using System;
using System.Text;

using Org.BouncyCastle.Utilities;

namespace Org.BouncyCastle.Asn1
{
	public class DerBitString
		: DerStringBase
	{
		private static readonly char[] table
			= { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };

		private readonly byte[]	data;
		private readonly int	padBits;

		/**
		 * return the correct number of pad bits for a bit string defined in
		 * a 32 bit constant
		 */
		static internal int GetPadBits(
			int bitString)
		{
			int val = 0;
			for (int i = 3; i >= 0; i--)
			{
				//
				// this may look a little odd, but if it isn't done like this pre jdk1.2
				// JVM's break!
				//
				if (i != 0)
				{
					if ((bitString >> (i * 8)) != 0)
					{
						val = (bitString >> (i * 8)) & 0xFF;
						break;
					}
				}
				else
				{
					if (bitString != 0)
					{
						val = bitString & 0xFF;
						break;
					}
				}
			}

			if (val == 0)
			{
				return 7;
			}

			int bits = 1;

			while (((val <<= 1) & 0xFF) != 0)
			{
				bits++;
			}

			return 8 - bits;
		}

		/**
		 * return the correct number of bytes for a bit string defined in
		 * a 32 bit constant
		 */
		static internal byte[] GetBytes(
			int bitString)
		{
			int bytes = 4;
			for (int i = 3; i >= 1; i--)
			{
				if ((bitString & (0xFF << (i * 8))) != 0)
				{
					break;
				}
				bytes--;
			}

			byte[] result = new byte[bytes];
			for (int i = 0; i < bytes; i++)
			{
				result[i] = (byte) ((bitString >> (i * 8)) & 0xFF);
			}

			return result;
		}

		/**
		 * return a Bit string from the passed in object
		 *
		 * @exception ArgumentException if the object cannot be converted.
		 */
		public static DerBitString GetInstance(
			object obj)
		{
			if (obj == null || obj is DerBitString)
			{
				return (DerBitString) obj;
			}

			throw new ArgumentException("illegal object in GetInstance: " + obj.GetType().Name);
		}

		/**
		 * return a Bit string from a tagged object.
		 *
		 * @param obj the tagged object holding the object we want
		 * @param explicitly true if the object is meant to be explicitly
		 *              tagged false otherwise.
		 * @exception ArgumentException if the tagged object cannot
		 *               be converted.
		 */
		public static DerBitString GetInstance(
			Asn1TaggedObject	obj,
			bool				isExplicit)
		{
			Asn1Object o = obj.GetObject();

			if (isExplicit || o is DerBitString)
			{
				return GetInstance(o);
			}

			return FromAsn1Octets(((Asn1OctetString)o).GetOctets());
		}

		internal DerBitString(
			byte	data,
			int		padBits)
		{
			this.data = new byte[]{ data };
			this.padBits = padBits;
		}

		/**
		 * @param data the octets making up the bit string.
		 * @param padBits the number of extra bits at the end of the string.
		 */
		public DerBitString(
			byte[]	data,
			int		padBits)
		{
			// TODO Deep copy?
			this.data = data;
			this.padBits = padBits;
		}

		public DerBitString(
			byte[] data)
		{
			// TODO Deep copy?
			this.data = data;
		}

		public DerBitString(
			Asn1Encodable obj)
		{
			this.data = obj.GetDerEncoded();
			//this.padBits = 0;
		}

		public byte[] GetBytes()
		{
			return data;
		}

		public int PadBits
		{
			get { return padBits; }
		}

		/**
		 * @return the value of the bit string as an int (truncating if necessary)
		 */
		public int IntValue
		{
			get
			{
				int value = 0;

				for (int i = 0; i != data.Length && i != 4; i++)
				{
					value |= (data[i] & 0xff) << (8 * i);
				}

				return value;
			}
		}

		internal override void Encode(
			DerOutputStream derOut)
		{
			byte[] bytes = new byte[GetBytes().Length + 1];

			bytes[0] = (byte) PadBits;
			Array.Copy(GetBytes(), 0, bytes, 1, bytes.Length - 1);

			derOut.WriteEncoded(Asn1Tags.BitString, bytes);
		}

		protected override int Asn1GetHashCode()
		{
			return padBits.GetHashCode() ^ Arrays.GetHashCode(data);
		}

		protected override bool Asn1Equals(
			Asn1Object asn1Object)
		{
			DerBitString other = asn1Object as DerBitString;

			if (other == null)
				return false;

			return this.padBits == other.padBits
				&& Arrays.AreEqual(this.data, other.data);
		}

		public override string GetString()
		{
			StringBuilder buffer = new StringBuilder("#");

			byte[] str = GetDerEncoded();

			for (int i = 0; i != str.Length; i++)
			{
				uint ubyte = str[i];
				buffer.Append(table[(ubyte >> 4) & 0xf]);
				buffer.Append(table[str[i] & 0xf]);
			}

			return buffer.ToString();
		}

		internal static DerBitString FromAsn1Octets(byte[] octets)
		{
	        if (octets.Length < 1)
	            throw new ArgumentException("truncated BIT STRING detected");

			int padBits = octets[0];
			byte[] data = new byte[octets.Length - 1];
			Array.Copy(octets, 1, data, 0, data.Length);
			return new DerBitString(data, padBits);
		}
	}
}