Make barback more package-aware.

pkg/barback/lib/src/utils.dart

Index: pkg/barback/lib/src/utils.dart
diff --git a/pkg/barback/lib/src/utils.dart b/pkg/barback/lib/src/utils.dart
index c4ab3a3f3ee0a0ce2a7031f03cbab012208b193d..94659bc88b4a16559e7ceab1ab186ac28d33b7d2 100644
--- a/pkg/barback/lib/src/utils.dart
+++ b/pkg/barback/lib/src/utils.dart
@@ -4,6 +4,8 @@
 
 library barback.utils;
 
+import 'dart:async';
+
 /// Converts a number in the range [0-255] to a two digit hex string.
 ///
 /// For example, given `255`, returns `ff`.
@@ -12,4 +14,86 @@ String byteToHex(int byte) {
 
   const DIGITS = "0123456789abcdef";
   return DIGITS[(byte ~/ 16) % 16] + DIGITS[byte % 16];
-}
+}
+
+/// Group the elements in [iter] by the value returned by [fn].
+///
+/// This returns a map whose keys are the return values of [fn] and whose values
+/// are lists of each element in [iter] for which [fn] returned that key.
+Map groupBy(Iterable iter, fn(element)) {
+  var map = {};
+  for (var element in iter) {
+    var list = map.putIfAbsent(fn(element), () => []);
+    list.add(element);
+  }
+  return map;
+}
+
+/// Flattens nested lists inside an iterable into a single list containing only
+/// non-list elements.
+List flatten(Iterable nested) {
+  var result = [];
+  helper(list) {
+    for (var element in list) {
+      if (element is List) {

[Bob Nystrom, 2013/07/11 23:03:40]

is Iterable

[nweiz, 2013/07/15 22:11:44]

That seems a little dangerous. A lot of things can extend Iterable that may not
want to be flattened.

[Bob Nystrom, 2013/07/16 17:36:01]

Conversely, a lot of things extend iterable that do want to be flattened. I
would expect [foo.where(...)] to flatten the results of that .where() call but
this won't do that.

[nweiz, 2013/07/16 19:39:39]

That case is more straightforward to detect. If the user uses [where] or
whatever it'll be immediately clear that the code isn't working as intended,
whereas an otherwise innocuous class could suddenly start implementing Iterable
and change the behavior of the code.

For reference, Ruby's List#flatten method only works with Arrays, not
Enumerables.

+        helper(element);
+      } else {
+        result.add(element);
+      }
+    }
+  }
+  helper(nested);
+  return result;
+}
+
+/// Passes each key/value pair in [map] to [fn] and returns a new [Map] whose
+/// values are the return values of [fn].
+Map mapMapValues(Map map, fn(key, value)) =>
+  new Map.fromIterable(map.keys, value: (key) => fn(key, map[key]));
+
+/// Merges [streams] into a single stream that emits events from all sources.
+Stream mergeStreams(Iterable<Stream> streams) {
+  streams = streams.toList();
+  var doneCount = 0;
+  var controller = new StreamController(sync: true);

[Bob Nystrom, 2013/07/11 23:03:40]

Document why "sync: true"

[nweiz, 2013/07/15 22:11:44]

Done.

+
+  for (var stream in streams) {
+    stream.listen((value) {
+      controller.add(value);
+    }, onError: (error) {
+      controller.addError(error);
+    }, onDone: () {
+      doneCount++;
+      if (doneCount == streams.length) controller.close();
+    });
+  }
+
+  return controller.stream;
+}
+
+/// Prepends each line in [text] with [prefix]. If [firstPrefix] is passed, the
+/// first line is prefixed with that instead.
+String prefixLines(String text, {String prefix: '| ', String firstPrefix}) {
+  var lines = text.split('\n');
+  if (firstPrefix == null) {
+    return lines.map((line) => '$prefix$line').join('\n');
+  }
+
+  var firstLine = "$firstPrefix${lines.first}";
+  lines = lines.skip(1).map((line) => '$prefix$line').toList();
+  lines.insert(0, firstLine);
+  return lines.join('\n');
+}
+
+/// Returns a [Future] that completes after pumping the event queue [times]
+/// times. By default, this should pump the event queue enough times to allow
+/// any code to run, as long as it's not waiting on some external event.
+Future pumpEventQueue([int times=20]) {
+  if (times == 0) return new Future.value();
+  // We use a delayed future to allow runAsync events to finish. The
+  // Future.value or Future() constructors use runAsync themselves and would
+  // therefore not wait for runAsync callbacks that are scheduled after invoking
+  // this method.
+  return new Future.delayed(Duration.ZERO, () => pumpEventQueue(times - 1));
+}
+