Add Google Calendar integration

- Add GoogleCalendarClient for fetching upcoming events
- Add GoogleCalendarAPI interface and CalendarEvent model
- Add config for GOOGLE_CREDENTIALS_FILE and GOOGLE_CALENDAR_ID
- Display events in Planning tab with date/time formatting
- Update handlers and tests to support optional calendar client

Config env vars:
- GOOGLE_CREDENTIALS_FILE: Path to service account JSON
- GOOGLE_CALENDAR_ID: Calendar ID (defaults to "primary")

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

4 files changed, 54 insertions, 20 deletions

diff --git a/internal/handlers/handlers.go b/internal/handlers/handlers.go
index 19415c7..1cb978d 100644
--- a/internal/handlers/handlers.go
+++ b/internal/handlers/handlers.go
@@ -22,16 +22,17 @@ import (
 
 // Handler holds dependencies for HTTP handlers
 type Handler struct {
-	store           *store.Store
-	todoistClient   api.TodoistAPI
-	trelloClient    api.TrelloAPI
-	planToEatClient api.PlanToEatAPI
-	config          *config.Config
-	templates       *template.Template
+	store                *store.Store
+	todoistClient        api.TodoistAPI
+	trelloClient         api.TrelloAPI
+	planToEatClient      api.PlanToEatAPI
+	googleCalendarClient api.GoogleCalendarAPI
+	config               *config.Config
+	templates            *template.Template
 }
 
 // New creates a new Handler instance
-func New(s *store.Store, todoist api.TodoistAPI, trello api.TrelloAPI, planToEat api.PlanToEatAPI, cfg *config.Config) *Handler {
+func New(s *store.Store, todoist api.TodoistAPI, trello api.TrelloAPI, planToEat api.PlanToEatAPI, googleCalendar api.GoogleCalendarAPI, cfg *config.Config) *Handler {
 	// Parse templates including partials
 	tmpl, err := template.ParseGlob(filepath.Join(cfg.TemplateDir, "*.html"))
 	if err != nil {
@@ -45,12 +46,13 @@ func New(s *store.Store, todoist api.TodoistAPI, trello api.TrelloAPI, planToEat
 	}
 
 	return &Handler{
-		store:           s,
-		todoistClient:   todoist,
-		trelloClient:    trello,
-		planToEatClient: planToEat,
-		config:          cfg,
-		templates:       tmpl,
+		store:                s,
+		todoistClient:        todoist,
+		trelloClient:         trello,
+		planToEatClient:      planToEat,
+		googleCalendarClient: googleCalendar,
+		config:               cfg,
+		templates:            tmpl,
 	}
 }
 
@@ -279,6 +281,22 @@ func (h *Handler) aggregateData(ctx context.Context, forceRefresh bool) (*models
 		}()
 	}
 
+	// Fetch Google Calendar events (if configured)
+	if h.googleCalendarClient != nil {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			events, err := h.googleCalendarClient.GetUpcomingEvents(ctx, 10)
+			mu.Lock()
+			defer mu.Unlock()
+			if err != nil {
+				data.Errors = append(data.Errors, "Google Calendar: "+err.Error())
+			} else {
+				data.Events = events
+			}
+		}()
+	}
+
 	wg.Wait()
 
 	// Filter Trello cards into tasks based on heuristic
diff --git a/internal/handlers/heuristic_test.go b/internal/handlers/heuristic_test.go
index dc8620a..2b70218 100644
--- a/internal/handlers/heuristic_test.go
+++ b/internal/handlers/heuristic_test.go
@@ -63,7 +63,7 @@ func TestHandleTasks_Heuristic(t *testing.T) {
 	}
 
 	// Create Handler
-	h := NewTabsHandler(db, "../../web/templates")
+	h := NewTabsHandler(db, nil, "../../web/templates")
 
 	// Skip if templates are not loaded
 	if h.templates == nil {
diff --git a/internal/handlers/tab_state_test.go b/internal/handlers/tab_state_test.go
index a4f6d23..d7bb8dd 100644
--- a/internal/handlers/tab_state_test.go
+++ b/internal/handlers/tab_state_test.go
@@ -30,7 +30,7 @@ func TestHandleDashboard_TabState(t *testing.T) {
 	}
 
 	// Create handler
-	h := New(db, todoistClient, trelloClient, nil, cfg)
+	h := New(db, todoistClient, trelloClient, nil, nil, cfg)
 
 	// Skip if templates are not loaded (test environment issue)
 	if h.templates == nil {
diff --git a/internal/handlers/tabs.go b/internal/handlers/tabs.go
index 2f22c44..b651dac 100644
--- a/internal/handlers/tabs.go
+++ b/internal/handlers/tabs.go
@@ -9,6 +9,7 @@ import (
 	"strings"
 	"time"
 
+	"task-dashboard/internal/api"
 	"task-dashboard/internal/models"
 	"task-dashboard/internal/store"
 )
@@ -46,12 +47,13 @@ func atomUrgencyTier(a models.Atom) int {
 
 // TabsHandler handles tab-specific rendering with Atom model
 type TabsHandler struct {
-	store     *store.Store
-	templates *template.Template
+	store                *store.Store
+	googleCalendarClient api.GoogleCalendarAPI
+	templates            *template.Template
 }
 
 // NewTabsHandler creates a new TabsHandler instance
-func NewTabsHandler(store *store.Store, templateDir string) *TabsHandler {
+func NewTabsHandler(store *store.Store, googleCalendarClient api.GoogleCalendarAPI, templateDir string) *TabsHandler {
 	// Parse templates including partials
 	tmpl, err := template.ParseGlob(filepath.Join(templateDir, "*.html"))
 	if err != nil {
@@ -65,8 +67,9 @@ func NewTabsHandler(store *store.Store, templateDir string) *TabsHandler {
 	}
 
 	return &TabsHandler{
-		store:     store,
-		templates: tmpl,
+		store:                store,
+		googleCalendarClient: googleCalendarClient,
+		templates:            tmpl,
 	}
 }
 
@@ -178,12 +181,25 @@ func (h *TabsHandler) HandlePlanning(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Fetch Google Calendar events
+	var events []models.CalendarEvent
+	if h.googleCalendarClient != nil {
+		var err error
+		events, err = h.googleCalendarClient.GetUpcomingEvents(r.Context(), 10)
+		if err != nil {
+			log.Printf("Error fetching calendar events: %v", err)
+			// Don't fail the whole request, just show empty events
+		}
+	}
+
 	data := struct {
 		Boards   []models.Board
 		Projects []models.Project
+		Events   []models.CalendarEvent
 	}{
 		Boards:   boards,
 		Projects: []models.Project{}, // Empty for now
+		Events:   events,
 	}
 
 	if err := h.templates.ExecuteTemplate(w, "planning-tab", data); err != nil {