feat: add daily cron to apply scheduled default hours changes

Add ApplyScheduledDefaultHours which checks default_hours_scheduled_changes at midnight, bulk-updates working_hours with staged values, and inserts an admin_notification. Register as the 'apply-default-hours' job in the scheduler (daily at 00:05).

backend/handlers/scheduling/scheduled-cleanup.go

@@ -2,10 +2,12 @@ package scheduling
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"log/slog"
 
+	"crussell/clock"
 	"crussell/db"
 
 	"github.com/jackc/pgx/v5"
@@ -253,3 +255,100 @@ func CleanupExpiredRefreshTokens(ctx context.Context) (int, error) {
 
 	return int(result.RowsAffected()), nil
 }
+
+// ApplyScheduledDefaultHours applies any pending default hours changes that
+// have reached their effective_date. Runs daily at 00:05 to catch midnight
+// roll-overs even if the cron is slightly delayed.
+func ApplyScheduledDefaultHours(ctx context.Context) (int, error) {
+	londonNow := clock.Now().In(clock.London)
+	todayStr := londonNow.Format("2006-01-02")
+
+	tx, err := db.Conn.Begin(ctx)
+	if err != nil {
+		return 0, fmt.Errorf("failed to begin transaction: %w", err)
+	}
+	defer func() {
+		if err := tx.Rollback(ctx); err != nil && !errors.Is(err, pgx.ErrTxClosed) {
+			slog.Error("failed to rollback transaction", "err", err)
+		}
+	}()
+
+	// Find any changes where effective_date <= today (London) and not yet applied/cancelled
+	var rowID int
+	var hoursJSON string
+	err = tx.QueryRow(ctx, `
+		SELECT id, hours::text
+		FROM default_hours_scheduled_changes
+		WHERE effective_date <= $1::date
+		  AND applied_at IS NULL
+		  AND cancelled_at IS NULL
+		LIMIT 1
+	`, todayStr).Scan(&rowID, &hoursJSON)
+	if err != nil {
+		// No matching change — nothing to do
+		return 0, tx.Commit(ctx)
+	}
+
+	// Parse the staged hours
+	var hours []struct {
+		Weekday   int    `json:"weekday"`
+		StartTime string `json:"startTime"`
+		EndTime   string `json:"endTime"`
+		IsOpen    bool   `json:"isOpen"`
+	}
+	if err := json.Unmarshal([]byte(hoursJSON), &hours); err != nil {
+		return 0, fmt.Errorf("failed to parse hours JSON for change %d: %w", rowID, err)
+	}
+
+	// Bulk-update working_hours with staged values
+	weekdays := make([]int, len(hours))
+	startTimes := make([]string, len(hours))
+	endTimes := make([]string, len(hours))
+	isOpenFlags := make([]bool, len(hours))
+	for i, h := range hours {
+		weekdays[i] = h.Weekday
+		startTimes[i] = h.StartTime
+		endTimes[i] = h.EndTime
+		isOpenFlags[i] = h.IsOpen
+	}
+
+	if _, err := tx.Exec(ctx, `
+		UPDATE working_hours AS wh
+		SET start_time = v.start_time,
+		    end_time = v.end_time,
+		    is_open = v.is_open
+		FROM (
+			SELECT unnest($1::smallint[]) AS weekday,
+			       unnest($2::time[]) AS start_time,
+			       unnest($3::time[]) AS end_time,
+			       unnest($4::boolean[]) AS is_open
+		) v
+		WHERE wh.weekday = v.weekday
+	`, weekdays, startTimes, endTimes, isOpenFlags); err != nil {
+		return 0, fmt.Errorf("failed to update working_hours for change %d: %w", rowID, err)
+	}
+
+	// Mark change as applied
+	if _, err := tx.Exec(ctx, `
+		UPDATE default_hours_scheduled_changes
+		SET applied_at = NOW()
+		WHERE id = $1
+	`, rowID); err != nil {
+		return 0, fmt.Errorf("failed to mark change %d as applied: %w", rowID, err)
+	}
+
+	// Insert admin notification
+	if _, err := tx.Exec(ctx, `
+		INSERT INTO admin_notifications (reason, created_at)
+		VALUES ('default_hours_changed', NOW())
+	`); err != nil {
+		return 0, fmt.Errorf("failed to insert notification for change %d: %w", rowID, err)
+	}
+
+	if err := tx.Commit(ctx); err != nil {
+		return 0, fmt.Errorf("failed to commit: %w", err)
+	}
+
+	slog.Info("Applied scheduled default hours change", "change_id", rowID, "effective_date", todayStr)
+	return 1, nil
+}