Rewrite difficulty mod combinations

osu.Game.Rulesets.Catch/CatchRuleset.cs

@@ -84,7 +84,6 @@ namespace osu.Game.Rulesets.Catch
                         new CatchModNoFail(),
                         new MultiMod(new CatchModHalfTime(), new CatchModDaycore())
                     };
-
                 case ModType.DifficultyIncrease:
                     return new Mod[]
                     {
@@ -94,7 +93,6 @@ namespace osu.Game.Rulesets.Catch
                         new CatchModHidden(),
                         new CatchModFlashlight(),
                     };
-
                 case ModType.Special:
                     return new Mod[]
                     {
@@ -103,7 +101,6 @@ namespace osu.Game.Rulesets.Catch
                         null,
                         new MultiMod(new CatchModAutoplay(), new ModCinema()),
                     };
-
                 default:
                     return new Mod[] { };
             }

osu.Game.Rulesets.Mania/Difficulty/ManiaDifficultyCalculator.cs

@@ -7,6 +7,7 @@ using System.Linq;
 using osu.Game.Beatmaps;
 using osu.Game.Rulesets.Difficulty;
 using osu.Game.Rulesets.Mania.Beatmaps;
+using osu.Game.Rulesets.Mania.Mods;
 using osu.Game.Rulesets.Mania.Objects;
 using osu.Game.Rulesets.Mods;
 
@@ -141,5 +142,22 @@ namespace osu.Game.Rulesets.Mania.Difficulty
 
             return difficulty;
         }
+
+        protected override Mod[] DifficultyAdjustmentMods => new Mod[]
+        {
+            new ManiaModDoubleTime(),
+            new ManiaModHalfTime(),
+            new ManiaModEasy(),
+            new ManiaModHardRock(),
+            new ManiaModKey1(),
+            new ManiaModKey2(),
+            new ManiaModKey3(),
+            new ManiaModKey4(),
+            new ManiaModKey5(),
+            new ManiaModKey6(),
+            new ManiaModKey7(),
+            new ManiaModKey8(),
+            new ManiaModKey9(),
+        };
     }
 }

osu.Game.Rulesets.Mania/ManiaRuleset.cs

@@ -147,85 +147,6 @@ namespace osu.Game.Rulesets.Mania
                         new ManiaModMirror(),
                         new MultiMod(new ManiaModAutoplay(), new ModCinema()),
                     };
-                case ModType.DifficultyCalculation:
-                    var mods = new List<Mod>();
-                    foreach (var keyMod in key_mods)
-                    {
-                        mods.AddRange(new[]
-                        {
-                            keyMod,
-                            new MultiMod
-                            {
-                                Mods = new[]
-                                {
-                                    keyMod,
-                                    new ManiaModDoubleTime(),
-                                }
-                            },
-                            new MultiMod
-                            {
-                                Mods = new[]
-                                {
-                                    keyMod,
-                                    new ManiaModHalfTime(),
-                                }
-                            },
-                            new MultiMod
-                            {
-                                Mods = new[]
-                                {
-                                    keyMod,
-                                    new ManiaModEasy(),
-                                }
-                            },
-                            new MultiMod
-                            {
-                                Mods = new[]
-                                {
-                                    keyMod,
-                                    new ManiaModHardRock(),
-                                }
-                            },
-                            new MultiMod
-                            {
-                                Mods = new[]
-                                {
-                                    keyMod,
-                                    new ManiaModEasy(),
-                                    new ManiaModDoubleTime(),
-                                }
-                            },
-                            new MultiMod
-                            {
-                                Mods = new[]
-                                {
-                                    keyMod,
-                                    new ManiaModEasy(),
-                                    new ManiaModHalfTime(),
-                                }
-                            },
-                            new MultiMod
-                            {
-                                Mods = new[]
-                                {
-                                    keyMod,
-                                    new ManiaModHardRock(),
-                                    new ManiaModDoubleTime(),
-                                }
-                            },
-                            new MultiMod
-                            {
-                                Mods = new[]
-                                {
-                                    keyMod,
-                                    new ManiaModHardRock(),
-                                    new ManiaModHalfTime(),
-                                }
-                            },
-                        });
-                    }
-
-                    return mods.ToArray();
                 default:
                     return new Mod[] { };
             }

osu.Game.Rulesets.Mania/Mods/ManiaKeyMod.cs

@@ -1,6 +1,8 @@
 // Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
+using System;
+using System.Linq;
 using osu.Game.Beatmaps;
 using osu.Game.Rulesets.Mania.Beatmaps;
 using osu.Game.Rulesets.Mods;
@@ -24,5 +26,18 @@ namespace osu.Game.Rulesets.Mania.Mods
 
             mbc.TargetColumns = KeyCount;
         }
+
+        public override Type[] IncompatibleMods => new[]
+        {
+            typeof(ManiaModKey1),
+            typeof(ManiaModKey2),
+            typeof(ManiaModKey3),
+            typeof(ManiaModKey4),
+            typeof(ManiaModKey5),
+            typeof(ManiaModKey6),
+            typeof(ManiaModKey7),
+            typeof(ManiaModKey8),
+            typeof(ManiaModKey9),
+        }.Except(new[] { GetType() }).ToArray();
     }
 }

osu.Game.Rulesets.Osu/Difficulty/OsuDifficultyCalculator.cs

@@ -8,6 +8,7 @@ using osu.Game.Rulesets.Difficulty;
 using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Osu.Difficulty.Preprocessing;
 using osu.Game.Rulesets.Osu.Difficulty.Skills;
+using osu.Game.Rulesets.Osu.Mods;
 using osu.Game.Rulesets.Osu.Objects;
 
 namespace osu.Game.Rulesets.Osu.Difficulty
@@ -71,5 +72,13 @@ namespace osu.Game.Rulesets.Osu.Difficulty
 
             return starRating;
         }
+
+        protected override Mod[] DifficultyAdjustmentMods => new Mod[]
+        {
+            new OsuModDoubleTime(),
+            new OsuModHalfTime(),
+            new OsuModEasy(),
+            new OsuModHardRock(),
+        };
     }
 }

osu.Game.Rulesets.Osu/OsuRuleset.cs

@@ -113,47 +113,6 @@ namespace osu.Game.Rulesets.Osu
                         new MultiMod(new OsuModAutoplay(), new ModCinema()),
                         new OsuModTarget(),
                     };
-                case ModType.DifficultyCalculation:
-                    return new Mod[]
-                    {
-                        new MultiMod(),
-                        new OsuModDoubleTime(),
-                        new OsuModHalfTime(),
-                        new OsuModEasy(),
-                        new OsuModHardRock(),
-                        new MultiMod
-                        {
-                            Mods = new Mod[]
-                            {
-                                new OsuModEasy(),
-                                new OsuModDoubleTime(),
-                            }
-                        },
-                        new MultiMod
-                        {
-                            Mods = new Mod[]
-                            {
-                                new OsuModEasy(),
-                                new OsuModHalfTime(),
-                            }
-                        },
-                        new MultiMod
-                        {
-                            Mods = new Mod[]
-                            {
-                                new OsuModHardRock(),
-                                new OsuModDoubleTime(),
-                            }
-                        },
-                        new MultiMod
-                        {
-                            Mods = new Mod[]
-                            {
-                                new OsuModHardRock(),
-                                new OsuModHalfTime(),
-                            }
-                        },
-                    };
                 default:
                     return new Mod[] { };
             }

osu.Game.Rulesets.Taiko/Difficulty/TaikoDifficultyCalculator.cs

@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using osu.Game.Beatmaps;
 using osu.Game.Rulesets.Difficulty;
 using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.Taiko.Mods;
 using osu.Game.Rulesets.Taiko.Objects;
 
 namespace osu.Game.Rulesets.Taiko.Difficulty
@@ -62,6 +63,14 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
             return starRating;
         }
 
+        protected override Mod[] DifficultyAdjustmentMods => new Mod[]
+        {
+            new TaikoModDoubleTime(),
+            new TaikoModHalfTime(),
+            new TaikoModEasy(),
+            new TaikoModHardRock(),
+        };
+
         private bool calculateStrainValues()
         {
             // Traverse hitObjects in pairs to calculate the strain value of NextHitObject from the strain value of CurrentHitObject and environment.

osu.Game.Rulesets.Taiko/TaikoRuleset.cs

@@ -103,47 +103,6 @@ namespace osu.Game.Rulesets.Taiko
                         null,
                         new MultiMod(new TaikoModAutoplay(), new ModCinema()),
                     };
-                case ModType.DifficultyCalculation:
-                    return new Mod[]
-                    {
-                        new MultiMod(),
-                        new TaikoModDoubleTime(),
-                        new TaikoModHalfTime(),
-                        new TaikoModEasy(),
-                        new TaikoModHardRock(),
-                        new MultiMod
-                        {
-                            Mods = new Mod[]
-                            {
-                                new TaikoModEasy(),
-                                new TaikoModDoubleTime(),
-                            }
-                        },
-                        new MultiMod
-                        {
-                            Mods = new Mod[]
-                            {
-                                new TaikoModEasy(),
-                                new TaikoModHalfTime(),
-                            }
-                        },
-                        new MultiMod
-                        {
-                            Mods = new Mod[]
-                            {
-                                new TaikoModHardRock(),
-                                new TaikoModDoubleTime(),
-                            }
-                        },
-                        new MultiMod
-                        {
-                            Mods = new Mod[]
-                            {
-                                new TaikoModHardRock(),
-                                new TaikoModHalfTime(),
-                            }
-                        },
-                    };
                 default:
                     return new Mod[] { };
             }

osu.Game.Tests/NonVisual/DifficultyAdjustmentModCombinationsTest.cs

@@ -0,0 +1,152 @@
+// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+using System.Collections.Generic;
+using NUnit.Framework;
+using osu.Game.Rulesets.Difficulty;
+using osu.Game.Rulesets.Mods;
+
+namespace osu.Game.Tests.NonVisual
+{
+    [TestFixture]
+    public class DifficultyAdjustmentModCombinationsTest
+    {
+        [Test]
+        public void TestNoMods()
+        {
+            var combinations = new TestDifficultyCalculator().CreateDifficultyAdjustmentModCombinations();
+
+            Assert.AreEqual(1, combinations.Length);
+            Assert.IsTrue(combinations[0] is NoModMod);
+        }
+
+        [Test]
+        public void TestSingleMod()
+        {
+            var combinations = new TestDifficultyCalculator(new ModA()).CreateDifficultyAdjustmentModCombinations();
+
+            Assert.AreEqual(2, combinations.Length);
+            Assert.IsTrue(combinations[0] is NoModMod);
+            Assert.IsTrue(combinations[1] is ModA);
+        }
+
+        [Test]
+        public void TestDoubleMod()
+        {
+            var combinations = new TestDifficultyCalculator(new ModA(), new ModB()).CreateDifficultyAdjustmentModCombinations();
+
+            Assert.AreEqual(4, combinations.Length);
+            Assert.IsTrue(combinations[0] is NoModMod);
+            Assert.IsTrue(combinations[1] is ModA);
+            Assert.IsTrue(combinations[2] is MultiMod);
+            Assert.IsTrue(combinations[3] is ModB);
+
+            Assert.IsTrue(((MultiMod)combinations[2]).Mods[0] is ModA);
+            Assert.IsTrue(((MultiMod)combinations[2]).Mods[1] is ModB);
+        }
+
+        [Test]
+        public void TestIncompatibleMods()
+        {
+            var combinations = new TestDifficultyCalculator(new ModA(), new ModIncompatibleWithA()).CreateDifficultyAdjustmentModCombinations();
+
+            Assert.AreEqual(3, combinations.Length);
+            Assert.IsTrue(combinations[0] is NoModMod);
+            Assert.IsTrue(combinations[1] is ModA);
+            Assert.IsTrue(combinations[2] is ModIncompatibleWithA);
+        }
+
+        [Test]
+        public void TestDoubleIncompatibleMods()
+        {
+            var combinations = new TestDifficultyCalculator(new ModA(), new ModB(), new ModIncompatibleWithA(), new ModIncompatibleWithAAndB()).CreateDifficultyAdjustmentModCombinations();
+
+            Assert.AreEqual(8, combinations.Length);
+            Assert.IsTrue(combinations[0] is NoModMod);
+            Assert.IsTrue(combinations[1] is ModA);
+            Assert.IsTrue(combinations[2] is MultiMod);
+            Assert.IsTrue(combinations[3] is ModB);
+            Assert.IsTrue(combinations[4] is MultiMod);
+            Assert.IsTrue(combinations[5] is ModIncompatibleWithA);
+            Assert.IsTrue(combinations[6] is MultiMod);
+            Assert.IsTrue(combinations[7] is ModIncompatibleWithAAndB);
+
+            Assert.IsTrue(((MultiMod)combinations[2]).Mods[0] is ModA);
+            Assert.IsTrue(((MultiMod)combinations[2]).Mods[1] is ModB);
+            Assert.IsTrue(((MultiMod)combinations[4]).Mods[0] is ModB);
+            Assert.IsTrue(((MultiMod)combinations[4]).Mods[1] is ModIncompatibleWithA);
+            Assert.IsTrue(((MultiMod)combinations[6]).Mods[0] is ModIncompatibleWithA);
+            Assert.IsTrue(((MultiMod)combinations[6]).Mods[1] is ModIncompatibleWithAAndB);
+        }
+
+        [Test]
+        public void TestIncompatibleThroughBaseType()
+        {
+            var combinations = new TestDifficultyCalculator(new ModAofA(), new ModIncompatibleWithAofA()).CreateDifficultyAdjustmentModCombinations();
+
+            Assert.AreEqual(3, combinations.Length);
+            Assert.IsTrue(combinations[0] is NoModMod);
+            Assert.IsTrue(combinations[1] is ModAofA);
+            Assert.IsTrue(combinations[2] is ModIncompatibleWithAofA);
+        }
+
+        private class ModA : Mod
+        {
+            public override string Name => nameof(ModA);
+            public override string ShortenedName => nameof(ModA);
+            public override double ScoreMultiplier => 1;
+
+            public override Type[] IncompatibleMods => new[] { typeof(ModIncompatibleWithA), typeof(ModIncompatibleWithAAndB) };
+        }
+
+        private class ModB : Mod
+        {
+            public override string Name => nameof(ModB);
+            public override string ShortenedName => nameof(ModB);
+            public override double ScoreMultiplier => 1;
+
+            public override Type[] IncompatibleMods => new[] { typeof(ModIncompatibleWithAAndB) };
+        }
+
+        private class ModIncompatibleWithA : Mod
+        {
+            public override string Name => $"Incompatible With {nameof(ModA)}";
+            public override string ShortenedName => $"Incompatible With {nameof(ModA)}";
+            public override double ScoreMultiplier => 1;
+
+            public override Type[] IncompatibleMods => new[] { typeof(ModA) };
+        }
+
+        private class ModAofA : ModA
+        {
+        }
+
+        private class ModIncompatibleWithAofA : ModIncompatibleWithA
+        {
+            // Incompatible through base type
+        }
+
+        private class ModIncompatibleWithAAndB : Mod
+        {
+            public override string Name => $"Incompatible With {nameof(ModA)} and {nameof(ModB)}";
+            public override string ShortenedName => $"Incompatible With {nameof(ModA)} and {nameof(ModB)}";
+            public override double ScoreMultiplier => 1;
+
+            public override Type[] IncompatibleMods => new[] { typeof(ModA), typeof(ModB) };
+        }
+
+        private class TestDifficultyCalculator : DifficultyCalculator
+        {
+            public TestDifficultyCalculator(params Mod[] mods)
+                : base(null)
+            {
+                DifficultyAdjustmentMods = mods;
+            }
+
+            public override double Calculate(Dictionary<string, double> categoryDifficulty = null) => throw new NotImplementedException();
+
+            protected override Mod[] DifficultyAdjustmentMods { get; }
+        }
+    }
+}

osu.Game/Rulesets/Difficulty/DifficultyCalculator.cs

@@ -1,6 +1,7 @@
 // Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using osu.Framework.Extensions.IEnumerableExtensions;
@@ -36,6 +37,44 @@ namespace osu.Game.Rulesets.Difficulty
         {
         }
 
+        /// <summary>
+        /// Creates all <see cref="Mod"/> combinations which adjust the <see cref="Beatmap"/> difficulty.
+        /// </summary>
+        public Mod[] CreateDifficultyAdjustmentModCombinations()
+        {
+            return createDifficultyAdjustmentModCombinations(Enumerable.Empty<Mod>(), DifficultyAdjustmentMods).ToArray();
+
+            IEnumerable<Mod> createDifficultyAdjustmentModCombinations(IEnumerable<Mod> currentSet, Mod[] adjustmentSet, int currentSetCount = 0, int adjustmentSetStart = 0)
+            {
+                // Initial-case: Empty current set
+                if (currentSetCount == 0)
+                    yield return new NoModMod();
+
+                if (currentSetCount == 1)
+                    yield return currentSet.Single();
+
+                if (currentSetCount > 1)
+                    yield return new MultiMod(currentSet.ToArray());
+
+                // Apply mods in the adjustment set recursively. Using the entire adjustment set would result in duplicate multi-mod mod
+                // combinations in further recursions, so a moving subset is used to eliminate this effect
+                for (int i = adjustmentSetStart; i < adjustmentSet.Length; i++)
+                {
+                    var adjustmentMod = adjustmentSet[i];
+                    if (currentSet.Any(c => c.IncompatibleMods.Any(m => m.IsInstanceOfType(adjustmentMod))))
+                        continue;
+
+                    foreach (var combo in createDifficultyAdjustmentModCombinations(currentSet.Append(adjustmentMod), adjustmentSet, currentSetCount + 1, i + 1))
+                        yield return combo;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Retrieves all <see cref="Mod"/>s which adjust the <see cref="Beatmap"/> difficulty.
+        /// </summary>
+        protected virtual Mod[] DifficultyAdjustmentMods => Array.Empty<Mod>();
+
         public abstract double Calculate(Dictionary<string, double> categoryDifficulty = null);
     }
 }

osu.Game/Rulesets/Mods/ModType.cs

@@ -7,7 +7,6 @@ namespace osu.Game.Rulesets.Mods
     {
         DifficultyReduction,
         DifficultyIncrease,
-        Special,
+        Special
-        DifficultyCalculation
     }
 }