Load data for StocksApp incrementally

Previously we would spend a lot of time during startup processing all 3k stocks
in the data set. This CL breaks the data up into 100 stock chunks and loads
them incrementally off the network. A future CL will switch to loading them on
demand.

R=ojan@chromium.org

Review URL: https://codereview.chromium.org/1038533002

examples/stocks-fn/lib/stock_app.dart

@@ -34,18 +34,16 @@ class StocksApp extends App {
     ${typography.white.title};'''
   );
 
-  List<Stock> _sortedStocks = [];
+  StockDataFetcher _stockDataFetcher;
+  List<Stock> _stocks = [];
   bool _isSearching = false;
   bool _isShowingMenu = false;
   String _searchQuery;
 
   StocksApp() : super() {
-    fetchStockOracle().then((oracle) {
+    _stockDataFetcher = new StockDataFetcher((StockData data) {
       setState(() {
-        _sortedStocks = oracle.stocks;
-        trace('StocksApp::sortStocks', () {
-          _sortedStocks.sort((a, b) => a.symbol.compareTo(b.symbol));
-        });
+        data.appendTo(_stocks);
       });
     });
   }
@@ -155,7 +153,7 @@ class StocksApp extends App {
 
     return new Scaffold(
       actionBar: actionBar,
-      content: new Stocklist(stocks: _sortedStocks, query: _searchQuery),
+      content: new Stocklist(stocks: _stocks, query: _searchQuery),
       fab: new FloatingActionButton(
         content: new Icon(type: 'content/add_white', size: 24), level: 3),
       drawer: drawer,

examples/stocks-fn/lib/stock_data.dart

@@ -12,6 +12,8 @@ import 'package:sky/framework/net/fetch.dart';
 // "Symbol","Name","LastSale","MarketCap","IPOyear","Sector","industry","Summary Quote",
 // Data in stock_data.json
 
+final Random _rng = new Random();
+
 class Stock {
   String symbol;
   String name;
@@ -31,36 +33,41 @@ class Stock {
     symbol = fields[0];
     name = fields[1];
     marketCap = fields[4];
-    var rng = new Random();
-    percentChange = (rng.nextDouble() * 20) - 10;
+    percentChange = (_rng.nextDouble() * 20) - 10;
   }
 }
 
-class StockOracle {
-  List<Stock> stocks;
+class StockData {
+  List<List<String>> _data;
 
-  StockOracle(this.stocks);
+  StockData(this._data);
 
-  StockOracle.fromCompanyList(List<List<String>> list) {
-    stocks = list.map((fields) => new Stock.fromFields(fields)).toList();
+  void appendTo(List<Stock> stocks) {
+    for (List<String> fields in _data)
+      stocks.add(new Stock.fromFields(fields));
   }
+}
 
-  Stock lookupBySymbol(String symbol) {
-    this.stocks.forEach((stock) {
-      if (stock.symbol == symbol)
-        return stock;
-    });
-    return null;
+typedef void StockDataCallback(StockData data);
+const _kChunkCount = 30;
+
+class StockDataFetcher {
+  int _currentChunk = 0;
+  final StockDataCallback callback;
+
+  StockDataFetcher(this.callback) {
+    _fetchNextChunk();
   }
-}
 
-Future<StockOracle> fetchStockOracle() async {
-  Response response = await fetch('lib/stock_data.json');
+  void _fetchNextChunk() {
+    fetch('data/stock_data_${_currentChunk++}.json').then((Response response) {
+      String json = response.bodyAsString();
+      JsonDecoder decoder = new JsonDecoder();
+
+      callback(new StockData(decoder.convert(json)));
 
-  return trace('stocks::fetchStockOracle', () {
-    String json = response.bodyAsString();
-    JsonDecoder decoder = new JsonDecoder();
-    var companyList = decoder.convert(json);
-    return new StockOracle.fromCompanyList(companyList);
-  });
+      if (_currentChunk < _kChunkCount)
+        _fetchNextChunk();
+    });
+  }
 }