using System;
using System.Text;
using System.Collections.Generic;
using System.Linq;

namespace ln.json
{
	public class JSONString : JSONValue
	{
		static System.Tuple<char,char>[] escapeCharacters = {
			System.Tuple.Create('\\','\\'),
			System.Tuple.Create('/','/'),
			System.Tuple.Create('"','"'),
			System.Tuple.Create('b','\b'),
			System.Tuple.Create('f','\f'),
			System.Tuple.Create('n','\n'),
			System.Tuple.Create('r','\r'),
			System.Tuple.Create('t','\t'),
		};

        static HashSet<char> escapeSet = new HashSet<char>(escapeCharacters.Select((x) => x.Item2));

        public string Value { get; private set; }
        public override object ToNative() => Value;

        public JSONString(String value)
			:base(JSONValueType.STRING)
		{
            Value = value;
		}

        public override string ToString()
        {
            return String.Format("\"{0}\"", Escape(Value));
        }

        public static string Escape(string source){
            StringBuilder sb = new StringBuilder();
			foreach (char ch in source){
                if (escapeSet.Contains(ch)) {
                    foreach (System.Tuple<char, char> repl in escapeCharacters) {
                        if (repl.Item2 == ch) {
                            sb.Append("\\");
                            sb.Append(repl.Item1);
                            break;
                        }
                    }
                }
                else if (ch < 128)
                {
                    sb.Append(ch);
                } else {
                    byte[] bytes = BitConverter.GetBytes((int)ch);
                    sb.Append("\\u");
                    sb.AppendFormat("{0:x2}{1:x2}", bytes[1], bytes[0]);
                }
			}
			return sb.ToString();
		}

        public static string Unescape(string jsonString)
		{
			StringBuilder sb = new StringBuilder();
			CharEnumerator ce = jsonString.GetEnumerator();
			char[] hex = new char[4];
				
			while (ce.MoveNext()){

				if (ce.Current == '\\'){
					ce.MoveNext();

                    if (ce.Current == 'u')
                    {
                        for (int n = 0; n < 4; n++)
                        {
                            ce.MoveNext();
                            hex[3 - n] = ce.Current;
                        }
                        sb.Append((char)Convert.ToInt16(new String(hex),16));
                    }
                    else
                    {
                        foreach (System.Tuple<char, char> repl in escapeCharacters)
                        {
                            if (repl.Item1 == ce.Current)
                            {
                                sb.Append(repl.Item2);
                                break;
                            }
                        }
                    }
				} else {
					sb.Append(ce.Current);
				}
			}
			return sb.ToString();
		}
	}
}