package controller

import (
	"context"
	"encoding/json"
	"errors"
	"io"
	"sync"
	"time"

	"github.com/hashicorp/go-uuid"

	"github.com/nezhahq/nezha/model"
	pb "github.com/nezhahq/nezha/proto"
	"github.com/nezhahq/nezha/service/rpc"
	"github.com/nezhahq/nezha/service/singleton"
)

// openFsTransferStream owns the task-to-agent IOStream lifecycle. The returned
// cleanup is safe for concurrent callers and shares ownership with cancellation.
func openFsTransferStream(ctx context.Context, serverID uint64, req *model.FsTransferRequest) (io.ReadWriteCloser, func(), error) {
	if singleton.Conf == nil || !singleton.Conf.MCPEnabled() {
		return nil, func() {}, errors.New("MCP is disabled by the dashboard administrator")
	}
	server, _ := singleton.ServerShared.Get(serverID)
	if server == nil || server.GetTaskStream() == nil {
		return nil, func() {}, errors.New("server offline")
	}
	handler := rpc.NezhaHandlerSingleton

	streamID, err := uuid.GenerateUUID()
	if err != nil {
		return nil, func() {}, err
	}
	req.StreamID = streamID
	if err := handler.CreateStreamWithPurpose(streamID, 0, serverID, rpc.PurposeMCPTransfer); err != nil {
		return nil, func() {}, err
	}
	var cleanupOnce sync.Once
	cleanup := func() { cleanupOnce.Do(func() { _ = handler.CloseStream(streamID) }) }

	body, err := json.Marshal(req)
	if err != nil {
		cleanup()
		return nil, func() {}, err
	}
	// The stream is owned by cleanup until the caller receives it; every failure path releases it.
	if singleton.Conf == nil || !singleton.Conf.MCPEnabled() {
		cleanup()
		return nil, func() {}, errors.New("MCP is disabled by the dashboard administrator")
	}
	if err := ctx.Err(); err != nil {
		cleanup()
		return nil, func() {}, err
	}
	if err := server.SendTask(&pb.Task{Type: model.TaskTypeFsTransfer, Data: string(body)}); err != nil {
		cleanup()
		if errors.Is(err, model.ErrTaskStreamOffline) {
			return nil, func() {}, errors.New("server offline")
		}
		return nil, func() {}, err
	}

	agentStream, ok := handler.WaitForAgent(ctx, streamID, 30*time.Second)
	if !ok {
		cleanup()
		return nil, func() {}, errors.New("agent did not attach within 30s")
	}

	watcherDone := make(chan struct{})
	var watcherOnce sync.Once
	go func() {
		select {
		case <-ctx.Done():
			cleanup()
		case <-watcherDone:
		}
	}()
	wrappedCleanup := func() {
		watcherOnce.Do(func() { close(watcherDone) })
		cleanup()
	}
	return agentStream, wrappedCleanup, nil
}