Add sort.Interface implementation for Feed (#141)

Order Feed.Items by oldest to newest publish time.

Author: grafoo

feed.go

@@ -10,6 +10,8 @@ import (
 // Feed is the universal Feed type that atom.Feed
 // and rss.Feed gets translated to. It represents
 // a web feed.
+// Sorting with sort.Sort will order the Items by
+// oldest to newest publish time.
 type Feed struct {
 	Title           string                   `json:"title,omitempty"`
 	Description     string                   `json:"description,omitempty"`
@@ -82,3 +84,21 @@ type Enclosure struct {
 	Length string `json:"length,omitempty"`
 	Type   string `json:"type,omitempty"`
 }
+
+// Len returns the length of Items.
+func (f Feed) Len() int {
+	return len(f.Items)
+}
+
+// Less compares PublishedParsed of Items[i], Items[k]
+// and returns true if Items[i] is less than Items[k].
+func (f Feed) Less(i, k int) bool {
+	return f.Items[i].PublishedParsed.Before(
+		*f.Items[k].PublishedParsed,
+	)
+}
+
+// Swap swaps Items[i] and Items[k].
+func (f Feed) Swap(i, k int) {
+	f.Items[i], f.Items[k] = f.Items[k], f.Items[i]
+}

feed_test.go

@@ -0,0 +1,50 @@
+package gofeed_test
+
+import (
+	"sort"
+	"testing"
+	"time"
+
+	"github.com/mmcdole/gofeed"
+)
+
+func TestFeedSort(t *testing.T) {
+	oldestItem := &gofeed.Item{
+		PublishedParsed: &[]time.Time{time.Unix(0, 0)}[0],
+	}
+	inbetweenItem := &gofeed.Item{
+		PublishedParsed: &[]time.Time{time.Unix(1, 0)}[0],
+	}
+	newestItem := &gofeed.Item{
+		PublishedParsed: &[]time.Time{time.Unix(2, 0)}[0],
+	}
+
+	feed := gofeed.Feed{
+		Items: []*gofeed.Item{
+			newestItem,
+			oldestItem,
+			inbetweenItem,
+		},
+	}
+	expected := gofeed.Feed{
+		Items: []*gofeed.Item{
+			oldestItem,
+			inbetweenItem,
+			newestItem,
+		},
+	}
+
+	sort.Sort(feed)
+
+	for i, item := range feed.Items {
+		if !item.PublishedParsed.Equal(
+			*expected.Items[i].PublishedParsed,
+		) {
+			t.Errorf(
+				"Item PublishedParsed = %s; want %s",
+				item.PublishedParsed,
+				expected.Items[i].PublishedParsed,
+			)
+		}
+	}
+}