New: Minimum Upgrade Score for Custom Formats

Closes #6800

src/NzbDrone.Core/DecisionEngine/Specifications/UpgradableSpecification.cs

@@ -95,6 +95,17 @@ namespace NzbDrone.Core.DecisionEngine.Specifications
                 return UpgradeableRejectReason.CustomFormatCutoff;
             }
 
+            if (newFormatScore < currentFormatScore + qualityProfile.MinUpgradeFormatScore)
+            {
+                _logger.Debug("New item's custom formats [{0}] ({1}) do not meet minimum custom format score increment of {3} required for upgrade, skipping. Existing: [{4}] ({5}).",
+                              newCustomFormats.ConcatToString(),
+                              newFormatScore,
+                              qualityProfile.MinUpgradeFormatScore,
+                              currentCustomFormats.ConcatToString(),
+                              currentFormatScore);
+                return UpgradeableRejectReason.MinCustomFormatScore;
+            }
+
             _logger.Debug("New item's custom formats [{0}] ({1}) improve on [{2}] ({3}), accepting",
                 newCustomFormats.ConcatToString(),
                 newFormatScore,

src/NzbDrone.Core/DecisionEngine/Specifications/UpgradeDiskSpecification.cs

@@ -77,6 +77,9 @@ namespace NzbDrone.Core.DecisionEngine.Specifications
 
                     case UpgradeableRejectReason.CustomFormatScore:
                         return Decision.Reject("Existing file on disk has a equal or higher custom format score: {0}", qualityProfile.CalculateCustomFormatScore(customFormats));
+
+                    case UpgradeableRejectReason.MinCustomFormatScore:
+                        return Decision.Reject("Existing file differential between new release does not meet minimum Custom Format score increment: {0}", qualityProfile.MinFormatScore);
                 }
             }