Add a simple prototype "terminal" example.

sky/examples/terminal/terminal.sky

Index: sky/examples/terminal/terminal.sky
diff --git a/sky/examples/terminal/terminal.sky b/sky/examples/terminal/terminal.sky
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+<!--
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+-->
+<import src="/sky/framework/sky-element.sky" />
+<import src="/sky/framework/sky-scrollable.sky" />
+<sky-element>
+<template>
+  <style>
+    #control {
+      height: -webkit-fill-available;
+      background-color: black;
+      color: rgb(255, 191, 0);
+      font-family: 'Courier', 'monospace';
+    }
+    span {
+      white-space: nowrap;
+    }
+  </style>
+  <sky-scrollable id="control" contenteditable />
+</template>
+<script>
+import 'dart:async';
+import 'dart:core';
+import 'dart:sky';
+import 'package:examples/echo_terminal/terminal_client.mojom.dart' as terminal;
+import '/sky/framework/embedder.dart';
+import 'terminal_display.dart';
+import 'terminal_file_impl.dart';
+
+// Implements the <terminal> element, which implements a "terminal display". Has
+// an |url| attribute, whose value should be a Mojo app that provides the
+// |terminal.TerminalClient| service.
+@Tagname('terminal')
+class TerminalDisplayImpl extends SkyElement implements TerminalDisplay {
+  Element _control;
+
+  // Queue of unconsumed input (keystrokes), with the head at index 0.
+  // Keystrokes end up here if there's no reader (i.e., |getChar()|) pending,
+  // i.e., if |_readerQueue| is empty. Invariant: At most one of |_inputQueue|
+  // and |_readerQueue| may be nonempty at any given time.
+  List<int> _inputQueue;
+
+  // Queue of things waiting for input, with the head at index 0. If a keystroke
+  // is received and this is nonempty, the head is given that keystroke (and
+  // dequeued).
+  List<Completer<int>> _readerQueue;
+
+  TerminalDisplayImpl()
+      : _inputQueue = new List<int>(),
+        _readerQueue = new List<Completer<int>>() {
+  }
+
+  void shadowRootReady() {
+    _control = shadowRoot.getElementById('control');
+    _control.addEventListener('keypress', _handleKeyPress);
+
+    // Initialize with the first line.
+    _newLine();
+
+    _connect(getAttribute('url'));
+  }
+
+  void _handleKeyPress(KeyboardEvent event) {
+    // TODO(vtl): Add "echo" mode; do |putChar(event.charCode);| if echo is on.
+
+    if (_readerQueue.isEmpty) {
+      _inputQueue.add(event.charCode);
+    } else {
+      _readerQueue.removeAt(0).complete(event.charCode);
+    }
+
+    event.preventDefault();
+  }
+
+  void _newLine() {
+    _control.appendChild(document.createElement('span'));
+  }
+
+  // TODO(vtl): Should we always auto-connect? Should there be facilities for
+  // programmatically connecting? (What if the |url| attribute isn't set?)
+  void _connect(String url) {
+    var terminalClient = new terminal.TerminalClientProxy.unbound();
+    embedder.connectToService(url, terminalClient);
+    terminalClient.ptr.connectToTerminal(new TerminalFileImpl(this).stub);
+    terminalClient.close();
+  }
+
+  // |TerminalDisplay| implementation:
+
+  @override
+  void putChar(int byte) {
+    if (byte == 10 || byte == 13) {
+      _newLine();
+      return;
+    }
+    _control.lastChild.textContent += new String.fromCharCode(byte);
+  }
+
+  @override
+  Future<int> getChar() async {
+    if (_inputQueue.isNotEmpty) {
+      return new Future.value(_inputQueue.removeAt(0));
+    }
+
+    var completer = new Completer<int>();
+    _readerQueue.add(completer);
+    return completer.future;
+  }
+}
+
+_init(script) => register(script, TerminalDisplayImpl);
+</script>
+</sky-element>