// Just enough iCalendar/vCard to drive a list view.
//
// SCOPE, DELIBERATELY SMALL. This unfolds lines, splits properties and pulls out the handful of fields a
// UI shows. It does NOT expand RRULE, and it does not resolve VTIMEZONE — see
// docs/nextcloud-replacement.md for why those are the expensive half and why Radicale, not this file,
// owns correctness. `rrule` is passed through raw so the UI can say "repeats" without either of us
// pretending to know when.
//
// Reading is display-only: the authoritative copy of an event is the .ics on disk that DAV clients read
// and write, and an edit patches THAT text rather than rebuilding it from what was parsed here.
//
// `buildEvent` is the one exception, and only because a NEW event has no original to preserve. It is
// deliberately the minimum a VEVENT can legally be — no RRULE, no alarms, no attendees. Officer's screens
// cannot express those, and writing a field the UI cannot show is how an editor starts lying.

/** Unfold RFC 5545 continuation lines (a leading space or tab continues the previous line). */
function unfold(text: string): string[] {
  const out: string[] = [];
  for (const raw of text.split(/\r?\n/)) {
    if ((raw.startsWith(' ') || raw.startsWith('\t')) && out.length > 0) {
      out[out.length - 1] += raw.slice(1);
    } else if (raw.length > 0) {
      out.push(raw);
    }
  }
  return out;
}

export type Prop = { name: string; params: Record<string, string>; value: string };

/** `DTSTART;TZID=Europe/Lisbon:20260805T090000` → name, params, value. */
function parseLine(line: string): Prop | null {
  const colon = line.indexOf(':');
  if (colon < 0) return null;
  const head = line.slice(0, colon);
  const value = line.slice(colon + 1);
  const [name, ...paramParts] = head.split(';');
  const params: Record<string, string> = {};
  for (const part of paramParts) {
    const eq = part.indexOf('=');
    if (eq > 0) params[part.slice(0, eq).toUpperCase()] = part.slice(eq + 1).replace(/^"|"$/g, '');
  }
  return { name: (name ?? '').toUpperCase(), params, value };
}

// Escaped per RFC 5545 §3.3.11. Order matters: backslash last, or it would un-escape the escapes.
const unescapeText = (value: string) =>
  value.replace(/\\n/gi, '\n').replace(/\\,/g, ',').replace(/\\;/g, ';').replace(/\\\\/g, '\\');

/**
 * iCalendar dates come in three shapes and conflating them is how an all-day event ends up on the wrong
 * day: `20260805` (date only), `20260805T090000Z` (UTC) and `20260805T090000` with a TZID parameter
 * (floating/local). Only the first two can be resolved here without a timezone database, so the third is
 * returned as-is with `allDay:false` and the UI treats it as local — which is what it means to whoever
 * typed it in.
 */
export function parseDate(prop: Prop): { iso: string; allDay: boolean } | null {
  const v = prop.value.trim();
  const dateOnly = /^(\d{4})(\d{2})(\d{2})$/.exec(v);
  if (dateOnly) return { iso: `${dateOnly[1]}-${dateOnly[2]}-${dateOnly[3]}`, allDay: true };

  const dateTime = /^(\d{4})(\d{2})(\d{2})T(\d{2})(\d{2})(\d{2})(Z)?$/.exec(v);
  if (!dateTime) return null;
  const [, y, mo, d, h, mi, s, z] = dateTime;
  return { iso: `${y}-${mo}-${d}T${h}:${mi}:${s}${z ? 'Z' : ''}`, allDay: false };
}

export type CalendarEvent = {
  uid: string;
  /** Where this event LIVES — the DAV href. Absent when parsed outside a listing. Needed to edit or delete it. */
  href?: string;
  summary: string;
  description?: string;
  location?: string;
  start?: string;
  end?: string;
  allDay: boolean;
  /** Raw RRULE, unexpanded. Present means "this repeats"; the UI must not infer occurrences from it. */
  rrule?: string;
  status?: string;
};

/** Every VEVENT in one .ics. A file usually holds one, plus overrides for a recurring series. */
export function parseEvents(ics: string): CalendarEvent[] {
  const events: CalendarEvent[] = [];
  let current: CalendarEvent | null = null;
  // Only VEVENT is collected; a VALARM or VTIMEZONE nested inside must not have its properties
  // attributed to the event that contains it.
  let depth: string[] = [];

  for (const line of unfold(ics)) {
    const prop = parseLine(line);
    if (!prop) continue;

    if (prop.name === 'BEGIN') {
      depth.push(prop.value.toUpperCase());
      if (prop.value.toUpperCase() === 'VEVENT') current = { uid: '', summary: '', allDay: false };
      continue;
    }
    if (prop.name === 'END') {
      if (prop.value.toUpperCase() === 'VEVENT' && current) {
        events.push(current);
        current = null;
      }
      depth.pop();
      continue;
    }
    if (!current || depth[depth.length - 1] !== 'VEVENT') continue;

    switch (prop.name) {
      case 'UID':
        current.uid = prop.value;
        break;
      case 'SUMMARY':
        current.summary = unescapeText(prop.value);
        break;
      case 'DESCRIPTION':
        current.description = unescapeText(prop.value);
        break;
      case 'LOCATION':
        current.location = unescapeText(prop.value);
        break;
      case 'STATUS':
        current.status = prop.value;
        break;
      case 'RRULE':
        current.rrule = prop.value;
        break;
      case 'DTSTART': {
        const parsed = parseDate(prop);
        if (parsed) {
          current.start = parsed.iso;
          current.allDay = parsed.allDay;
        }
        break;
      }
      case 'DTEND': {
        const parsed = parseDate(prop);
        if (parsed) current.end = parsed.iso;
        break;
      }
    }
  }
  return events;
}

export type Contact = {
  uid: string;
  /** Where this contact LIVES — the DAV href. Absent when parsed outside a listing. Needed to edit or delete it. */
  href?: string;
  fullName: string;
  emails: string[];
  phones: string[];
  org?: string;
  title?: string;
  /** Present when the card carries an embedded photo; the bytes are not inlined into list responses. */
  hasPhoto: boolean;
};

/** Every VCARD in one .vcf. */
export function parseContacts(vcf: string): Contact[] {
  const contacts: Contact[] = [];
  let current: Contact | null = null;

  for (const line of unfold(vcf)) {
    const prop = parseLine(line);
    if (!prop) continue;

    if (prop.name === 'BEGIN' && prop.value.toUpperCase() === 'VCARD') {
      current = { uid: '', fullName: '', emails: [], phones: [], hasPhoto: false };
      continue;
    }
    if (prop.name === 'END' && prop.value.toUpperCase() === 'VCARD') {
      if (current) contacts.push(current);
      current = null;
      continue;
    }
    if (!current) continue;

    switch (prop.name) {
      case 'UID':
        current.uid = prop.value;
        break;
      case 'FN':
        current.fullName = unescapeText(prop.value);
        break;
      case 'EMAIL':
        current.emails.push(prop.value.trim());
        break;
      case 'TEL':
        current.phones.push(prop.value.trim());
        break;
      case 'ORG':
        // ORG is structured: `Company;Department`. The first component is the one a list shows.
        current.org = unescapeText(prop.value.split(';')[0] ?? '');
        break;
      case 'TITLE':
        current.title = unescapeText(prop.value);
        break;
      case 'PHOTO':
        current.hasPhoto = true;
        break;
    }
  }
  // A card with no FN is legal but unshowable; fall back to the first email so it is at least findable.
  for (const contact of contacts) {
    if (!contact.fullName) contact.fullName = contact.emails[0] ?? contact.uid ?? 'Unnamed';
  }
  return contacts;
}

// ─── Writing ────────────────────────────────────────────────────────────────────────────────────────

export const escapeText = (value: string) =>
  value
    .replace(/\\/g, '\\\\')
    .replace(/\r?\n/g, '\\n')
    .replace(/([,;])/g, '\\$1');

/**
 * RFC 5545 §3.1: no content line over 75 OCTETS, continued by a line starting with one space.
 *
 * Octets, not characters — so this measures encoded length and breaks between code points. A pasted
 * title with an accent in it is exactly where a naive `slice(0, 75)` splits a multi-byte character in
 * half and produces a file some clients refuse and others render as mojibake.
 */
export function fold(line: string): string {
  const encoder = new TextEncoder();
  const out: string[] = [];
  let current = '';
  let bytes = 0;
  for (const ch of line) {
    const size = encoder.encode(ch).length;
    if (bytes + size > 75) {
      out.push(current);
      current = ' ';
      bytes = 1;
    }
    current += ch;
    bytes += size;
  }
  out.push(current);
  return out.join('\r\n');
}

export const pad = (n: number) => String(n).padStart(2, '0');

/** `20260827T140000Z`. Always UTC, so the file carries no timezone this codebase would have to resolve. */
export const utcStamp = (date: Date) =>
  `${date.getUTCFullYear()}${pad(date.getUTCMonth() + 1)}${pad(date.getUTCDate())}T` +
  `${pad(date.getUTCHours())}${pad(date.getUTCMinutes())}${pad(date.getUTCSeconds())}Z`;

/** `2026-08-27` → `20260827`. */
export const dateStamp = (iso: string) => iso.slice(0, 10).replace(/-/g, '');

export const addDay = (iso: string) => {
  const d = new Date(`${iso.slice(0, 10)}T00:00:00Z`);
  d.setUTCDate(d.getUTCDate() + 1);
  return d.toISOString().slice(0, 10);
};

export type NewEvent = {
  summary: string;
  location?: string;
  /** An ISO instant for a timed event; `YYYY-MM-DD` when `allDay`. */
  start: string;
  /** Same shape as `start`. For an all-day event this is the LAST day, inclusive, as a person means it. */
  end?: string;
  allDay: boolean;
};

/**
 * A minimal VEVENT, wrapped in its own VCALENDAR — one event per file, which is what every DAV client
 * writes and what makes an href addressable.
 *
 * TIMES ARE WRITTEN IN UTC. The alternative is `DTSTART;TZID=Europe/Lisbon` plus a VTIMEZONE block
 * defining that zone's rules, and getting a VTIMEZONE subtly wrong moves an event by an hour twice a
 * year. UTC needs no definition and every client renders it in local time.
 *
 * ALL-DAY IS DIFFERENT, and its trap is DTEND. RFC 5545 makes the end date EXCLUSIVE, so a one-day
 * event on the 27th ends on the 28th. Writing the 27th produces a zero-length event that some clients
 * hide entirely; callers pass the last day they mean and this adds the day.
 */
export function buildEvent(uid: string, event: NewEvent): string {
  const lines = ['BEGIN:VCALENDAR', 'VERSION:2.0', 'PRODID:-//Officer//caldav//EN', 'BEGIN:VEVENT', `UID:${uid}`];
  lines.push(`DTSTAMP:${utcStamp(new Date())}`);

  if (event.allDay) {
    const last = event.end?.slice(0, 10) || event.start.slice(0, 10);
    lines.push(`DTSTART;VALUE=DATE:${dateStamp(event.start)}`);
    lines.push(`DTEND;VALUE=DATE:${dateStamp(addDay(last))}`);
  } else {
    const start = new Date(event.start);
    // An hour is the default a calendar has taught everyone to expect from an event with no end.
    const end = event.end ? new Date(event.end) : new Date(start.getTime() + 60 * 60 * 1000);
    lines.push(`DTSTART:${utcStamp(start)}`);
    lines.push(`DTEND:${utcStamp(end)}`);
  }

  lines.push(`SUMMARY:${escapeText(event.summary)}`);
  if (event.location) lines.push(`LOCATION:${escapeText(event.location)}`);
  lines.push('END:VEVENT', 'END:VCALENDAR');

  return lines.map(fold).join('\r\n') + '\r\n';
}

/** The inverse of `addDay`. Turns a file's EXCLUSIVE all-day DTEND back into the last day a person means. */
export const subDay = (iso: string) => {
  const d = new Date(`${iso.slice(0, 10)}T00:00:00Z`);
  d.setUTCDate(d.getUTCDate() - 1);
  return d.toISOString().slice(0, 10);
};

export type NewContact = {
  fullName: string;
  emails?: string[];
  phones?: string[];
  org?: string;
  title?: string;
};

/**
 * A minimal vCard 3.0 — the version CardDAV clients, iOS included, actually write.
 *
 * `N` is REQUIRED in 3.0 and is `Family;Given;Middle;Prefix;Suffix`. Nobody supplies it, so it is split
 * out of the full name: last word is the family name, everything before it is given. That is wrong for
 * some names in the world and right for most, and `FN` — which is what a phone displays — is whatever
 * was actually typed either way.
 */
export function buildContact(uid: string, contact: NewContact): string {
  const [family, ...given] = contact.fullName.trim().split(/\s+/).reverse();
  const lines = [
    'BEGIN:VCARD',
    'VERSION:3.0',
    `UID:${uid}`,
    `FN:${escapeText(contact.fullName)}`,
    `N:${escapeText(family ?? '')};${escapeText(given.reverse().join(' '))};;;`,
  ];
  for (const email of contact.emails ?? []) lines.push(`EMAIL;TYPE=INTERNET:${escapeText(email)}`);
  for (const phone of contact.phones ?? []) lines.push(`TEL;TYPE=CELL:${escapeText(phone)}`);
  if (contact.org) lines.push(`ORG:${escapeText(contact.org)}`);
  if (contact.title) lines.push(`TITLE:${escapeText(contact.title)}`);
  lines.push('END:VCARD');
  return lines.map(fold).join('\r\n') + '\r\n';
}