Pretty printing JSON data to a file

PrettyJsonTest.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.Serialization;
using System.Text;
using System.Threading.Tasks;
using ServiceStack.Text;

namespace PrettyJsonTest
{
    class Program
    {
        static void Main(string[] args)
        {
            //  Load up some test data:
            TestData data1 = new TestData()
            {
                Name = "Test",
                Description = "This is a nice long description",
                Score = 42
            };

            TestData data2 = new TestData()
            {
                Name = "Test",
                Description = "This is a nice long description",
                Score = 42
            };

            TestData data3 = new TestData()
            {
                Name = "Test",
                Description = "This is a nice long description",
                Score = 42
            };

            List<TestData> listOfStuff = new List<TestData>();
            listOfStuff.Add(data1);
            listOfStuff.Add(data2);
            listOfStuff.Add(data3);

            //  Write it out to a file:
            string jsonString = listOfStuff.ToJson();
            string formattedJSON = PrettyJson.FormatJson(jsonString);
            File.WriteAllText(@"c:\temp\test.json", formattedJSON);
        }
    }

    [DataContract]
    class TestData
    {
        [DataMember]
        public string Name { get; set; }

        [DataMember]
        public string Description { get; set; }

        [DataMember]
        public int Score { get; set; }
    }

    public class PrettyJson
    {
        private const string INDENT_STRING = "    ";

        public static string FormatJson(string str)
        {
            var indent = 0;
            var quoted = false;
            var sb = new StringBuilder();
            for(var i = 0; i < str.Length; i++)
            {
                var ch = str[i];
                switch(ch)
                {
                    case '{':
                    case '[':
                        sb.Append(ch);
                        if(!quoted)
                        {
                            sb.AppendLine();
                            Enumerable.Range(0, ++indent).ForEach(item => sb.Append(INDENT_STRING));
                        }
                        break;
                    case '}':
                    case ']':
                        if(!quoted)
                        {
                            sb.AppendLine();
                            Enumerable.Range(0, --indent).ForEach(item => sb.Append(INDENT_STRING));
                        }
                        sb.Append(ch);
                        break;
                    case '"':
                        sb.Append(ch);
                        bool escaped = false;
                        var index = i;
                        while(index > 0 && str[--index] == '\\')
                            escaped = !escaped;
                        if(!escaped)
                            quoted = !quoted;
                        break;
                    case ',':
                        sb.Append(ch);
                        if(!quoted)
                        {
                            sb.AppendLine();
                            Enumerable.Range(0, indent).ForEach(item => sb.Append(INDENT_STRING));
                        }
                        break;
                    case ':':
                        sb.Append(ch);
                        if(!quoted)
                            sb.Append(" ");
                        break;
                    default:
                        sb.Append(ch);
                        break;
                }
            }
            return sb.ToString();
        }
    }

    static class Extensions
    {
        public static void ForEach<T>(this IEnumerable<T> ie, Action<T> action)
        {
            foreach(var i in ie)
            {
                action(i);
            }
        }
    }
}