Improve disk UI and build performance

internal/db/db.go

@@ -47,6 +47,10 @@ func (d *DB) migrate() error {
 		);
 		CREATE UNIQUE INDEX IF NOT EXISTS idx_copy_history_disk_path
 			ON copy_history (disk_id, source_path);
+		CREATE TABLE IF NOT EXISTS disk_stats (
+			disk_id        TEXT PRIMARY KEY,
+			last_copied_at DATETIME NOT NULL
+		);
 	`)
 	return err
 }
@@ -65,11 +69,26 @@ func (d *DB) RecordCopy(rec CopyRecord) error {
 	if t.IsZero() {
 		t = time.Now().UTC()
 	}
-	_, err := d.sql.Exec(
+	tx, err := d.sql.Begin()
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+
+	if _, err := tx.Exec(
 		`INSERT OR IGNORE INTO copy_history (disk_id, source_path, file_size, copied_at) VALUES (?,?,?,?)`,
 		rec.DiskID, rec.SourcePath, rec.FileSize, t.Format(time.RFC3339),
-	)
-	return err
+	); err != nil {
+		return err
+	}
+	if _, err := tx.Exec(
+		`INSERT INTO disk_stats (disk_id, last_copied_at) VALUES (?, ?)
+		 ON CONFLICT(disk_id) DO UPDATE SET last_copied_at=excluded.last_copied_at`,
+		rec.DiskID, t.Format(time.RFC3339),
+	); err != nil {
+		return err
+	}
+	return tx.Commit()
 }
 
 func (d *DB) CopiedPaths(diskID string) (map[string]struct{}, error) {
@@ -90,3 +109,23 @@ func (d *DB) CopiedPaths(diskID string) (map[string]struct{}, error) {
 	}
 	return m, rows.Err()
 }
+
+func (d *DB) LastCopiedAt(diskID string) (time.Time, bool, error) {
+	var raw string
+	err := d.sql.QueryRow(
+		`SELECT last_copied_at FROM disk_stats WHERE disk_id=?`,
+		diskID,
+	).Scan(&raw)
+	if err == sql.ErrNoRows {
+		return time.Time{}, false, nil
+	}
+	if err != nil {
+		return time.Time{}, false, err
+	}
+
+	t, err := time.Parse(time.RFC3339, raw)
+	if err != nil {
+		return time.Time{}, false, err
+	}
+	return t, true, nil
+}