New: Calculate custom formats on demand

src/NzbDrone.Core/CustomFormats/CustomFormatsComparer.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using NzbDrone.Common.EnsureThat;
+using NzbDrone.Core.Profiles;
+
+namespace NzbDrone.Core.CustomFormats
+{
+    public class CustomFormatsComparer : IComparer<List<CustomFormat>>
+    {
+        private readonly Profile _profile;
+
+        public CustomFormatsComparer(Profile profile)
+        {
+            Ensure.That(profile, () => profile).IsNotNull();
+            Ensure.That(profile.Items, () => profile.Items).HasItems();
+
+            _profile = profile;
+        }
+
+        public int Compare(List<CustomFormat> left, List<CustomFormat> right)
+        {
+            var leftIndicies = _profile.GetIndices(left);
+            var rightIndicies = _profile.GetIndices(right);
+
+            // Summing powers of two ensures last format always trumps, but we order correctly if we
+            // have extra formats lower down the list
+            var leftTotal = leftIndicies.Select(x => Math.Pow(2, x)).Sum();
+            var rightTotal = rightIndicies.Select(x => Math.Pow(2, x)).Sum();
+
+            return leftTotal.CompareTo(rightTotal);
+        }
+    }
+}