encapsulate common JSON converter code, improve parse errors (#423)

1 files changed, 77 insertions, 0 deletions

diff --git a/src/SMAPI/Framework/Serialisation/SimpleReadOnlyConverter.cs b/src/SMAPI/Framework/Serialisation/SimpleReadOnlyConverter.cs
new file mode 100644
index 00000000..9308456b
--- /dev/null
+++ b/src/SMAPI/Framework/Serialisation/SimpleReadOnlyConverter.cs
@@ -0,0 +1,77 @@
+using System;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+using StardewModdingAPI.Framework.Exceptions;
+
+namespace StardewModdingAPI.Framework.Serialisation
+{
+    /// <summary>The base implementation for simplified converters which deserialise <typeparamref name="T"/> without overriding serialisation.</summary>
+    /// <typeparam name="T">The type to deserialise.</typeparam>
+    internal abstract class SimpleReadOnlyConverter<T> : JsonConverter
+    {
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>Whether this converter can write JSON.</summary>
+        public override bool CanWrite => false;
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Get whether this instance can convert the specified object type.</summary>
+        /// <param name="objectType">The object type.</param>
+        public override bool CanConvert(Type objectType)
+        {
+            return objectType == typeof(T);
+        }
+
+        /// <summary>Writes the JSON representation of the object.</summary>
+        /// <param name="writer">The JSON writer.</param>
+        /// <param name="value">The value.</param>
+        /// <param name="serializer">The calling serializer.</param>
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            throw new InvalidOperationException("This converter does not write JSON.");
+        }
+
+        /// <summary>Reads the JSON representation of the object.</summary>
+        /// <param name="reader">The JSON reader.</param>
+        /// <param name="objectType">The object type.</param>
+        /// <param name="existingValue">The object being read.</param>
+        /// <param name="serializer">The calling serializer.</param>
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            string path = reader.Path;
+            switch (reader.TokenType)
+            {
+                case JsonToken.StartObject:
+                    return this.ReadObject(JObject.Load(reader), path);
+                case JsonToken.String:
+                    return this.ReadString(JToken.Load(reader).Value<string>(), path);
+                default:
+                    throw new SParseException($"Can't parse {typeof(T).Name} from {reader.TokenType} (path: {reader.Path}).");
+            }
+        }
+
+
+        /*********
+        ** Protected methods
+        *********/
+        /// <summary>Read a JSON object.</summary>
+        /// <param name="obj">The JSON object to read.</param>
+        /// <param name="path">The path to the current JSON node.</param>
+        protected virtual T ReadObject(JObject obj, string path)
+        {
+            throw new SParseException($"Can't parse {typeof(T).Name} from object (path: {path}).");
+        }
+
+        /// <summary>Read a JSON string.</summary>
+        /// <param name="str">The JSON string value.</param>
+        /// <param name="path">The path to the current JSON node.</param>
+        protected virtual T ReadString(string str, string path)
+        {
+            throw new SParseException($"Can't parse {typeof(T).Name} from string (path: {path}).");
+        }
+    }
+}