1 files changed, 123 insertions, 0 deletions
diff --git a/src/StardewModdingAPI.Toolkit/Serialisation/JsonHelper.cs b/src/StardewModdingAPI.Toolkit/Serialisation/JsonHelper.cs
new file mode 100644
index 00000000..00f334ad
--- /dev/null
+++ b/src/StardewModdingAPI.Toolkit/Serialisation/JsonHelper.cs
@@ -0,0 +1,123 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using Newtonsoft.Json;
+using StardewModdingAPI.Toolkit.Serialisation.Converters;
+
+namespace StardewModdingAPI.Toolkit.Serialisation
+{
+    /// <summary>Encapsulates SMAPI's JSON file parsing.</summary>
+    public class JsonHelper
+    {
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>The JSON settings to use when serialising and deserialising files.</summary>
+        public JsonSerializerSettings JsonSettings { get; } = new JsonSerializerSettings
+        {
+            Formatting = Formatting.Indented,
+            ObjectCreationHandling = ObjectCreationHandling.Replace, // avoid issue where default ICollection<T> values are duplicated each time the config is loaded
+            Converters = new List<JsonConverter> { new SemanticVersionConverter() }
+        };
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Read a JSON file.</summary>
+        /// <typeparam name="TModel">The model type.</typeparam>
+        /// <param name="fullPath">The absolete file path.</param>
+        /// <returns>Returns the deserialised model, or <c>null</c> if the file doesn't exist or is empty.</returns>
+        /// <exception cref="InvalidOperationException">The given path is empty or invalid.</exception>
+        public TModel ReadJsonFile<TModel>(string fullPath)
+            where TModel : class
+        {
+            // validate
+            if (string.IsNullOrWhiteSpace(fullPath))
+                throw new ArgumentException("The file path is empty or invalid.", nameof(fullPath));
+
+            // read file
+            string json;
+            try
+            {
+                json = File.ReadAllText(fullPath);
+            }
+            catch (Exception ex) when (ex is DirectoryNotFoundException || ex is FileNotFoundException)
+            {
+                return null;
+            }
+
+            // deserialise model
+            try
+            {
+                return this.Deserialise<TModel>(json);
+            }
+            catch (Exception ex)
+            {
+                string error = $"Can't parse JSON file at {fullPath}.";
+
+                if (ex is JsonReaderException)
+                {
+                    error += " This doesn't seem to be valid JSON.";
+                    if (json.Contains("“") || json.Contains("”"))
+                        error += " Found curly quotes in the text; note that only straight quotes are allowed in JSON.";
+                }
+                error += $"\nTechnical details: {ex.Message}";
+                throw new JsonReaderException(error);
+            }
+        }
+
+        /// <summary>Save to a JSON file.</summary>
+        /// <typeparam name="TModel">The model type.</typeparam>
+        /// <param name="fullPath">The absolete file path.</param>
+        /// <param name="model">The model to save.</param>
+        /// <exception cref="InvalidOperationException">The given path is empty or invalid.</exception>
+        public void WriteJsonFile<TModel>(string fullPath, TModel model)
+            where TModel : class
+        {
+            // validate
+            if (string.IsNullOrWhiteSpace(fullPath))
+                throw new ArgumentException("The file path is empty or invalid.", nameof(fullPath));
+
+            // create directory if needed
+            string dir = Path.GetDirectoryName(fullPath);
+            if (dir == null)
+                throw new ArgumentException("The file path is invalid.", nameof(fullPath));
+            if (!Directory.Exists(dir))
+                Directory.CreateDirectory(dir);
+
+            // write file
+            string json = JsonConvert.SerializeObject(model, this.JsonSettings);
+            File.WriteAllText(fullPath, json);
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Deserialize JSON text if possible.</summary>
+        /// <typeparam name="TModel">The model type.</typeparam>
+        /// <param name="json">The raw JSON text.</param>
+        private TModel Deserialise<TModel>(string json)
+        {
+            try
+            {
+                return JsonConvert.DeserializeObject<TModel>(json, this.JsonSettings);
+            }
+            catch (JsonReaderException)
+            {
+                // try replacing curly quotes
+                if (json.Contains("“") || json.Contains("”"))
+                {
+                    try
+                    {
+                        return JsonConvert.DeserializeObject<TModel>(json.Replace('“', '"').Replace('”', '"'), this.JsonSettings);
+                    }
+                    catch { /* rethrow original error */ }
+                }
+
+                throw;
+            }
+        }
+    }
+}