export interface ParsedVCard {
  body: string;
  size: number;
  uid: string;
  version: "3.0" | "4.0";
  fn: string | null;
  nFamily: string | null;
  nGiven: string | null;
  org: string | null;
  emails: string[];
  tels: string[];
}

function byteLength(value: string): number {
  return new TextEncoder().encode(value).byteLength;
}

function decodeUtf8(bytes: ArrayBuffer): string {
  return new TextDecoder("utf-8", { fatal: true, ignoreBOM: false }).decode(bytes);
}

function normalizeLineEndings(text: string): string {
  return `${text.replace(/\r\n/g, "\n").replace(/\r/g, "\n").replace(/\n+$/g, "").split("\n").join("\r\n")}\r\n`;
}

function unfoldLines(body: string): string[] {
  const lines = body.replace(/\r\n/g, "\n").split("\n");
  const unfolded: string[] = [];
  for (const line of lines) {
    if ((line.startsWith(" ") || line.startsWith("\t")) && unfolded.length > 0) {
      unfolded[unfolded.length - 1] += line.slice(1);
    } else if (line !== "") {
      unfolded.push(line);
    }
  }
  return unfolded;
}

function propertyName(line: string): string {
  const end = line.search(/[:;]/);
  const name = (end === -1 ? line : line.slice(0, end)).toUpperCase();
  const groupIndex = name.lastIndexOf(".");
  return groupIndex === -1 ? name : name.slice(groupIndex + 1);
}

function propertyValue(line: string): string | null {
  const colon = line.indexOf(":");
  return colon === -1 ? null : line.slice(colon + 1);
}

function firstValue(lines: string[], name: string): string | null {
  const line = lines.find((candidate) => propertyName(candidate) === name);
  return line ? propertyValue(line) : null;
}

function firstPropertyIndex(lines: string[], name: string): number {
  return lines.findIndex((candidate) => propertyName(candidate) === name);
}

function allValues(lines: string[], name: string): string[] {
  return lines
    .filter((line) => propertyName(line) === name)
    .map(propertyValue)
    .filter((value): value is string => value !== null && value !== "");
}

export function parseVCardBytes(bytes: ArrayBuffer, maxBytes: number): ParsedVCard {
  if (bytes.byteLength > maxBytes) throw new Error("vCard exceeds configured maximum size");
  const body = normalizeLineEndings(decodeUtf8(bytes));
  const size = byteLength(body);
  if (size > maxBytes) throw new Error("vCard exceeds configured maximum size after normalization");
  const lines = unfoldLines(body);
  if (lines[0]?.toUpperCase() !== "BEGIN:VCARD" || lines.at(-1)?.toUpperCase() !== "END:VCARD") {
    throw new Error("vCard must contain one VCARD");
  }
  if (lines.slice(1, -1).some((line) => line.toUpperCase() === "BEGIN:VCARD" || line.toUpperCase() === "END:VCARD")) {
    throw new Error("Multiple vCards are not supported");
  }

  const versionIndex = firstPropertyIndex(lines, "VERSION");
  const version = versionIndex === -1 ? null : propertyValue(lines[versionIndex]!);
  if (version !== "3.0" && version !== "4.0") throw new Error("vCard VERSION must be 3.0 or 4.0");
  if (version === "4.0" && versionIndex !== 1) throw new Error("vCard 4.0 VERSION must immediately follow BEGIN");
  const uid = firstValue(lines, "UID");
  if (!uid) throw new Error("vCard UID is required");
  const fn = firstValue(lines, "FN");
  if (version === "4.0" && !fn) throw new Error("vCard 4.0 FN is required");

  const nParts = (firstValue(lines, "N") ?? "").split(";");
  return {
    body,
    size,
    uid,
    version,
    fn,
    nFamily: nParts[0] || null,
    nGiven: nParts[1] || null,
    org: firstValue(lines, "ORG"),
    emails: allValues(lines, "EMAIL"),
    tels: allValues(lines, "TEL"),
  };
}