using System;
using System.Text;

namespace TinaX
{
    public static class StringHelper
    {
        /// <summary>
        /// Generate a random letter (with case), a string of numbers. | 生成一个随机字母（含大小写），数字的字符串。
        /// </summary>
        /// <param name="length">The length of the generate string. | 生成字符串长度</param>
        /// <param name="seed">The random seed. | 随机种子</param>
        /// <returns></returns>
        public static string GetRandom(int length = 16, int? seed = null)
        {
            length = Math.Max(1, length);

            var ret = new StringBuilder();
            var random = MakeRandom(seed);
            for (int len; (len = ret.Length) < length;)
            {
                var size = length - len;
                var bytes = new byte[size];
                random.NextBytes(bytes);

                var code = Replace(new[] { "/", "+", "=" }, string.Empty, Convert.ToBase64String(bytes));
                ret.Append(code.Substring(0, Math.Min(size, code.Length)));
            }
            return ret.ToString();
        }

        /// <summary>
        /// Replace the match in the specified string. | 在规定字符串中替换匹配项。
        /// </summary>
        /// <param name="matches">An array of the match string. </param>
        /// <param name="replace">The replacement value.</param>
        /// <param name="str">The specified string.</param>
        /// <returns></returns>
        public static string Replace(string[] matches, string replace, string str)
        {
            matches = matches ?? Array.Empty<string>();
            replace = replace ?? string.Empty;

            if (string.IsNullOrEmpty(str))
            {
                return string.Empty;
            }

            foreach (var match in matches)
            {
                if (match == null)
                {
                    continue;
                }

                str = str.Replace(match, replace);
            }

            return str;
        }


        private static byte[] UTF8_BOM = new byte[3] { 239, 187, 191 };

        public static bool HaveUTF8BOM(ref byte[] data)
        {
            if (data != null && data.Length > 3)
                return data[0] == UTF8_BOM[0] && data[1] == UTF8_BOM[1] && data[2] == UTF8_BOM[2];
            else
                return false;
        }

        public static bool HaveUTF8BOM(byte[] data)
        {
            if (data != null && data.Length > 3)
                return data[0] == UTF8_BOM[0] && data[1] == UTF8_BOM[1] && data[2] == UTF8_BOM[2];
            else
                return false;
        }

        public static string RemoveUTF8BOM(byte[] data)
        {
            if (HaveUTF8BOM(ref data))
                return Encoding.UTF8.GetString(data, 3, data.Length - 3);
            else
                return Encoding.UTF8.GetString(data);
        }

        private static Random MakeRandom(int? seed = null)
        {
            return new Random(seed.GetValueOrDefault(MakeSeed()));
        }

        private static int MakeSeed()
        {
            return Environment.TickCount ^ Guid.NewGuid().GetHashCode();
        }
    }
}