notely/backend/internal/application/services/task_service.go

package services

import (
	"context"
	"errors"
	"fmt"
	"sort"
	"strings"
	"time"

	"gitea.hostxtra.co.uk/mrhid6/notely/backend/internal/application/dto"
	"gitea.hostxtra.co.uk/mrhid6/notely/backend/internal/domain/entities"
	"gitea.hostxtra.co.uk/mrhid6/notely/backend/internal/domain/repositories"
	"go.mongodb.org/mongo-driver/v2/bson"
)

// TaskService handles task and task status operations.
type TaskService struct {
	taskRepo          repositories.TaskRepository
	taskListRepo      repositories.TaskListRepository
	taskStatusRepo    repositories.TaskStatusRepository
	noteRepo          repositories.NoteRepository
	categoryRepo      repositories.CategoryRepository
	membershipRepo    repositories.MembershipRepository
	permissionService *PermissionService
}

// NewTaskService creates a task service.
func NewTaskService(
	taskRepo repositories.TaskRepository,
	taskListRepo repositories.TaskListRepository,
	taskStatusRepo repositories.TaskStatusRepository,
	noteRepo repositories.NoteRepository,
	categoryRepo repositories.CategoryRepository,
	membershipRepo repositories.MembershipRepository,
	permissionService *PermissionService,
) *TaskService {
	return &TaskService{
		taskRepo:          taskRepo,
		taskListRepo:      taskListRepo,
		taskStatusRepo:    taskStatusRepo,
		noteRepo:          noteRepo,
		categoryRepo:      categoryRepo,
		membershipRepo:    membershipRepo,
		permissionService: permissionService,
	}
}

func (s *TaskService) ensureDefaultStatuses(ctx context.Context, spaceID bson.ObjectID) error {
	statuses, err := s.taskStatusRepo.ListStatuses(ctx, spaceID)
	if err != nil {
		return err
	}
	if len(statuses) > 0 {
		return nil
	}

	defaults := []struct {
		name  string
		color string
	}{
		{name: "Pending", color: "#7c8596"},
		{name: "In Progress", color: "#3b82f6"},
		{name: "Done", color: "#22c55e"},
	}

	for idx, status := range defaults {
		if err := s.taskStatusRepo.CreateStatus(ctx, &entities.TaskStatus{
			SpaceID: spaceID,
			Name:    status.name,
			Color:   status.color,
			Order:   idx,
		}); err != nil {
			return err
		}
	}

	return nil
}

func (s *TaskService) hasTaskPermission(ctx context.Context, userID, spaceID bson.ObjectID, action string) (bool, error) {
	if s.permissionService == nil {
		return false, errors.New("permission service unavailable")
	}
	return s.permissionService.HasSpacePermission(ctx, userID, spaceID, action)
}

func (s *TaskService) requireSpaceAccess(ctx context.Context, userID, spaceID bson.ObjectID) error {
	if _, err := s.membershipRepo.GetUserMembership(ctx, userID, spaceID); err != nil {
		return errors.New("unauthorized")
	}
	return nil
}

func toObjectIDPtr(hexID *string) (*bson.ObjectID, error) {
	if hexID == nil || strings.TrimSpace(*hexID) == "" {
		return nil, nil
	}
	id, err := bson.ObjectIDFromHex(*hexID)
	if err != nil {
		return nil, errors.New("invalid object id")
	}
	return &id, nil
}

func toObjectIDs(hexIDs []string) ([]bson.ObjectID, error) {
	result := make([]bson.ObjectID, 0, len(hexIDs))
	seen := map[bson.ObjectID]struct{}{}
	for _, hexID := range hexIDs {
		hexID = strings.TrimSpace(hexID)
		if hexID == "" {
			continue
		}
		id, err := bson.ObjectIDFromHex(hexID)
		if err != nil {
			return nil, errors.New("invalid linked note id")
		}
		if _, exists := seen[id]; exists {
			continue
		}
		seen[id] = struct{}{}
		result = append(result, id)
	}
	return result, nil
}

func (s *TaskService) validateTaskList(ctx context.Context, spaceID, taskListID bson.ObjectID) error {
	taskList, err := s.taskListRepo.GetTaskListByID(ctx, taskListID)
	if err != nil || taskList.SpaceID != spaceID {
		return errors.New("invalid task list")
	}
	return nil
}

func (s *TaskService) validateNoteLinks(ctx context.Context, spaceID bson.ObjectID, noteLinks []bson.ObjectID) error {
	for _, noteID := range noteLinks {
		note, err := s.noteRepo.GetNoteByID(ctx, noteID)
		if err != nil || note.SpaceID != spaceID {
			return errors.New("invalid linked note")
		}
	}
	return nil
}

func (s *TaskService) validateStatus(ctx context.Context, spaceID, statusID bson.ObjectID) (*entities.TaskStatus, error) {
	status, err := s.taskStatusRepo.GetStatusByID(ctx, statusID)
	if err != nil || status.SpaceID != spaceID {
		return nil, errors.New("invalid task status")
	}
	return status, nil
}

func (s *TaskService) resolveDepthAndParent(ctx context.Context, spaceID bson.ObjectID, parentTaskID *bson.ObjectID) (int, error) {
	if parentTaskID == nil {
		return 0, nil
	}
	parent, err := s.taskRepo.GetTaskByID(ctx, *parentTaskID)
	if err != nil || parent.SpaceID != spaceID {
		return 0, errors.New("invalid parent task")
	}
	depth := parent.Depth + 1
	if depth > entities.MaxTaskDepth {
		return 0, fmt.Errorf("max task depth is %d", entities.MaxTaskDepth+1)
	}
	return depth, nil
}

func (s *TaskService) isAdjacentStatusMove(ctx context.Context, spaceID, currentStatusID, requestedStatusID bson.ObjectID) (bool, error) {
	if currentStatusID == requestedStatusID {
		return true, nil
	}
	statuses, err := s.taskStatusRepo.ListStatuses(ctx, spaceID)
	if err != nil {
		return false, err
	}
	currentIdx := -1
	requestedIdx := -1
	for idx, status := range statuses {
		if status.ID == currentStatusID {
			currentIdx = idx
		}
		if status.ID == requestedStatusID {
			requestedIdx = idx
		}
	}
	if currentIdx == -1 || requestedIdx == -1 {
		return false, errors.New("status not found in sequence")
	}
	delta := requestedIdx - currentIdx
	if delta < 0 {
		delta = -delta
	}
	return delta == 1, nil
}

func (s *TaskService) CreateTask(ctx context.Context, spaceID, userID bson.ObjectID, req *dto.CreateTaskRequest) (*dto.TaskDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.create")
	if err != nil {
		return nil, err
	}
	if !hasPermission {
		return nil, errors.New("insufficient permissions")
	}

	if err := s.ensureDefaultStatuses(ctx, spaceID); err != nil {
		return nil, err
	}

	parentTaskID, err := toObjectIDPtr(req.ParentTaskID)
	if err != nil {
		return nil, errors.New("invalid parent task")
	}
	depth, err := s.resolveDepthAndParent(ctx, spaceID, parentTaskID)
	if err != nil {
		return nil, err
	}

	taskListID, err := bson.ObjectIDFromHex(strings.TrimSpace(req.TaskListID))
	if err != nil {
		return nil, errors.New("invalid task list")
	}
	if err := s.validateTaskList(ctx, spaceID, taskListID); err != nil {
		return nil, err
	}

	noteLinks, err := toObjectIDs(req.NoteLinks)
	if err != nil {
		return nil, err
	}
	if err := s.validateNoteLinks(ctx, spaceID, noteLinks); err != nil {
		return nil, err
	}

	statuses, err := s.taskStatusRepo.ListStatuses(ctx, spaceID)
	if err != nil {
		return nil, err
	}
	if len(statuses) == 0 {
		return nil, errors.New("no task statuses configured")
	}
	sort.Slice(statuses, func(i, j int) bool {
		return statuses[i].Order < statuses[j].Order
	})

	statusID := statuses[0].ID
	requestedStatusID := strings.TrimSpace(req.StatusID)
	if requestedStatusID != "" && parentTaskID == nil {
		parsedStatusID, parseErr := bson.ObjectIDFromHex(requestedStatusID)
		if parseErr != nil {
			return nil, errors.New("invalid task status")
		}
		if _, validateErr := s.validateStatus(ctx, spaceID, parsedStatusID); validateErr != nil {
			return nil, validateErr
		}
		statusID = parsedStatusID
	}

	if parentTaskID != nil {
		parent, parentErr := s.taskRepo.GetTaskByID(ctx, *parentTaskID)
		if parentErr != nil || parent.SpaceID != spaceID {
			return nil, errors.New("invalid parent task")
		}
		taskListID = parent.TaskListID
	}

	task := &entities.Task{
		SpaceID:      spaceID,
		Title:        strings.TrimSpace(req.Title),
		Description:  strings.TrimSpace(req.Description),
		TaskListID:   taskListID,
		StatusID:     statusID,
		ParentTaskID: parentTaskID,
		Depth:        depth,
		NoteLinks:    noteLinks,
		CreatedBy:    userID,
		UpdatedBy:    userID,
	}

	if task.Title == "" {
		return nil, errors.New("title is required")
	}

	if err := s.taskRepo.CreateTask(ctx, task); err != nil {
		return nil, err
	}
	return dto.NewTaskDTO(task), nil
}

func (s *TaskService) GetTaskByID(ctx context.Context, spaceID, taskID, userID bson.ObjectID) (*dto.TaskWithStatusDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}

	task, err := s.taskRepo.GetTaskByID(ctx, taskID)
	if err != nil || task.SpaceID != spaceID {
		return nil, errors.New("task not found")
	}

	status, err := s.validateStatus(ctx, spaceID, task.StatusID)
	if err != nil {
		return nil, err
	}

	subtasks, err := s.taskRepo.ListTasks(ctx, spaceID, map[string]any{"parent_task_id": task.ID})
	if err != nil {
		return nil, err
	}

	subtaskDTOs := make([]*dto.TaskDTO, 0, len(subtasks))
	for _, subtask := range subtasks {
		subtaskDTOs = append(subtaskDTOs, dto.NewTaskDTO(subtask))
	}

	return &dto.TaskWithStatusDTO{
		TaskDTO:     dto.NewTaskDTO(task),
		StatusName:  status.Name,
		StatusColor: status.Color,
		StatusOrder: status.Order,
		Subtasks:    subtaskDTOs,
	}, nil
}

func (s *TaskService) ListTasks(
	ctx context.Context,
	spaceID, userID bson.ObjectID,
	taskListID, statusID, parentTaskID *string,
) ([]*dto.TaskDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	if err := s.ensureDefaultStatuses(ctx, spaceID); err != nil {
		return nil, err
	}

	filters := map[string]any{}
	if taskListID != nil && strings.TrimSpace(*taskListID) != "" {
		id, err := bson.ObjectIDFromHex(*taskListID)
		if err != nil {
			return nil, errors.New("invalid task list filter")
		}
		filters["task_list_id"] = id
	}
	if statusID != nil && strings.TrimSpace(*statusID) != "" {
		id, err := bson.ObjectIDFromHex(*statusID)
		if err != nil {
			return nil, errors.New("invalid status filter")
		}
		filters["status_id"] = id
	}
	if parentTaskID != nil {
		parentFilter := strings.TrimSpace(*parentTaskID)
		switch parentFilter {
		case "":
		case "root":
			filters["parent_task_id"] = nil
		default:
			id, err := bson.ObjectIDFromHex(parentFilter)
			if err != nil {
				return nil, errors.New("invalid parent task filter")
			}
			filters["parent_task_id"] = id
		}
	}

	tasks, err := s.taskRepo.ListTasks(ctx, spaceID, filters)
	if err != nil {
		return nil, err
	}

	result := make([]*dto.TaskDTO, 0, len(tasks))
	for _, task := range tasks {
		result = append(result, dto.NewTaskDTO(task))
	}
	return result, nil
}

func (s *TaskService) SearchTasks(ctx context.Context, spaceID, userID bson.ObjectID, query string) ([]*dto.TaskDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	query = strings.TrimSpace(query)
	if query == "" {
		return []*dto.TaskDTO{}, nil
	}
	tasks, err := s.taskRepo.SearchTasks(ctx, spaceID, query)
	if err != nil {
		return nil, err
	}
	result := make([]*dto.TaskDTO, 0, len(tasks))
	for _, task := range tasks {
		result = append(result, dto.NewTaskDTO(task))
	}
	return result, nil
}

func (s *TaskService) ListTasksLinkedToNote(ctx context.Context, spaceID, noteID, userID bson.ObjectID) ([]*dto.TaskWithStatusDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	if _, err := s.noteRepo.GetNoteByID(ctx, noteID); err != nil {
		return nil, errors.New("note not found")
	}
	statuses, err := s.taskStatusRepo.ListStatuses(ctx, spaceID)
	if err != nil {
		return nil, err
	}
	statusByID := map[bson.ObjectID]*entities.TaskStatus{}
	for _, status := range statuses {
		statusByID[status.ID] = status
	}

	tasks, err := s.taskRepo.ListTasks(ctx, spaceID, map[string]any{"note_links": noteID})
	if err != nil {
		return nil, err
	}

	result := make([]*dto.TaskWithStatusDTO, 0, len(tasks))
	for _, task := range tasks {
		status := statusByID[task.StatusID]
		if status == nil {
			continue
		}
		result = append(result, &dto.TaskWithStatusDTO{
			TaskDTO:     dto.NewTaskDTO(task),
			StatusName:  status.Name,
			StatusColor: status.Color,
			StatusOrder: status.Order,
			Subtasks:    []*dto.TaskDTO{},
		})
	}
	return result, nil
}

func (s *TaskService) UpdateTask(ctx context.Context, spaceID, taskID, userID bson.ObjectID, req *dto.UpdateTaskRequest) (*dto.TaskDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.edit")
	if err != nil {
		return nil, err
	}
	if !hasPermission {
		return nil, errors.New("insufficient permissions")
	}

	task, err := s.taskRepo.GetTaskByID(ctx, taskID)
	if err != nil || task.SpaceID != spaceID {
		return nil, errors.New("task not found")
	}

	if req.Title != nil {
		task.Title = strings.TrimSpace(*req.Title)
		if task.Title == "" {
			return nil, errors.New("title is required")
		}
	}
	if req.Description != nil {
		task.Description = strings.TrimSpace(*req.Description)
	}

	if req.TaskListID != nil {
		if strings.TrimSpace(*req.TaskListID) == "" {
			return nil, errors.New("task list is required")
		}
		taskListID, parseErr := bson.ObjectIDFromHex(*req.TaskListID)
		if parseErr != nil {
			return nil, errors.New("invalid task list")
		}
		if task.ParentTaskID != nil {
			return nil, errors.New("subtasks inherit task list from parent")
		}
		if err := s.validateTaskList(ctx, spaceID, taskListID); err != nil {
			return nil, err
		}
		task.TaskListID = taskListID
	}

	if req.ParentTaskID != nil {
		if strings.TrimSpace(*req.ParentTaskID) == "" {
			task.ParentTaskID = nil
			task.Depth = 0
		} else {
			parentID, parseErr := bson.ObjectIDFromHex(*req.ParentTaskID)
			if parseErr != nil {
				return nil, errors.New("invalid parent task")
			}
			if parentID == task.ID {
				return nil, errors.New("task cannot be its own parent")
			}
			depth, depthErr := s.resolveDepthAndParent(ctx, spaceID, &parentID)
			if depthErr != nil {
				return nil, depthErr
			}
			task.ParentTaskID = &parentID
			task.Depth = depth
			parentTask, parentErr := s.taskRepo.GetTaskByID(ctx, parentID)
			if parentErr != nil || parentTask.SpaceID != spaceID {
				return nil, errors.New("invalid parent task")
			}
			task.TaskListID = parentTask.TaskListID
		}
	}

	if req.StatusID != nil {
		statusID, parseErr := bson.ObjectIDFromHex(*req.StatusID)
		if parseErr != nil {
			return nil, errors.New("invalid status")
		}
		if _, err := s.validateStatus(ctx, spaceID, statusID); err != nil {
			return nil, err
		}
		adjacent, err := s.isAdjacentStatusMove(ctx, spaceID, task.StatusID, statusID)
		if err != nil {
			return nil, err
		}
		if !adjacent {
			return nil, errors.New("status transition must follow adjacent order sequence")
		}
		task.StatusID = statusID
	}

	if req.NoteLinks != nil {
		noteLinks, convertErr := toObjectIDs(req.NoteLinks)
		if convertErr != nil {
			return nil, convertErr
		}
		if err := s.validateNoteLinks(ctx, spaceID, noteLinks); err != nil {
			return nil, err
		}
		task.NoteLinks = noteLinks
	}

	task.UpdatedBy = userID
	task.UpdatedAt = time.Now()
	if err := s.taskRepo.UpdateTask(ctx, task); err != nil {
		return nil, err
	}
	return dto.NewTaskDTO(task), nil
}

func (s *TaskService) DeleteTask(ctx context.Context, spaceID, taskID, userID bson.ObjectID) error {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.delete")
	if err != nil {
		return err
	}
	if !hasPermission {
		return errors.New("insufficient permissions")
	}

	task, err := s.taskRepo.GetTaskByID(ctx, taskID)
	if err != nil || task.SpaceID != spaceID {
		return errors.New("task not found")
	}

	if childCount, err := s.taskRepo.CountChildren(ctx, task.ID); err == nil && childCount > 0 {
		return errors.New("cannot delete task with subtasks")
	}

	return s.taskRepo.DeleteTask(ctx, taskID)
}

func (s *TaskService) TransitionTaskStatus(ctx context.Context, spaceID, taskID, userID bson.ObjectID, direction string) (*dto.TaskDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.edit")
	if err != nil {
		return nil, err
	}
	if !hasPermission {
		return nil, errors.New("insufficient permissions")
	}

	task, err := s.taskRepo.GetTaskByID(ctx, taskID)
	if err != nil || task.SpaceID != spaceID {
		return nil, errors.New("task not found")
	}

	statuses, err := s.taskStatusRepo.ListStatuses(ctx, spaceID)
	if err != nil {
		return nil, err
	}
	current := -1
	for idx, status := range statuses {
		if status.ID == task.StatusID {
			current = idx
			break
		}
	}
	if current == -1 {
		return nil, errors.New("task has invalid status")
	}

	switch strings.ToLower(strings.TrimSpace(direction)) {
	case "forward":
		if current+1 >= len(statuses) {
			return nil, errors.New("task is already at final status")
		}
		task.StatusID = statuses[current+1].ID
	case "backward":
		if current-1 < 0 {
			return nil, errors.New("task is already at initial status")
		}
		task.StatusID = statuses[current-1].ID
	default:
		return nil, errors.New("invalid transition direction")
	}

	task.UpdatedBy = userID
	if err := s.taskRepo.UpdateTask(ctx, task); err != nil {
		return nil, err
	}
	return dto.NewTaskDTO(task), nil
}

func (s *TaskService) LinkNoteToTask(ctx context.Context, spaceID, taskID, noteID, userID bson.ObjectID) (*dto.TaskDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.edit")
	if err != nil {
		return nil, err
	}
	if !hasPermission {
		return nil, errors.New("insufficient permissions")
	}

	task, err := s.taskRepo.GetTaskByID(ctx, taskID)
	if err != nil || task.SpaceID != spaceID {
		return nil, errors.New("task not found")
	}

	note, err := s.noteRepo.GetNoteByID(ctx, noteID)
	if err != nil || note.SpaceID != spaceID {
		return nil, errors.New("note not found")
	}

	for _, linkedNoteID := range task.NoteLinks {
		if linkedNoteID == noteID {
			return dto.NewTaskDTO(task), nil
		}
	}
	task.NoteLinks = append(task.NoteLinks, noteID)
	task.UpdatedBy = userID
	if err := s.taskRepo.UpdateTask(ctx, task); err != nil {
		return nil, err
	}
	return dto.NewTaskDTO(task), nil
}

func (s *TaskService) UnlinkNoteFromTask(ctx context.Context, spaceID, taskID, noteID, userID bson.ObjectID) (*dto.TaskDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.edit")
	if err != nil {
		return nil, err
	}
	if !hasPermission {
		return nil, errors.New("insufficient permissions")
	}

	task, err := s.taskRepo.GetTaskByID(ctx, taskID)
	if err != nil || task.SpaceID != spaceID {
		return nil, errors.New("task not found")
	}

	filtered := make([]bson.ObjectID, 0, len(task.NoteLinks))
	for _, linkedNoteID := range task.NoteLinks {
		if linkedNoteID != noteID {
			filtered = append(filtered, linkedNoteID)
		}
	}
	task.NoteLinks = filtered
	task.UpdatedBy = userID
	if err := s.taskRepo.UpdateTask(ctx, task); err != nil {
		return nil, err
	}
	return dto.NewTaskDTO(task), nil
}

func (s *TaskService) ListTaskLists(ctx context.Context, spaceID, userID bson.ObjectID) ([]*dto.TaskListDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	lists, err := s.taskListRepo.ListTaskLists(ctx, spaceID)
	if err != nil {
		return nil, err
	}
	result := make([]*dto.TaskListDTO, 0, len(lists))
	for _, list := range lists {
		result = append(result, dto.NewTaskListDTO(list))
	}
	return result, nil
}

func (s *TaskService) CreateTaskList(ctx context.Context, spaceID, userID bson.ObjectID, req *dto.CreateTaskListRequest) (*dto.TaskListDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.create")
	if err != nil {
		return nil, err
	}
	if !hasPermission {
		return nil, errors.New("insufficient permissions")
	}

	name := strings.TrimSpace(req.Name)
	if name == "" {
		return nil, errors.New("task list name is required")
	}

	var categoryID *bson.ObjectID
	if req.CategoryID != nil && strings.TrimSpace(*req.CategoryID) != "" {
		id, parseErr := bson.ObjectIDFromHex(*req.CategoryID)
		if parseErr != nil {
			return nil, errors.New("invalid category")
		}
		category, categoryErr := s.categoryRepo.GetCategoryByID(ctx, id)
		if categoryErr != nil || category.SpaceID != spaceID {
			return nil, errors.New("invalid category")
		}
		categoryID = &id
	}

	list := &entities.TaskList{
		SpaceID:     spaceID,
		CategoryID:  categoryID,
		Name:        name,
		Description: strings.TrimSpace(req.Description),
		CreatedBy:   userID,
		UpdatedBy:   userID,
	}

	if err := s.taskListRepo.CreateTaskList(ctx, list); err != nil {
		return nil, err
	}
	return dto.NewTaskListDTO(list), nil
}

func (s *TaskService) UpdateTaskList(ctx context.Context, spaceID, taskListID, userID bson.ObjectID, req *dto.UpdateTaskListRequest) (*dto.TaskListDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.edit")
	if err != nil {
		return nil, err
	}
	if !hasPermission {
		return nil, errors.New("insufficient permissions")
	}

	list, err := s.taskListRepo.GetTaskListByID(ctx, taskListID)
	if err != nil || list.SpaceID != spaceID {
		return nil, errors.New("task list not found")
	}

	if req.Name != nil {
		name := strings.TrimSpace(*req.Name)
		if name == "" {
			return nil, errors.New("task list name is required")
		}
		list.Name = name
	}
	if req.Description != nil {
		list.Description = strings.TrimSpace(*req.Description)
	}
	if req.CategoryID != nil {
		if strings.TrimSpace(*req.CategoryID) == "" {
			list.CategoryID = nil
		} else {
			categoryID, parseErr := bson.ObjectIDFromHex(*req.CategoryID)
			if parseErr != nil {
				return nil, errors.New("invalid category")
			}
			category, categoryErr := s.categoryRepo.GetCategoryByID(ctx, categoryID)
			if categoryErr != nil || category.SpaceID != spaceID {
				return nil, errors.New("invalid category")
			}
			list.CategoryID = &categoryID
		}
	}

	list.UpdatedBy = userID
	if err := s.taskListRepo.UpdateTaskList(ctx, list); err != nil {
		return nil, err
	}
	return dto.NewTaskListDTO(list), nil
}

func (s *TaskService) DeleteTaskList(ctx context.Context, spaceID, taskListID, userID bson.ObjectID) error {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.delete")
	if err != nil {
		return err
	}
	if !hasPermission {
		return errors.New("insufficient permissions")
	}

	list, err := s.taskListRepo.GetTaskListByID(ctx, taskListID)
	if err != nil || list.SpaceID != spaceID {
		return errors.New("task list not found")
	}

	tasks, err := s.taskRepo.ListTasks(ctx, spaceID, map[string]any{"task_list_id": taskListID})
	if err != nil {
		return err
	}
	if len(tasks) > 0 {
		return errors.New("cannot delete task list with tasks")
	}

	return s.taskListRepo.DeleteTaskList(ctx, taskListID)
}

func (s *TaskService) ListStatuses(ctx context.Context, spaceID, userID bson.ObjectID) ([]*dto.TaskStatusDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	if err := s.ensureDefaultStatuses(ctx, spaceID); err != nil {
		return nil, err
	}
	statuses, err := s.taskStatusRepo.ListStatuses(ctx, spaceID)
	if err != nil {
		return nil, err
	}
	result := make([]*dto.TaskStatusDTO, 0, len(statuses))
	for _, status := range statuses {
		result = append(result, dto.NewTaskStatusDTO(status))
	}
	return result, nil
}

func (s *TaskService) CreateStatus(ctx context.Context, spaceID, userID bson.ObjectID, req *dto.CreateTaskStatusRequest) (*dto.TaskStatusDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.status.manage")
	if err != nil {
		return nil, err
	}
	if !hasPermission {
		return nil, errors.New("insufficient permissions")
	}

	statuses, err := s.taskStatusRepo.ListStatuses(ctx, spaceID)
	if err != nil {
		return nil, err
	}
	status := &entities.TaskStatus{
		SpaceID: spaceID,
		Name:    strings.TrimSpace(req.Name),
		Color:   strings.TrimSpace(req.Color),
		Order:   len(statuses),
	}
	if status.Name == "" {
		return nil, errors.New("status name is required")
	}
	if err := s.taskStatusRepo.CreateStatus(ctx, status); err != nil {
		return nil, err
	}
	return dto.NewTaskStatusDTO(status), nil
}

func (s *TaskService) UpdateStatus(ctx context.Context, spaceID, statusID, userID bson.ObjectID, req *dto.UpdateTaskStatusRequest) (*dto.TaskStatusDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.status.manage")
	if err != nil {
		return nil, err
	}
	if !hasPermission {
		return nil, errors.New("insufficient permissions")
	}

	status, err := s.taskStatusRepo.GetStatusByID(ctx, statusID)
	if err != nil || status.SpaceID != spaceID {
		return nil, errors.New("task status not found")
	}

	status.Name = strings.TrimSpace(req.Name)
	status.Color = strings.TrimSpace(req.Color)
	if status.Name == "" {
		return nil, errors.New("status name is required")
	}
	if err := s.taskStatusRepo.UpdateStatus(ctx, status); err != nil {
		return nil, err
	}
	return dto.NewTaskStatusDTO(status), nil
}

func (s *TaskService) DeleteStatus(ctx context.Context, spaceID, statusID, userID bson.ObjectID) error {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.status.manage")
	if err != nil {
		return err
	}
	if !hasPermission {
		return errors.New("insufficient permissions")
	}

	statuses, err := s.taskStatusRepo.ListStatuses(ctx, spaceID)
	if err != nil {
		return err
	}
	if len(statuses) <= 1 {
		return errors.New("at least one status is required")
	}

	tasks, err := s.taskRepo.ListTasks(ctx, spaceID, map[string]any{"status_id": statusID})
	if err != nil {
		return err
	}
	if len(tasks) > 0 {
		return errors.New("cannot delete status used by tasks")
	}

	if err := s.taskStatusRepo.DeleteStatus(ctx, statusID); err != nil {
		return err
	}

	return s.normalizeStatusOrder(ctx, spaceID)
}

func (s *TaskService) ReorderStatuses(ctx context.Context, spaceID, userID bson.ObjectID, orderedStatusIDs []string) ([]*dto.TaskStatusDTO, error) {
	if err := s.requireSpaceAccess(ctx, userID, spaceID); err != nil {
		return nil, err
	}
	hasPermission, err := s.hasTaskPermission(ctx, userID, spaceID, "tasks.status.manage")
	if err != nil {
		return nil, err
	}
	if !hasPermission {
		return nil, errors.New("insufficient permissions")
	}

	statuses, err := s.taskStatusRepo.ListStatuses(ctx, spaceID)
	if err != nil {
		return nil, err
	}
	if len(statuses) != len(orderedStatusIDs) {
		return nil, errors.New("ordered status list must include every status exactly once")
	}

	statusByID := make(map[bson.ObjectID]*entities.TaskStatus, len(statuses))
	for _, status := range statuses {
		statusByID[status.ID] = status
	}

	seen := map[bson.ObjectID]struct{}{}
	orderedStatuses := make([]*entities.TaskStatus, 0, len(orderedStatusIDs))
	for _, statusIDHex := range orderedStatusIDs {
		statusID, parseErr := bson.ObjectIDFromHex(statusIDHex)
		if parseErr != nil {
			return nil, errors.New("invalid status id in ordered_status_ids")
		}
		status := statusByID[statusID]
		if status == nil {
			return nil, errors.New("status id does not belong to this space")
		}
		if _, exists := seen[statusID]; exists {
			return nil, errors.New("duplicate status id in ordered_status_ids")
		}
		seen[statusID] = struct{}{}
		orderedStatuses = append(orderedStatuses, status)
	}

	minOrder := statuses[0].Order
	for _, status := range statuses {
		if status.Order < minOrder {
			minOrder = status.Order
		}
	}

	tempBase := minOrder - len(statuses) - 1
	for idx, status := range orderedStatuses {
		status.Order = tempBase + idx
		if err := s.taskStatusRepo.UpdateStatus(ctx, status); err != nil {
			return nil, err
		}
	}

	for idx, status := range orderedStatuses {
		status.Order = idx
		if err := s.taskStatusRepo.UpdateStatus(ctx, status); err != nil {
			return nil, err
		}
	}

	updatedStatuses, err := s.taskStatusRepo.ListStatuses(ctx, spaceID)
	if err != nil {
		return nil, err
	}

	result := make([]*dto.TaskStatusDTO, 0, len(updatedStatuses))
	for _, status := range updatedStatuses {
		result = append(result, dto.NewTaskStatusDTO(status))
	}
	return result, nil
}

func (s *TaskService) normalizeStatusOrder(ctx context.Context, spaceID bson.ObjectID) error {
	statuses, err := s.taskStatusRepo.ListStatuses(ctx, spaceID)
	if err != nil {
		return err
	}
	sort.SliceStable(statuses, func(i, j int) bool {
		return statuses[i].Order < statuses[j].Order
	})
	for idx, status := range statuses {
		if status.Order == idx {
			continue
		}
		status.Order = idx
		if err := s.taskStatusRepo.UpdateStatus(ctx, status); err != nil {
			return err
		}
	}
	return nil
}