1 files changed, 82 insertions, 0 deletions
diff --git a/src/SMAPI/Framework/ModData/ModDataField.cs b/src/SMAPI/Framework/ModData/ModDataField.cs
new file mode 100644
index 00000000..fa8dd6d0
--- /dev/null
+++ b/src/SMAPI/Framework/ModData/ModDataField.cs
@@ -0,0 +1,82 @@
+using System.Linq;
+
+namespace StardewModdingAPI.Framework.ModData
+{
+    /// <summary>A versioned mod metadata field.</summary>
+    internal class ModDataField
+    {
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>The field key.</summary>
+        public ModDataFieldKey Key { get; }
+
+        /// <summary>The field value.</summary>
+        public string Value { get; }
+
+        /// <summary>Whether this field should only be applied if it's not already set.</summary>
+        public bool IsDefault { get; }
+
+        /// <summary>The lowest version in the range, or <c>null</c> for all past versions.</summary>
+        public ISemanticVersion LowerVersion { get; }
+
+        /// <summary>The highest version in the range, or <c>null</c> for all future versions.</summary>
+        public ISemanticVersion UpperVersion { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="key">The field key.</param>
+        /// <param name="value">The field value.</param>
+        /// <param name="isDefault">Whether this field should only be applied if it's not already set.</param>
+        /// <param name="lowerVersion">The lowest version in the range, or <c>null</c> for all past versions.</param>
+        /// <param name="upperVersion">The highest version in the range, or <c>null</c> for all future versions.</param>
+        public ModDataField(ModDataFieldKey key, string value, bool isDefault, ISemanticVersion lowerVersion, ISemanticVersion upperVersion)
+        {
+            this.Key = key;
+            this.Value = value;
+            this.IsDefault = isDefault;
+            this.LowerVersion = lowerVersion;
+            this.UpperVersion = upperVersion;
+        }
+
+        /// <summary>Get whether this data field applies for the given manifest.</summary>
+        /// <param name="manifest">The mod manifest.</param>
+        public bool IsMatch(IManifest manifest)
+        {
+            return
+                manifest?.Version != null // ignore invalid manifest
+                && (!this.IsDefault || !this.HasFieldValue(manifest, this.Key))
+                && (this.LowerVersion == null || !manifest.Version.IsOlderThan(this.LowerVersion))
+                && (this.UpperVersion == null || !manifest.Version.IsNewerThan(this.UpperVersion));
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Get whether a manifest field has a meaningful value for the purposes of enforcing <see cref="IsDefault"/>.</summary>
+        /// <param name="manifest">The mod manifest.</param>
+        /// <param name="key">The field key matching <see cref="ModDataFieldKey"/>.</param>
+        private bool HasFieldValue(IManifest manifest, ModDataFieldKey key)
+        {
+            switch (key)
+            {
+                // update key
+                case ModDataFieldKey.UpdateKey:
+                    return manifest.UpdateKeys != null && manifest.UpdateKeys.Any();
+
+                // non-manifest fields
+                case ModDataFieldKey.AlternativeUrl:
+                case ModDataFieldKey.StatusReasonPhrase:
+                case ModDataFieldKey.Status:
+                    return false;
+
+                default:
+                    return false;
+            }
+        }
+    }
+}