import 'dart:convert';

import 'package:bip340/bip340.dart' as bip340;
import 'package:crypto/crypto.dart';

/// A minimal Nostr event (NIP-01): enough to build, id, sign and serialise
/// NIP-99 classified listings. Throwaway — production would use a vetted client.
class NostrEvent {
  NostrEvent({
    required this.pubkey,
    required this.createdAt,
    required this.kind,
    required this.tags,
    required this.content,
    this.id = '',
    this.sig = '',
  });

  final String pubkey; // x-only hex
  final int createdAt; // unix seconds
  final int kind;
  final List<List<String>> tags;
  final String content;
  String id;
  String sig;

  /// NIP-01 id: sha256 of the compact JSON array
  /// `[0, pubkey, created_at, kind, tags, content]`.
  String computeId() {
    final serialized = jsonEncode([0, pubkey, createdAt, kind, tags, content]);
    final digest = sha256.convert(utf8.encode(serialized));
    return digest.toString(); // lower-case hex
  }

  /// Fills [id] and [sig] (BIP340 Schnorr over the id) with [privateKeyHex].
  void signWith(String privateKeyHex, {String? auxRandHex}) {
    id = computeId();
    // Deterministic aux in the spike (derived from id) so round-trip tests are
    // reproducible; production uses fresh randomness per BIP340.
    final aux = auxRandHex ?? id;
    sig = bip340.sign(privateKeyHex, id, aux);
  }

  /// Verifies the signature against [pubkey]. Cross-checks that a real relay /
  /// peer would accept what we produced.
  bool verify() => id == computeId() && bip340.verify(pubkey, id, sig);

  Map<String, dynamic> toJson() => {
    'id': id,
    'pubkey': pubkey,
    'created_at': createdAt,
    'kind': kind,
    'tags': tags,
    'content': content,
    'sig': sig,
  };

  static NostrEvent fromJson(Map<String, dynamic> j) => NostrEvent(
    id: j['id'] as String,
    pubkey: j['pubkey'] as String,
    createdAt: j['created_at'] as int,
    kind: j['kind'] as int,
    tags: (j['tags'] as List)
        .map((t) => (t as List).map((e) => e as String).toList())
        .toList(),
    content: j['content'] as String,
    sig: j['sig'] as String,
  );

  /// First value of the first tag named [name], or null.
  String? tag(String name) {
    for (final t in tags) {
      if (t.isNotEmpty && t[0] == name && t.length > 1) return t[1];
    }
    return null;
  }
}