تا به حال تعجب کرده اید که چگونه می توان لیست قیمت صاف و زنده را برای سهام و رمزنگاری قدرت داد؟

class MarketSymbol {
  final String id; // e.g., "BTCUSDT"
  final String baseAsset; // "BTC"
  final String quoteAsset; // "USDT"
  final SymbolSnapshot? snapshot; // Live price stats
  MarketSymbol({required this.id, required this.baseAsset, required this.quoteAsset, this.snapshot});
}

class SymbolSnapshot {
  final String symbol;
  final double lastPrice; // Latest price
  final double priceChangePercent; // 24hr change
  // ... openPrice, highPrice, etc.
}

class SymbolTickerEvent {
  final String eventType; // "24hrTicker"
  final int eventTime; // Timestamp
  final String symbol; // "BTCUSDT"
  final double closePrice; // Latest price
  final double openPrice;
  final double highPrice;
  final double lowPrice;
  final double totalTradedBaseAssetVolume; // Base volume
  final double totalTradedQuoteAssetVolume; // Quote volume

  SymbolSnapshot get snapshot => SymbolSnapshot(
    symbol: symbol,
    lastPrice: closePrice,
    priceChangePercent: (closePrice - openPrice) / openPrice * 100,
    // ... other fields
  );
}

void _onSymbolTickerEvent(SymbolTickerEvent event) {
  final symbol = state.symbolMap[event.symbol];
  if (symbol != null && symbol.snapshot?.lastPrice != event.snapshot.lastPrice) {
    state = state.copyWith(
      symbolMap: {
        ...state.symbolMap,
        symbol.id: symbol.copyWith(snapshot: event.snapshot),
      },
    );
  }
}

class MarketSymbolRow extends ConsumerWidget {
  const MarketSymbolRow({required this.symbolId});
  static const double height = 60;

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final symbol = ref.watch(marketVMProvider.select((state) => state.symbolMap[symbolId]!));
    // Returns fancy UI with a height of 60 px
  }
}

void _updateVisibleSymbols() {
  final symbolIds = ref.read(marketVMProvider.select((state) => state.symbolIds));

  final viewportSymbolRows = (_viewportKey.height / MarketSymbolRow.height).ceil(); // Visible rows
  final firstIndex = max(_scrollController.offset ~/ MarketSymbolRow.height, 0); // Top row
  final lastIndex = min(firstIndex + viewportSymbolRows, symbolIds.length - 1); // Bottom row
  final newVisibleSymbolIds = symbolIds.toList().sublist(firstIndex, lastIndex + 1).toSet();

  if (newVisibleSymbolIds.difference(_visibleSymbolIds).isNotEmpty) {
    _visibleSymbolIds = newVisibleSymbolIds;
    ref.read(marketVMProvider.notifier).syncPriceTracking(_visibleSymbolIds);
  }
}

void syncPriceTracking(Set<String> symbolIds) async {
  final symbolIdsToUnsubscribe = _currentSubscribedSymbolIds.where((s) => !symbolIds.contains(s)).toList();
  final symbolIdsToSubscribe = symbolIds.where((s) => !_currentSubscribedSymbolIds.contains(s)).toList();

  if (symbolIdsToUnsubscribe.isNotEmpty) _marketRepository.unsubscribeSymbolMiniTickerStream(symbols: symbolIdsToUnsubscribe);
  if (symbolIdsToSubscribe.isNotEmpty) {
    await _marketRepository.subscribeSymbolMiniTickerStream(symbols: symbolIdsToSubscribe);
    _currentSubscribedSymbolIds = symbolIds;
  }
}

void _onScroll() {
  _debounceTimer?.cancel();
  if ((_scrollController.offset - _lastOffset).abs() < 30) return; // Skip small nudges

  _debounceTimer = Timer(Duration(milliseconds: 300), () {
    _lastOffset = _scrollController.offset;
    _updateVisibleSymbols(); // Update after a breather
  });
}

ListView.builder(
  key: _viewportKey,
  controller: _scrollController,
  itemExtent: MarketSymbolRow.height, // Locked at 60px
  itemCount: symbolIds.length,
  itemBuilder: (context, index) {
    final symbolId = symbolIds[index];
    return MarketSymbolRow(symbolId: symbolId);
  },
)