import { rangeDates } from "@/lib/planMeta";
import type { TripItem } from "@/lib/types";

function pad(n: number) {
  return String(n).padStart(2, "0");
}

function formatDate(d: Date): string {
  return `${d.getFullYear()}${pad(d.getMonth() + 1)}${pad(d.getDate())}`;
}

function formatStamp(d = new Date()): string {
  return `${formatDate(d)}T${pad(d.getHours())}${pad(d.getMinutes())}${pad(d.getSeconds())}Z`;
}

function escapeText(s: string): string {
  return s.replace(/\\/g, "\\\\").replace(/;/g, "\\;").replace(/,/g, "\\,").replace(/\n/g, "\\n");
}

export interface IcsStop extends TripItem {
  offset: number;
}

/** Build an ICS calendar from plan stops (requires startMonth YYYY-MM). */
export function buildPlanIcs(opts: {
  title: string;
  startMonth: string;
  stops: IcsStop[];
}): string | null {
  if (!opts.startMonth || opts.stops.length === 0) return null;
  const now = formatStamp();
  const lines = [
    "BEGIN:VCALENDAR",
    "VERSION:2.0",
    "PRODID:-//nomadro//Move Plan//CN",
    "CALSCALE:GREGORIAN",
    "METHOD:PUBLISH",
    `X-WR-CALNAME:${escapeText(opts.title || "nomadro 旅居计划")}`,
  ];

  opts.stops.forEach((stop, i) => {
    const range = rangeDates(opts.startMonth, stop.offset, stop.months);
    if (!range) return;
    const summary = `${stop.emoji} ${stop.name}, ${stop.country}`;
    const descParts = [
      `停留 ${stop.months} 个月`,
      `约 ¥${(stop.cost * stop.months).toLocaleString()}`,
      stop.note ? `备注：${stop.note}` : "",
      "由 nomadro 旅居计划中心生成",
    ].filter(Boolean);
    lines.push(
      "BEGIN:VEVENT",
      `UID:nomadro-${stop.slug}-${i}@nomadro.com`,
      `DTSTAMP:${now}`,
      `DTSTART;VALUE=DATE:${formatDate(range.start)}`,
      `DTEND;VALUE=DATE:${formatDate(range.endExclusive)}`,
      `SUMMARY:${escapeText(summary)}`,
      `DESCRIPTION:${escapeText(descParts.join(" · "))}`,
      `LOCATION:${escapeText(`${stop.name}, ${stop.country}`)}`,
      "END:VEVENT"
    );
  });

  lines.push("END:VCALENDAR");
  return lines.join("\r\n");
}

export function downloadPlanIcs(filename: string, ics: string) {
  const blob = new Blob([ics], { type: "text/calendar;charset=utf-8" });
  const url = URL.createObjectURL(blob);
  const a = document.createElement("a");
  a.href = url;
  a.download = filename;
  a.click();
  URL.revokeObjectURL(url);
}