arp/mcp/handler.go

package mcp

import (
	"context"
	"encoding/json"

	"gogs.dmsc.dev/arp/auth"
	"gogs.dmsc.dev/arp/mcp/tools"
)

// handleToolsList returns the list of available tools
func (s *Server) handleToolsList(ctx context.Context, req *JSONRPCRequest) *JSONRPCResponse {
	toolList := []Tool{
		{
			Name:        "introspect",
			Description: "Get GraphQL schema information - types, fields, queries, mutations. Use this to discover the API structure before making queries or mutations.",
			InputSchema: InputSchema{
				Type:                 "object",
				AdditionalProperties: false,
				Properties: map[string]Property{
					"typeName": {
						Type:        "string",
						Description: "Optional - specific type to introspect (e.g., 'Query', 'Mutation', 'User', 'Task'). If omitted, returns full schema overview.",
					},
				},
			},
		},
		{
			Name:        "query",
			Description: "Execute GraphQL queries (read operations). Use for fetching data from the API. The query must be a valid GraphQL query string.",
			InputSchema: InputSchema{
				Type:                 "object",
				AdditionalProperties: false,
				Properties: map[string]Property{
					"query": {
						Type:        "string",
						Description: "GraphQL query string (e.g., 'query { users { id email } }')",
					},
					"variables": {
						Type:        "object",
						Description: "Optional query variables as key-value pairs",
					},
				},
				Required: []string{"query"},
			},
		},
		{
			Name:        "mutate",
			Description: "Execute GraphQL mutations (create/update/delete operations). Use for modifying data in the API. The mutation must be a valid GraphQL mutation string.",
			InputSchema: InputSchema{
				Type:                 "object",
				AdditionalProperties: false,
				Properties: map[string]Property{
					"mutation": {
						Type:        "string",
						Description: "GraphQL mutation string (e.g., 'mutation { createUser(input: {email: \"test@example.com\", password: \"pass\", roles: []}) { id } }')",
					},
					"variables": {
						Type:        "object",
						Description: "Optional mutation variables as key-value pairs",
					},
				},
				Required: []string{"mutation"},
			},
		},
	}

	return &JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      req.ID,
		Result:  ListToolsResult{Tools: toolList},
	}
}

// handleToolsCall executes a tool call
func (s *Server) handleToolsCall(ctx context.Context, req *JSONRPCRequest) *JSONRPCResponse {
	var params CallToolParams
	if req.Params != nil {
		if err := json.Unmarshal(req.Params, &params); err != nil {
			return &JSONRPCResponse{
				JSONRPC: "2.0",
				ID:      req.ID,
				Error:   ErrInvalidParams,
			}
		}
	}

	var result tools.CallToolResult
	var err error

	switch params.Name {
	case "introspect":
		result, err = tools.Introspect(ctx, s.schema, params.Arguments)
	case "query":
		result, err = tools.Query(ctx, s.resolver, s.schema, params.Arguments)
	case "mutate":
		result, err = tools.Mutate(ctx, s.resolver, s.schema, params.Arguments)
	default:
		return &JSONRPCResponse{
			JSONRPC: "2.0",
			ID:      req.ID,
			Error:   ErrMethodNotFound,
		}
	}

	if err != nil {
		return &JSONRPCResponse{
			JSONRPC: "2.0",
			ID:      req.ID,
			Result: tools.CallToolResult{
				Content: []tools.ContentBlock{
					{Type: "text", Text: err.Error()},
				},
				IsError: true,
			},
		}
	}

	return &JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      req.ID,
		Result:  result,
	}
}

// handleResourcesList returns the list of available subscription resources
func (s *Server) handleResourcesList(ctx context.Context, req *JSONRPCRequest) *JSONRPCResponse {
	resources := []Resource{
		{
			URI:         "graphql://subscription/taskCreated",
			Name:        "taskCreated",
			Description: "Subscribe to task creation events. Receives Task objects when new tasks are created and assigned to you.",
			MimeType:    "application/json",
		},
		{
			URI:         "graphql://subscription/taskUpdated",
			Name:        "taskUpdated",
			Description: "Subscribe to task update events. Receives Task objects when tasks assigned to you are updated.",
			MimeType:    "application/json",
		},
		{
			URI:         "graphql://subscription/taskDeleted",
			Name:        "taskDeleted",
			Description: "Subscribe to task deletion events. Receives Task objects when tasks assigned to you are deleted.",
			MimeType:    "application/json",
		},
		{
			URI:         "graphql://subscription/messageAdded",
			Name:        "messageAdded",
			Description: "Subscribe to new message events. Receives Message objects when messages are sent to you.",
			MimeType:    "application/json",
		},
	}

	return &JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      req.ID,
		Result:  ListResourcesResult{Resources: resources},
	}
}

// handleResourcesRead returns current state of a resource (for subscriptions, this is a description)
func (s *Server) handleResourcesRead(ctx context.Context, req *JSONRPCRequest) *JSONRPCResponse {
	var params ReadResourceParams
	if req.Params != nil {
		if err := json.Unmarshal(req.Params, &params); err != nil {
			return &JSONRPCResponse{
				JSONRPC: "2.0",
				ID:      req.ID,
				Error:   ErrInvalidParams,
			}
		}
	}

	// For subscriptions, reading returns a description
	description := "This is a subscription resource. Use resources/subscribe to receive real-time updates."

	return &JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      req.ID,
		Result: ReadResourceResult{
			Contents: []ResourceContents{
				{
					URI:      params.URI,
					MimeType: "text/plain",
					Text:     description,
				},
			},
		},
	}
}

// handleResourcesSubscribe starts a subscription for real-time updates
func (s *Server) handleResourcesSubscribe(ctx context.Context, req *JSONRPCRequest, session *Session) *JSONRPCResponse {
	var params SubscribeParams
	if req.Params != nil {
		if err := json.Unmarshal(req.Params, &params); err != nil {
			return &JSONRPCResponse{
				JSONRPC: "2.0",
				ID:      req.ID,
				Error:   ErrInvalidParams,
			}
		}
	}

	// Check authentication
	user, err := auth.CurrentUser(ctx)
	if err != nil {
		return &JSONRPCResponse{
			JSONRPC: "2.0",
			ID:      req.ID,
			Error:   &RPCError{Code: -32603, Message: "Authentication required for subscriptions"},
		}
	}

	// Create cancellable context for this subscription
	subCtx, cancel := context.WithCancel(context.Background())

	// Store the cancel function
	session.SubsMu.Lock()
	session.Subscriptions[params.URI] = cancel
	session.SubsMu.Unlock()

	// Start the subscription based on URI
	go s.runSubscription(subCtx, params.URI, user.ID, session)

	return &JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      req.ID,
		Result:  map[string]interface{}{"subscribed": true, "uri": params.URI},
	}
}

// handleResourcesUnsubscribe stops a subscription
func (s *Server) handleResourcesUnsubscribe(ctx context.Context, req *JSONRPCRequest, session *Session) *JSONRPCResponse {
	var params UnsubscribeParams
	if req.Params != nil {
		if err := json.Unmarshal(req.Params, &params); err != nil {
			return &JSONRPCResponse{
				JSONRPC: "2.0",
				ID:      req.ID,
				Error:   ErrInvalidParams,
			}
		}
	}

	session.SubsMu.Lock()
	if cancel, ok := session.Subscriptions[params.URI]; ok {
		cancel()
		delete(session.Subscriptions, params.URI)
	}
	session.SubsMu.Unlock()

	return &JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      req.ID,
		Result:  map[string]interface{}{"unsubscribed": true, "uri": params.URI},
	}
}

// runSubscription handles the actual subscription event streaming
func (s *Server) runSubscription(ctx context.Context, uri string, userID uint, session *Session) {
	switch uri {
	case "graphql://subscription/taskCreated":
		s.streamTaskEvents(ctx, userID, session, "created")
	case "graphql://subscription/taskUpdated":
		s.streamTaskEvents(ctx, userID, session, "updated")
	case "graphql://subscription/taskDeleted":
		s.streamTaskEvents(ctx, userID, session, "deleted")
	case "graphql://subscription/messageAdded":
		s.streamMessageEvents(ctx, userID, session)
	}
}

// streamTaskEvents streams task events to the session
func (s *Server) streamTaskEvents(ctx context.Context, userID uint, session *Session, eventType string) {
	eventChan := s.resolver.SubscribeToTasks(userID)

	for {
		select {
		case <-ctx.Done():
			return
		case <-session.Done:
			return
		case event, ok := <-eventChan:
			if !ok {
				return
			}
			if event.EventType == eventType && event.Task != nil {
				notification := CreateResourceNotification(
					"graphql://subscription/task"+capitalize(eventType),
					event.Task,
				)
				s.sendNotification(session, notification)
			}
		}
	}
}

// streamMessageEvents streams message events to the session
func (s *Server) streamMessageEvents(ctx context.Context, userID uint, session *Session) {
	eventChan := s.resolver.SubscribeToMessages(userID)

	for {
		select {
		case <-ctx.Done():
			return
		case <-session.Done:
			return
		case event, ok := <-eventChan:
			if !ok {
				return
			}
			// Check if user is a receiver
			isReceiver := false
			for _, receiverID := range event.ReceiverIDs {
				if receiverID == userID {
					isReceiver = true
					break
				}
			}
			if isReceiver && event.Message != nil {
				notification := CreateResourceNotification(
					"graphql://subscription/messageAdded",
					event.Message,
				)
				s.sendNotification(session, notification)
			}
		}
	}
}

// sendNotification sends a JSON-RPC notification to the session
func (s *Server) sendNotification(session *Session, notification *JSONRPCNotification) {
	notifBytes, err := json.Marshal(notification)
	if err != nil {
		return
	}
	select {
	case session.Events <- notifBytes:
	default:
		// Channel full, skip
	}
}

// capitalize helper
func capitalize(s string) string {
	if len(s) == 0 {
		return s
	}
	return string(s[0]-32) + s[1:]
}