeout(context.Background(), opts.RequestTimeout)
	defer cancel()

	resp, err := service.Complete(ctx, completion.Request{
		Language:  req.Language,
		SessionID: req.SessionID,
		URI:       req.URI,
		Text:      req.Text,
		Line:      req.Line,
		Character: req.Character,
	})
	if err != nil {
		sendWSRPCResponse(conn, writeMu, wsRPCResponse{
			JSONRPC: "2.0",
			ID:      rpcReq.ID,
			Error: map[string]any{
				"code":    -32000,
				"message": err.Error(),
			},
		})
		return true
	}

	sendWSRPCResponse(conn, writeMu, wsRPCResponse{
		JSONRPC: "2.0",
		ID:      rpcReq.ID,
		Result:  resp,
	})
	return true
}

func processWSCompletion(
	conn *websocket.Conn,
	writeMu *sync.Mutex,
	service CompletionService,
	req wsCompletionRequest,
	opts RouteOptions,
) {
	ctx, cancel := context.WithTimeout(context.Background(), opts.RequestTimeout)
	defer cancel()

	resp, err := service.Complete(ctx, completion.Request{
		Language:  req.Language,
		SessionID: req.SessionID,
		URI:       req.URI,
		Text:      req.Text,
		Line:      req.Line,
		Character: req.Character,
	})
	if err != nil {
		msg := "completion failed"
		routeTo := ""
		ownerID := ""
		switch {
		case errors.Is(err, completion.ErrInvalidRequest):
			msg = err.Error()
		case errors.Is(err, completion.ErrUnsupportedLanguage):
			msg = err.Error()
		case errors.Is(err, completion.ErrTooManySessions):
			msg = err.Error()
		default:
			var ownedErr *completion.ErrSessionOwnedByOtherInstance
			if errors.As(err, &ownedErr) {
				msg = err.Error()
				routeTo = ownedErr.OwnerEndpoint
				ownerID = ownedErr.OwnerID
			}
		}
		sendWSResponse(conn, writeMu, wsCompletionResponse{
			ID:      req.ID,
			RouteTo: routeTo,
			OwnerID: ownerID,
			Error:   msg,
		})
		return
	}

	sendWSResponse(conn, writeMu, wsCompletionResponse{
		ID:           req.ID,
		Items:        resp.Items,
		IsIncomplete: resp.IsIncomplete,
	})
}

func sendWSResponse(conn *websocket.Conn, writeMu *sync.Mutex, resp wsCompletionResponse) {
	writeMu.Lock()
	defer writeMu.Unlock()
	_ = conn.WriteJSON(resp)
}

func sendWSRPCResponse(conn *websocket.Conn, writeMu *sync.Mutex, resp wsRPCResponse) {
	writeMu.Lock()
	defer writeMu.Unlock()
	_ = conn.WriteJSON(resp)
}