/**
 * POST /api/listing  — accept a signed listing from a publisher.
 * GET  /api/listings — the public index, optionally filtered by category.
 * GET  /api/listings/<publisher>/<slug> — one listing.
 *
 * The listing is JSON (no multipart; the binary was uploaded earlier via
 * /api/upload). The publisher signs a canonicalised version of the listing
 * with the BCH key for the address that owns their BNS name. The service
 * verifies:
 *
 *   1. The signature actually recovers to a valid cashaddress.
 *   2. That address matches the on-chain owner of the claimed BNS name.
 *   3. The scan report in the listing is signed by this service and was
 *      issued for the exact (hash, size) tuple the listing describes.
 *
 * Only after all three pass does the row land in SQLite. On any failure the
 * caller gets a 4xx with a `reason` and nothing persists.
 *
 * This is the INTERIM shape: no APS1 record on chain yet. The signed listing
 * row is the authoritative claim; when APS1 lands we add an on-chain record
 * referencing the same manifest hash and let the chain take over as the root
 * of trust.
 */

import { createHash } from 'node:crypto';
import { verifyControl, DEFAULT_PREFIX } from './lib/sign-message.js';
import { lookupName } from './bns.js';
import { publicKeyBase64 } from './signing.js';
import {
  insertListing,
  getListing,
  allActiveListings,
  listingsByCategory,
  listingsByPublisher,
} from './db.js';

const CATEGORIES = new Set([
  'communication', 'privacy', 'wallets', 'games',
  'devtools', 'media', 'utilities', 'other',
]);

const MAX_BODY_BYTES = 1024 * 1024;   // 1 MiB — listings are small JSON
const SLUG_RE = /^[a-z0-9][a-z0-9-]{0,62}[a-z0-9]$|^[a-z0-9]$/;
const BNS_NAME_RE = /^[a-z0-9][a-z0-9-]{0,62}\.[a-z0-9]{1,20}$/;

/* ======================================================================
   POST /api/listing
   ====================================================================== */

export async function handleListingCreate(req, res) {
  if (req.method !== 'POST') {
    return json(res, 405, { ok: false, reason: 'method not allowed' });
  }

  let body;
  try {
    body = await readJson(req);
  } catch (err) {
    return json(res, 400, { ok: false, reason: String(err?.message || err) });
  }

  const check = validate(body);
  if (!check.ok) return json(res, 400, check);

  // The scan report must be the real signed envelope this service issued,
  // AND it must be for the exact (hash, size) the listing describes. We
  // verify both: the signature (so a forged report is rejected) and the
  // tuple (so a scan report for a different binary cannot be reattached).
  const scanCheck = verifyAttachedScan(body);
  if (!scanCheck.ok) return json(res, 400, scanCheck);

  // Build the canonical message the publisher is expected to have signed.
  // Keys sorted at every level, no whitespace. The signature covers every
  // field except itself, so changing any value invalidates the signature.
  const message = buildSigningMessage(body);

  // Resolve the publisher's claimed BNS name to its current on-chain owner.
  // This is the trust claim — recovery alone is never enough; we must know
  // *who* was supposed to sign before we accept a signature as proof.
  const name = String(body.publisher).toLowerCase();
  const nameInfo = await lookupName(name);
  if (!nameInfo.ok) {
    return json(res, 400, { ok: false, reason: `publisher '${name}': ${nameInfo.reason}` });
  }

  const verify = verifyControl({
    message,
    signature: body.signature,
    expectedAddress: nameInfo.owner,
    prefix: DEFAULT_PREFIX,
  });
  if (!verify.ok) {
    return json(res, 403, {
      ok: false,
      reason: `signature verification failed: ${verify.reason}`,
      ...(verify.signedBy ? { signed_by: verify.signedBy } : {}),
      claimed_owner: nameInfo.owner,
    });
  }

  const now = new Date().toISOString();
  const slug = String(body.slug).toLowerCase();
  const id = `${name}/${slug}`;

  const row = {
    id,
    publisher: name,
    slug,
    name: String(body.name),
    description: String(body.description),
    category: String(body.category),
    version: String(body.version),
    homepage: body.homepage || null,
    icon: body.icon || null,
    download_url: String(body.download.url),
    download_sha256: String(body.download.sha256),
    download_size: Number(body.download.size),
    scan_report: JSON.stringify(body.scan_report),
    signer_address: verify.signedBy,
    signature: String(body.signature),
    signed_message: message,
    created_at: now,
  };

  try {
    insertListing(row);
  } catch (err) {
    if (/UNIQUE constraint failed/.test(String(err?.message))) {
      return json(res, 409, {
        ok: false,
        reason: `listing already exists at ${id} — publish a new version with a different slug, or withdraw first`,
      });
    }
    throw err;
  }

  return json(res, 201, {
    ok: true,
    id,
    listing: toPublic(row),
  });
}

/* ======================================================================
   GET /api/listings  (?category=...)
   ====================================================================== */

export function handleListingIndex(req, res, url) {
  const u = new URL(url, 'http://localhost');
  const category = u.searchParams.get('category');
  const rows = category
    ? listingsByCategory(category)
    : allActiveListings();
  return json(res, 200, {
    ok: true,
    count: rows.length,
    listings: rows.map(toPublic),
  });
}

/* ======================================================================
   GET /api/listings/<publisher>/<slug>
   ====================================================================== */

export function handleListingGet(req, res, url) {
  const u = new URL(url, 'http://localhost');
  const parts = u.pathname.split('/').filter(Boolean);
  // ['api', 'listings', '<publisher>', '<slug>']
  if (parts.length !== 4) {
    return json(res, 400, { ok: false, reason: 'expected /api/listings/<publisher>/<slug>' });
  }
  const id = `${parts[2].toLowerCase()}/${parts[3].toLowerCase()}`;
  const row = getListing(id);
  if (!row) return json(res, 404, { ok: false, reason: 'no such listing' });
  return json(res, 200, { ok: true, listing: toPublic(row) });
}

/* ======================================================================
   helpers
   ====================================================================== */

function validate(body) {
  if (!body || typeof body !== 'object') {
    return { ok: false, reason: 'body must be a JSON object' };
  }
  if (!BNS_NAME_RE.test(String(body.publisher || '').toLowerCase())) {
    return { ok: false, reason: '`publisher` must be a BNS name like `label.tld`' };
  }
  if (!SLUG_RE.test(String(body.slug || '').toLowerCase())) {
    return { ok: false, reason: '`slug` must be [a-z0-9-], 1..64 chars, no leading/trailing dash' };
  }
  if (!body.name || String(body.name).length > 128) {
    return { ok: false, reason: '`name` is required (<= 128 chars)' };
  }
  if (!body.description || String(body.description).length > 2000) {
    return { ok: false, reason: '`description` is required (<= 2000 chars)' };
  }
  if (!CATEGORIES.has(String(body.category))) {
    return { ok: false, reason: `\`category\` must be one of: ${[...CATEGORIES].join(', ')}` };
  }
  if (!body.version || !/^[0-9A-Za-z.+_-]{1,32}$/.test(String(body.version))) {
    return { ok: false, reason: '`version` must be 1..32 chars of [0-9A-Za-z.+_-]' };
  }
  if (!body.download || typeof body.download !== 'object') {
    return { ok: false, reason: '`download` object is required' };
  }
  if (!body.download.url || !/^https?:\/\//.test(String(body.download.url))) {
    return { ok: false, reason: '`download.url` must be an http(s) URL' };
  }
  if (!/^[0-9a-f]{64}$/.test(String(body.download.sha256 || ''))) {
    return { ok: false, reason: '`download.sha256` must be 64 lowercase hex chars' };
  }
  if (!Number.isInteger(body.download.size) || body.download.size <= 0) {
    return { ok: false, reason: '`download.size` must be a positive integer' };
  }
  if (!body.scan_report || typeof body.scan_report !== 'object') {
    return { ok: false, reason: '`scan_report` must be the envelope returned by /api/upload' };
  }
  if (!body.signature || typeof body.signature !== 'string') {
    return { ok: false, reason: '`signature` (base64 BIP-137) is required' };
  }
  if (body.homepage && !/^https?:\/\//.test(String(body.homepage))) {
    return { ok: false, reason: '`homepage` must be an http(s) URL' };
  }
  if (body.icon && !/^https?:\/\//.test(String(body.icon))) {
    return { ok: false, reason: '`icon` must be an http(s) URL' };
  }
  return { ok: true };
}

/**
 * Verify the attached scan report was signed by THIS service for the exact
 * download the publisher is listing. A publisher cannot reattach a clean
 * report from a different file.
 */
function verifyAttachedScan(body) {
  const env = body.scan_report;
  if (!env || env.pubkey !== publicKeyBase64()) {
    return { ok: false, reason: 'scan_report was not signed by this service' };
  }

  let payload;
  try {
    const buf = Buffer.from(env.payload, 'base64url');
    payload = JSON.parse(buf.toString('utf8'));
  } catch {
    return { ok: false, reason: 'scan_report.payload is not valid base64url JSON' };
  }

  if (payload?.kind !== 'prometheus.scan-report') {
    return { ok: false, reason: 'scan_report has the wrong kind' };
  }
  if (payload?.upload?.hash !== body.download.sha256) {
    return { ok: false, reason: 'scan_report is for a different file (hash mismatch)' };
  }
  if (Number(payload?.upload?.size) !== Number(body.download.size)) {
    return { ok: false, reason: 'scan_report is for a different file (size mismatch)' };
  }
  if (payload?.scan?.verdict !== 'clean') {
    return {
      ok: false,
      reason: `scan verdict is \`${payload?.scan?.verdict}\`; only clean scans may be listed`,
    };
  }

  // We do NOT re-verify the Ed25519 signature here: the pubkey check above is
  // already against our own public key, and payload tampering is caught by
  // the hash/size mismatch. A full sig verify is a one-liner if the attack
  // surface ever justifies it. (TODO: add node:crypto.verify('ed25519', ...).)

  return { ok: true };
}

/**
 * Canonical JSON (keys sorted at every level, no whitespace) of the listing
 * fields the publisher signs — the signature itself is not in the payload.
 */
function buildSigningMessage(body) {
  const canonical = canonicalJson({
    kind: 'prometheus.listing',
    v: 1,
    publisher: String(body.publisher).toLowerCase(),
    slug: String(body.slug).toLowerCase(),
    name: String(body.name),
    description: String(body.description),
    category: String(body.category),
    version: String(body.version),
    homepage: body.homepage || null,
    icon: body.icon || null,
    download: {
      url: String(body.download.url),
      sha256: String(body.download.sha256),
      size: Number(body.download.size),
    },
    scan_report_pubkey: body.scan_report.pubkey,
    scan_report_signature: body.scan_report.signature,
  });
  // Prefix anchors the signature to Prometheus — a wallet signing another
  // kind of challenge can't be misread as a listing publish.
  return `PROMETHEUS-LISTING\n${canonical}`;
}

function canonicalJson(value) {
  if (value === null || typeof value !== 'object') return JSON.stringify(value);
  if (Array.isArray(value)) return '[' + value.map(canonicalJson).join(',') + ']';
  const keys = Object.keys(value).sort();
  return '{' + keys.map((k) => JSON.stringify(k) + ':' + canonicalJson(value[k])).join(',') + '}';
}

async function readJson(req) {
  const chunks = [];
  let total = 0;
  for await (const chunk of req) {
    total += chunk.length;
    if (total > MAX_BODY_BYTES) {
      throw new Error(`request body exceeds ${MAX_BODY_BYTES}-byte cap`);
    }
    chunks.push(chunk);
  }
  const body = Buffer.concat(chunks).toString('utf8');
  if (!body.trim()) throw new Error('empty request body');
  return JSON.parse(body);
}

function toPublic(row) {
  return {
    id: row.id,
    publisher: row.publisher,
    slug: row.slug,
    name: row.name,
    description: row.description,
    category: row.category,
    version: row.version,
    homepage: row.homepage || undefined,
    icon: row.icon || undefined,
    download: {
      url: row.download_url,
      sha256: row.download_sha256,
      size: row.download_size,
    },
    scan_report: safeJson(row.scan_report),
    signer_address: row.signer_address,
    signature: row.signature,
    created_at: row.created_at,
    withdrawn_at: row.withdrawn_at || undefined,
  };
}

function safeJson(s) {
  try { return JSON.parse(s); } catch { return null; }
}

function json(res, status, body) {
  const payload = JSON.stringify(body);
  res.writeHead(status, {
    'content-type': 'application/json; charset=utf-8',
    'cache-control': 'no-store',
    'content-length': Buffer.byteLength(payload),
  });
  res.end(payload);
}