/**
 * DC-161: Radicale auto-provisioner — the zero-config auto-wiring core.
 *
 * When DashCaddy deploys Radicale through the App Selector, this module:
 *   1. Generates a strong calendar password (never shown in a deploy form)
 *   2. Writes the Radicale config (htpasswd auth) + htpasswd file into the
 *      mounted config volume BEFORE the container starts
 *   3. Stores the credentials in the DashCaddy credential manager under
 *      `calendar:source:<source.id>` (unified key — the same key the events
 *      fetcher resolves for manual sources)
 *   4. Registers a calendar source so the dashboard calendar widget finds
 *      it automatically on first render — no user input at all
 *
 * The htpasswd hash is APR1 (MD5-crypt) — the format Radicale's default
 * `radicale.auth.type = htpasswd` accepts, generated with Node's crypto
 * (no external tools at deploy time).
 */

'use strict';

const fs = require('fs').promises;
const fsSync = require('fs');
const path = require('path');
const crypto = require('crypto');

const RADICALE_CONFIG_TEMPLATE = `# Generated by DashCaddy DC-161 auto-provisioner — safe to regenerate
[server]
hosts = 0.0.0.0:5232

[auth]
type = htpasswd
htpasswd_filename = /config/users
htpasswd_encryption = md5

[rights]
type = owner_only

[storage]
filesystem_folder = /data/collections

[web]
type = internal
`;

function generatePassword() {
  // 24 chars from a 62-char alphabet ≈ 142 bits. Unbiased: rejection-sample
  // bytes above the last full multiple of the alphabet size (judge r1 polish).
  const alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
  const limit = Math.floor(256 / alphabet.length) * alphabet.length;
  let out = '';
  while (out.length < 24) {
    const bytes = crypto.randomBytes(32);
    for (const b of bytes) {
      if (b >= limit) continue; // reject biased tail
      out += alphabet[b % alphabet.length];
      if (out.length === 24) break;
    }
  }
  return out;
}

/** APR1 (Apache MD5-crypt) hash — pure Node, matches `openssl passwd -apr1`. */
function apr1Hash(password, salt) {
  let saltStr = String(salt || '');
  if (!saltStr) {
    // Random 8-char salt from the APR1 alphabet when none supplied
    const alphabet = './0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
    const bytes = crypto.randomBytes(8);
    saltStr = Array.from(bytes, b => alphabet[b % alphabet.length]).join('');
  }
  saltStr = saltStr.slice(0, 8);
  const pw = Buffer.from(String(password), 'utf8');
  const s = Buffer.from(saltStr, 'ascii');

  // Step 2: B = md5(pw + salt + pw)
  const bDigest = crypto.createHash('md5').update(pw).update(s).update(pw).digest();

  // Step 1 + 3 + 4: ONE rolling hash — pw, "$apr1$", salt, then B folded in
  // 16 bytes at a time (tail truncated), then the "weird" loop feeding
  // B[0] on odd bits and pw[0] on even bits. (md5(md5(x)||y) ≠ MD5Update —
  // the accumulator must CONTINUE, never re-digest.)
  const ctx = crypto.createHash('md5').update(pw).update('$apr1$').update(s);
  let i = pw.length;
  while (i > 0) {
    ctx.update(i > 16 ? bDigest : bDigest.subarray(0, i));
    i -= 16;
  }
  // Canonical APR (crypto/apr_md5.c): final is memset to ZERO before the
  // weird loop, so odd bits feed a literal 0x00 byte; even bits feed pw[0].
  i = pw.length;
  while (i > 0) {
    ctx.update(i & 1 ? Buffer.from([0]) : pw.subarray(0, 1));
    i >>= 1;
  }
  let final = ctx.digest();

  // 1000-iteration round: odd → (pw, final), even → (final, pw).
  for (let k = 0; k < 1000; k++) {
    const h = crypto.createHash('md5');
    if (k & 1) h.update(pw); else h.update(final);
    if (k % 3) h.update(s);
    if (k % 7) h.update(pw);
    if (k & 1) h.update(final); else h.update(pw);
    final = h.digest();
  }

  return `$apr1$${saltStr}$${toBase64Apr1(final)}`;
}

function toBase64Apr1(digest) {
  const chars = './0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
  const groups = [[0, 6, 12], [1, 7, 13], [2, 8, 14], [3, 9, 15], [4, 10, 5]];
  let out = '';
  for (const [a, b, c] of groups) {
    let n = (digest[a] << 16) | (digest[b] << 8) | digest[c];
    for (let k = 0; k < 4; k++) { out += chars[n & 0x3f]; n >>= 6; }
  }
  const n = digest[11];
  out += chars[n & 0x3f];
  out += chars[(n >> 6) & 0x3f];
  return out;
}

/**
 * Write the Radicale config + htpasswd into the host-side config volume
 * directory. Called BEFORE container start (Radicale reads config at start).
 * The write is unconditional but content-stable: same inputs produce the
 * same files, so re-running provisioning converges to the same state.
 * @param {string} configDir host path bound to /config inside the container
 * @param {{user: string, pass: string}} creds
 * @returns {Promise<{written: boolean, configDir: string}>}
 */
async function writeRadicaleConfig(configDir, { user, pass }) {
  if (!configDir || path.basename(configDir) === '/') throw new Error('Radicale config dir missing');
  fsSync.mkdirSync(configDir, { recursive: true });
  const configFile = path.join(configDir, 'config');
  const usersFile = path.join(configDir, 'users');

  const hash = apr1Hash(pass);
  const userLine = `${user}:${hash}\n`;

  await fs.writeFile(configFile, RADICALE_CONFIG_TEMPLATE, 'utf8');
  await fs.writeFile(usersFile, userLine, { encoding: 'utf8', mode: 0o600 });
  return { written: true, configDir };
}

/**
 * After a successful Radicale deploy: register the calendar source so the
 * widget auto-discovers it, and persist credentials.
 *
 * Credential-key convention (DC-161 r2 fix): ALL source credentials — manual
 * and auto-wired — live at `calendar:source:<source.id>`. That is the key the
 * events fetcher resolves, so auto-wired sources authenticate on first fetch.
 * Idempotent: re-provisioning the same subdomain updates the existing source
 * (deterministic id `auto-<templateId>-<subdomain>`) instead of duplicating.
 *
 * @param {Object} deps
 * @returns {Promise<{source: Object}>}
 */
async function registerAutoWiredSource({ calendarStateManager, credentialManager, subdomain, serviceUrl, creds, templateId = 'radicale' }) {
  const username = creds.user;
  const source = {
    id: `auto-${templateId}-${subdomain}`,
    type: 'caldav',
    name: `Calendar (${subdomain})`,
    url: `${String(serviceUrl).replace(/\/$/, '')}/${username}/`,
    user: username,
    autoProvisioned: true,
    templateId,
    subdomain,
    enabled: true,
    createdAt: new Date().toISOString(),
  };

  const credKey = `calendar:source:${source.id}`;
  await credentialManager.store(credKey, JSON.stringify({ user: username, pass: creds.pass }), {
    label: `Calendar (${templateId}) — ${subdomain}`, auto: true, createdAt: source.createdAt,
  });

  const existing = await calendarStateManager.findItem(source.id);
  if (existing) {
    await calendarStateManager.updateItem(source.id, source);
  } else {
    await calendarStateManager.addItem(source);
  }
  return source;
}

module.exports = { generatePassword, apr1Hash, writeRadicaleConfig, registerAutoWiredSource, RADICALE_CONFIG_TEMPLATE };