1 files changed, 78 insertions, 0 deletions
diff --git a/src/SMAPI/Framework/Input/KeyboardStateBuilder.cs b/src/SMAPI/Framework/Input/KeyboardStateBuilder.cs
new file mode 100644
index 00000000..f95a28bf
--- /dev/null
+++ b/src/SMAPI/Framework/Input/KeyboardStateBuilder.cs
@@ -0,0 +1,78 @@
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.Xna.Framework.Input;
+
+namespace StardewModdingAPI.Framework.Input
+{
+    /// <summary>Manages keyboard state.</summary>
+    internal class KeyboardStateBuilder : IInputStateBuilder<KeyboardStateBuilder, KeyboardState>
+    {
+        /*********
+        ** Fields
+        *********/
+        /// <summary>The underlying keyboard state.</summary>
+        private KeyboardState? State;
+
+        /// <summary>The pressed buttons.</summary>
+        private readonly HashSet<Keys> PressedButtons = new HashSet<Keys>();
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="state">The initial state, or <c>null</c> to get the latest state.</param>
+        public KeyboardStateBuilder(KeyboardState? state = null)
+        {
+            this.Reset(state);
+        }
+
+        /// <summary>Reset the tracked state.</summary>
+        /// <param name="state">The state from which to reset, or <c>null</c> to get the latest state.</param>
+        public KeyboardStateBuilder Reset(KeyboardState? state = null)
+        {
+            this.State = state ??= Keyboard.GetState();
+
+            this.PressedButtons.Clear();
+            foreach (var button in state.Value.GetPressedKeys())
+                this.PressedButtons.Add(button);
+
+            return this;
+        }
+
+        /// <summary>Override the states for a set of buttons.</summary>
+        /// <param name="overrides">The button state overrides.</param>
+        public KeyboardStateBuilder OverrideButtons(IDictionary<SButton, SButtonState> overrides)
+        {
+            foreach (var pair in overrides)
+            {
+                if (pair.Key.TryGetKeyboard(out Keys key))
+                {
+                    this.State = null;
+
+                    if (pair.Value.IsDown())
+                        this.PressedButtons.Add(key);
+                    else
+                        this.PressedButtons.Remove(key);
+                }
+            }
+
+            return this;
+        }
+
+        /// <summary>Get the currently pressed buttons.</summary>
+        public IEnumerable<SButton> GetPressedButtons()
+        {
+            foreach (Keys key in this.PressedButtons)
+                yield return key.ToSButton();
+        }
+
+        /// <summary>Get the equivalent state.</summary>
+        public KeyboardState GetState()
+        {
+            return
+                this.State
+                ?? (this.State = new KeyboardState(this.PressedButtons.ToArray())).Value;
+        }
+    }
+}