Add utility AI (#806)

Co-authored-by: Pieter-Jan Briers <pieterjan.briers@gmail.com>
Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>
Co-authored-by: Pieter-Jan Briers <pieterjan.briers+git@gmail.com>

Content.Server/AI/Utility/Curves/BoolCurve.cs

@@ -0,0 +1,13 @@
+namespace Content.Server.AI.Utility.Curves
+{
+    /// <summary>
+    /// For stuff that's a simple 0.0f or 1.0f
+    /// </summary>
+    public struct BoolCurve : IResponseCurve
+    {
+        public float GetResponse(float score)
+        {
+            return score > 0.0f ? 1.0f : 0.0f;
+        }
+    }
+}

Content.Server/AI/Utility/Curves/IResponseCurve.cs

@@ -0,0 +1,10 @@
+namespace Content.Server.AI.Utility.Curves
+{
+    /// <summary>
+    /// Using an interface also lets us define preset curves that can be re-used
+    /// </summary>
+    public interface IResponseCurve
+    {
+        float GetResponse(float score);
+    }
+}

Content.Server/AI/Utility/Curves/InverseBoolCurve.cs

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+namespace Content.Server.AI.Utility.Curves
+{
+    public struct InverseBoolCurve : IResponseCurve
+    {
+        public float GetResponse(float score)
+        {
+            // ReSharper disable once CompareOfFloatsByEqualityOperator
+            return score == 0.0f ? 1.0f : 0.0f;
+        }
+    }
+}

Content.Server/AI/Utility/Curves/LogisticCurve.cs

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+using System;
+
+namespace Content.Server.AI.Utility.Curves
+{
+    public struct LogisticCurve : IResponseCurve
+    {
+        private readonly float _slope;
+
+        private readonly float _exponent;
+        // Vertical shift
+        private readonly float _yOffset;
+        // Horizontal shift
+        private readonly float _xOffset;
+
+        public LogisticCurve(float slope, float exponent, float yOffset, float xOffset)
+        {
+            _slope = slope;
+            _exponent = exponent;
+            _yOffset = yOffset;
+            _xOffset = xOffset;
+        }
+
+        public float GetResponse(float score)
+        {
+            return _exponent * (1 / (1 + (float) Math.Pow(Math.Log(1000) * _slope, -1 * score + _xOffset))) + _yOffset;
+        }
+    }
+}

Content.Server/AI/Utility/Curves/QuadraticCurve.cs

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+using System;
+
+namespace Content.Server.AI.Utility.Curves
+{
+    /// <summary>
+    /// Also Linear
+    /// </summary>
+    public struct QuadraticCurve : IResponseCurve
+    {
+        private readonly float _slope;
+
+        private readonly float _exponent;
+        // Vertical shift
+        private readonly float _yOffset;
+        // Horizontal shift
+        private readonly float _xOffset;
+
+        public QuadraticCurve(float slope, float exponent, float yOffset, float xOffset)
+        {
+            _slope = slope;
+            _exponent = exponent;
+            _yOffset = yOffset;
+            _xOffset = xOffset;
+        }
+
+        public float GetResponse(float score)
+        {
+            return _slope * (float) Math.Pow(score - _xOffset, _exponent) + _yOffset;
+        }
+    }
+}