// SPDX-FileCopyrightText: 2026 Paul Schoeneck
//
// SPDX-License-Identifier: AGPL-3.0-only AND LicenseRef-KIBU-Additional-Terms

export function localClock(now = new Date()) {
  const parts = new Intl.DateTimeFormat("en-GB", {
    timeZone: process.env.APP_TIMEZONE ?? "Europe/Berlin",
    year: "numeric", month: "2-digit", day: "2-digit",
    hour: "2-digit", minute: "2-digit", hourCycle: "h23",
  }).formatToParts(now);
  const get = (type: Intl.DateTimeFormatPartTypes) => parts.find((p) => p.type === type)!.value;
  const day = `${get("year")}-${get("month")}-${get("day")}`;
  const weekday = new Date(`${day}T12:00:00Z`).getUTCDay() || 7;
  return { day, time: `${get("hour")}:${get("minute")}`, weekday };
}

export function pickupState(pickup: string | null, time: string, end?: string | null) {
  if (!pickup) return "none";
  const minutes = (value: string) => Number(value.slice(0, 2)) * 60 + Number(value.slice(3, 5));
  const delta = minutes(pickup) - minutes(time);
  if (minutes(end ?? pickup) < minutes(time)) return "overdue";
  if (delta <= 15) return "due";
  return "later";
}

export function displayDay(day: string) {
  return new Intl.DateTimeFormat("de-DE", {
    weekday: "long", day: "numeric", month: "long", timeZone: "UTC",
  }).format(new Date(`${day}T12:00:00Z`));
}

export function timeInZone(instant: string, timeZone: string) {
  return new Intl.DateTimeFormat("en-GB", { timeZone, hour: "2-digit", minute: "2-digit", hourCycle: "h23" })
    .format(new Date(instant));
}

export function localInstant(day: string, time: string, timeZone: string): Date {
  const wall = Date.parse(`${day}T${time}:00Z`);
  const format = (date: Date) => new Intl.DateTimeFormat("sv-SE", {
    timeZone, year: "numeric", month: "2-digit", day: "2-digit", hour: "2-digit",
    minute: "2-digit", second: "2-digit", hourCycle: "h23",
  }).format(date).replace(" ", "T");
  const offsets = new Set([-36, 0, 36].map((hours) => {
    const sample = new Date(wall + hours * 3_600_000);
    return Date.parse(`${format(sample)}Z`) - sample.getTime();
  }));
  const candidates = [...offsets].map((offset) => new Date(wall - offset))
    .filter((date) => format(date) === `${day}T${time}:00`);
  if (candidates.length !== 1) {
    throw new Error("Diese Uhrzeit ist wegen der Zeitumstellung nicht eindeutig oder existiert nicht. Bitte eine andere Uhrzeit wählen.");
  }
  return candidates[0];
}