Command line parsing utilities. Not yet used in observatory.

runtime/observatory/lib/src/cli/command.dart

Index: runtime/observatory/lib/src/cli/command.dart
diff --git a/runtime/observatory/lib/src/cli/command.dart b/runtime/observatory/lib/src/cli/command.dart
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+++ b/runtime/observatory/lib/src/cli/command.dart
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+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+part of cli;
+
+// Splits a line into a list of string args.
+List<String> _splitLine(String line) {
+  var args = line.split(' ').where((arg) {
+      return arg != ' ' && arg != '';
+    }).toList();
+  return args;
+}
+
+// Concatenates the first 'count' args.
+String _concatArgs(List<String> args, int count) {
+  if (count == 0) {
+    return '';
+  }
+  return '${args.sublist(0, count).join(" ")} ';
+}
+
+// Shared functionality for RootCommand and Command.
+abstract class _CommandBase {
+  _CommandBase(List<Command> children) {
+    assert(children != null);
+    _children.addAll(children);
+    for (var child in _children) {
+      child._parent = this;
+    }
+  }
+
+  // A command may optionally have sub-commands.
+  List<Command> _children = [];
+
+  _CommandBase _parent;
+  int get _depth => (_parent == null ? 0 : _parent._depth + 1);
+
+  // Override in subclasses to provide command-specific argument completion.
+  //
+  // Given a list of arguments to this command, provide a list of
+  // possible completions for those arguments.
+  List<String> complete(List<String> args) => [];
+
+  // Override in subclasses to provide command-specific execution.
+  Future run(List<String> args);
+
+  // Returns a list of local subcommands which match the args.
+  List<Command> _matchLocal(String arg, bool preferExact) {
+    var matches = new List<Command>();
+    for (var child in _children) {
+      if (child.name.startsWith(arg)) {
+        if (preferExact && child.name == arg) {
+          return [child];
+        }
+        matches.add(child);
+      }
+    }
+    return matches;
+  }
+
+  // Returns the set of commands could be triggered by a list of
+  // arguments.
+  List<Command> _match(List<String> args, bool preferExact) {
+    if (args.isEmpty) {
+      return [];
+    }    
+    bool lastArg = (args.length == 1);
+    var matches = _matchLocal(args[0], !lastArg || preferExact);
+    if (matches.isEmpty) {
+      return [];
+    } else if (matches.length == 1) {
+      var childMatches =  matches[0]._match(args.sublist(1), preferExact);
+      if (childMatches.isEmpty) {
+        return matches;
+      } else {
+        return childMatches;
+      }
+    } else {
+      return matches;
+    }
+  }
+
+  // Builds a list of completions for this command.
+  List<String> _buildCompletions(List<String> args,
+                                 bool addEmptyString) {
+    var completions = complete(args.sublist(_depth, args.length));
+    if (addEmptyString && completions.isEmpty && args[args.length - 1] == '') {
+      // Special case allowance for an empty particle at the end of
+      // the command.
+      completions = [''];
+    }
+    var prefix = _concatArgs(args, _depth);
+    return completions.map((str) => '${prefix}${str}').toList();
+  }
+
+}
+
+// The root of a tree of commands.
+class RootCommand extends _CommandBase {
+  RootCommand(List<Command> children) : super(children);
+
+  // Provides a list of possible completions for a line of text.
+  List<String> completeCommand(String line) {
+    var args = _splitLine(line);
+    bool showAll = line.endsWith(' ') || args.isEmpty;
+    if (showAll) {
+      // Adding an empty string to the end causes us to match all
+      // subcommands of the last command.
+      args.add('');
+    }
+    var commands =  _match(args, false);
+    if (commands.isEmpty) {
+      // No matching commands.
+      return [];
+    }
+    int matchLen = commands[0]._depth;
+    if (matchLen < args.length) {
+      // We were able to find a command which matches a prefix of the
+      // args, but not the full list.
+      if (commands.length == 1) {
+        // The matching command is unique.  Attempt to provide local
+        // argument completion from the command.
+        return commands[0]._buildCompletions(args, true);
+      } else {
+        // An ambiguous prefix match leaves us nowhere.  The user is
+        // typing a bunch of stuff that we don't know how to complete.
+        return [];
+      }
+    }
+
+    // We have found a set of commands which match all of the args.
+    // Return the completions strings.
+    var prefix = _concatArgs(args, args.length - 1);
+    var completions =
+        commands.map((command) => '${prefix}${command.name} ').toList();
+    if (showAll && matchLen == args.length) {
+      // If we are showing all possiblities, also include local
+      // completions for the parent command.
+      completions.addAll(commands[0]._parent._buildCompletions(args, false));
+    }
+    return completions;
+  }
+
+  // Runs a command.
+  Future runCommand(String line) {
+    var args = _splitLine(line);
+    var commands =  _match(args, true);
+    if (commands.isEmpty) {
+      // TODO(turnidge): Add a proper exception class for this.
+      return new Future.error('notfound');
+    } else if (commands.length == 1) {
+      return commands[0].run(args.sublist(commands[0]._depth));
+    } else {
+      // TODO(turnidge): Add a proper exception class for this.
+      return new Future.error('ambiguous');
+    }
+  }
+
+  Future run(List<String> args) {
+    throw 'should-not-execute-the-root-command';
+  }
+
+  toString() => 'RootCommand';
+}
+
+// A node in the command tree.
+abstract class Command extends _CommandBase {
+  Command(this.name, List<Command> children) : super(children);
+
+  final name;
+
+  toString() => 'Command(${name})';
+}