import { BERLIN_VTIMEZONE_LINES, toBerlinICSDateTime, toUTCICSStamp } from "./timezone";

export type ICSEvent = {
  uid: string;
  start: Date;
  end: Date;
  summary: string;
  description?: string;
  location?: string;
  url?: string;
};

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

/** RFC 5545 line folding: lines must not exceed 75 octets; continuations start with a single space. */
function foldLine(line: string): string {
  const encoder = new TextEncoder();
  if (encoder.encode(line).length <= 75) return line;

  const chunks: string[] = [];
  let current = "";
  for (const char of line) {
    const candidate = current + char;
    if (encoder.encode(candidate).length > 75) {
      chunks.push(current);
      current = char;
    } else {
      current = candidate;
    }
  }
  if (current) chunks.push(current);
  return chunks.join("\r\n ");
}

/** Builds a complete RFC 5545 VCALENDAR document, Europe/Berlin timezone-aware throughout. */
export function buildICSCalendar(args: { calendarName: string; events: ICSEvent[] }): string {
  const lines: string[] = [
    "BEGIN:VCALENDAR",
    "VERSION:2.0",
    "PRODID:-//ANOUMA//Calendar Feed//DE",
    "CALSCALE:GREGORIAN",
    "METHOD:PUBLISH",
    `X-WR-CALNAME:${escapeICSText(args.calendarName)}`,
    "X-WR-TIMEZONE:Europe/Berlin",
    ...BERLIN_VTIMEZONE_LINES,
  ];

  const stamp = toUTCICSStamp(new Date());
  for (const ev of args.events) {
    lines.push(
      "BEGIN:VEVENT",
      `UID:${ev.uid}`,
      `DTSTAMP:${stamp}`,
      `DTSTART;TZID=Europe/Berlin:${toBerlinICSDateTime(ev.start)}`,
      `DTEND;TZID=Europe/Berlin:${toBerlinICSDateTime(ev.end)}`,
      `SUMMARY:${escapeICSText(ev.summary)}`,
    );
    if (ev.description) lines.push(`DESCRIPTION:${escapeICSText(ev.description)}`);
    if (ev.location) lines.push(`LOCATION:${escapeICSText(ev.location)}`);
    if (ev.url) lines.push(`URL:${ev.url}`);
    lines.push("STATUS:CONFIRMED", "END:VEVENT");
  }

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