// Milestone A3 demo — download block headers from a real DGB peer,
// chain them by prev-hash, report tip height and hash.
//
// Scope note: this does NOT do PoW validation. That requires
// implementing the 5 DGB algos (SHA256/Scrypt/Skein/Qubit/Odocrypt)
// with per-algo difficulty targets (MultiShield). Separate milestone.
// For now we trust the peer's chain and validate only the prev-hash
// linkage — enough to prove the wire protocol works end-to-end.

import { PeerPool, HeaderChain, encodeGetHeaders, type BlockHeader } from '../src/index.js';

// DGB mainnet genesis block hash (chainparams.cpp). Verified via
// `digibyte-cli getblockhash 0` on a synced Core.
const DGB_GENESIS_HASH = '7497ea1b465eb39f1c8f507bc877078fe016d6fcb6dfad3a64c98dcc6e1e8496';

const RUN_MS = Number(process.argv[2]) || 60_000;
const TARGET_HEADERS = Number(process.argv[3]) || 20_000; // stop when we hit this many

console.log('\n=== DigiByte P2P Header Sync Demo ===\n');
console.log(`Runtime cap:   ${RUN_MS / 1000}s`);
console.log(`Target:        ${TARGET_HEADERS.toLocaleString()} headers\n`);

const pool = new PeerPool({ poolSize: 3, peerOpts: { handshakeTimeoutMs: 10_000 } });
const chain = new HeaderChain();
// Seed with a stub genesis (hash-only) so buildLocator() has an anchor.
// We don't actually have the 80-byte genesis header, but for chaining
// forward only the hash matters.
chain.appendGenesis(
  {
    hash: DGB_GENESIS_HASH,
    prevBlock: '00'.repeat(32),
    merkleRoot: '',
    version: 0,
    timestamp: 0,
    bits: 0,
    nonce: 0,
    raw: Buffer.alloc(80),
  },
  0,
);
let startedRequest = false;
let received = 0;
let batches = 0;
const t0 = Date.now();

// Wait for at least one peer to be ready, then start syncing through it.
pool.on(
  'connect',
  ({ host, port }: { host: string; port: number }) => {
    if (startedRequest) return;
    startedRequest = true;
    console.log(`Using peer ${host}:${port} for header sync.\n`);
    const peer = pool.pickReady()[0];
    if (!peer) return;

    peer.on('headers', (headers: BlockHeader[]) => {
      batches++;
      received += headers.length;
      const res = chain.append(headers);
      const tipStr = chain.tip ? chain.tip.hash.slice(0, 12) + '...' : '(none)';
      console.log(
        `  batch #${batches}: got ${headers.length}, appended ${res.appended}, tip=${chain.tipHeight} ${tipStr}` +
          (res.rejectedAt ? `  [REJECTED: ${res.reason}]` : ''),
      );

      if (chain.tipHeight >= TARGET_HEADERS) {
        finish('target reached');
        return;
      }

      // Request the next batch: locator = our current tip.
      if (headers.length >= 2000) {
        // Peer will send at most 2000 per batch; if it sent 2000 there
        // are likely more. Request next.
        peer.send('getheaders', encodeGetHeaders(70019, chain.buildLocator()));
      } else {
        finish(`peer sent short batch (${headers.length}) — at their tip`);
      }
    });

    // Kick off the sync — locator = [genesis]. Peer sends 2000
    // headers starting from block 1 forward.
    peer.send('getheaders', encodeGetHeaders(70019, chain.buildLocator()));
  },
);

const runTimer = setTimeout(() => finish('runtime cap reached'), RUN_MS);

function finish(reason: string): void {
  clearTimeout(runTimer);
  const elapsed = ((Date.now() - t0) / 1000).toFixed(1);
  const rate = received > 0 ? (received / (Date.now() - t0) * 1000).toFixed(0) : '0';
  console.log('\n--- summary ---');
  console.log(`  reason:          ${reason}`);
  console.log(`  elapsed:         ${elapsed}s`);
  console.log(`  batches:         ${batches}`);
  console.log(`  headers total:   ${received.toLocaleString()}`);
  console.log(`  chain tip:       ${chain.tipHeight.toLocaleString()}`);
  console.log(`  chain size:      ${chain.size.toLocaleString()}`);
  console.log(`  effective rate:  ${rate} headers/sec`);
  if (chain.tip) console.log(`  tip hash:        ${chain.tip.hash}`);
  pool.stop();
  process.exit(0);
}