From 348fc5f33fd5818203560a041834e5a0380eee80 Mon Sep 17 00:00:00 2001
From: Peter Stuifzand <peter@stuifzand.eu>
Date: Sun, 2 Sep 2018 11:12:07 +0200
Subject: [PATCH] StablePartition the channels based on unread count

---
 cmd/eksterd/memory.go |  5 ++++
 pkg/util/algorithm.go | 59 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)
 create mode 100644 pkg/util/algorithm.go

diff --git a/cmd/eksterd/memory.go b/cmd/eksterd/memory.go
index b3a41e0..90b38a2 100644
--- a/cmd/eksterd/memory.go
+++ b/cmd/eksterd/memory.go
@@ -34,6 +34,7 @@ import (
 
 	"p83.nl/go/ekster/pkg/fetch"
 	"p83.nl/go/ekster/pkg/microsub"
+	"p83.nl/go/ekster/pkg/util"
 
 	"github.com/gomodule/redigo/redis"
 	"willnorris.com/go/microformats"
@@ -185,6 +186,10 @@ func (b *memoryBackend) ChannelsGetList() ([]microsub.Channel, error) {
 			}
 		}
 	}
+	util.StablePartition(channels, 0, len(channels), func(i int) bool {
+		return channels[i].Unread > 0
+	})
+
 	return channels, nil
 }
 
diff --git a/pkg/util/algorithm.go b/pkg/util/algorithm.go
new file mode 100644
index 0000000..b409518
--- /dev/null
+++ b/pkg/util/algorithm.go
@@ -0,0 +1,59 @@
+package util
+
+import "reflect"
+
+func Rotate(a interface{}, f, k, l int) int {
+	swapper := reflect.Swapper(a)
+	if f == k {
+		return l
+	}
+	if k == l {
+		return f
+	}
+	next := k
+
+	for {
+		swapper(f, next)
+		f++
+		next++
+		if f == k {
+			k = next
+		}
+		if next == l {
+			break
+		}
+	}
+
+	ret := f
+	for next = k; next != l; {
+		swapper(f, next)
+		f++
+		next++
+		if f == k {
+			k = next
+		} else if next == l {
+			next = k
+		}
+	}
+	return ret
+}
+
+func StablePartition(a interface{}, f, l int, p func(i int) bool) int {
+	n := l - f
+
+	if n == 0 {
+		return f
+	}
+
+	if n == 1 {
+		t := f
+		if p(f) {
+			t += 1
+		}
+		return t
+	}
+
+	m := f + (n / 2)
+
+	return Rotate(a, StablePartition(a, f, m, p), m, StablePartition(a, m, l, p))
+}