From fe85a304079421c43aced7ae6777d76e05053c35 Mon Sep 17 00:00:00 2001
From: DualFroz <me@dualfroz.com>
Date: Wed, 26 Aug 2026 12:34:54 +0200
Subject: [PATCH] feat(replay): add key mask input encoding

---
 src/Chip8.Replay/KeyMask.cs | 143 ++++++++++++++++++++++++++++++++++++
 1 file changed, 143 insertions(+)
 create mode 100644 src/Chip8.Replay/KeyMask.cs

diff --git a/src/Chip8.Replay/KeyMask.cs b/src/Chip8.Replay/KeyMask.cs
new file mode 100644
index 0000000..b4c2b2a
--- /dev/null
+++ b/src/Chip8.Replay/KeyMask.cs
@@ -0,0 +1,143 @@
+using System;
+using System.Text;
+
+namespace Chip8.Replay;
+
+public readonly struct KeyMask : IEquatable<KeyMask>
+{
+    public const int keyCount = 16;
+    public const ushort fullMask = 0xFFFF;
+
+    public ushort bits { get; }
+
+    public KeyMask(ushort bits)
+    {
+        this.bits = bits;
+    }
+
+    public static KeyMask empty => new KeyMask(0);
+
+    public bool isEmpty => bits == 0;
+
+    public int pressedCount
+    {
+        get
+        {
+            int count = 0;
+            for (int key = 0; key < keyCount; key++)
+            {
+                if ((bits & (1 << key)) != 0)
+                {
+                    count++;
+                }
+            }
+            return count;
+        }
+    }
+
+    public bool isPressed(int key) => (bits & (1 << (key & 0xF))) != 0;
+
+    public KeyMask withPressed(int key) => new KeyMask((ushort)(bits | (1 << (key & 0xF))));
+
+    public KeyMask withReleased(int key) => new KeyMask((ushort)(bits & ~(1 << (key & 0xF))));
+
+    public KeyMask with(int key, bool pressed) => pressed ? withPressed(key) : withReleased(key);
+
+    public KeyMask union(KeyMask other) => new KeyMask((ushort)(bits | other.bits));
+
+    public KeyMask intersect(KeyMask other) => new KeyMask((ushort)(bits & other.bits));
+
+    public static KeyMask fromKeys(params int[] keys)
+    {
+        ushort acc = 0;
+        foreach (int key in keys)
+        {
+            acc |= (ushort)(1 << (key & 0xF));
+        }
+        return new KeyMask(acc);
+    }
+
+    public static KeyMask fromKeypad(bool[] keypad)
+    {
+        ushort acc = 0;
+        for (int key = 0; key < keyCount && key < keypad.Length; key++)
+        {
+            if (keypad[key])
+            {
+                acc |= (ushort)(1 << key);
+            }
+        }
+        return new KeyMask(acc);
+    }
+
+    public void applyTo(bool[] keypad)
+    {
+        for (int key = 0; key < keyCount && key < keypad.Length; key++)
+        {
+            keypad[key] = (bits & (1 << key)) != 0;
+        }
+    }
+
+    public string toHex() => bits.ToString("X4", System.Globalization.CultureInfo.InvariantCulture);
+
+    public string toKeyList()
+    {
+        if (bits == 0)
+        {
+            return "-";
+        }
+
+        var builder = new StringBuilder();
+        for (int key = 0; key < keyCount; key++)
+        {
+            if ((bits & (1 << key)) != 0)
+            {
+                if (builder.Length > 0)
+                {
+                    builder.Append(',');
+                }
+                builder.Append(key.ToString("X1", System.Globalization.CultureInfo.InvariantCulture));
+            }
+        }
+        return builder.ToString();
+    }
+
+    public static KeyMask parseHex(string text)
+    {
+        ushort value = ushort.Parse(text, System.Globalization.NumberStyles.HexNumber, System.Globalization.CultureInfo.InvariantCulture);
+        return new KeyMask(value);
+    }
+
+    public static KeyMask parseKeyList(string text)
+    {
+        if (text == "-" || text.Length == 0)
+        {
+            return empty;
+        }
+
+        ushort acc = 0;
+        foreach (string chunk in text.Split(','))
+        {
+            string trimmed = chunk.Trim();
+            if (trimmed.Length == 0)
+            {
+                continue;
+            }
+            int key = Convert.ToInt32(trimmed, 16);
+            acc |= (ushort)(1 << (key & 0xF));
+        }
+        return new KeyMask(acc);
+    }
+
+    public bool Equals(KeyMask other) => bits == other.bits;
+
+    public override bool Equals(object? obj) => obj is KeyMask other && Equals(other);
+
+    public override int GetHashCode() => bits;
+
+    public override string ToString() => "KeyMask(" + toKeyList() + ")";
+
+    public static bool operator ==(KeyMask left, KeyMask right) => left.bits == right.bits;
+
+    public static bool operator !=(KeyMask left, KeyMask right) => left.bits != right.bits;
+}