mal/static/timezone.ts

export {};

// JST offset from UTC in minutes (UTC+9)
const jstOffsetMinutes = 9 * 60;

type ParsedBroadcast = {
  day: string;
  hour: number;
  minute: number;
};

const parseBroadcastTime = (value: string | null): { hour: number; minute: number } | null => {
  if (!value || typeof value !== 'string') {
    return null;
  }

  const match = value.trim().match(/^(\d{1,2}):(\d{2})$/);
  if (!match) {
    return null;
  }

  const hour = Number.parseInt(match[1], 10);
  const minute = Number.parseInt(match[2], 10);
  // validate ranges
  if (
    Number.isNaN(hour) ||
    Number.isNaN(minute) ||
    hour < 0 ||
    hour > 23 ||
    minute < 0 ||
    minute > 59
  ) {
    return null;
  }

  return { hour, minute };
};

const isJstTimezone = (timezone: string | null): boolean => {
  if (!timezone) {
    return true; // treat missing timezone as JST (anime default)
  }

  const normalized = timezone.trim().toLowerCase();
  return normalized === 'asia/tokyo' || normalized === 'jst';
};

const parseFromStructuredAttrs = (node: Element): ParsedBroadcast | null => {
  const day = node.getAttribute('data-broadcast-day');
  const time = node.getAttribute('data-broadcast-time');
  const timezone = node.getAttribute('data-broadcast-timezone');

  if (!day || !time || !isJstTimezone(timezone)) {
    return null;
  }

  const parsedTime = parseBroadcastTime(time);
  if (!parsedTime) {
    return null;
  }

  return { day: day.trim(), hour: parsedTime.hour, minute: parsedTime.minute };
};

const parseBroadcast = (text: string | null): ParsedBroadcast | null => {
  if (!text || typeof text !== 'string') {
    return null;
  }

  // matches "Monday at 00:00 (JST)" format
  const match = text.match(/^(.*) at (\d{1,2}):(\d{2}) \(JST\)$/i);
  if (!match) {
    return null;
  }

  const day = match[1].trim();
  const hour = Number.parseInt(match[2], 10);
  const minute = Number.parseInt(match[3], 10);

  if (Number.isNaN(hour) || Number.isNaN(minute)) {
    return null;
  }

  if (hour < 0 || hour > 23 || minute < 0 || minute > 59) {
    return null;
  }

  return { day, hour, minute };
};

const normalizeDay = (day: string): number | null => {
  // strip trailing 's' for plural forms, then lookup
  const key = day.trim().toLowerCase().replace(/s$/, '');
  const days: Record<string, number> = {
    mon: 1,
    monday: 1,
    tue: 2,
    tues: 2,
    tuesday: 2,
    wed: 3,
    wednesday: 3,
    thu: 4,
    thur: 4,
    thurs: 4,
    thursday: 4,
    fri: 5,
    friday: 5,
    sat: 6,
    saturday: 6,
    sun: 0,
    sunday: 0,
  };

  if (typeof days[key] !== 'number') {
    return null;
  }

  return days[key];
};

const convertToLocal = (parsed: ParsedBroadcast, localOffsetMinutes: number): string | null => {
  const sourceMinutes = parsed.hour * 60 + parsed.minute;
  const diff = jstOffsetMinutes - localOffsetMinutes; // JST ahead of local
  const localTotal = sourceMinutes - diff;

  const dayShift = Math.floor(localTotal / 1440);
  const normalizedMinutes = ((localTotal % 1440) + 1440) % 1440; // handle negatives
  const localHour = Math.floor(normalizedMinutes / 60);
  const localMinute = normalizedMinutes % 60;

  const sourceDayIndex = normalizeDay(parsed.day);
  if (sourceDayIndex === null) {
    return null;
  }

  const localDayIndex = (((sourceDayIndex + dayShift) % 7) + 7) % 7; // proper modulo
  const localDay = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'][
    localDayIndex
  ];

  const time = `${localHour.toString().padStart(2, '0')}:${localMinute.toString().padStart(2, '0')}`;
  return `${localDay} at ${time} (Local)`;
};

const nextAiringUTC = (parsed: ParsedBroadcast): Date | null => {
  const targetDay = normalizeDay(parsed.day);
  if (targetDay === null) {
    return null;
  }

  // convert local time to JST to compare against JST now
  const now = new Date();
  const jstNow = new Date(now.getTime() + jstOffsetMinutes * 60 * 1000);

  const currentDay = jstNow.getUTCDay();
  const currentMinuteOfDay = jstNow.getUTCHours() * 60 + jstNow.getUTCMinutes();
  const targetMinuteOfDay = parsed.hour * 60 + parsed.minute;

  let dayDelta = (targetDay - currentDay + 7) % 7;
  // if same day but time has passed, schedule for next week
  if (dayDelta === 0 && targetMinuteOfDay <= currentMinuteOfDay) {
    dayDelta = 7;
  }

  const minuteDelta = dayDelta * 1440 + (targetMinuteOfDay - currentMinuteOfDay);
  return new Date(now.getTime() + minuteDelta * 60 * 1000);
};

const formatRelative = (value: number, unit: Intl.RelativeTimeFormatUnit): string => {
  // Intl.RelativeTimeFormat not available in all environments
  if (typeof Intl !== 'undefined' && typeof Intl.RelativeTimeFormat === 'function') {
    const formatter = new Intl.RelativeTimeFormat(undefined, { numeric: 'auto' });
    return formatter.format(value, unit);
  }

  // fallback: "in X minutes/hours/days"
  const suffix = value === 1 ? unit : `${unit}s`;
  return `in ${value} ${suffix}`;
};

const relativeText = (target: Date): string => {
  const diffMs = target.getTime() - Date.now();
  if (diffMs <= 0) {
    return 'soon';
  }

  const minutes = Math.ceil(diffMs / 60000);
  if (minutes < 60) {
    return formatRelative(minutes, 'minute');
  }

  const hours = Math.ceil(minutes / 60);
  if (hours < 36) {
    return formatRelative(hours, 'hour');
  }

  const days = Math.ceil(hours / 24);
  return formatRelative(days, 'day');
};

const localDateTimeText = (date: Date): string => {
  const formatter = new Intl.DateTimeFormat(undefined, {
    weekday: 'short',
    hour: '2-digit',
    minute: '2-digit',
  });
  return formatter.format(date);
};

const updateNextAiring = (node: Element, parsed: ParsedBroadcast): void => {
  const card = node.closest('[data-notification-content]');
  if (!card) {
    return;
  }

  const nextNode = card.querySelector('[data-next-airing]');
  if (!(nextNode instanceof HTMLElement)) {
    return;
  }

  const nextDate = nextAiringUTC(parsed);
  if (!nextDate) {
    nextNode.remove();
    return;
  }

  nextNode.textContent = `Next episode ${relativeText(nextDate)} (${localDateTimeText(nextDate)})`;
};

const updateNode = (node: Element, localOffsetMinutes: number): void => {
  const card = node.closest('[data-notification-content]');
  const nextNode = card ? card.querySelector('[data-next-airing]') : null;

  // try structured attrs first, fall back to text parsing
  const structured = parseFromStructuredAttrs(node);
  const source = node.getAttribute('data-jst-text');
  const parsed = structured || parseBroadcast(source);
  if (!parsed) {
    if (nextNode instanceof HTMLElement) {
      nextNode.remove();
    }
    return;
  }

  const converted = convertToLocal(parsed, localOffsetMinutes);
  if (!converted) {
    if (nextNode instanceof HTMLElement) {
      nextNode.remove();
    }
    return;
  }

  node.textContent = converted;
  updateNextAiring(node, parsed);
};

const updateAll = (): void => {
  const localOffsetMinutes = -new Date().getTimezoneOffset();
  const nodes = document.querySelectorAll('[data-jst-text]');
  nodes.forEach(node => updateNode(node, localOffsetMinutes));
};

const initTimezoneConversion = (): void => {
  // run on initial load and after htmx swaps (content may change)
  document.addEventListener('DOMContentLoaded', updateAll);
  document.body.addEventListener('htmx:afterSwap', updateAll);
};

initTimezoneConversion();