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

namespace Teknik.Utilities
{
    public static class StringHelper
    {
        public static string RandomString(int length)
        {
            return RandomString(length, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789");
        }

        public static string RandomString(int length, string allowedChars)
        {
            const int byteSize = 0x100;
            var allowedCharSet = new HashSet<char>(allowedChars).ToArray();
            if (byteSize < allowedCharSet.Length) throw new ArgumentException(String.Format("allowedChars may contain no more than {0} characters.", byteSize));

            // Guid.NewGuid and System.Random are not particularly random. By using a
            // cryptographically-secure random number generator, the caller is always
            // protected, regardless of use.
            using (var rng = new System.Security.Cryptography.RNGCryptoServiceProvider())
            {
                var result = new StringBuilder();
                var buf = new byte[128];
                while (result.Length < length)
                {
                    rng.GetBytes(buf);
                    for (var i = 0; i < buf.Length && result.Length < length; ++i)
                    {
                        // Divide the byte into allowedCharSet-sized groups. If the
                        // random value falls into the last group and the last group is
                        // too small to choose from the entire allowedCharSet, ignore
                        // the value in order to avoid biasing the result.
                        var outOfRangeStart = byteSize - (byteSize % allowedCharSet.Length);
                        if (outOfRangeStart <= buf[i]) continue;
                        result.Append(allowedCharSet[buf[i] % allowedCharSet.Length]);
                    }
                }
                return result.ToString();
            }
        }

        public static string GetBytesReadable(long i)
        {
            // Get absolute value
            long absolute_i = (i < 0 ? -i : i);
            // Determine the suffix and readable value
            string suffix;
            double readable;
            if (absolute_i >= 0x1000000000000000) // Exabyte
            {
                suffix = "EB";
                readable = (i >> 50);
            }
            else if (absolute_i >= 0x4000000000000) // Petabyte
            {
                suffix = "PB";
                readable = (i >> 40);
            }
            else if (absolute_i >= 0x10000000000) // Terabyte
            {
                suffix = "TB";
                readable = (i >> 30);
            }
            else if (absolute_i >= 0x40000000) // Gigabyte
            {
                suffix = "GB";
                readable = (i >> 20);
            }
            else if (absolute_i >= 0x100000) // Megabyte
            {
                suffix = "MB";
                readable = (i >> 10);
            }
            else if (absolute_i >= 0x400) // Kilobyte
            {
                suffix = "KB";
                readable = i;
            }
            else
            {
                return i.ToString("0 B"); // Byte
            }
            // Divide by 1024 to get fractional value
            readable = (readable / 1024);
            // Return formatted number with suffix
            return readable.ToString("0.### ") + suffix;
        }

        public static KeyValuePair<string, string> ParseBasicAuthHeader(string value)
        {
            return ParseBasicAuthHeader(value, Encoding.UTF8);
        }

        public static KeyValuePair<string, string> ParseBasicAuthHeader(string value, Encoding encoding)
        {
            KeyValuePair<string, string> result = new KeyValuePair<string, string>();

            if (!string.IsNullOrEmpty(value))
            {
                byte[] rawVal = Convert.FromBase64String(value);
                string stringVal = encoding.GetString(rawVal);
                string[] parts = stringVal.Split(new char[] { ':' }, StringSplitOptions.RemoveEmptyEntries);
                if (parts.Length > 1)
                {
                    result = new KeyValuePair<string, string>(parts[0], parts[1]);
                }
            }

            return result;
        }
    }
}