import type { EmailDraft } from "./types.js";

/**
 * Convert a draft to RFC 5322 EML format with MIME multipart/alternative.
 */
export function draftToEml(draft: EmailDraft, from: string): string {
  const boundary = `----=_Part_${Date.now()}_${Math.random().toString(36).slice(2)}`;
  const date = new Date().toUTCString();
  const messageId = `<${Date.now()}.${Math.random().toString(36).slice(2)}@outreach.local>`;

  const toHeader = draft.recipient_name
    ? `"${draft.recipient_name}" <${draft.recipient_email}>`
    : draft.recipient_email;

  const headers = [
    `From: ${from}`,
    `To: ${toHeader}`,
    `Subject: ${encodeSubject(draft.subject)}`,
    `Date: ${date}`,
    `Message-ID: ${messageId}`,
    `MIME-Version: 1.0`,
    `Content-Type: multipart/alternative; boundary="${boundary}"`,
    `X-Mailer: email-export-skill`,
  ];

  const textPart = [
    `--${boundary}`,
    `Content-Type: text/plain; charset="utf-8"`,
    `Content-Transfer-Encoding: quoted-printable`,
    ``,
    quotedPrintableEncode(draft.body_text),
  ].join("\r\n");

  const htmlPart = [
    `--${boundary}`,
    `Content-Type: text/html; charset="utf-8"`,
    `Content-Transfer-Encoding: quoted-printable`,
    ``,
    quotedPrintableEncode(draft.body_html),
  ].join("\r\n");

  return [
    headers.join("\r\n"),
    ``,
    textPart,
    ``,
    htmlPart,
    ``,
    `--${boundary}--`,
    ``,
  ].join("\r\n");
}

/** RFC 2047 encoded-word for non-ASCII subjects */
function encodeSubject(subject: string): string {
  if (/^[\x20-\x7E]*$/.test(subject)) return subject;
  const encoded = Buffer.from(subject, "utf-8").toString("base64");
  return `=?UTF-8?B?${encoded}?=`;
}

/** Simple quoted-printable encoding */
function quotedPrintableEncode(text: string): string {
  const lines: string[] = [];
  let current = "";

  for (const char of text) {
    const code = char.charCodeAt(0);
    let encoded: string;

    if (char === "\r" || char === "\n") {
      lines.push(current);
      current = "";
      continue;
    } else if (code === 9 || (code >= 32 && code <= 126 && char !== "=")) {
      encoded = char;
    } else {
      const buf = Buffer.from(char, "utf-8");
      encoded = Array.from(buf).map(b => `=${b.toString(16).toUpperCase().padStart(2, "0")}`).join("");
    }

    if (current.length + encoded.length > 75) {
      lines.push(current + "=");
      current = encoded;
    } else {
      current += encoded;
    }
  }
  if (current) lines.push(current);
  return lines.join("\r\n");
}

/** Generate a safe filename from draft */
export function emlFilename(draft: EmailDraft, index: number): string {
  const domain = draft.recipient_email.split("@")[1] || "unknown";
  const safe = domain.replace(/[^a-zA-Z0-9.-]/g, "_");
  return `${String(index + 1).padStart(3, "0")}_${safe}.eml`;
}