- Refactored code

- Implemented basic JSON Path interpreter
- Clean up

DevDisciples.Json.Parser.Tests/JsonParserTests.cs

@@ -1,4 +1,6 @@
-namespace DevDisciples.Json.Parser.Tests;
+using DevDisciples.Json.Parser.Syntax;
+
+namespace DevDisciples.Json.Parser.Tests;
 
 public class JsonParserTests
 {
@@ -12,7 +14,7 @@ public class JsonParserTests
     {
         const string source = "null";
         var node = JsonParser.Parse(nameof(Can_parse_null), source);
-        Assert.That(node is JsonNull);
+        Assert.That(node is JsonNullSyntax);
     }
 
     [Test]
@@ -25,8 +27,8 @@ public class JsonParserTests
 
         Assert.Multiple(() =>
         {
-            Assert.That(trueNode is JsonBool { Value: true });
+            Assert.That(trueNode is JsonBoolSyntax { Value: true });
-            Assert.That(falseNode is JsonBool { Value: false });
+            Assert.That(falseNode is JsonBoolSyntax { Value: false });
         });
     }
 
@@ -35,15 +37,15 @@ public class JsonParserTests
     {
         const string source = "1";
         var node = JsonParser.Parse(nameof(Can_parse_an_integer), source);
-        Assert.That(node is JsonNumber { Value: 1 });
+        Assert.That(node is JsonNumberSyntax { Value: 1 });
     }
 
     [Test]
-    public void Can_lex_a_decimal()
+    public void Can_parse_a_decimal()
     {
         const string source = "1.0";
-        var node = JsonParser.Parse(nameof(Can_lex_a_decimal), source);
+        var node = JsonParser.Parse(nameof(Can_parse_a_decimal), source);
-        Assert.That(node is JsonNumber { Value: 1.0 });
+        Assert.That(node is JsonNumberSyntax { Value: 1.0 });
     }
 
     [Test]
@@ -51,7 +53,7 @@ public class JsonParserTests
     {
         const string source = "\"Hello world!\"";
         var tokens = JsonParser.Parse(nameof(Can_parse_a_string), source);
-        Assert.That(tokens is JsonString { Value: "Hello world!" });
+        Assert.That(tokens is JsonStringSyntax { Value: "Hello world!" });
     }
 
     [Test]
@@ -59,7 +61,7 @@ public class JsonParserTests
     {
         const string source = "[]";
         var tokens = JsonParser.Parse(nameof(Can_parse_an_empty_array), source);
-        Assert.That(tokens is JsonArray);
+        Assert.That(tokens is JsonArraySyntax);
     }
 
     [Test]
@@ -68,9 +70,9 @@ public class JsonParserTests
         const string source = "[1]";
         var tokens = JsonParser.Parse(nameof(Can_parse_a_single_item_array), source);
 
-        Assert.That(tokens is JsonArray
+        Assert.That(tokens is JsonArraySyntax
         {
-            Elements: [JsonNumber { Value: 1 }]
+            Elements: [JsonNumberSyntax { Value: 1 }]
         });
     }
 
@@ -80,15 +82,15 @@ public class JsonParserTests
         const string source = "[1,true,{},[],null]";
         var node = JsonParser.Parse(nameof(Can_parse_an_array_with_multiple_items), source);
 
-        Assert.That(node is JsonArray
+        Assert.That(node is JsonArraySyntax
         {
             Elements:
             [
-                JsonNumber { Value: 1 },
+                JsonNumberSyntax { Value: 1 },
-                JsonBool { Value: true },
+                JsonBoolSyntax { Value: true },
-                JsonObject { Properties.Length: 0 },
+                JsonObjectSyntax { Properties.Length: 0 },
-                JsonArray { Elements.Length: 0 },
+                JsonArraySyntax { Elements.Length: 0 },
-                JsonNull
+                JsonNullSyntax
             ]
         });
     }
@@ -98,7 +100,7 @@ public class JsonParserTests
     {
         const string source = "{}";
         var tokens = JsonParser.Parse(nameof(Can_parse_an_empty_object), source);
-        Assert.That(tokens is JsonObject { Properties.Length: 0 });
+        Assert.That(tokens is JsonObjectSyntax { Properties.Length: 0 });
     }
 
     [Test]
@@ -107,10 +109,10 @@ public class JsonParserTests
         const string source = "{\"first_name\":\"John\"}";
         var node = JsonParser.Parse(nameof(Can_parse_an_object_with_one_entry), source);
 
-        Assert.That(node is JsonObject { Properties.Length: 1 });
+        Assert.That(node is JsonObjectSyntax { Properties.Length: 1 });
-        var @object = (JsonObject)node;
+        var @object = (JsonObjectSyntax)node;
-        Assert.That(@object.Properties.Any(property => property.Key == "first_name"));
+        Assert.That(@object.Properties.Any(property => property.Key.Lexeme == "first_name"));
-        Assert.That(@object.Properties.First(property => property.Key == "first_name").Value is JsonString { Value: "John" });
+        Assert.That(@object.Properties.First(property => property.Key.Lexeme == "first_name").Value is JsonStringSyntax { Value: "John" });
     }
 
     [Test]
@@ -121,12 +123,12 @@ public class JsonParserTests
 
         Assert.Multiple(() =>
         {
-            Assert.That(node is JsonObject { Properties.Length: 2 });
+            Assert.That(node is JsonObjectSyntax { Properties.Length: 2 });
-            var @object = (JsonObject)node;
+            var @object = (JsonObjectSyntax)node;
-            Assert.That(@object.Properties.Any(property => property.Key == "first_name"));
+            Assert.That(@object.Properties.Any(property => property.Key.Lexeme == "first_name"));
-            Assert.That(@object.Properties.First(property => property.Key == "first_name").Value is JsonString { Value: "John" });
+            Assert.That(@object.Properties.First(property => property.Key.Lexeme == "first_name").Value is JsonStringSyntax { Value: "John" });
-            Assert.That(@object.Properties.Any(property => property.Key == "last_name"));
+            Assert.That(@object.Properties.Any(property => property.Key.Lexeme == "last_name"));
-            Assert.That(@object.Properties.First(property => property.Key == "last_name").Value is JsonString { Value: "Doe" });
+            Assert.That(@object.Properties.First(property => property.Key.Lexeme == "last_name").Value is JsonStringSyntax { Value: "Doe" });
         });
     }
 }

DevDisciples.Json.Parser/JsonArray.cs

@@ -1,15 +0,0 @@
-using DevDisciples.Parsing;
-
-namespace DevDisciples.Json.Parser;
-
-public readonly struct JsonArray : ISyntaxNode
-{
-    public Lexer<JsonToken>.Token Token { get; }
-    public ISyntaxNode[] Elements { get; }
-
-    public JsonArray(Lexer<JsonToken>.Token token, ISyntaxNode[] elements)
-    {
-        Token = token;
-        Elements = elements;
-    }
-}

DevDisciples.Json.Parser/JsonBool.cs

@@ -1,14 +0,0 @@
-using DevDisciples.Parsing;
-
-namespace DevDisciples.Json.Parser;
-
-public readonly struct JsonBool : ISyntaxNode
-{
-    public Lexer<JsonToken>.Token Token { get; }
-    public bool Value => bool.TryParse(Token.Lexeme, out var val) && val;
-
-    public JsonBool(Lexer<JsonToken>.Token token)
-    {
-        Token = token;
-    }
-}

DevDisciples.Json.Parser/JsonNull.cs

@@ -1,13 +0,0 @@
-using DevDisciples.Parsing;
-
-namespace DevDisciples.Json.Parser;
-
-public readonly struct JsonNull : ISyntaxNode
-{
-    public Lexer<JsonToken>.Token Token { get; }
-
-    public JsonNull(Lexer<JsonToken>.Token token)
-    {
-        Token = token;
-    }
-}

DevDisciples.Json.Parser/JsonNumber.cs

@@ -1,14 +0,0 @@
-using DevDisciples.Parsing;
-
-namespace DevDisciples.Json.Parser;
-
-public readonly struct JsonNumber : ISyntaxNode
-{
-    public Lexer<JsonToken>.Token Token { get; }
-    public double Value => double.TryParse(Token.Lexeme.Replace('.', ','), out var val) ? val : default;
-
-    public JsonNumber(Lexer<JsonToken>.Token token)
-    {
-        Token = token;
-    }
-}

DevDisciples.Json.Parser/JsonObject.Property.cs

@@ -1,18 +0,0 @@
-using DevDisciples.Parsing;
-
-namespace DevDisciples.Json.Parser;
-
-public readonly partial struct JsonObject
-{
-    public readonly struct Property : ISyntaxNode
-    {
-        public string Key { get; }
-        public ISyntaxNode Value { get; }
-
-        public Property(string key, ISyntaxNode value)
-        {
-            Key = key;
-            Value = value;
-        }
-    }
-}

DevDisciples.Json.Parser/JsonObject.cs

@@ -1,15 +0,0 @@
-using DevDisciples.Parsing;
-
-namespace DevDisciples.Json.Parser;
-
-public readonly partial struct JsonObject : ISyntaxNode
-{
-    public Lexer<JsonToken>.Token Token { get; }
-    public Property[] Properties { get; }
-
-    public JsonObject(Lexer<JsonToken>.Token token, Property[] properties)
-    {
-        Token = token;
-        Properties = properties;
-    }
-}

DevDisciples.Json.Parser/JsonParser.cs

@@ -1,10 +1,11 @@
-using DevDisciples.Parsing;
+using DevDisciples.Json.Parser.Syntax;
+using DevDisciples.Parsing;
 
 namespace DevDisciples.Json.Parser;
 
 public static partial class JsonParser
 {
-    public static ISyntaxNode Parse(string file, string source)
+    public static IJsonSyntax Parse(string file, string source)
     {
         var tokens = JsonLexer.Default.Lex(file, source).ToArray();
         var context = new Context(tokens);
@@ -12,33 +13,33 @@ public static partial class JsonParser
         return nodes;
     }
 
-    private static ISyntaxNode Expression(ParserContext<JsonToken> ctx)
+    private static IJsonSyntax Expression(ParserContext<JsonToken> ctx)
     {
         if (ctx.Match(JsonToken.LeftBracket))
-            return Array(ctx);
+            return ArrayExpression(ctx);
 
         if (ctx.Match(JsonToken.LeftBrace))
-            return Object(ctx);
+            return ObjectExpression(ctx);
 
         if (ctx.Match(JsonToken.Minus) || ctx.Match(JsonToken.Number))
-            return Number(ctx);
+            return NumberExpression(ctx);
 
         if (ctx.Match(JsonToken.String))
-            return String(ctx);
+            return StringExpression(ctx);
 
         if (ctx.Match(JsonToken.Null))
-            return Null(ctx);
+            return NullExpression(ctx);
 
         if (ctx.Match(JsonToken.True) || ctx.Match(JsonToken.False))
-            return Bool(ctx);
+            return BoolExpression(ctx);
 
         throw Report.Error(ctx.Current, $"Expected a JSON expression, got '{ctx.Current.Lexeme}'");
     }
 
-    private static ISyntaxNode Array(ParserContext<JsonToken> ctx)
+    private static IJsonSyntax ArrayExpression(ParserContext<JsonToken> ctx)
     {
         var previous = ctx.Previous();
-        List<ISyntaxNode>? elements = null;
+        List<IJsonSyntax>? elements = null;
 
         if (!ctx.Check(JsonToken.RightBracket))
         {
@@ -51,13 +52,13 @@ public static partial class JsonParser
 
         ctx.Consume(JsonToken.RightBracket, "Expected ']'");
 
-        return new JsonArray(previous, elements?.ToArray() ?? System.Array.Empty<ISyntaxNode>());
+        return new JsonArraySyntax(previous, elements?.ToArray() ?? System.Array.Empty<IJsonSyntax>());
     }
 
-    private static ISyntaxNode Object(ParserContext<JsonToken> ctx)
+    private static IJsonSyntax ObjectExpression(ParserContext<JsonToken> ctx)
     {
         var previous = ctx.Previous();
-        Dictionary<string, ISyntaxNode>? properties = null;
+        Dictionary<Lexer<JsonToken>.Token, IJsonSyntax>? properties = null;
 
         if (!ctx.Check(JsonToken.RightBrace))
         {
@@ -66,32 +67,32 @@ public static partial class JsonParser
                 var key = ctx.Consume(JsonToken.String, "Expected property name");
                 ctx.Consume(JsonToken.Colon, "Expected ':' after property name");
                 properties ??= new();
-                properties[key.Lexeme] = Expression(ctx);
+                properties[key] = Expression(ctx);
             } while (ctx.Match(JsonToken.Comma));
         }
 
         ctx.Consume(JsonToken.RightBrace, "Expected '}'");
 
-        var propertiesArray = properties?.Select(kv => new JsonObject.Property(kv.Key, kv.Value)).ToArray();
+        var propertiesArray = properties?.Select(kv => new JsonPropertySyntax(kv.Key, kv.Value)).ToArray();
 
-        return new JsonObject(previous, propertiesArray ?? System.Array.Empty<JsonObject.Property>());
+        return new JsonObjectSyntax(previous, propertiesArray ?? System.Array.Empty<JsonPropertySyntax>());
     }
 
-    private static ISyntaxNode Number(ParserContext<JsonToken> ctx)
+    private static IJsonSyntax NumberExpression(ParserContext<JsonToken> ctx)
     {
-        if (ctx.Previous().Type != JsonToken.Minus) return new JsonNumber(ctx.Previous());
+        if (ctx.Previous().Type != JsonToken.Minus) return new JsonNumberSyntax(ctx.Previous());
 
         var minus = ctx.Previous();
         var number = ctx.Consume(JsonToken.Number, "Expected a number after '-'.");
 
-        return new JsonNumber(
+        return new JsonNumberSyntax(
             new Lexer<JsonToken>.Token(minus.File, JsonToken.Number, $"-{number.Lexeme}", minus.Line, minus.Column)
         );
     }
 
-    private static ISyntaxNode String(ParserContext<JsonToken> ctx) => new JsonString(ctx.Previous());
+    private static IJsonSyntax StringExpression(ParserContext<JsonToken> ctx) => new JsonStringSyntax(ctx.Previous());
 
-    private static ISyntaxNode Null(ParserContext<JsonToken> ctx) => new JsonNull(ctx.Previous());
+    private static IJsonSyntax NullExpression(ParserContext<JsonToken> ctx) => new JsonNullSyntax(ctx.Previous());
 
-    private static ISyntaxNode Bool(ParserContext<JsonToken> ctx) => new JsonBool(ctx.Previous());
+    private static IJsonSyntax BoolExpression(ParserContext<JsonToken> ctx) => new JsonBoolSyntax(ctx.Previous());
 }

DevDisciples.Json.Parser/JsonString.cs

@@ -1,14 +0,0 @@
-using DevDisciples.Parsing;
-
-namespace DevDisciples.Json.Parser;
-
-public readonly struct JsonString : ISyntaxNode
-{
-    public Lexer<JsonToken>.Token Token { get; }
-    public string Value => Token.Lexeme;
-
-    public JsonString(Lexer<JsonToken>.Token token)
-    {
-        Token = token;
-    }
-}

DevDisciples.Json.Parser/Syntax/IJsonSyntax.cs

@@ -0,0 +1,8 @@
+using DevDisciples.Parsing;
+
+namespace DevDisciples.Json.Parser.Syntax;
+
+public interface IJsonSyntax
+{
+    public Lexer<JsonToken>.Token Token { get; }
+}

DevDisciples.Json.Parser/Syntax/JsonArraySyntax.cs

@@ -0,0 +1,15 @@
+using DevDisciples.Parsing;
+
+namespace DevDisciples.Json.Parser.Syntax;
+
+public readonly struct JsonArraySyntax : IJsonSyntax
+{
+    public Lexer<JsonToken>.Token Token { get; }
+    public IJsonSyntax[] Elements { get; }
+
+    public JsonArraySyntax(Lexer<JsonToken>.Token token, IJsonSyntax[] elements)
+    {
+        Token = token;
+        Elements = elements;
+    }
+}

DevDisciples.Json.Parser/Syntax/JsonBoolSyntax.cs

@@ -0,0 +1,14 @@
+using DevDisciples.Parsing;
+
+namespace DevDisciples.Json.Parser.Syntax;
+
+public readonly struct JsonBoolSyntax : IJsonSyntax
+{
+    public Lexer<JsonToken>.Token Token { get; }
+    public bool Value => bool.TryParse(Token.Lexeme, out var val) && val;
+
+    public JsonBoolSyntax(Lexer<JsonToken>.Token token)
+    {
+        Token = token;
+    }
+}

DevDisciples.Json.Parser/Syntax/JsonNullSyntax.cs

@@ -0,0 +1,13 @@
+using DevDisciples.Parsing;
+
+namespace DevDisciples.Json.Parser.Syntax;
+
+public readonly struct JsonNullSyntax : IJsonSyntax
+{
+    public Lexer<JsonToken>.Token Token { get; }
+
+    public JsonNullSyntax(Lexer<JsonToken>.Token token)
+    {
+        Token = token;
+    }
+}

DevDisciples.Json.Parser/Syntax/JsonNumberSyntax.cs

@@ -0,0 +1,14 @@
+using DevDisciples.Parsing;
+
+namespace DevDisciples.Json.Parser.Syntax;
+
+public readonly struct JsonNumberSyntax : IJsonSyntax
+{
+    public Lexer<JsonToken>.Token Token { get; }
+    public double Value => double.TryParse(Token.Lexeme.Replace('.', ','), out var val) ? val : default;
+
+    public JsonNumberSyntax(Lexer<JsonToken>.Token token)
+    {
+        Token = token;
+    }
+}

DevDisciples.Json.Parser/Syntax/JsonObjectSyntax.cs

@@ -0,0 +1,15 @@
+using DevDisciples.Parsing;
+
+namespace DevDisciples.Json.Parser.Syntax;
+
+public readonly partial struct JsonObjectSyntax : IJsonSyntax
+{
+    public Lexer<JsonToken>.Token Token { get; }
+    public JsonPropertySyntax[] Properties { get; }
+
+    public JsonObjectSyntax(Lexer<JsonToken>.Token token, JsonPropertySyntax[] properties)
+    {
+        Token = token;
+        Properties = properties;
+    }
+}

DevDisciples.Json.Parser/Syntax/JsonPropertySyntax.cs

@@ -0,0 +1,16 @@
+using DevDisciples.Parsing;
+
+namespace DevDisciples.Json.Parser.Syntax;
+
+public readonly struct JsonPropertySyntax : IJsonSyntax
+{
+    public Lexer<JsonToken>.Token Token => Key;
+    public Lexer<JsonToken>.Token Key { get; }
+    public IJsonSyntax Value { get; }
+
+    public JsonPropertySyntax(Lexer<JsonToken>.Token key, IJsonSyntax value)
+    {
+        Key = key;
+        Value = value;
+    }
+}

DevDisciples.Json.Parser/Syntax/JsonStringSyntax.cs

@@ -0,0 +1,14 @@
+using DevDisciples.Parsing;
+
+namespace DevDisciples.Json.Parser.Syntax;
+
+public readonly struct JsonStringSyntax : IJsonSyntax
+{
+    public Lexer<JsonToken>.Token Token { get; }
+    public string Value => Token.Lexeme;
+
+    public JsonStringSyntax(Lexer<JsonToken>.Token token)
+    {
+        Token = token;
+    }
+}

DevDisciples.Json.Tools.API/Controllers/TransformController.cs

@@ -40,4 +40,11 @@ public class TransformController : ControllerBase
 
         return Ok(new { Result = result });
     }
+
+    [HttpPost("jsonpath")]
+    public IActionResult JsonPath([FromBody] JsonPathRequest request)
+    {
+        var result = Tools.JsonPath.Interpreter.Evaluate(request.Source, request.Path);
+        return Ok(new { Result = JsonFormatter.Format(result, new() { Beautify = true }) });
+    }
 }

DevDisciples.Json.Tools.API/Requests/Json2CsharpRequest.cs

@@ -2,6 +2,6 @@
 
 public class Json2CsharpRequest : TransformRequest
 {
-    public string RootClassName { get; } = Json2CSharpTranslator.Context.DefaultRootClassName;
+    public string RootClassName { get; init; } = Json2CSharpTranslator.Context.DefaultRootClassName;
-    public string Namespace { get; } = Json2CSharpTranslator.Context.DefaultNamespace;
+    public string Namespace { get; init; } = Json2CSharpTranslator.Context.DefaultNamespace;
 }

DevDisciples.Json.Tools.API/Requests/JsonPathRequest.cs

@@ -0,0 +1,6 @@
+namespace DevDisciples.Json.Tools.API.Requests;
+
+public class JsonPathRequest : TransformRequest
+{
+    public string Path { get; init; } = string.Empty;
+}

DevDisciples.Json.Tools.API/Requests/PrettifyRequest.cs

@@ -2,5 +2,5 @@
 
 public class PrettifyRequest : TransformRequest
 {
-    public int IndentSize { get; } = JsonFormatter.Context.DefaultIndentSize;
+    public int IndentSize { get; init; } = JsonFormatter.Context.DefaultIndentSize;
 }

DevDisciples.Json.Tools.App/src/app/app.routes.ts

@@ -1,13 +1,14 @@
 import { Routes } from '@angular/router';
-import {AppComponent} from "./app.component";
 import {HomeComponent} from "./home/home.component";
 import {PrettifyComponent} from "./prettify/prettify.component";
 import {UglifyComponent} from "./uglify/uglify.component";
 import {Json2CsharpComponent} from "./json2csharp/json2-csharp.component";
+import {JsonPathComponent} from "./json-path/json-path.component";
 
 export const routes: Routes = [
   { path: 'home', component: HomeComponent },
   { path: 'prettify', component: PrettifyComponent },
   { path: 'uglify', component: UglifyComponent },
   { path: 'json2csharp', component: Json2CsharpComponent },
+  { path: 'jsonpath', component: JsonPathComponent },
 ];

DevDisciples.Json.Tools.App/src/app/json-path/json-path.component.html

@@ -0,0 +1,13 @@
+<h1>JSON to C#</h1>
+
+<mat-form-field>
+  <mat-label>Path</mat-label>
+  <input matInput placeholder="$.*" [value]="$path.value" (input)="handlePathChange($event)">
+</mat-form-field>
+
+<app-input-output [input]="$input.value"
+                  [inputOptions]="inputOptions"
+                  (onInputChange)="handleInputChange($event)"
+                  [output]="output"
+                  [outputOptions]="outputOptions">
+</app-input-output>

DevDisciples.Json.Tools.App/src/app/json-path/json-path.component.scss

@@ -0,0 +1,3 @@
+mat-form-field {
+  width: 100%;
+}

DevDisciples.Json.Tools.App/src/app/json-path/json-path.component.spec.ts

@@ -0,0 +1,23 @@
+import { ComponentFixture, TestBed } from '@angular/core/testing';
+
+import { JsonPathComponent } from './json-path.component';
+
+describe('JsonPathComponent', () => {
+  let component: JsonPathComponent;
+  let fixture: ComponentFixture<JsonPathComponent>;
+
+  beforeEach(async () => {
+    await TestBed.configureTestingModule({
+      imports: [JsonPathComponent]
+    })
+    .compileComponents();
+
+    fixture = TestBed.createComponent(JsonPathComponent);
+    component = fixture.componentInstance;
+    fixture.detectChanges();
+  });
+
+  it('should create', () => {
+    expect(component).toBeTruthy();
+  });
+});

DevDisciples.Json.Tools.App/src/app/json-path/json-path.component.ts

@@ -0,0 +1,69 @@
+import {Component, OnInit} from '@angular/core';
+import {InputOutputComponent} from "../input-output/input-output.component";
+import {DebounceTime, GenerateDefaultJsonObjectString, MonacoJsonConfig, ReadOnlyMonacoCSharpConfig} from "../defaults";
+import {BehaviorSubject, debounceTime} from "rxjs";
+import {JsonTransformService} from "../json-transform.service";
+import {MatFormField} from "@angular/material/form-field";
+import {MatInputModule} from "@angular/material/input";
+
+@Component({
+  selector: 'app-json-path',
+  standalone: true,
+  imports: [
+    InputOutputComponent,
+    MatFormField,
+    MatInputModule
+  ],
+  templateUrl: './json-path.component.html',
+  styleUrl: './json-path.component.scss'
+})
+export class JsonPathComponent implements OnInit {
+  $path: BehaviorSubject<string> = new BehaviorSubject<string>("$.*");
+  $input: BehaviorSubject<string> = new BehaviorSubject<string>(GenerateDefaultJsonObjectString(2));
+  inputOptions = MonacoJsonConfig;
+  output: string = "";
+  outputOptions = ReadOnlyMonacoCSharpConfig;
+
+  constructor(private service: JsonTransformService) {
+  }
+
+  ngOnInit(): void {
+    this.$input
+      .pipe(debounceTime(DebounceTime))
+      .subscribe(input => this.update(input, this.$path.value));
+
+    this.$path
+      .pipe(debounceTime(DebounceTime))
+      .subscribe(path => this.update(this.$input.value, path));
+
+    this.update(this.$input.value, this.$path.value);
+  }
+
+  update(input: string, path: string): void {
+    this.service
+      .jsonPath(input, path)
+      .subscribe({
+        next: response => {
+          console.log(response);
+          this.output = response.body.result;
+        },
+        error: response => {
+          console.log(response)
+          if (response.status === 499) {
+            this.output = response.error.detail;
+            console.log(response.error.detail);
+          }
+        }
+      });
+  }
+
+  handlePathChange($event: any): void {
+    console.log($event);
+    this.$path.next($event.target.value);
+  }
+
+  handleInputChange($event: any): void {
+    console.log($event);
+    this.$input.next($event);
+  }
+}

DevDisciples.Json.Tools.App/src/app/json-transform.service.ts

@@ -22,4 +22,8 @@ export class JsonTransformService {
   public json2csharp(source: string): Observable<HttpResponse<any>> {
     return this.http.post(`${this.url}/api/transform/json2csharp`, {Source: source}, {observe: "response"});
   }
+
+  public jsonPath(source: string, path: string): Observable<HttpResponse<any>> {
+    return this.http.post(`${this.url}/api/transform/jsonpath`, {source: source, path: path}, {observe: "response"});
+  }
 }

DevDisciples.Json.Tools.App/src/app/json2csharp/json2-csharp.component.html

@@ -1,6 +1,6 @@
 <h1>JSON to C#</h1>
 
-<app-input-output [input]="input"
+<app-input-output [input]="$input.value"
                   [inputOptions]="inputOptions"
                   (onInputChange)="handleInputChange($event)"
                   [output]="output"

DevDisciples.Json.Tools.App/src/app/json2csharp/json2-csharp.component.ts

@@ -7,7 +7,7 @@ import {
   MonacoJsonConfig,
   ReadOnlyMonacoCSharpConfig
 } from "../defaults";
-import {debounceTime, Subject} from "rxjs";
+import {BehaviorSubject, debounceTime} from "rxjs";
 
 @Component({
   selector: 'app-json2csharp',
@@ -19,8 +19,7 @@ import {debounceTime, Subject} from "rxjs";
   styleUrl: './json2-csharp.component.scss'
 })
 export class Json2CsharpComponent implements OnInit {
-  input: string = GenerateDefaultJsonObjectString(2);
+  $input: BehaviorSubject<string> = new BehaviorSubject<string>(GenerateDefaultJsonObjectString(2));
-  $input: Subject<string> = new Subject<string>();
   inputOptions = MonacoJsonConfig;
   output: string = "";
   outputOptions = ReadOnlyMonacoCSharpConfig;
@@ -33,7 +32,7 @@ export class Json2CsharpComponent implements OnInit {
       .pipe(debounceTime(DebounceTime))
       .subscribe(input => this.update(input));
 
-    this.update(this.input);
+    this.update(this.$input.value);
   }
 
   update(input: string): void {

DevDisciples.Json.Tools.App/src/app/layout/layout.component.html

@@ -6,6 +6,7 @@
       <mat-list-item routerLink="/prettify">Prettify</mat-list-item>
       <mat-list-item routerLink="/uglify">Uglify</mat-list-item>
       <mat-list-item routerLink="/json2csharp">JSON to C#</mat-list-item>
+      <mat-list-item routerLink="/jsonpath">JSON Path</mat-list-item>
     </mat-nav-list>
   </mat-sidenav>
 

DevDisciples.Json.Tools.App/src/app/layout/layout.component.scss

@@ -12,4 +12,5 @@ mat-sidenav {
 
 main {
   height: 100%;
+  padding: 20px;
 }

DevDisciples.Json.Tools.App/src/app/prettify/prettify.component.html

@@ -1,6 +1,6 @@
 <h1>JSON Prettify</h1>
 
-<app-input-output [input]="input"
+<app-input-output [input]="$input.value"
                   [inputOptions]="inputOptions"
                   (onInputChange)="handleInputChange($event)"
                   [output]="output"

DevDisciples.Json.Tools.App/src/app/prettify/prettify.component.ts

@@ -9,7 +9,7 @@ import {
   MonacoJsonConfig,
   ReadOnlyMonacoJsonConfig
 } from "../defaults";
-import {debounceTime, Subject} from "rxjs";
+import {BehaviorSubject, debounceTime} from "rxjs";
 
 @Component({
   selector: 'app-prettify',
@@ -23,12 +23,12 @@ import {debounceTime, Subject} from "rxjs";
   styleUrl: './prettify.component.scss'
 })
 export class PrettifyComponent implements OnInit {
-  input: string = GenerateDefaultJsonObjectString();
+  // input: string = ;
-  $input: Subject<string> = new Subject<string>();
+  $input: BehaviorSubject<string> = new BehaviorSubject<string>(GenerateDefaultJsonObjectString());
   inputOptions = MonacoJsonConfig;
   output: string = GenerateDefaultJsonObjectString(2);
   outputOptions = ReadOnlyMonacoJsonConfig;
-  error: string = "";
+  // error: string = "";
 
   constructor(private service: JsonTransformService) {
   }

DevDisciples.Json.Tools.App/src/app/uglify/uglify.component.html

@@ -1,6 +1,6 @@
 <h1>JSON Uglify</h1>
 
-<app-input-output [input]="input"
+<app-input-output [input]="$input.value"
                   [inputOptions]="inputOptions"
                   (onInputChange)="handleInputChange($event)"
                   [output]="output"

DevDisciples.Json.Tools.App/src/app/uglify/uglify.component.ts

@@ -7,7 +7,7 @@ import {
   MonacoJsonConfig,
   ReadOnlyMonacoJsonConfig
 } from "../defaults";
-import {debounceTime, Subject} from "rxjs";
+import {debounceTime, BehaviorSubject} from "rxjs";
 
 @Component({
   selector: 'app-uglify',
@@ -19,8 +19,8 @@ import {debounceTime, Subject} from "rxjs";
   styleUrl: './uglify.component.scss'
 })
 export class UglifyComponent implements OnInit {
-  input: string = GenerateDefaultJsonObjectString(2);
+  // input: string = ;
-  $input: Subject<string> = new Subject<string>();
+  $input: BehaviorSubject<string> = new BehaviorSubject<string>(GenerateDefaultJsonObjectString(2));
   inputOptions = MonacoJsonConfig;
   output: string = GenerateDefaultJsonObjectString();
   outputOptions = ReadOnlyMonacoJsonConfig;

DevDisciples.Json.Tools/Json2CSharpTranslator.Context.cs

@@ -11,6 +11,8 @@ public static partial class Json2CSharpTranslator
 
         public string RootClassName { get; init; } = DefaultRootClassName;
         public string Namespace { get; init; } = DefaultNamespace;
+        public string CurrentName { get; set; } = string.Empty;
+
         public List<ClassTranslation> Classes { get; } = new();
         public readonly StringBuilder Builder = new();
     }

DevDisciples.Json.Tools/Json2CSharpTranslator.JsonArrayTranslator.cs

@@ -1,63 +0,0 @@
-using DevDisciples.Json.Parser;
-using DevDisciples.Parsing;
-using Humanizer;
-
-namespace DevDisciples.Json.Tools;
-
-public static partial class Json2CSharpTranslator
-{
-    public static class JsonArrayTranslator
-    {
-        public static ITranslation Translate(ISyntaxNode visitee, object[] args)
-        {
-            var context = ContextFromArgs(args);
-            var name = NameFromArgs(args);
-            var array = (JsonArray)visitee;
-            var type = "object";
-
-            if (array.Elements.All(e => e is JsonObject))
-            {
-                context.Classes.Add(SquashObjects(name, array.Elements, args));
-                type = context.Classes.Last().Name;
-            }
-            else if (array.Elements.All(e => e is JsonString es && DateTime.TryParse(es.Value, out _)))
-            {
-                type = "DateTime";
-            }
-            else if (array.Elements.All(e => e is JsonString))
-            {
-                type = "string";
-            }
-            else if (array.Elements.All(e => e is JsonNumber))
-            {
-                type = array.Elements.Any(e => ((JsonNumber)e).Token.Lexeme.Contains('.')) ? "double" : "int";
-            }
-
-            return new PropertyTranslation
-            {
-                Type = $"List<{type}>",
-                Name = name,
-            };
-        }
-
-        private static ClassTranslation SquashObjects(string className, IEnumerable<ISyntaxNode> objects, object[] args)
-        {
-            var classes = objects
-                .Select(@object => JsonObjectTranslator.Translate(@object, args))
-                .ToArray();
-
-            var squashed = new ClassTranslation
-            {
-                Name = className.Singularize(),
-                Properties = new()
-            };
-
-            foreach (var @class in classes)
-            foreach (var prop in ((ClassTranslation)@class).Properties)
-                if (squashed.Properties.All(p => p.Name != prop.Name))
-                    squashed.Properties.Add(prop);
-
-            return squashed;
-        }
-    }
-}

DevDisciples.Json.Tools/Json2CSharpTranslator.JsonBoolTranslator.cs

@@ -1,18 +0,0 @@
-using DevDisciples.Parsing;
-
-namespace DevDisciples.Json.Tools;
-
-public static partial class Json2CSharpTranslator
-{
-    public static class JsonBoolTranslator
-    {
-        public static ITranslation Translate(ISyntaxNode visitee, object[] args)
-        {
-            return new PropertyTranslation
-            {
-                Type = "bool",
-                Name = NameFromArgs(args),
-            };
-        }
-    }
-}

DevDisciples.Json.Tools/Json2CSharpTranslator.JsonNullTranslator.cs

@@ -1,18 +0,0 @@
-using DevDisciples.Parsing;
-
-namespace DevDisciples.Json.Tools;
-
-public static partial class Json2CSharpTranslator
-{
-    public static class JsonNullTranslator
-    {
-        public static ITranslation Translate(ISyntaxNode visitee, object[] args)
-        {
-            return new PropertyTranslation
-            {
-                Type = "object",
-                Name = NameFromArgs(args),
-            };
-        }
-    }
-}

DevDisciples.Json.Tools/Json2CSharpTranslator.JsonNumberTranslator.cs

@@ -1,19 +0,0 @@
-using DevDisciples.Json.Parser;
-using DevDisciples.Parsing;
-
-namespace DevDisciples.Json.Tools;
-
-public static partial class Json2CSharpTranslator
-{
-    public static class JsonNumberTranslator
-    {
-        public static ITranslation Translate(ISyntaxNode visitee, object[] args)
-        {
-            return new PropertyTranslation
-            {
-                Type = ((JsonNumber)visitee).Token.Lexeme.Contains('.') ? "double" : "int",
-                Name = NameFromArgs(args),
-            };
-        }
-    }
-}

DevDisciples.Json.Tools/Json2CSharpTranslator.JsonObjectTranslator.cs

@@ -1,42 +0,0 @@
-using DevDisciples.Json.Parser;
-using DevDisciples.Parsing;
-
-namespace DevDisciples.Json.Tools;
-
-public static partial class Json2CSharpTranslator
-{
-    public static class JsonObjectTranslator
-    {
-        public static ITranslation Translate(ISyntaxNode visitee, object[] args)
-        {
-            var context = ContextFromArgs(args);
-            var name = NameFromArgs(args);
-            var @class = new ClassTranslation { Name = name, Properties = new() };
-            var @object = (JsonObject)visitee;
-
-            context.Classes.Add(@class);
-
-            foreach (var prop in @object.Properties)
-            {
-                var visitor = Visitors[prop.Value.GetType()];
-                var translation = visitor(prop.Value, context, prop.Key);
-
-                switch (translation)
-                {
-                    case ClassTranslation:
-                        @class.Properties.Add(new PropertyTranslation
-                        {
-                            Type = translation.Name,
-                            Name = translation.Name,
-                        });
-                        break;
-                    case PropertyTranslation property:
-                        @class.Properties.Add(property);
-                        break;
-                }
-            }
-
-            return @class;
-        }
-    }
-}

DevDisciples.Json.Tools/Json2CSharpTranslator.JsonStringTranslator.cs

@@ -1,22 +0,0 @@
-using DevDisciples.Json.Parser;
-using DevDisciples.Parsing;
-
-namespace DevDisciples.Json.Tools;
-
-public static partial class Json2CSharpTranslator
-{
-    public static class JsonStringTranslator
-    {
-        public static ITranslation Translate(ISyntaxNode visitee, object[] args)
-        {
-            var @string = (JsonString)visitee;
-            var type = DateTime.TryParse(@string.Value, out _) ? "DateTime" : "string";
-
-            return new PropertyTranslation
-            {
-                Type = type,
-                Name = NameFromArgs(args),
-            };
-        }
-    }
-}

DevDisciples.Json.Tools/Json2CSharpTranslator.cs

@@ -1,4 +1,5 @@
 using DevDisciples.Json.Parser;
+using DevDisciples.Json.Parser.Syntax;
 using DevDisciples.Parsing;
 using Humanizer;
 
@@ -6,28 +7,28 @@ namespace DevDisciples.Json.Tools;
 
 public static partial class Json2CSharpTranslator
 {
-    public static readonly VisitorContainer<ISyntaxNode, ITranslation> Visitors;
+    private static readonly VisitorContainer<IJsonSyntax, Context, ITranslation> Visitors = new();
 
     static Json2CSharpTranslator()
     {
-        Visitors = new();
+        Visitors.Register<JsonObjectSyntax>(Object);
-        Visitors.Register<JsonObject>(JsonObjectTranslator.Translate);
+        Visitors.Register<JsonArraySyntax>(Array);
-        Visitors.Register<JsonArray>(JsonArrayTranslator.Translate);
+        Visitors.Register<JsonStringSyntax>(String);
-        Visitors.Register<JsonString>(JsonStringTranslator.Translate);
+        Visitors.Register<JsonNumberSyntax>(Number);
-        Visitors.Register<JsonNumber>(JsonNumberTranslator.Translate);
+        Visitors.Register<JsonBoolSyntax>(Bool);
-        Visitors.Register<JsonBool>(JsonBoolTranslator.Translate);
+        Visitors.Register<JsonNullSyntax>(Null);
-        Visitors.Register<JsonNull>(JsonNullTranslator.Translate);
     }
 
     public static string Translate(string source, Context? context = null)
     {
-        if (JsonParser.Parse("<source>", source) is not JsonObject root)
+        if (JsonParser.Parse("<source>", source) is not JsonObjectSyntax root)
             throw new ParsingException("Expected a JSON object.");
 
         context ??= new();
+        context.CurrentName = context.RootClassName;
 
-        var visitor = Visitors[typeof(JsonObject)];
+        var visitor = Visitors[typeof(JsonObjectSyntax)];
-        visitor(root, context, context.RootClassName);
+        visitor(root, context);
 
         context.Builder.Append("//using System;\n");
         context.Builder.Append("//using System.Collections.Generic;\n");
@@ -38,7 +39,127 @@ public static partial class Json2CSharpTranslator
         return context.Builder.ToString();
     }
 
-    private static Context ContextFromArgs(object[] args) => (args[0] as Context)!;
+    private static ITranslation Object(IJsonSyntax visitee, Context context)
+    {
+        var @object = (JsonObjectSyntax)visitee;
+        var @class = new ClassTranslation
+        {
+            Name = context.CurrentName,
+            Properties = new()
+        };
 
-    private static string NameFromArgs(object[] args) => ((string)args[1]).Camelize();
+        context.Classes.Add(@class);
+
+        foreach (var prop in @object.Properties)
+        {
+            context.CurrentName = prop.Key.Lexeme;
+            var visitor = Visitors[prop.Value.GetType()];
+            var translation = visitor(prop.Value, context);
+
+            switch (translation)
+            {
+                case ClassTranslation:
+                    @class.Properties.Add(new PropertyTranslation
+                    {
+                        Type = translation.Name,
+                        Name = translation.Name,
+                    });
+                    break;
+                case PropertyTranslation property:
+                    @class.Properties.Add(property);
+                    break;
+            }
+        }
+
+        return @class;
+    }
+
+    private static ITranslation Array(IJsonSyntax visitee, Context context)
+    {
+        var array = (JsonArraySyntax)visitee;
+        var type = "object";
+
+        if (array.Elements.All(e => e is JsonObjectSyntax))
+        {
+            context.Classes.Add(SquashObjects(context.CurrentName, array.Elements, context));
+            type = context.Classes.Last().Name;
+        }
+        else if (array.Elements.All(e => e is JsonStringSyntax es && DateTime.TryParse(es.Value, out _)))
+        {
+            type = "DateTime";
+        }
+        else if (array.Elements.All(e => e is JsonStringSyntax))
+        {
+            type = "string";
+        }
+        else if (array.Elements.All(e => e is JsonNumberSyntax))
+        {
+            type = array.Elements.Any(e => ((JsonNumberSyntax)e).Token.Lexeme.Contains('.')) ? "double" : "int";
+        }
+
+        return new PropertyTranslation
+        {
+            Type = $"List<{type}>",
+            Name = context.CurrentName,
+        };
+    }
+
+    private static ITranslation String(IJsonSyntax visitee, Context context)
+    {
+        var @string = (JsonStringSyntax)visitee;
+        var type = DateTime.TryParse(@string.Value, out _) ? "DateTime" : "string";
+
+        return new PropertyTranslation
+        {
+            Type = type,
+            Name = context.CurrentName,
+        };
+    }
+
+    private static ITranslation Number(IJsonSyntax visitee, Context context)
+    {
+        return new PropertyTranslation
+        {
+            Type = ((JsonNumberSyntax)visitee).Token.Lexeme.Contains('.') ? "double" : "int",
+            Name = context.CurrentName,
+        };
+    }
+
+    private static ITranslation Bool(IJsonSyntax visitee, Context context)
+    {
+        return new PropertyTranslation
+        {
+            Type = "bool",
+            Name = context.CurrentName,
+        };
+    }
+
+    private static ITranslation Null(IJsonSyntax visitee, Context context)
+    {
+        return new PropertyTranslation
+        {
+            Type = "object",
+            Name = context.CurrentName,
+        };
+    }
+
+    private static ClassTranslation SquashObjects(string className, IEnumerable<IJsonSyntax> objects, Context context)
+    {
+        var classes = objects
+            .Select(@object => Object(@object, context))
+            .ToArray();
+
+        var squashed = new ClassTranslation
+        {
+            Name = className.Singularize(),
+            Properties = new()
+        };
+
+        foreach (var @class in classes)
+        foreach (var prop in ((ClassTranslation)@class).Properties)
+            if (squashed.Properties.All(p => p.Name != prop.Name))
+                squashed.Properties.Add(prop);
+
+        return squashed;
+    }
 }

DevDisciples.Json.Tools/JsonFormatter.cs

@@ -1,45 +1,39 @@
 using DevDisciples.Json.Parser;
+using DevDisciples.Json.Parser.Syntax;
 using DevDisciples.Parsing;
 
 namespace DevDisciples.Json.Tools;
 
 public static partial class JsonFormatter
 {
-    public static VisitorContainer Visitors { get; }
+    private static VisitorContainer<IJsonSyntax, Context> Visitors { get; } = new();
 
     static JsonFormatter()
     {
-        Visitors = new();
+        Visitors.Register<JsonArraySyntax>(PrintArray);
-        Visitors.Register<JsonArray>(PrintArray);
+        Visitors.Register<JsonObjectSyntax>(PrintObject);
-        Visitors.Register<JsonObject>(PrintObject);
+        Visitors.Register<JsonStringSyntax>(PrintString);
-        Visitors.Register<JsonString>(PrintString);
+        Visitors.Register<JsonNumberSyntax>(PrintNumber);
-        Visitors.Register<JsonNumber>(PrintNumber);
+        Visitors.Register<JsonBoolSyntax>(PrintBool);
-        Visitors.Register<JsonBool>(PrintBool);
+        Visitors.Register<JsonNullSyntax>(PrintNull);
-        Visitors.Register<JsonNull>(PrintNull);
     }
 
     public static string Format(string source, Context? context)
     {
-        var nodes = JsonParser.Parse("<source>", source);
+        var node = JsonParser.Parse("<source>", source);
-        return Format(nodes, context);
+        return Format(node, context);
     }
 
-    private static string Format(ISyntaxNode visitee, Context? context = null)
+    public static string Format(IJsonSyntax visitee, Context? context = null)
     {
-        var ctx = context ?? new();
+        context ??= new();
-        Visitors[visitee.GetType()](visitee, ctx);
+        Visitors[visitee.GetType()](visitee, context);
-        return context!.Builder.ToString();
+        return context.Builder.ToString();
     }
 
-    private static Context ContextFromArgs(object[] args)
+    private static void PrintArray(IJsonSyntax visitee, Context context)
     {
-        return (args[0] as Context)!;
+        var array = (JsonArraySyntax)visitee;
-    }
-
-    private static void PrintArray(object visitee, object[] args)
-    {
-        var context = ContextFromArgs(args);
-        var array = (JsonArray)visitee;
 
         context.Builder.Append($"[{context.NewLine}");
         context.IncrementDepth();
@@ -48,7 +42,7 @@ public static partial class JsonFormatter
         {
             var node = array.Elements[i];
             context.Builder.Append(context.Indent);
-            Visitors[node.GetType()](node, args);
+            Visitors[node.GetType()](node, context);
             if (i < array.Elements.Length - 1) context.Builder.Append($",{context.NewLine}");
         }
 
@@ -56,10 +50,9 @@ public static partial class JsonFormatter
         context.Builder.Append($"{context.NewLine}{context.Indent}]");
     }
 
-    private static void PrintObject(object visitee, object[] args)
+    private static void PrintObject(IJsonSyntax visitee, Context context)
     {
-        var context = ContextFromArgs(args);
+        var @object = (JsonObjectSyntax)visitee;
-        var @object = (JsonObject)visitee;
 
         context.Builder.Append($"{{{context.NewLine}");
         context.IncrementDepth();
@@ -68,8 +61,8 @@ public static partial class JsonFormatter
         for (var i = 0; i < count; i++)
         {
             var property = @object.Properties.ElementAt(i);
-            context.Builder.Append($"{context.Indent}\"{property.Key}\":{context.Space}");
+            context.Builder.Append($"{context.Indent}\"{property.Key.Lexeme}\":{context.Space}");
-            Visitors[property.Value.GetType()](property.Value, args);
+            Visitors[property.Value.GetType()](property.Value, context);
             if (i < count - 1) context.Builder.Append($",{context.NewLine}");
         }
 
@@ -77,30 +70,26 @@ public static partial class JsonFormatter
         context.Builder.Append($"{context.NewLine}{context.Indent}}}");
     }
 
-    private static void PrintString(object visitee, object[] args)
+    private static void PrintString(IJsonSyntax visitee, Context context)
     {
-        var context = ContextFromArgs(args);
+        var @string = (JsonStringSyntax)visitee;
-        var @string = (JsonString)visitee;
         context.Builder.Append($"\"{@string.Token.Lexeme}\"");
     }
 
-    private static void PrintNumber(object visitee, object[] args)
+    private static void PrintNumber(IJsonSyntax visitee, Context context)
     {
-        var context = ContextFromArgs(args);
+        var number = (JsonNumberSyntax)visitee;
-        var number = (JsonNumber)visitee;
         context.Builder.Append($"{number.Value}");
     }
 
-    private static void PrintBool(object visitee, object[] args)
+    private static void PrintBool(IJsonSyntax visitee, Context context)
     {
-        var context = ContextFromArgs(args);
+        var @bool = (JsonBoolSyntax)visitee;
-        var @bool = (JsonBool)visitee;
         context.Builder.Append($"{@bool.Value.ToString().ToLower()}");
     }
 
-    private static void PrintNull(object visitee, object[] args)
+    private static void PrintNull(IJsonSyntax visitee, Context context)
     {
-        var context = ContextFromArgs(args);
         context.Builder.Append("null");
     }
 }

DevDisciples.Json.Tools/JsonPath.Interpreter.Context.cs

@@ -0,0 +1,14 @@
+using DevDisciples.Json.Parser.Syntax;
+
+namespace DevDisciples.Json.Tools;
+
+public static partial class JsonPath
+{
+    public static partial class Interpreter
+    {
+        public class Context
+        {
+            public IJsonSyntax Target { get; set; } = default!;
+        }
+    }
+}

DevDisciples.Json.Tools/JsonPath.Interpreter.cs

@@ -0,0 +1,167 @@
+using DevDisciples.Json.Parser;
+using DevDisciples.Json.Parser.Syntax;
+using DevDisciples.Parsing;
+using DevDisciples.Parsing.Extensions;
+
+namespace DevDisciples.Json.Tools;
+
+public static partial class JsonPath
+{
+    public static partial class Interpreter
+    {
+        private static readonly VisitorContainer<IJsonPathSyntax, Context> Visitors = new();
+
+        static Interpreter()
+        {
+            Visitors.Register<WildCardSyntax>(WildCardExpression);
+            Visitors.Register<PropertyAccessorSyntax>(PropertyAccessorExpression);
+            Visitors.Register<PropertySyntax>(PropertyExpression);
+            Visitors.Register<ArrayIndexSyntax>(ArrayIndexExpression);
+            Visitors.Register<ArrayIndexListSyntax>(ArrayIndexListExpression);
+            Visitors.Register<ObjectIndexSyntax>(ObjectIndexExpression);
+            Visitors.Register<ObjectIndexListSyntax>(ObjectIndexListExpression);
+        }
+
+        public static IJsonSyntax Evaluate(string source, string path)
+        {
+            var root = JsonParser.Parse("<json>", source);
+
+            if (root is not JsonArraySyntax && root is not JsonObjectSyntax)
+                throw Report.Error(root.Token, "Expected a JSON array or object.");
+
+            var expressions = Parser.Parse(path);
+
+            var context = new Context { Target = root };
+
+            foreach (var expr in expressions)
+                Visitors[expr.GetType()](expr, context);
+
+            return context.Target;
+        }
+
+        private static void Evaluate(IJsonPathSyntax node, Context context) => Visitors[node.GetType()](node, context);
+
+        private static void WildCardExpression(IJsonPathSyntax visitee, Context context)
+        {
+            switch (context.Target)
+            {
+                case JsonObjectSyntax @object:
+                    var elements = @object.Properties.Select(p => p.Value).ToArray();
+                    var target = new JsonArraySyntax(@object.Token, elements);
+                    context.Target = target;
+                    break;
+
+                case JsonArraySyntax array:
+                    context.Target = array;
+                    break;
+
+                default:
+                    var syntax = visitee.As<WildCardSyntax>();
+                    throw Report.Error(syntax.Token, "Invalid target for '*'.");
+            }
+        }
+
+        private static void PropertyAccessorExpression(IJsonPathSyntax visitee, Context context)
+        {
+            var accessor = visitee.As<PropertyAccessorSyntax>();
+            Evaluate(accessor.Getter, context);
+        }
+
+        private static void PropertyExpression(IJsonPathSyntax visitee, Context context)
+        {
+            var property = visitee.As<PropertySyntax>();
+
+            switch (context.Target)
+            {
+                case JsonObjectSyntax @object:
+                    foreach (var objectProperty in @object.Properties)
+                    {
+                        if (objectProperty.Key.Lexeme != property.Token.Lexeme) continue;
+                        context.Target = objectProperty.Value;
+                        return;
+                    }
+
+                    context.Target = new JsonNullSyntax();
+                    break;
+
+                default:
+                    context.Target = new JsonNullSyntax();
+                    break;
+            }
+        }
+
+        private static void ArrayIndexExpression(IJsonPathSyntax visitee, Context context)
+        {
+            if (context.Target is not JsonArraySyntax array)
+                throw Report.Error(context.Target.Token, "Integer indexes are only allowed on arrays.");
+
+            var index = visitee.As<ArrayIndexSyntax>();
+
+            var value = index.IndexAsInt;
+
+            if (value >= 0 && value < array.Elements.Length)
+                context.Target = array.Elements[value];
+
+            else throw Report.Error(index.Token, "Index out of range.");
+        }
+
+        private static void ArrayIndexListExpression(IJsonPathSyntax visitee, Context context)
+        {
+            var indices = visitee.As<ArrayIndexListSyntax>();
+
+            if (context.Target is not JsonArraySyntax array)
+                throw Report.Error(indices.Token, "Integer indices are only allowed on arrays.");
+
+            var list = new List<IJsonSyntax>();
+
+            for (var i = 0; i < indices.Indices.Length; i++)
+            {
+                var index = indices.ValueAt(i);
+
+                if (index >= 0 && index < array.Elements.Length)
+                    list.Add(array.Elements.ElementAt(index));
+            }
+
+            context.Target = new JsonArraySyntax(array.Token, list.ToArray());
+        }
+
+        private static void ObjectIndexExpression(IJsonPathSyntax visitee, Context context)
+        {
+            if (context.Target is not JsonObjectSyntax @object)
+                throw Report.Error(context.Target.Token, "String indices are only allowed on objects.");
+
+            var index = visitee.As<ObjectIndexSyntax>();
+
+            foreach (var property in @object.Properties)
+            {
+                if (property.Key.Lexeme != index.Index.Lexeme) continue;
+                context.Target = property.Value;
+                return;
+            }
+
+            context.Target = new JsonNullSyntax(@object.Token);
+        }
+
+        private static void ObjectIndexListExpression(IJsonPathSyntax visitee, Context context)
+        {
+            if (context.Target is not JsonObjectSyntax @object)
+                throw Report.Error(context.Target.Token, "Index strings are only allowed on objects.");
+
+            var indices = visitee.As<ObjectIndexListSyntax>();
+
+            var elements = new List<IJsonSyntax>();
+
+            foreach (var index in indices.Indexes)
+            {
+                foreach (var property in @object.Properties)
+                {
+                    if (property.Key.Lexeme != index.Lexeme) continue;
+                    elements.Add(property.Value);
+                    break;
+                }
+            }
+
+            context.Target = new JsonArraySyntax(@object.Token, elements.ToArray());
+        }
+    }
+}

DevDisciples.Json.Tools/JsonPath.Lexer.cs

@@ -0,0 +1,38 @@
+using DevDisciples.Parsing;
+
+namespace DevDisciples.Json.Tools;
+
+public static partial class JsonPath
+{
+    public class Lexer : Lexer<JsonPathToken>
+    {
+        public static readonly Lexer Default = new();
+
+        protected override JsonPathToken EndOfSource => JsonPathToken.EndOfSource;
+
+        public Lexer()
+        {
+            Rules =
+            [
+                DefaultRule.NewLine,
+                DefaultRule.Number(JsonPathToken.Number),
+                DefaultRule.Identifier(JsonPathToken.Identifier),
+                DefaultRule.DoubleQuoteString(JsonPathToken.String),
+
+                ctx => DefaultRule.IgnoreWhitespace(ctx),
+                ctx => Match(ctx, JsonPathToken.False, "false"),
+                ctx => Match(ctx, JsonPathToken.True, "true"),
+                ctx => Match(ctx, JsonPathToken.Null, "null"),
+                ctx => Match(ctx, JsonPathToken.DotDot, ".."),
+                ctx => Match(ctx, JsonPathToken.DollarSign, '$'),
+                ctx => Match(ctx, JsonPathToken.Asterisk, '*'),
+                ctx => Match(ctx, JsonPathToken.Dot, '.'),
+                ctx => Match(ctx, JsonPathToken.Minus, '-'),
+                ctx => Match(ctx, JsonPathToken.Colon, ':'),
+                ctx => Match(ctx, JsonPathToken.LeftBracket, '['),
+                ctx => Match(ctx, JsonPathToken.Comma, ','),
+                ctx => Match(ctx, JsonPathToken.RightBracket, ']'),
+            ];
+        }
+    }
+}

DevDisciples.Json.Tools/JsonPath.Parser.Context.cs

@@ -0,0 +1,16 @@
+using DevDisciples.Parsing;
+
+namespace DevDisciples.Json.Tools;
+
+public static partial class JsonPath
+{
+    public static partial class Parser
+    {
+        public class Context : ParserContext<JsonPathToken>
+        {
+            public Context(Memory<Lexer<JsonPathToken>.Token> tokens) : base(tokens, JsonPathToken.EndOfSource)
+            {
+            }
+        }
+    }
+}

DevDisciples.Json.Tools/JsonPath.Parser.cs

@@ -0,0 +1,110 @@
+using DevDisciples.Parsing;
+
+namespace DevDisciples.Json.Tools;
+
+public static partial class JsonPath
+{
+    public static partial class Parser
+    {
+        public static List<IJsonPathSyntax> Parse(string path)
+        {
+            var pathTokens = Lexer.Default.Lex("<path>", path);
+            var context = new Context(pathTokens.ToArray());
+
+            context.Match(JsonPathToken.DollarSign); // Match the '$' eagerly. This will make it optional by default.
+
+            var syntax = new List<IJsonPathSyntax>();
+            while (!context.Ended())
+                syntax.Add(Expression(context));
+
+            return syntax;
+        }
+
+        private static IJsonPathSyntax Expression(Context context)
+        {
+            if (context.Match(JsonPathToken.Dot))
+                return PropertyAccessorExpression(context);
+
+            if (context.Match(JsonPathToken.LeftBracket))
+                return IndexAccessorExpression(context);
+
+            throw context.Error("Invalid expression.");
+        }
+
+        private static IJsonPathSyntax PropertyAccessorExpression(Context context)
+        {
+            var token = context.Previous();
+
+            IJsonPathSyntax getter;
+
+            if (context.Match(JsonPathToken.Asterisk))
+                getter = new WildCardSyntax(context.Previous());
+
+            else if (context.Match(JsonPathToken.Identifier))
+                getter = new PropertySyntax(context.Previous());
+
+            else throw context.Error("Expected a getter expression");
+
+            return new PropertyAccessorSyntax(token, getter);
+        }
+
+        private static IJsonPathSyntax IndexAccessorExpression(Context context)
+        {
+            var token = context.Previous();
+
+            IJsonPathSyntax syntax;
+
+            if (context.Match(JsonPathToken.Asterisk))
+                syntax = new WildCardSyntax(context.Previous());
+
+            else if (context.Match(JsonPathToken.Number))
+                syntax = ArrayIndexExpression(token, context);
+
+            else if (context.Match(JsonPathToken.String))
+                syntax = ObjectIndexExpression(token, context);
+
+            else throw context.Error("Expected an index expression.");
+
+            context.Consume(JsonPathToken.RightBracket, "Expected ']' after index expression.");
+
+            return syntax;
+        }
+
+        private static IJsonPathSyntax ArrayIndexExpression(Lexer<JsonPathToken>.Token token, Context context)
+        {
+            var index = context.Previous();
+
+            if (!context.Match(JsonPathToken.Comma)) return new ArrayIndexSyntax(token, index);
+
+            var indexes = new List<Lexer<JsonPathToken>.Token> { index };
+
+            do
+            {
+                index = context.Consume(JsonPathToken.Number, "Invalid array index.");
+
+                if (!int.TryParse(index.Lexeme, out _)) throw context.Error(index, "Invalid array index.");
+
+                indexes.Add(index);
+            } while (!context.Ended() && context.Match(JsonPathToken.Comma));
+
+            return new ArrayIndexListSyntax(token, indexes.ToArray());
+        }
+
+        private static IJsonPathSyntax ObjectIndexExpression(Lexer<JsonPathToken>.Token token, Context context)
+        {
+            var index = context.Previous();
+
+            if (!context.Match(JsonPathToken.Comma)) return new ObjectIndexSyntax(token, index);
+
+            var indexes = new List<Lexer<JsonPathToken>.Token> { index };
+
+            do
+            {
+                index = context.Consume(JsonPathToken.String, "Invalid object index.");
+                indexes.Add(index);
+            } while (!context.Ended() && context.Match(JsonPathToken.Comma));
+
+            return new ObjectIndexListSyntax(token, indexes.ToArray());
+        }
+    }
+}

DevDisciples.Json.Tools/JsonPath.Syntax.cs

@@ -0,0 +1,96 @@
+using DevDisciples.Parsing;
+
+namespace DevDisciples.Json.Tools;
+
+// See https://docs.hevodata.com/sources/engg-analytics/streaming/rest-api/writing-jsonpath-expressions/
+
+public static partial class JsonPath
+{
+    
+    public interface IJsonPathSyntax
+    {
+        public Lexer<JsonPathToken>.Token Token { get; }
+    }
+    
+    public readonly struct WildCardSyntax : IJsonPathSyntax
+    {
+        public Lexer<JsonPathToken>.Token Token { get; }
+
+        public WildCardSyntax(Lexer<JsonPathToken>.Token token)
+        {
+            Token = token;
+        }
+    }
+
+    public readonly struct ArrayIndexSyntax : IJsonPathSyntax
+    {
+        public Lexer<JsonPathToken>.Token Token { get; }
+        public Lexer<JsonPathToken>.Token Index { get; }
+        public int IndexAsInt => int.Parse(Token.Lexeme);
+
+        public ArrayIndexSyntax(Lexer<JsonPathToken>.Token token, Lexer<JsonPathToken>.Token index)
+        {
+            Token = token;
+            Index = index;
+        }
+    }
+
+    public readonly struct ArrayIndexListSyntax : IJsonPathSyntax
+    {
+        public Lexer<JsonPathToken>.Token Token { get; }
+        public Lexer<JsonPathToken>.Token[] Indices { get; }
+        public int ValueAt(int index) => int.Parse(Indices[index].Lexeme);
+
+        public ArrayIndexListSyntax(Lexer<JsonPathToken>.Token token, Lexer<JsonPathToken>.Token[] indices)
+        {
+            Token = token;
+            Indices = indices;
+        }
+    }
+
+    public readonly struct ObjectIndexSyntax : IJsonPathSyntax
+    {
+        public Lexer<JsonPathToken>.Token Token { get; }
+        public Lexer<JsonPathToken>.Token Index { get; }
+
+        public ObjectIndexSyntax(Lexer<JsonPathToken>.Token token, Lexer<JsonPathToken>.Token index)
+        {
+            Token = token;
+            Index = index;
+        }
+    }
+
+    public readonly struct ObjectIndexListSyntax : IJsonPathSyntax
+    {
+        public Lexer<JsonPathToken>.Token Token { get; }
+        public Lexer<JsonPathToken>.Token[] Indexes { get; }
+
+        public ObjectIndexListSyntax(Lexer<JsonPathToken>.Token token, Lexer<JsonPathToken>.Token[] indexes)
+        {
+            Token = token;
+            Indexes = indexes;
+        }
+    }
+
+    public readonly struct PropertyAccessorSyntax : IJsonPathSyntax
+    {
+        public Lexer<JsonPathToken>.Token Token { get; }
+        public IJsonPathSyntax Getter { get; }
+
+        public PropertyAccessorSyntax(Lexer<JsonPathToken>.Token token, IJsonPathSyntax getter)
+        {
+            Token = token;
+            Getter = getter;
+        }
+    }
+
+    public readonly struct PropertySyntax : IJsonPathSyntax
+    {
+        public Lexer<JsonPathToken>.Token Token { get; }
+
+        public PropertySyntax(Lexer<JsonPathToken>.Token token)
+        {
+            Token = token;
+        }
+    }
+}

DevDisciples.Json.Tools/JsonPathToken.cs

@@ -0,0 +1,21 @@
+namespace DevDisciples.Json.Tools;
+
+public enum JsonPathToken
+{
+    DollarSign,
+    Asterisk,
+    Dot,
+    DotDot,
+    LeftBracket,
+    RightBracket,
+    Identifier,
+    String,
+    Minus,
+    Number,
+    Comma,
+    Colon,
+    Null,
+    True,
+    False,
+    EndOfSource,
+}

DevDisciples.Parsing/Extensions/CastingExtensions.cs

@@ -0,0 +1,10 @@
+namespace DevDisciples.Parsing.Extensions;
+
+public static class CastingExtensions
+{
+    public static T As<T>(this object @object)
+    {
+        ArgumentNullException.ThrowIfNull(@object);
+        return (T)@object;
+    }
+}

DevDisciples.Parsing/ISyntaxNode.cs

@@ -1,3 +0,0 @@
-namespace DevDisciples.Parsing;
-
-public interface ISyntaxNode { }

DevDisciples.Parsing/Lexer.Rule.cs

@@ -187,10 +187,8 @@ public abstract partial class Lexer<TToken> where TToken : Enum
 
                 ProcessDigits(src);
 
-                if (src.Peek() == '.' && IsDigit(src.Peek(1)))
+                if (IsDigit(src.Peek(1)) && src.Match('.'))
                 {
-                    // Consume the "."                                      
-                    src.Advance();
                     ProcessDigits(src);
                 }
 

DevDisciples.Parsing/ParsableStream.cs

@@ -6,11 +6,11 @@ public abstract class ParsableStream<T>
 
     protected ReadOnlySpan<T> Tokens => _tokens.Span;
 
-    public int Position { get; set; }
+    protected int Position { get; set; }
 
     public T Current => Position < Tokens.Length ? Tokens[Position] : default!;
 
-    public ParsableStream(ReadOnlyMemory<T> tokens)
+    protected ParsableStream(ReadOnlyMemory<T> tokens)
     {
         _tokens = tokens;
     }

DevDisciples.Parsing/ParserContext.cs

@@ -2,9 +2,9 @@
 
 public class ParserContext<TToken> : ParsableStream<Lexer<TToken>.Token> where TToken : Enum
 {
-    protected readonly TToken _endOfSource;
+    private readonly TToken _endOfSource;
 
-    public ParserContext(Memory<Lexer<TToken>.Token> tokens, TToken endOfSource) : base(tokens)
+    protected ParserContext(Memory<Lexer<TToken>.Token> tokens, TToken endOfSource) : base(tokens)
     {
         _endOfSource = endOfSource;
     }
@@ -98,9 +98,4 @@ public class ParserContext<TToken> : ParsableStream<Lexer<TToken>.Token> where T
     {
         return new ParsingException(Report.FormatMessage(token, message));
     }
-
-    public void Halt(Lexer<TToken>.Token token, string message)
-    {
-        throw new ParsingException(Report.FormatMessage(token, message));
-    }
 }

DevDisciples.Parsing/Report.cs

@@ -2,7 +2,7 @@
 
 public static class Report
 {
-    public static Exception Error(ISourceLocation token, string message)
+    public static ParsingException Error(ISourceLocation token, string message)
     {
         return new ParsingException(FormatMessage(token, message));
     }

DevDisciples.Parsing/Visitor.cs

@@ -1,8 +1,10 @@
-namespace DevDisciples.Parsing;
+namespace DevDisciples.Parsing;
 
 public static class Visitor
 {
-    public delegate void Visit(object visitee, params object[] args);
+    public delegate void Visit<TVisitee>(TVisitee visitee);
-    public delegate TOut Visit<TOut>(object visitee, params object[] args);
+
-    public delegate TOut Visit<TIn, TOut>(TIn visitee, params object[] args);
+    public delegate void Visit<TVisitee, TContext>(TVisitee visitee, TContext context);
+
+    public delegate TOut Visit<TVisitee, TContext, TOut>(TVisitee visitee, TContext context);
 }

DevDisciples.Parsing/VisitorContainer.cs

@@ -1,42 +1,40 @@
-namespace DevDisciples.Parsing;
+namespace DevDisciples.Parsing;
 
-public class VisitorContainer
+public class VisitorContainer<TBase>
 {
-    private Dictionary<Type, Visitor.Visit> Visitors { get; } = new();
+    private Dictionary<Type, Visitor.Visit<TBase>> Visitors { get; } = new();
-    private Visitor.Visit Default { get; set; } = default!;
+    private Visitor.Visit<TBase> Default { get; set; } = default!;
 
-    public void Register<TVisitee>(Visitor.Visit visitor)
+    public void Register<T>(Visitor.Visit<TBase> visitor)
     {
-        Visitors[typeof(TVisitee)] = visitor;
+        Visitors[typeof(T)] = visitor;
     }
 
-    public Visitor.Visit this[Type type] => Visitors.GetValueOrDefault(type, Default);
+    public Visitor.Visit<TBase> this[Type type] => Visitors.GetValueOrDefault(type, Default);
 }
 
-public class VisitorContainer<T>
+public class VisitorContainer<TBase, TContext>
 {
-    protected Dictionary<Type, Visitor.Visit<T>> Visitors { get; } = new();
+    private Dictionary<Type, Visitor.Visit<TBase, TContext>> Visitors { get; } = new();
-    public Visitor.Visit<T> Default { get; } = default!;
+    private Visitor.Visit<TBase, TContext> Default { get; set; } = default!;
 
-
+    public void Register<T>(Visitor.Visit<TBase, TContext> visitor)
-    public VisitorContainer<T> Register<TVisitee>(Visitor.Visit<T> visitor)
     {
-        Visitors[typeof(TVisitee)] = visitor;
+        Visitors[typeof(T)] = visitor;
-        return this;
     }
 
-    public Visitor.Visit<T> this[Type type] => Visitors.ContainsKey(type) ? Visitors[type] : Default;
+    public Visitor.Visit<TBase, TContext> this[Type type] => Visitors.GetValueOrDefault(type, Default);
 }
 
-public class VisitorContainer<TIn, TOut>
+public class VisitorContainer<TBase, TContext, TResult>
 {
-    protected Dictionary<Type, Visitor.Visit<TIn, TOut>> Visitors { get; } = new();
+    private Dictionary<Type, Visitor.Visit<TBase, TContext, TResult>> Visitors { get; } = new();
-    public Visitor.Visit<TIn, TOut> Default { get; } = default!;
+    private Visitor.Visit<TBase, TContext, TResult> Default { get; set; } = default!;
 
-    public void Register<TVisitee>(Visitor.Visit<TIn, TOut> visitor)
+    public void Register<T>(Visitor.Visit<TBase, TContext, TResult> visitor)
     {
-        Visitors[typeof(TVisitee)] = visitor;
+        Visitors[typeof(T)] = visitor;
     }
 
-    public Visitor.Visit<TIn, TOut> this[Type type] => Visitors.ContainsKey(type) ? Visitors[type] : Default;
+    public Visitor.Visit<TBase, TContext, TResult> this[Type type] => Visitors.GetValueOrDefault(type, Default);
 }