From aa582fb0e1a15de97b48203a7bcaed3c84a4d6c7 Mon Sep 17 00:00:00 2001
From: Nitrous <nathan.alo2000@gmail.com>
Date: Sat, 29 Jan 2022 20:38:12 +0800
Subject: [PATCH] add Alternate Mod

---
 osu.Game.Rulesets.Osu/Mods/OsuModAlternate.cs | 45 +++++++++++
 osu.Game.Rulesets.Osu/OsuRuleset.cs           |  1 +
 osu.Game/Rulesets/Mods/ModAlternate.cs        | 77 +++++++++++++++++++
 3 files changed, 123 insertions(+)
 create mode 100644 osu.Game.Rulesets.Osu/Mods/OsuModAlternate.cs
 create mode 100644 osu.Game/Rulesets/Mods/ModAlternate.cs

diff --git a/osu.Game.Rulesets.Osu/Mods/OsuModAlternate.cs b/osu.Game.Rulesets.Osu/Mods/OsuModAlternate.cs
new file mode 100644
index 0000000000..9a9074ee52
--- /dev/null
+++ b/osu.Game.Rulesets.Osu/Mods/OsuModAlternate.cs
@@ -0,0 +1,45 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Graphics;
+using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.Osu.Objects;
+using osu.Game.Rulesets.UI;
+
+namespace osu.Game.Rulesets.Osu.Mods
+{
+    public class OsuModAlternate : ModAlternate<OsuHitObject, OsuAction>
+    {
+        private const double flash_duration = 1000;
+        private OsuAction? lastActionPressed;
+        private DrawableRuleset<OsuHitObject> ruleset;
+
+        public override void ApplyToDrawableRuleset(DrawableRuleset<OsuHitObject> drawableRuleset)
+        {
+            ruleset = drawableRuleset;
+            base.ApplyToDrawableRuleset(drawableRuleset);
+        }
+
+        protected override void Reset()
+        {
+            lastActionPressed = null;
+        }
+
+        protected override bool OnPressed(OsuAction key)
+        {
+            if (lastActionPressed == key)
+            {
+                ruleset.Cursor.FlashColour(Colour4.Red, flash_duration, Easing.OutQuint);
+                return true;
+            }
+
+            lastActionPressed = key;
+
+            return false;
+        }
+
+        protected override void OnReleased(OsuAction key)
+        {
+        }
+    }
+}
diff --git a/osu.Game.Rulesets.Osu/OsuRuleset.cs b/osu.Game.Rulesets.Osu/OsuRuleset.cs
index 18e4bb259c..7e8974b5ed 100644
--- a/osu.Game.Rulesets.Osu/OsuRuleset.cs
+++ b/osu.Game.Rulesets.Osu/OsuRuleset.cs
@@ -159,6 +159,7 @@ namespace osu.Game.Rulesets.Osu
                         new MultiMod(new OsuModDoubleTime(), new OsuModNightcore()),
                         new OsuModHidden(),
                         new MultiMod(new OsuModFlashlight(), new OsuModBlinds()),
+                        new OsuModAlternate(),
                     };
 
                 case ModType.Conversion:
diff --git a/osu.Game/Rulesets/Mods/ModAlternate.cs b/osu.Game/Rulesets/Mods/ModAlternate.cs
new file mode 100644
index 0000000000..683654f605
--- /dev/null
+++ b/osu.Game/Rulesets/Mods/ModAlternate.cs
@@ -0,0 +1,77 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using osu.Framework.Bindables;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Sprites;
+using osu.Framework.Input.Bindings;
+using osu.Framework.Input.Events;
+using osu.Game.Rulesets.Objects;
+using osu.Game.Rulesets.UI;
+using osu.Game.Screens.Play;
+
+namespace osu.Game.Rulesets.Mods
+{
+    public abstract class ModAlternate : Mod
+    {
+        public override string Name => @"Alternate";
+        public override string Acronym => @"AL";
+        public override string Description => @"Never hit the same key twice!";
+        public override double ScoreMultiplier => 1.0;
+        public override Type[] IncompatibleMods => new[] { typeof(ModAutoplay) };
+        public override ModType Type => ModType.DifficultyIncrease;
+        public override IconUsage? Icon => FontAwesome.Solid.Keyboard;
+    }
+
+    public abstract class ModAlternate<THitObject, TAction> : ModAlternate, IApplicableToDrawableRuleset<THitObject>, IApplicableToPlayer
+        where THitObject : HitObject
+        where TAction : struct
+    {
+        public bool CanIntercept => !isBreakTime.Value;
+
+        private IBindable<bool> isBreakTime;
+
+        public virtual void ApplyToDrawableRuleset(DrawableRuleset<THitObject> drawableRuleset)
+        {
+            drawableRuleset.KeyBindingInputManager.Add(new InputInterceptor(this));
+        }
+
+        public void ApplyToPlayer(Player player)
+        {
+            isBreakTime = player.IsBreakTime.GetBoundCopy();
+            isBreakTime.ValueChanged += e =>
+            {
+                if (e.NewValue)
+                    Reset();
+            };
+        }
+
+        protected abstract void Reset();
+
+        protected abstract bool OnPressed(TAction key);
+
+        protected abstract void OnReleased(TAction key);
+
+        private class InputInterceptor : Component, IKeyBindingHandler<TAction>
+        {
+            private readonly ModAlternate<THitObject, TAction> mod;
+
+            public InputInterceptor(ModAlternate<THitObject, TAction> mod)
+            {
+                this.mod = mod;
+            }
+
+            public bool OnPressed(KeyBindingPressEvent<TAction> e)
+            {
+                return mod.CanIntercept && mod.OnPressed(e.Action);
+            }
+
+            public void OnReleased(KeyBindingReleaseEvent<TAction> e)
+            {
+                if (mod.CanIntercept)
+                    mod.OnReleased(e.Action);
+            }
+        }
+    }
+}