From 9fa34273082e588f8876c4f4d1f658f4b3590e92 Mon Sep 17 00:00:00 2001
From: James Mills <prologic@shortcircuit.net.au>
Date: Wed, 25 Mar 2020 16:22:41 +1000
Subject: Add trending and ability to sort playlist by views

---
 media/playlist.go | 49 +++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 39 insertions(+), 10 deletions(-)

(limited to 'media/playlist.go')

diff --git a/media/playlist.go b/media/playlist.go
index cf8edcf..ccfcc79 100644
--- a/media/playlist.go
+++ b/media/playlist.go
@@ -1,19 +1,48 @@
 package media
 
-// Playlist holds an array of videos capable of sorting by Timestamp.
+import (
+	"sort"
+)
+
 type Playlist []*Video
 
-// Len returns length of array (for sorting).
-func (p Playlist) Len() int {
-	return len(p)
+// By is the type of a "less" function that defines the ordering of its Playlist arguments.
+type By func(p1, p2 *Video) bool
+
+// Sort is a method on the function type, By, that sorts the argument slice according to the function.
+func (by By) Sort(pl Playlist) {
+	ps := &playlistSorter{
+		pl: pl,
+		by: by, // The Sort method's receiver is the function (closure) that defines the sort order.
+	}
+	sort.Sort(ps)
+}
+
+// playlistSorter joins a By function and a slice of Playlist to be sorted.
+type playlistSorter struct {
+	pl Playlist
+	by func(p1, p2 *Video) bool // Closure used in the Less method.
+}
+
+// Len is part of sort.Interface.
+func (s *playlistSorter) Len() int {
+	return len(s.pl)
+}
+
+// Swap is part of sort.Interface.
+func (s *playlistSorter) Swap(i, j int) {
+	s.pl[i], s.pl[j] = s.pl[j], s.pl[i]
+}
+
+// Less is part of sort.Interface. It is implemented by calling the "by" closure in the sorter.
+func (s *playlistSorter) Less(i, j int) bool {
+	return s.by(s.pl[i], s.pl[j])
 }
 
-// Swap swaps two values in array by index (for sorting).
-func (p Playlist) Swap(i, j int) {
-	p[i], p[j] = p[j], p[i]
+func SortByTimestamp(v1, v2 *Video) bool {
+	return v1.Timestamp.After(v2.Timestamp)
 }
 
-// Less returns true if p[i] Timestamp is after p[j] (for sorting).
-func (p Playlist) Less(i, j int) bool {
-	return p[i].Timestamp.After(p[j].Timestamp)
+func SortByViews(v1, v2 *Video) bool {
+	return v1.Views < v2.Views
 }
-- 
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