using System;

namespace Cosmos.Common.Extensions
{
    // This class duplicates BitConvertor. BitConvertor uses ulong though and currently does not
    // work in Cosmos. But even when it does work, this syntax is more convenient and we use
    // these conversions frequently.
    // TODO: In the future we should find a way to inline and asm these, or maybe use way to map
    // a record structure on top of a byte array for speed.
    //
    // BitConverter also uses platform specific endianness and cannot be changed.
    // Since we read from disk, network etc we must be able to specify and change endianness.
    //
    // Default methods are LittleEndian
    static public class ByteConverter
    {
        static public UInt16 ToUInt16(this byte[] n, UInt64 aPos)
        {
            return (UInt16)(n[aPos + 1] << 8 | n[aPos]);
        }

        static public UInt32 ToUInt32(this byte[] n, UInt64 aPos)
        {
            return (UInt32)(n[aPos + 3] << 24 | n[aPos + 2] << 16 | n[aPos + 1] << 8 | n[aPos]);
        }

        public static void SetUInt16(this byte[] n, UInt64 aPos, UInt16 value)
        {
            n[aPos + 0] = (byte)value;
            n[aPos + 1] = (byte)(value >> 8);
        }

        public static void SetUInt32(this byte[] n, UInt64 aPos, UInt32 value)
        {
            n[aPos + 0] = (byte)value;
            n[aPos + 1] = (byte)(value >> 8);
            n[aPos + 2] = (byte)(value >> 16);
            n[aPos + 3] = (byte)(value >> 24);
        }

        public static void SetUInt64(this byte[] n, UInt64 aPos, UInt64 value)
        {
            n[aPos + 0] = (byte)value;
            n[aPos + 1] = (byte)(value >> 8);
            n[aPos + 2] = (byte)(value >> 16);
            n[aPos + 3] = (byte)(value >> 24);
            n[aPos + 4] = (byte)(value >> 32);
            n[aPos + 5] = (byte)(value >> 40);
            n[aPos + 6] = (byte)(value >> 48);
            n[aPos + 7] = (byte)(value >> 56);
        }

        static public string GetAsciiString(this byte[] n, UInt32 aStart, UInt32 aCharCount)
        {
            var xChars = new char[aCharCount];
            for (int i = 0; i < aCharCount; i++)
            {
                xChars[i] = (char)n[(aStart) + i];
                if (xChars[i] == 0)
                {
                    return new string(xChars, 0, i);
                }
            }
            return new string(xChars);
        }

        static public string GetUtf8String(this byte[] n, UInt32 aStart, uint aCharCount)
        {
            // TODO: This method handles ASCII only currently, no unicode.
            var xChars = new char[aCharCount];
            for (int i = 0; i < aCharCount; i++)
            {
                xChars[i] = (char)n[(aStart) + i];
                if (xChars[i] == 0)
                {
                    return new string(xChars, 0, i);
                }
            }
            return new string(xChars);
        }

        static public byte[] GetUtf8Bytes(this string n, UInt32 aStart, UInt32 aCharCount)
        {
            // TODO: This method handles ASCII only currently, no unicode.
            var xBytes = new byte[aCharCount];
            for (int i = 0; i < aCharCount; i++)
            {
                xBytes[i] = (byte)n[(int)((aStart) + i)];
            }
            return xBytes;
        }

        static public string GetUtf16String(this byte[] n, UInt32 aStart, UInt32 aCharCount)
        {
            //TODO: This routine only handles ASCII. It does not handle unicode yet.
            var xChars = new char[aCharCount];
            for (int i = 0; i < aCharCount; i++)
            {
                UInt32 xPos = (UInt32)(aStart + i * 2);
                var xChar = (UInt16)(n[xPos + 1] << 8 | n[xPos]);
                if (xChar == 0)
                {
                    return new string(xChars, 0, i);
                }
                xChars[i] = (char)xChar;
            }
            return new string(xChars);
        }
    }
}