From 005219acef452b0ba7f869daef935bd23f135519 Mon Sep 17 00:00:00 2001
From: Rico Suter <mail@rsuter.com>
Date: Thu, 2 Jun 2022 16:53:03 +0200
Subject: [PATCH] Add GenerateTypeCheckFunctions

---
 .../InheritanceTests.cs                       | 28 +++++++++++++++++--
 .../Models/ClassTemplateModel.cs              |  3 ++
 .../Templates/Interface.liquid                |  8 +++++-
 .../TypeScriptGeneratorSettings.cs            |  4 +++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/src/NJsonSchema.CodeGeneration.TypeScript.Tests/InheritanceTests.cs b/src/NJsonSchema.CodeGeneration.TypeScript.Tests/InheritanceTests.cs
index 1b8b355b8..e95145535 100644
--- a/src/NJsonSchema.CodeGeneration.TypeScript.Tests/InheritanceTests.cs
+++ b/src/NJsonSchema.CodeGeneration.TypeScript.Tests/InheritanceTests.cs
@@ -119,6 +119,28 @@ public async Task When_class_with_discriminator_has_base_class_then_csharp_is_ge
             Assert.Contains("if (data[\"kind\"] === \"MyException\") {", code);
         }
 
+        [Fact]
+        public async Task When_interfaces_are_generated_with_inheritance_then_type_check_methods_are_generated()
+        {
+            //// Arrange
+            var schema = JsonSchema.FromType<ExceptionContainer>();
+            var data = schema.ToJson();
+
+            var generator = new TypeScriptGenerator(schema, new TypeScriptGeneratorSettings
+            {
+                TypeScriptVersion = 2.0m,
+                TypeStyle = TypeScriptTypeStyle.Interface,
+                GenerateTypeCheckFunctions = true
+            });
+
+            //// Act
+            var code = generator.GenerateFile();
+
+            //// Assert
+            Assert.Contains("export function isExceptionBase(object: any): object is ExceptionBase {", code);
+            Assert.Contains("function isMyException(object: any): object is MyException {", code);
+        }
+
         [Fact]
         public async Task When_discriminator_does_not_match_typename_then_TypeScript_is_correct()
         {
@@ -322,7 +344,8 @@ public async Task When_schema_with_inheritance_and_references_is_generated_then_
 
 
         [Fact]
-        public async Task When_class_has_baseclass_and_extension_code_baseclass_is_preserved() {
+        public async Task When_class_has_baseclass_and_extension_code_baseclass_is_preserved()
+        {
             //// Arrange
             string extensionCode = @"
 import * as generated from ""./generated"";
@@ -333,7 +356,8 @@ export class ExceptionBase extends generated.ExceptionBase {
             ";
 
             var schema = JsonSchema.FromType<ExceptionContainer>();
-            var generator = new TypeScriptGenerator(schema, new TypeScriptGeneratorSettings {
+            var generator = new TypeScriptGenerator(schema, new TypeScriptGeneratorSettings
+            {
                 ExtensionCode = extensionCode,
                 ExtendedClasses = new[] { "ExceptionBase" },
             });
diff --git a/src/NJsonSchema.CodeGeneration.TypeScript/Models/ClassTemplateModel.cs b/src/NJsonSchema.CodeGeneration.TypeScript/Models/ClassTemplateModel.cs
index e87a5d757..a82264f1f 100644
--- a/src/NJsonSchema.CodeGeneration.TypeScript/Models/ClassTemplateModel.cs
+++ b/src/NJsonSchema.CodeGeneration.TypeScript/Models/ClassTemplateModel.cs
@@ -149,6 +149,9 @@ public string IndexerPropertyValueType
         /// <summary>Gets a value indicating whether the export keyword should be added to all classes.</summary>
         public bool ExportTypes => _settings.ExportTypes;
 
+        /// <summary>Gets a value indicating whether to generate type check functions.</summary>
+        public bool GenerateTypeCheckFunctions => _settings.GenerateTypeCheckFunctions;
+
         /// <summary>Gets the inherited schema.</summary>
         private JsonSchema InheritedSchema => _schema.InheritedSchema?.ActualSchema;
     }
diff --git a/src/NJsonSchema.CodeGeneration.TypeScript/Templates/Interface.liquid b/src/NJsonSchema.CodeGeneration.TypeScript/Templates/Interface.liquid
index 1396d01ed..554f4c559 100644
--- a/src/NJsonSchema.CodeGeneration.TypeScript/Templates/Interface.liquid
+++ b/src/NJsonSchema.CodeGeneration.TypeScript/Templates/Interface.liquid
@@ -12,4 +12,10 @@
 
     [key: string]: {{ IndexerPropertyValueType }};
 {%- endif -%}
-}
\ No newline at end of file
+}
+{%- if GenerateTypeCheckFunctions and HasInheritance -%}
+
+{% if ExportTypes %}export {% endif %}function is{{ ClassName }}(object: any): object is {{ ClassName }} {
+    return object && object['{{ BaseDiscriminator }}'] === '{{ DiscriminatorName }}';
+}
+{%- endif -%}
\ No newline at end of file
diff --git a/src/NJsonSchema.CodeGeneration.TypeScript/TypeScriptGeneratorSettings.cs b/src/NJsonSchema.CodeGeneration.TypeScript/TypeScriptGeneratorSettings.cs
index 5727ec58d..f92bbfa14 100644
--- a/src/NJsonSchema.CodeGeneration.TypeScript/TypeScriptGeneratorSettings.cs
+++ b/src/NJsonSchema.CodeGeneration.TypeScript/TypeScriptGeneratorSettings.cs
@@ -43,6 +43,7 @@ public TypeScriptGeneratorSettings()
             ExtendedClasses = Array.Empty<string>();
 
             InlineNamedDictionaries = false;
+            GenerateTypeCheckFunctions = false;
         }
 
         /// <summary>Gets or sets the target TypeScript version (default: 2.7).</summary>
@@ -108,6 +109,9 @@ public TypeScriptGeneratorSettings()
         /// <summary>Gets or sets a value indicating whether named/referenced dictionaries should be inlined or generated as class with an indexer.</summary>
         public bool InlineNamedDictionaries { get; set; }
 
+        /// <summary>Gets a value indicating whether to generate type check functions (for type style interface only, default: false).</summary>
+        public bool GenerateTypeCheckFunctions { get; set; }
+
         internal ITemplate CreateTemplate(string typeName, object model)
         {
             if (ClassTypes != null && ClassTypes.Contains(typeName))