add reflection API for mods (#185)

1 files changed, 94 insertions, 0 deletions

diff --git a/src/StardewModdingAPI/Framework/Reflection/PrivateField.cs b/src/StardewModdingAPI/Framework/Reflection/PrivateField.cs
new file mode 100644
index 00000000..6e7e3382
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/Reflection/PrivateField.cs
@@ -0,0 +1,94 @@
+using System;
+using System.Reflection;
+using StardewModdingAPI.Reflection;
+
+namespace StardewModdingAPI.Framework.Reflection
+{
+    /// <summary>A private field obtained through reflection.</summary>
+    /// <typeparam name="TValue">The field value type.</typeparam>
+    internal class PrivateField<TValue> : IPrivateField<TValue>
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>The type that has the field.</summary>
+        private readonly Type ParentType;
+
+        /// <summary>The object that has the instance field (if applicable).</summary>
+        private readonly object Parent;
+
+        /// <summary>The display name shown in error messages.</summary>
+        private string DisplayName => $"{this.ParentType.FullName}::{this.FieldInfo.Name}";
+
+
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>The reflection metadata.</summary>
+        public FieldInfo FieldInfo { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="parentType">The type that has the field.</param>
+        /// <param name="obj">The object that has the instance field (if applicable).</param>
+        /// <param name="field">The reflection metadata.</param>
+        /// <param name="isStatic">Whether the field is static.</param>
+        /// <exception cref="ArgumentNullException">The <paramref name="parentType"/> or <paramref name="field"/> is null.</exception>
+        /// <exception cref="ArgumentException">The <paramref name="obj"/> is null for a non-static field, or not null for a static field.</exception>
+        public PrivateField(Type parentType, object obj, FieldInfo field, bool isStatic)
+        {
+            // validate
+            if (parentType == null)
+                throw new ArgumentNullException(nameof(parentType));
+            if (field == null)
+                throw new ArgumentNullException(nameof(field));
+            if (isStatic && obj != null)
+                throw new ArgumentException("A static field cannot have an object instance.");
+            if (!isStatic && obj == null)
+                throw new ArgumentException("A non-static field must have an object instance.");
+
+            // save
+            this.ParentType = parentType;
+            this.Parent = obj;
+            this.FieldInfo = field;
+        }
+
+        /// <summary>Get the field value.</summary>
+        public TValue GetValue()
+        {
+            try
+            {
+                return (TValue)this.FieldInfo.GetValue(this.Parent);
+            }
+            catch (InvalidCastException)
+            {
+                throw new InvalidCastException($"Can't convert the private {this.DisplayName} field from {this.FieldInfo.FieldType.FullName} to {typeof(TValue).FullName}.");
+            }
+            catch (Exception ex)
+            {
+                throw new Exception($"Couldn't get the value of the private {this.DisplayName} field", ex);
+            }
+        }
+
+        /// <summary>Set the field value.</summary>
+        //// <param name="value">The value to set.</param>
+        public void SetValue(TValue value)
+        {
+            try
+            {
+                this.FieldInfo.SetValue(this.Parent, value);
+            }
+            catch (InvalidCastException)
+            {
+                throw new InvalidCastException($"Can't assign the private {this.DisplayName} field a {typeof(TValue).FullName} value, must be compatible with {this.FieldInfo.FieldType.FullName}.");
+            }
+            catch (Exception ex)
+            {
+                throw new Exception($"Couldn't set the value of the private {this.DisplayName} field", ex);
+            }
+        }
+    }
+}