export const STALE_CANVAS_REVISION_CODE = "STALE_CANVAS_REVISION";

export function parseCanvasRevisionDate(value: unknown) {
  const raw = String(value || "").trim();
  if (!raw) return null;
  const parsed = new Date(raw);
  return Number.isNaN(parsed.getTime()) ? null : parsed;
}

export function isStaleCanvasSaveBaseRevision(params: {
  baseCanvasRevision?: unknown;
  baseCanvasUpdatedAt?: unknown;
  currentUpdatedAt: Date;
}) {
  const baseDate = parseCanvasRevisionDate(
    params.baseCanvasUpdatedAt || params.baseCanvasRevision
  );
  if (!baseDate) return false;
  return baseDate.getTime() < params.currentUpdatedAt.getTime();
}

export function buildStaleCanvasSaveConflictPayload(currentUpdatedAt: Date) {
  return {
    success: false,
    error: "画布已更新，请刷新后再保存",
    code: STALE_CANVAS_REVISION_CODE,
    canvasUpdatedAt: currentUpdatedAt.toISOString(),
  };
}