import { formatDateTime, formatTime } from "@/shared/utils/date-time";

const zonedTime = /(?<![\w/+:.-])(\d{4}-\d{2}-\d{2})[T ](\d{2}:\d{2}(?::\d{2}(?:\.\d{1,9})?)?)(Z|[+-]\d{2}:\d{2})(?![\w:+/-])/g;
const utcMarker = String.raw`(?:Z|(?:[（(]\s*)?UTC(?:\s*\+?0(?::00)?)?(?:\s*[）)])?)(?![\w:+/-])`;
const utcRange = new RegExp(String.raw`(?<![\w/+:.-])(?:(\d{4}-\d{2}-\d{2})[T ])?(\d{2}:\d{2})\s*[–—~至-]\s*(\d{2}:\d{2})\s*${utcMarker}`, "g");
const utcPoint = new RegExp(String.raw`(?<![\w/+:.-])(?:(\d{4}-\d{2}-\d{2})[T ])?(\d{2}:\d{2}(?::\d{2}(?:\.\d{1,9})?)?)\s*${utcMarker}`, "g");

function parseTime(day: string, clock: string, zone = "Z"): number | null {
  const date = new Date(`${day}T00:00:00Z`);
  const [hours, minutes, seconds = "0"] = clock.split(":");
  if (!Number.isFinite(date.getTime()) || date.toISOString().slice(0, 10) !== day
    || Number(hours) > 23 || Number(minutes) > 59 || Number(seconds) >= 60) return null;
  const value = Date.parse(`${day}T${clock}${zone}`);
  return Number.isFinite(value) ? value : null;
}

/** Display historical report prose without changing stored facts, IDs, URLs or code. */
export function formatDisplayText(text: string | null | undefined): string {
  if (!text) return text ?? "";
  return text.split(/(https?:\/\/\S+|tjwater:\/\/\S+|`[^`]*`)/g).map((part, index) => {
    if (index % 2) return part;
    return part.replace(utcRange, (original, day: string | undefined, start: string, end: string) => {
      const startAt = parseTime(day ?? "2000-01-01", start);
      let endAt = parseTime(day ?? "2000-01-01", end);
      if (startAt === null || endAt === null) return original;
      if (endAt < startAt) endAt += 24 * 60 * 60_000;
      const dateOptions = { year: "numeric", month: "numeric", day: "numeric" } as const;
      const crossesDay = formatDateTime(startAt, dateOptions) !== formatDateTime(endAt, dateOptions);
      const startLabel = day ? formatDateTime(startAt, { ...dateOptions, hour: "2-digit", minute: "2-digit" }) : formatTime(startAt);
      const endLabel = crossesDay && day
        ? formatDateTime(endAt, { ...dateOptions, hour: "2-digit", minute: "2-digit" })
        : `${crossesDay ? "次日 " : ""}${formatTime(endAt)}`;
      return `${startLabel}–${endLabel}（UTC+8）`;
    }).replace(zonedTime, (original, day: string, clock: string, zone: string) => {
      const value = parseTime(day, clock, zone);
      return value === null ? original : `${formatDateTime(value)}（UTC+8）`;
    }).replace(utcPoint, (original, day: string | undefined, clock: string) => {
      const value = parseTime(day ?? "2000-01-01", clock);
      if (value === null) return original;
      return `${day ? formatDateTime(value) : formatTime(value)}（UTC+8）`;
    });
  }).join("");
}