canvasManagement/src/app/course/[courseName]/context/drag/getNewLockDate.ts

"use client";
import {
  getDateFromStringOrThrow,
  dateToMarkdownString,
} from "@/features/local/utils/timeUtils";

export function getNewLockDate(
  originalDueDate: string,
  originalLockDate: string | undefined,
  dayAsDate: Date
): string | undefined {
  // todo: preserve previous due date / lock date offset
  const dueDate = getDateFromStringOrThrow(originalDueDate, "dueAt date");
  const lockDate =
    originalLockDate === undefined
      ? undefined
      : getDateFromStringOrThrow(originalLockDate, "lockAt date");

  const originalOffset =
    lockDate === undefined ? undefined : lockDate.getTime() - dueDate.getTime();

  const newLockDate =
    originalOffset === undefined
      ? undefined
      : new Date(dayAsDate.getTime() + originalOffset);

  return newLockDate === undefined
    ? undefined
    : dateToMarkdownString(newLockDate);
}