1 files changed, 98 insertions, 0 deletions
diff --git a/internal/handlers/budget_logic_test.go b/internal/handlers/budget_logic_test.go
new file mode 100644
index 0000000..1e16595
--- /dev/null
+++ b/internal/handlers/budget_logic_test.go
@@ -0,0 +1,98 @@
+package handlers
+
+import (
+	"testing"
+	"time"
+
+	"task-dashboard/internal/models"
+)
+
+func mustParseInLoc(t *testing.T, layout, value string, loc *time.Location) time.Time {
+	t.Helper()
+	parsed, err := time.ParseInLocation(layout, value, loc)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return parsed
+}
+
+func TestComputeBudgetPeriod_SumsAvailabilityMinusOverlappingEvent(t *testing.T) {
+	loc := time.UTC
+	// A Wednesday: 2026-07-15 is a Wednesday.
+	day := mustParseInLoc(t, "2006-01-02", "2026-07-15", loc)
+	start := day
+	end := day.AddDate(0, 0, 1)
+
+	blocks := []models.AvailabilityBlock{
+		{ID: "b1", Weekday: int(day.Weekday()), StartTime: "18:00", EndTime: "20:00"}, // 120 min
+	}
+	events := []models.CalendarEvent{
+		{ID: "e1", Start: mustParseInLoc(t, "2006-01-02 15:04", "2026-07-15 18:30", loc), End: mustParseInLoc(t, "2006-01-02 15:04", "2026-07-15 19:00", loc)}, // 30 min overlap
+	}
+
+	status := ComputeBudgetPeriod(blocks, events, nil, nil, nil, start, end)
+	if status.AvailableMinutes != 90 {
+		t.Errorf("AvailableMinutes = %d, want 90 (120 - 30 overlap)", status.AvailableMinutes)
+	}
+}
+
+func TestComputeBudgetPeriod_EventFullyOutsideBlockDoesNotReduceIt(t *testing.T) {
+	loc := time.UTC
+	day := mustParseInLoc(t, "2006-01-02", "2026-07-15", loc)
+	start := day
+	end := day.AddDate(0, 0, 1)
+
+	blocks := []models.AvailabilityBlock{
+		{ID: "b1", Weekday: int(day.Weekday()), StartTime: "18:00", EndTime: "20:00"},
+	}
+	events := []models.CalendarEvent{
+		{ID: "e1", Start: mustParseInLoc(t, "2006-01-02 15:04", "2026-07-15 09:00", loc), End: mustParseInLoc(t, "2006-01-02 15:04", "2026-07-15 10:00", loc)},
+	}
+
+	status := ComputeBudgetPeriod(blocks, events, nil, nil, nil, start, end)
+	if status.AvailableMinutes != 120 {
+		t.Errorf("AvailableMinutes = %d, want 120 (event doesn't overlap the block)", status.AvailableMinutes)
+	}
+}
+
+func TestComputeBudgetPeriod_AvailableNeverGoesNegative(t *testing.T) {
+	loc := time.UTC
+	day := mustParseInLoc(t, "2006-01-02", "2026-07-15", loc)
+	start := day
+	end := day.AddDate(0, 0, 1)
+
+	blocks := []models.AvailabilityBlock{
+		{ID: "b1", Weekday: int(day.Weekday()), StartTime: "18:00", EndTime: "20:00"},
+	}
+	events := []models.CalendarEvent{
+		{ID: "e1", Start: mustParseInLoc(t, "2006-01-02 15:04", "2026-07-15 17:00", loc), End: mustParseInLoc(t, "2006-01-02 15:04", "2026-07-15 21:00", loc)},
+	}
+
+	status := ComputeBudgetPeriod(blocks, events, nil, nil, nil, start, end)
+	if status.AvailableMinutes != 0 {
+		t.Errorf("AvailableMinutes = %d, want 0 (event fully covers the block)", status.AvailableMinutes)
+	}
+}
+
+func TestComputeBudgetPeriod_OnlySumsTrackedIncompleteTasksDueInWindow(t *testing.T) {
+	loc := time.UTC
+	start := mustParseInLoc(t, "2006-01-02", "2026-07-15", loc)
+	end := start.AddDate(0, 0, 1)
+	due := mustParseInLoc(t, "2006-01-02 15:04", "2026-07-15 12:00", loc)
+	outsideWindow := end.AddDate(0, 0, 5)
+
+	tasks := []models.Task{
+		{ID: "t-tracked-project", ProjectID: "p1", EstimatedMinutes: 30, DueDate: &due},
+		{ID: "t-tracked-label", Labels: []string{"errands"}, EstimatedMinutes: 20, DueDate: &due},
+		{ID: "t-untracked", ProjectID: "p2", EstimatedMinutes: 999, DueDate: &due},
+		{ID: "t-completed", ProjectID: "p1", EstimatedMinutes: 999, DueDate: &due, Completed: true},
+		{ID: "t-outside-window", ProjectID: "p1", EstimatedMinutes: 999, DueDate: &outsideWindow},
+	}
+	trackedProjects := map[string]bool{"p1": true}
+	trackedLabels := map[string]bool{"errands": true}
+
+	status := ComputeBudgetPeriod(nil, nil, tasks, trackedProjects, trackedLabels, start, end)
+	if status.ScheduledMinutes != 50 {
+		t.Errorf("ScheduledMinutes = %d, want 50 (30 + 20, excluding untracked/completed/out-of-window)", status.ScheduledMinutes)
+	}
+}