// SiYuan - Refactor your thinking
// Copyright (c) 2020-present, b3log.org
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

package mcp

import (
	"encoding/json"
	"io"
	"net/http"

	"github.com/gin-gonic/gin"
	"github.com/siyuan-note/siyuan/kernel/model"
)

func Serve(ginServer *gin.Engine) {
	ginServer.POST("/mcp", model.CheckAuth, handlePost)
	ginServer.GET("/mcp", model.CheckAuth, func(c *gin.Context) {
		c.Status(http.StatusMethodNotAllowed)
	})
	ginServer.DELETE("/mcp", model.CheckAuth, handleDelete)
}

func handlePost(c *gin.Context) {
	body, err := io.ReadAll(c.Request.Body)
	if err != nil {
		c.JSON(http.StatusOK, JsonRpcErrorResponse{
			JsonRpc: "2.0",
			Error:   RpcError{Code: -32700, Message: "Parse error"},
			ID:      nil,
		})
		return
	}

	var req JsonRpcRequest
	if err := json.Unmarshal(body, &req); err != nil {
		c.JSON(http.StatusOK, JsonRpcErrorResponse{
			JsonRpc: "2.0",
			Error:   RpcError{Code: -32700, Message: "Parse error"},
			ID:      nil,
		})
		return
	}

	if req.JsonRpc != "2.0" {
		c.JSON(http.StatusOK, JsonRpcErrorResponse{
			JsonRpc: "2.0",
			Error:   RpcError{Code: -32600, Message: "Invalid Request"},
			ID:      req.ID,
		})
		return
	}

	if req.Method == "" {
		c.JSON(http.StatusOK, JsonRpcErrorResponse{
			JsonRpc: "2.0",
			Error:   RpcError{Code: -32600, Message: "Invalid Request"},
			ID:      req.ID,
		})
		return
	}

	protoVersion := c.GetHeader("MCP-Protocol-Version")
	if protoVersion == ProtocolV20260728 {
		handlePost2026(c, &req)
		return
	}

	var session *Session
	if req.Method == "initialize" {
		session = newSession()
	} else {
		sessionID := c.GetHeader("Mcp-Session-Id")
		if sessionID == "" {
			c.JSON(http.StatusBadRequest, gin.H{"error": "Mcp-Session-Id required"})
			return
		}
		session = getSession(sessionID)
		if session == nil {
			c.JSON(http.StatusNotFound, gin.H{"error": "session not found"})
			return
		}
	}

	response := processRequest(&req, session, protoVersion)

	if req.Method == "initialize" {
		c.Header("Mcp-Session-Id", session.ID)
	}

	writeResponse(c, response)
}

func handlePost2026(c *gin.Context, req *JsonRpcRequest) {
	mcpMethod := c.GetHeader("Mcp-Method")
	if mcpMethod != "" && mcpMethod != req.Method {
		c.JSON(http.StatusBadRequest, gin.H{"error": "Mcp-Method header does not match body method"})
		return
	}

	response := processRequest2026(req)
	writeResponse(c, response)
}

func writeResponse(c *gin.Context, response any) {
	switch v := response.(type) {
	case nil:
		c.Status(http.StatusAccepted)
	case *JsonRpcResponse:
		c.JSON(http.StatusOK, v)
	case *JsonRpcErrorResponse:
		c.JSON(http.StatusOK, v)
	}
}

func handleDelete(c *gin.Context) {
	sessionID := c.GetHeader("Mcp-Session-Id")
	if sessionID == "" {
		c.Status(http.StatusBadRequest)
		return
	}
	removeSession(sessionID)
	c.Status(http.StatusOK)
}