using System.Text;

namespace YLErp.Helpers
{
    static class SqlHelper
    {
        enum CharClass : byte
        {
            None,
            Quote,
            Backslash
        }

        private const string stringOfBackslashChars = "\u005c\u00a5\u0160\u20a9\u2216\ufe68\uff3c";
        private const string stringOfQuoteChars =
            "\u0022\u0027\u0060\u00b4\u02b9\u02ba\u02bb\u02bc\u02c8\u02ca\u02cb\u02d9\u0300\u0301\u2018\u2019\u201a\u2032\u2035\u275b\u275c\uff07";

        private static CharClass[] charClassArray;

        static SqlHelper()
        {
            charClassArray = MakeCharClassArray();
        }

        private static CharClass[] MakeCharClassArray()
        {
            CharClass[] a = new CharClass[65536];
            foreach (char c in stringOfBackslashChars)
            {
                a[c] = CharClass.Backslash;
            }
            foreach (char c in stringOfQuoteChars)
            {
                a[c] = CharClass.Quote;
            }
            return a;
        }

        private static bool NeedsQuoting(string s)
        {
            return s.Any(c => charClassArray[c] != CharClass.None);
        }

        /// <summary>
        /// Escapes the string.
        /// </summary>
        /// <param name="value">The string to escape.</param>
        /// <returns>The string with all quotes escaped.</returns>
        public static string EscapeString(string value)
        {
            if (!NeedsQuoting(value))
            {
                return value;
            }

            StringBuilder sb = new StringBuilder();

            foreach (char c in value)
            {
                CharClass charClass = charClassArray[c];
                if (charClass != CharClass.None)
                {
                    sb.Append("\\");
                }
                sb.Append(c);
            }
            return sb.ToString();
        }

        /// <summary>
        /// Replaces quotes with double quotes.
        /// </summary>
        /// <param name="value">The string to modidify.</param>
        /// <returns>A string containing double quotes instead of single quotes.</returns>
        public static string DoubleQuoteString(string value)
        {
            if (!NeedsQuoting(value))
            {
                return value;
            }

            StringBuilder sb = new StringBuilder();
            foreach (char c in value)
            {
                CharClass charClass = charClassArray[c];
                if (charClass == CharClass.Quote)
                {
                    sb.Append(c);
                }
                else if (charClass == CharClass.Backslash)
                {
                    sb.Append("\\");
                }

                sb.Append(c);
            }
            return sb.ToString();
        }
    }
}