/** Product UI dates for session titles and subtitles are wall-clock in China. */

export const SESSION_CLOCK_TIMEZONE = "Asia/Shanghai";

function part(
  parts: Intl.DateTimeFormatPart[],
  type: Intl.DateTimeFormatPartTypes,
): string {
  return parts.find((item) => item.type === type)?.value ?? "";
}

export function shanghaiDateParts(at: Date, timeZone = SESSION_CLOCK_TIMEZONE): {
  month: number;
  day: number;
} {
  const parts = new Intl.DateTimeFormat("en-US", {
    timeZone,
    month: "numeric",
    day: "numeric",
  }).formatToParts(at);
  return {
    month: Number(part(parts, "month")),
    day: Number(part(parts, "day")),
  };
}

export function shanghaiDateTimeLabel(at: Date, timeZone = SESSION_CLOCK_TIMEZONE): string {
  const parts = new Intl.DateTimeFormat("en-US", {
    timeZone,
    month: "numeric",
    day: "numeric",
    hour: "2-digit",
    minute: "2-digit",
    hourCycle: "h23",
  }).formatToParts(at);
  const month = Number(part(parts, "month"));
  const day = Number(part(parts, "day"));
  const hour = part(parts, "hour").padStart(2, "0");
  const minute = part(parts, "minute").padStart(2, "0");
  return `${month}月${day}日 ${hour}:${minute}`;
}