Add date formatting and parsing code.

lib/i18n/_date_format_helpers.dart

+/**

[Emily Fortuna, 2012/08/06 22:43:00]

copyright notice at top

[Alan Knight, 2012/08/08 00:47:44]

Oops. Done.

+ * A class for holding onto the data for a date so that it can be built
+ * up incrementally.
+ */
+class _DateBuilder {
+  int year = 0,
+      month = 0,
+      day = 0,
+      hour = 0,
+      minute = 0,
+      second = 0,
+      fractionalSecond = 0;
+  bool pm = false;
+  bool utc = false;
+
+  // Functions that exist just be closurized so we can pass them to a general

[Emily Fortuna, 2012/08/06 22:43:00]

missing word in here "exist just be closurized"

[Alan Knight, 2012/08/08 00:47:44]

Done.

+  // method.
+  void setYear(x) { year = x; }
+  void setMonth(x) { month = x; }
+  void setDay(x) { day = x; }
+  void setHour(x) { hour = x; }
+  void setMinute(x) { minute = x; }
+  void setSecond(x) { second = x; }
+  void setFractionalSecond(x) { fractionalSecond = x; }
+
+  /**
+   * Return a date built using our values. If no date portion is set,
+   * use today's date, as otherwise the constructor will fail.
+   */
+  Date asDate() {
+    if (year == 0 || month == 0 || day == 0) {
+      var today = new Date.now();
+      if (year == 0) year = today.year;
+      if (month == 0) month = today.month;
+      if (day == 0) day = today.day;
+    }
+
+    // TODO(alanknight): Validate the date, especially for things which
+    // can crash the VM, e.g. large month values.
+    return new Date(
+      year,

[Emily Fortuna, 2012/08/06 22:43:00]

indent 4 spaces here

[Alan Knight, 2012/08/08 00:47:44]

Done.

+      month,
+      day,
+      pm ? hour + 12 : hour,
+      minute,
+      second,
+      fractionalSecond,
+      utc);
+  }
+}
+
+/**
+ * A simple and not particularly general stream class to make parsing
+ * dates from strings simpler. It is general enough to operate on either
+ * lists or strings.
+ */
+class _Stream {
+  var contents;
+  int index = 0;
+
+  _Stream(this.contents);
+
+  bool atEnd() => index >= contents.length;
+
+  Dynamic next() => contents[index++];
+
+  /**
+   * Return the next [howMany] items, or as many as there are remaining.
+   * Advance the stream by that many positions.
+   */
+  read([howMany = 1]) {
+    var result = peek(howMany);
+    index += howMany;
+    return result;
+  }
+
+  /**
+   *  Return the next [howMany] items, or as many as there are remaining.
+   * Does not modify the stream position.
+   */
+  peek([howMany = 1]) {
+    var result;
+    if (contents is String) {
+      result = contents.substring(
+        index,

[Emily Fortuna, 2012/08/06 22:43:00]

4 spaces indent if it's after an opening (

[Alan Knight, 2012/08/08 00:47:44]

Done.

+        Math.min(index + howMany, contents.length));
+    } else {
+      // Assume List
+      result = contents.getRange(index,howMany);
+    }
+    return result;
+  }
+
+  /** Return the remaining contents of the stream */
+  rest() => peek(contents.length - index);
+
+  /** Find the index of the first element for which [f] returns true.*/

[Emily Fortuna, 2012/08/06 22:43:00]

mention this has the side effect of advancing the steam's index

[Alan Knight, 2012/08/08 00:47:44]

Done.

+  int findIndex(Function f) {
+    while (!atEnd()) {
+      if (f(next())) return index - 1;
+    }
+    return null;
+  }
+
+  /**
+   * Find the indexes of all the elements for which [f] returns true.
+   * Also leaves the stream positioned at the end.
+   */
+  List findIndexes(Function f) {
+    var results = [];
+    while (!atEnd()) {
+      if (f(next())) results.add(index - 1);
+    }
+    return results;
+  }
+
+  /**
+   * Assuming that the contents are characters, read as many digits as we
+   * can see and then return the corresponding integer. Advance the stream.
+   */
+  int nextInteger() {
+    var validDigits = '0123456789';
+    var digits = [];
+    while (!atEnd() && (validDigits.contains(peek()))) {
+      digits.add(next().charCodeAt(0));
+    }
+    return Math.parseInt(new String.fromCharCodes(digits));
+  }
+}
+
+/**
+ * Exception indicating that we could not parse a particular string into a
+ * Date according to the specified pattern.
+ */
+class FormatException implements Exception {

[Emily Fortuna, 2012/08/06 22:43:00]

We now have a FormatException as a subclass of the main Exception class! So we
can get rid of this. (Hooray!)

[Alan Knight, 2012/08/08 00:47:44]

Done.

+  final _Stream input;
+  final _DateFormatField field;
+
+  const FormatException(this.input, this.field);
+
+  toString() => "FormatException: $field matching ${input.rest}";
+}