1 files changed, 140 insertions, 1 deletions
diff --git a/internal/api/todoist.go b/internal/api/todoist.go
index 511753d..b51fffd 100644
--- a/internal/api/todoist.go
+++ b/internal/api/todoist.go
@@ -13,7 +13,8 @@ import (
 )
 
 const (
-	todoistBaseURL = "https://api.todoist.com/rest/v2"
+	todoistBaseURL     = "https://api.todoist.com/rest/v2"
+	todoistSyncBaseURL = "https://api.todoist.com/sync/v9"
 )
 
 // TodoistClient handles interactions with the Todoist API
@@ -56,6 +57,40 @@ type todoistProjectResponse struct {
 	Name string `json:"name"`
 }
 
+// Sync API v9 response types
+
+// TodoistSyncResponse represents the Sync API response
+type TodoistSyncResponse struct {
+	SyncToken string                `json:"sync_token"`
+	FullSync  bool                  `json:"full_sync"`
+	Items     []SyncItemResponse    `json:"items"`
+	Projects  []SyncProjectResponse `json:"projects"`
+}
+
+// SyncItemResponse represents a task item from Sync API
+type SyncItemResponse struct {
+	ID          string   `json:"id"`
+	Content     string   `json:"content"`
+	Description string   `json:"description"`
+	ProjectID   string   `json:"project_id"`
+	Priority    int      `json:"priority"`
+	Labels      []string `json:"labels"`
+	Due         *struct {
+		Date     string `json:"date"`
+		Datetime string `json:"datetime"`
+	} `json:"due"`
+	IsCompleted bool   `json:"is_completed"`
+	IsDeleted   bool   `json:"is_deleted"`
+	AddedAt     string `json:"added_at"`
+}
+
+// SyncProjectResponse represents a project from Sync API
+type SyncProjectResponse struct {
+	ID        string `json:"id"`
+	Name      string `json:"name"`
+	IsDeleted bool   `json:"is_deleted"`
+}
+
 // GetTasks fetches all active tasks from Todoist
 func (c *TodoistClient) GetTasks(ctx context.Context) ([]models.Task, error) {
 	req, err := http.NewRequestWithContext(ctx, "GET", c.baseURL+"/tasks", nil)
@@ -167,6 +202,110 @@ func (c *TodoistClient) GetProjects(ctx context.Context) ([]models.Project, erro
 	return projects, nil
 }
 
+// Sync performs an incremental sync using the Sync API v9
+// If syncToken is empty or "*", a full sync is performed
+// Returns the new sync token and the sync response
+func (c *TodoistClient) Sync(ctx context.Context, syncToken string) (*TodoistSyncResponse, error) {
+	if syncToken == "" {
+		syncToken = "*" // Full sync
+	}
+
+	// Prepare sync request
+	payload := map[string]interface{}{
+		"sync_token":     syncToken,
+		"resource_types": []string{"items", "projects"},
+	}
+
+	jsonData, err := json.Marshal(payload)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal sync request: %w", err)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, "POST", todoistSyncBaseURL+"/sync", bytes.NewBuffer(jsonData))
+	if err != nil {
+		return nil, fmt.Errorf("failed to create sync request: %w", err)
+	}
+
+	req.Header.Set("Authorization", "Bearer "+c.apiKey)
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("failed to perform sync: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("todoist sync API error (status %d): %s", resp.StatusCode, string(body))
+	}
+
+	var syncResp TodoistSyncResponse
+	if err := json.NewDecoder(resp.Body).Decode(&syncResp); err != nil {
+		return nil, fmt.Errorf("failed to decode sync response: %w", err)
+	}
+
+	return &syncResp, nil
+}
+
+// ConvertSyncItemsToTasks converts sync API items to Task models
+func ConvertSyncItemsToTasks(items []SyncItemResponse, projectMap map[string]string) []models.Task {
+	tasks := make([]models.Task, 0, len(items))
+	for _, item := range items {
+		// Skip completed or deleted items
+		if item.IsCompleted || item.IsDeleted {
+			continue
+		}
+
+		task := models.Task{
+			ID:          item.ID,
+			Content:     item.Content,
+			Description: item.Description,
+			ProjectID:   item.ProjectID,
+			ProjectName: projectMap[item.ProjectID],
+			Priority:    item.Priority,
+			Completed:   false,
+			Labels:      item.Labels,
+			URL:         fmt.Sprintf("https://todoist.com/showTask?id=%s", item.ID),
+		}
+
+		// Parse added_at
+		if item.AddedAt != "" {
+			if createdAt, err := time.Parse(time.RFC3339, item.AddedAt); err == nil {
+				task.CreatedAt = createdAt
+			}
+		}
+
+		// Parse due date
+		if item.Due != nil {
+			var dueDate time.Time
+			var err error
+			if item.Due.Datetime != "" {
+				dueDate, err = time.Parse(time.RFC3339, item.Due.Datetime)
+			} else if item.Due.Date != "" {
+				dueDate, err = time.Parse("2006-01-02", item.Due.Date)
+			}
+			if err == nil {
+				task.DueDate = &dueDate
+			}
+		}
+
+		tasks = append(tasks, task)
+	}
+	return tasks
+}
+
+// BuildProjectMapFromSync builds a project ID to name map from sync response
+func BuildProjectMapFromSync(projects []SyncProjectResponse) map[string]string {
+	projectMap := make(map[string]string)
+	for _, proj := range projects {
+		if !proj.IsDeleted {
+			projectMap[proj.ID] = proj.Name
+		}
+	}
+	return projectMap
+}
+
 // CreateTask creates a new task in Todoist
 func (c *TodoistClient) CreateTask(ctx context.Context, content, projectID string, dueDate *time.Time, priority int) (*models.Task, error) {
 	// Prepare request payload