Implement Task operations

Add tasks.go with TaskService for full task CRUD:
- client.Tasks(checklistID) returns TaskService
- List(ctx) - get all tasks in checklist
- Get(ctx, taskID) - get single task with parent hierarchy
- Create(ctx, builder) - create task using TaskBuilder
- Update(ctx, taskID, req) - update task properties
- Delete(ctx, taskID) - permanently delete task
- Close(ctx, taskID) - mark task as completed
- Reopen(ctx, taskID) - reopen closed/invalidated task
- Invalidate(ctx, taskID) - mark task as invalidated (strikethrough)

TaskBuilder fluent interface for task creation:
- NewTask(content) - create builder
- WithParent(id) - set parent for subtask
- WithPosition(pos) - set position in list
- WithDueDate(due) - set due date using DueDate type
- WithPriority(level) - set priority (0=normal, 1=highest, 2=high)
- WithTags(tags...) - set tags

Automatic DueDate parsing from DueDateRaw (ISO 8601 format).

Closes checkvist-api-rl9

.beads/issues.jsonl

@@ -20,7 +20,7 @@
 {"id":"checkvist-api-lpn","title":"Implement authentication with auto token renewal","description":"Add to client.go:\n- Authenticate(ctx context.Context) error - explicit login\n- refreshToken(ctx context.Context) error - token renewal\n- ensureAuthenticated(ctx context.Context) error - auto-auth before requests\n- CurrentUser(ctx context.Context) (*User, error) - get logged in user\n- Token management: store token and expiry, auto-refresh before expiry\n- Thread-safe token access using mutex\n- Support for optional 2FA token\nAPI endpoints:\n- POST /auth/login.json?version=2 (login)\n- POST /auth/refresh_token.json?version=2 (refresh)\n- GET /auth/curr_user.json (current user)\nToken sent via X-Client-Token header","status":"closed","priority":0,"issue_type":"task","owner":"mail@oliverjakoubek.de","created_at":"2026-01-14T12:31:08.358878117+01:00","created_by":"Oliver Jakoubek","updated_at":"2026-01-14T13:26:32.668016856+01:00","closed_at":"2026-01-14T13:26:32.668016856+01:00","close_reason":"Closed","dependencies":[{"issue_id":"checkvist-api-lpn","depends_on_id":"checkvist-api-ymg","type":"blocks","created_at":"2026-01-14T12:32:47.656124681+01:00","created_by":"Oliver Jakoubek"}]}
 {"id":"checkvist-api-mnh","title":"Implement error types and sentinel errors","description":"Create errors.go with:\n- APIError struct (StatusCode, Message, RequestID, Err) with Error() and Unwrap() methods\n- Sentinel errors: ErrUnauthorized, ErrNotFound, ErrRateLimited, ErrBadRequest, ErrServerError\n- Helper function to create APIError from HTTP response","status":"closed","priority":0,"issue_type":"task","owner":"mail@oliverjakoubek.de","created_at":"2026-01-14T12:31:07.619359293+01:00","created_by":"Oliver Jakoubek","updated_at":"2026-01-14T13:23:43.296883265+01:00","closed_at":"2026-01-14T13:23:43.296883265+01:00","close_reason":"Closed","dependencies":[{"issue_id":"checkvist-api-mnh","depends_on_id":"checkvist-api-5wr","type":"blocks","created_at":"2026-01-14T12:32:46.754134799+01:00","created_by":"Oliver Jakoubek"}]}
 {"id":"checkvist-api-nrk","title":"Create README with quickstart","description":"Create README.md (in English) with:\n- Project description\n- Installation: go get code.beautifulmachines.dev/jakoubek/checkvist-api\n- Quick start example (init client, list checklists, create task)\n- API overview (Checklists, Tasks, Notes, Filters)\n- Builder pattern examples\n- Error handling examples\n- Configuration options\n- Link to GoDoc\n- License (MIT)","status":"open","priority":0,"issue_type":"task","owner":"mail@oliverjakoubek.de","created_at":"2026-01-14T12:31:38.724338606+01:00","created_by":"Oliver Jakoubek","updated_at":"2026-01-14T12:31:38.724338606+01:00","dependencies":[{"issue_id":"checkvist-api-nrk","depends_on_id":"checkvist-api-c2k","type":"blocks","created_at":"2026-01-14T12:33:15.785698203+01:00","created_by":"Oliver Jakoubek"},{"issue_id":"checkvist-api-nrk","depends_on_id":"checkvist-api-rl9","type":"blocks","created_at":"2026-01-14T12:33:16.125115134+01:00","created_by":"Oliver Jakoubek"}]}
-{"id":"checkvist-api-rl9","title":"Implement Task operations","description":"Create tasks.go with TaskService:\n- client.Tasks(checklistID) returns TaskService\n- List(ctx) ([]Task, error) - GET /checklists/{id}/tasks.json\n- Get(ctx, taskID) (*Task, error) - GET /checklists/{id}/tasks/{task_id}.json (includes parent hierarchy)\n- Create(ctx, builder *TaskBuilder) (*Task, error) - POST /checklists/{id}/tasks.json\n- Update(ctx, taskID, opts) (*Task, error) - PUT /checklists/{id}/tasks/{task_id}.json\n- Delete(ctx, taskID) error - DELETE /checklists/{id}/tasks/{task_id}.json\n- Close(ctx, taskID) (*Task, error) - POST /checklists/{id}/tasks/{task_id}/close.json\n- Reopen(ctx, taskID) (*Task, error) - POST /checklists/{id}/tasks/{task_id}/reopen.json\n- Invalidate(ctx, taskID) (*Task, error) - POST /checklists/{id}/tasks/{task_id}/invalidate.json\nParse DueDate from DueDateRaw when retrieving tasks.","status":"open","priority":0,"issue_type":"feature","owner":"mail@oliverjakoubek.de","created_at":"2026-01-14T12:30:53.90629838+01:00","created_by":"Oliver Jakoubek","updated_at":"2026-01-14T12:30:53.90629838+01:00","dependencies":[{"issue_id":"checkvist-api-rl9","depends_on_id":"checkvist-api-8u6","type":"blocks","created_at":"2026-01-14T12:32:55.247292478+01:00","created_by":"Oliver Jakoubek"},{"issue_id":"checkvist-api-rl9","depends_on_id":"checkvist-api-lpn","type":"blocks","created_at":"2026-01-14T12:32:55.536931433+01:00","created_by":"Oliver Jakoubek"}]}
+{"id":"checkvist-api-rl9","title":"Implement Task operations","description":"Create tasks.go with TaskService:\n- client.Tasks(checklistID) returns TaskService\n- List(ctx) ([]Task, error) - GET /checklists/{id}/tasks.json\n- Get(ctx, taskID) (*Task, error) - GET /checklists/{id}/tasks/{task_id}.json (includes parent hierarchy)\n- Create(ctx, builder *TaskBuilder) (*Task, error) - POST /checklists/{id}/tasks.json\n- Update(ctx, taskID, opts) (*Task, error) - PUT /checklists/{id}/tasks/{task_id}.json\n- Delete(ctx, taskID) error - DELETE /checklists/{id}/tasks/{task_id}.json\n- Close(ctx, taskID) (*Task, error) - POST /checklists/{id}/tasks/{task_id}/close.json\n- Reopen(ctx, taskID) (*Task, error) - POST /checklists/{id}/tasks/{task_id}/reopen.json\n- Invalidate(ctx, taskID) (*Task, error) - POST /checklists/{id}/tasks/{task_id}/invalidate.json\nParse DueDate from DueDateRaw when retrieving tasks.","status":"closed","priority":0,"issue_type":"feature","owner":"mail@oliverjakoubek.de","created_at":"2026-01-14T12:30:53.90629838+01:00","created_by":"Oliver Jakoubek","updated_at":"2026-01-14T13:39:29.443727155+01:00","closed_at":"2026-01-14T13:39:29.443727155+01:00","close_reason":"Closed","dependencies":[{"issue_id":"checkvist-api-rl9","depends_on_id":"checkvist-api-8u6","type":"blocks","created_at":"2026-01-14T12:32:55.247292478+01:00","created_by":"Oliver Jakoubek"},{"issue_id":"checkvist-api-rl9","depends_on_id":"checkvist-api-lpn","type":"blocks","created_at":"2026-01-14T12:32:55.536931433+01:00","created_by":"Oliver Jakoubek"}]}
 {"id":"checkvist-api-tjk","title":"Implement TaskBuilder fluent interface","description":"Enhance task creation with builder pattern:\n- NewTask(content string) *TaskBuilder\n- WithTags(tags ...string) *TaskBuilder\n- WithDueDate(due DueDate) *TaskBuilder\n- WithPriority(p int) *TaskBuilder\n- WithParent(parentID int64) *TaskBuilder\n- WithPosition(pos int) *TaskBuilder\n- Build() returns parameters for API call\nTaskBuilder should be chainable and return itself for fluent usage:\n  checkvist.NewTask(\"Content\").WithTags(\"tag1\").WithDueDate(checkvist.DueTomorrow).WithPriority(1)","status":"open","priority":1,"issue_type":"feature","owner":"mail@oliverjakoubek.de","created_at":"2026-01-14T12:30:55.929907579+01:00","created_by":"Oliver Jakoubek","updated_at":"2026-01-14T12:30:55.929907579+01:00","dependencies":[{"issue_id":"checkvist-api-tjk","depends_on_id":"checkvist-api-rl9","type":"blocks","created_at":"2026-01-14T12:33:02.20339206+01:00","created_by":"Oliver Jakoubek"}]}
 {"id":"checkvist-api-v2f","title":"Write unit tests for Tasks","description":"Create tasks_test.go with tests:\n- TestTasks_List\n- TestTasks_Get\n- TestTasks_Get_WithParentHierarchy\n- TestTasks_Create\n- TestTasks_Create_WithBuilder\n- TestTasks_Update\n- TestTasks_Delete\n- TestTasks_Close\n- TestTasks_Reopen\n- TestTasks_Invalidate\n- TestDueDate_Parsing\nUse table-driven tests. Create testdata/tasks/ fixtures.","status":"open","priority":0,"issue_type":"task","owner":"mail@oliverjakoubek.de","created_at":"2026-01-14T12:31:37.538754679+01:00","created_by":"Oliver Jakoubek","updated_at":"2026-01-14T12:31:37.538754679+01:00","dependencies":[{"issue_id":"checkvist-api-v2f","depends_on_id":"checkvist-api-rl9","type":"blocks","created_at":"2026-01-14T12:33:13.81085058+01:00","created_by":"Oliver Jakoubek"}]}
 {"id":"checkvist-api-ymg","title":"Implement Client struct with functional options","description":"Create client.go with:\n- Client struct (baseURL, username, remoteKey, token, tokenExp, httpClient, retryConf, logger, mu sync.RWMutex)\n- NewClient(username, remoteKey string, opts ...Option) *Client constructor\n- Create options.go with Option type and functional options:\n  - WithHTTPClient(*http.Client)\n  - WithTimeout(time.Duration)\n  - WithRetryConfig(RetryConfig)\n  - WithLogger(*slog.Logger)\n  - WithBaseURL(string) for testing\n- RetryConfig struct (MaxRetries, BaseDelay, MaxDelay, Jitter)\n- Default values: 3 retries, 1s base delay, 30s max delay, jitter enabled","status":"closed","priority":0,"issue_type":"task","owner":"mail@oliverjakoubek.de","created_at":"2026-01-14T12:31:08.021154076+01:00","created_by":"Oliver Jakoubek","updated_at":"2026-01-14T13:24:55.101093793+01:00","closed_at":"2026-01-14T13:24:55.101093793+01:00","close_reason":"Closed","dependencies":[{"issue_id":"checkvist-api-ymg","depends_on_id":"checkvist-api-e9p","type":"blocks","created_at":"2026-01-14T12:32:47.077541448+01:00","created_by":"Oliver Jakoubek"},{"issue_id":"checkvist-api-ymg","depends_on_id":"checkvist-api-mnh","type":"blocks","created_at":"2026-01-14T12:32:47.358639632+01:00","created_by":"Oliver Jakoubek"}]}

tasks.go

@@ -1,3 +1,223 @@
 package checkvist
 
+import (
+	"context"
+	"fmt"
+	"time"
+)
+
 // tasks.go contains the TaskService for CRUD operations on tasks within a checklist.
+
+// TaskService provides operations on tasks within a specific checklist.
+type TaskService struct {
+	client      *Client
+	checklistID int
+}
+
+// Tasks returns a TaskService for performing task operations on the specified checklist.
+func (c *Client) Tasks(checklistID int) *TaskService {
+	return &TaskService{
+		client:      c,
+		checklistID: checklistID,
+	}
+}
+
+// List returns all tasks in the checklist.
+func (s *TaskService) List(ctx context.Context) ([]Task, error) {
+	path := fmt.Sprintf("/checklists/%d/tasks.json", s.checklistID)
+
+	var tasks []Task
+	if err := s.client.doGet(ctx, path, &tasks); err != nil {
+		return nil, err
+	}
+
+	// Parse due dates
+	for i := range tasks {
+		parseDueDate(&tasks[i])
+	}
+
+	return tasks, nil
+}
+
+// Get returns a single task by ID, including its parent hierarchy.
+func (s *TaskService) Get(ctx context.Context, taskID int) (*Task, error) {
+	path := fmt.Sprintf("/checklists/%d/tasks/%d.json", s.checklistID, taskID)
+
+	var task Task
+	if err := s.client.doGet(ctx, path, &task); err != nil {
+		return nil, err
+	}
+
+	parseDueDate(&task)
+	return &task, nil
+}
+
+// CreateTaskRequest represents the request body for creating a task.
+type CreateTaskRequest struct {
+	Content   string `json:"content"`
+	ParentID  int    `json:"parent_id,omitempty"`
+	Position  int    `json:"position,omitempty"`
+	Due       string `json:"due,omitempty"`
+	Priority  int    `json:"priority,omitempty"`
+	Tags      string `json:"tags,omitempty"`
+}
+
+// TaskBuilder provides a fluent interface for building task creation requests.
+type TaskBuilder struct {
+	content  string
+	parentID int
+	position int
+	due      string
+	priority int
+	tags     []string
+}
+
+// NewTask creates a new TaskBuilder with the given content.
+func NewTask(content string) *TaskBuilder {
+	return &TaskBuilder{content: content}
+}
+
+// WithParent sets the parent task ID for creating a subtask.
+func (b *TaskBuilder) WithParent(parentID int) *TaskBuilder {
+	b.parentID = parentID
+	return b
+}
+
+// WithPosition sets the position of the task within its siblings.
+func (b *TaskBuilder) WithPosition(position int) *TaskBuilder {
+	b.position = position
+	return b
+}
+
+// WithDueDate sets the due date using a DueDate value.
+func (b *TaskBuilder) WithDueDate(due DueDate) *TaskBuilder {
+	b.due = due.String()
+	return b
+}
+
+// WithPriority sets the priority level (1 = highest, 2 = high, 0 = normal).
+func (b *TaskBuilder) WithPriority(priority int) *TaskBuilder {
+	b.priority = priority
+	return b
+}
+
+// WithTags sets the tags for the task.
+func (b *TaskBuilder) WithTags(tags ...string) *TaskBuilder {
+	b.tags = tags
+	return b
+}
+
+// build converts the TaskBuilder to a CreateTaskRequest.
+func (b *TaskBuilder) build() CreateTaskRequest {
+	req := CreateTaskRequest{
+		Content:  b.content,
+		ParentID: b.parentID,
+		Position: b.position,
+		Due:      b.due,
+		Priority: b.priority,
+	}
+	if len(b.tags) > 0 {
+		for i, tag := range b.tags {
+			if i > 0 {
+				req.Tags += ", "
+			}
+			req.Tags += tag
+		}
+	}
+	return req
+}
+
+// Create creates a new task using a TaskBuilder.
+func (s *TaskService) Create(ctx context.Context, builder *TaskBuilder) (*Task, error) {
+	path := fmt.Sprintf("/checklists/%d/tasks.json", s.checklistID)
+	body := builder.build()
+
+	var task Task
+	if err := s.client.doPost(ctx, path, body, &task); err != nil {
+		return nil, err
+	}
+
+	parseDueDate(&task)
+	return &task, nil
+}
+
+// UpdateTaskRequest represents the request body for updating a task.
+type UpdateTaskRequest struct {
+	Content  *string `json:"content,omitempty"`
+	ParentID *int    `json:"parent_id,omitempty"`
+	Position *int    `json:"position,omitempty"`
+	Due      *string `json:"due,omitempty"`
+	Priority *int    `json:"priority,omitempty"`
+	Tags     *string `json:"tags,omitempty"`
+}
+
+// Update updates an existing task.
+func (s *TaskService) Update(ctx context.Context, taskID int, req UpdateTaskRequest) (*Task, error) {
+	path := fmt.Sprintf("/checklists/%d/tasks/%d.json", s.checklistID, taskID)
+
+	var task Task
+	if err := s.client.doPut(ctx, path, req, &task); err != nil {
+		return nil, err
+	}
+
+	parseDueDate(&task)
+	return &task, nil
+}
+
+// Delete permanently deletes a task.
+func (s *TaskService) Delete(ctx context.Context, taskID int) error {
+	path := fmt.Sprintf("/checklists/%d/tasks/%d.json", s.checklistID, taskID)
+	return s.client.doDelete(ctx, path)
+}
+
+// Close marks a task as completed.
+func (s *TaskService) Close(ctx context.Context, taskID int) (*Task, error) {
+	path := fmt.Sprintf("/checklists/%d/tasks/%d/close.json", s.checklistID, taskID)
+
+	var task Task
+	if err := s.client.doPost(ctx, path, nil, &task); err != nil {
+		return nil, err
+	}
+
+	parseDueDate(&task)
+	return &task, nil
+}
+
+// Reopen reopens a closed or invalidated task.
+func (s *TaskService) Reopen(ctx context.Context, taskID int) (*Task, error) {
+	path := fmt.Sprintf("/checklists/%d/tasks/%d/reopen.json", s.checklistID, taskID)
+
+	var task Task
+	if err := s.client.doPost(ctx, path, nil, &task); err != nil {
+		return nil, err
+	}
+
+	parseDueDate(&task)
+	return &task, nil
+}
+
+// Invalidate marks a task as invalidated (strikethrough).
+func (s *TaskService) Invalidate(ctx context.Context, taskID int) (*Task, error) {
+	path := fmt.Sprintf("/checklists/%d/tasks/%d/invalidate.json", s.checklistID, taskID)
+
+	var task Task
+	if err := s.client.doPost(ctx, path, nil, &task); err != nil {
+		return nil, err
+	}
+
+	parseDueDate(&task)
+	return &task, nil
+}
+
+// parseDueDate attempts to parse the DueDateRaw string into a time.Time.
+// It supports ISO 8601 date format (YYYY-MM-DD).
+func parseDueDate(task *Task) {
+	if task.DueDateRaw == "" {
+		return
+	}
+
+	// Try to parse as ISO date
+	if t, err := time.Parse("2006-01-02", task.DueDateRaw); err == nil {
+		task.DueDate = &t
+	}
+}