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

namespace Biff8Excel.Excel
{
    public class SheetProtection : IDisposable 
    {
        Records.Password m_password;
        Records.Protect m_protect;
        Records.ObjectProtection m_objProtect;
        Records.ScenProtect m_scenProtect;
        //Records.WindowsProtect m_winProtect;

        internal byte[] WriteRecord()
        {
            byte[] b = new byte[24];        // each record is 6 bytes long;

            // Protect Record;
            m_protect.GetByte().CopyTo(b, 0);

            // ScenProtect 
            m_scenProtect.GetByte().CopyTo(b, 6);

            // objProtect
            m_objProtect.GetByte().CopyTo(b, 12);

            // Password
            m_password.GetByte().CopyTo(b, 18);

            return b;
        }

        internal void ProtectSheet(string password)
        {
            m_protect.SetProtect = 1;
            m_scenProtect.Protect = 1;
            m_objProtect.Protect = 1;

            if (password.Length > 0)
                m_password.PasswordHash = GetPassWordHash(password);
        }

        private ushort GetPassWordHash(string password)
        {
            ushort hash = 0;
            //ushort char_index = 0;
            ushort char_count = (ushort)password.Length;
            ushort chars;
            ushort y;

            for (int i = 0; i < char_count; i++)
            {
                chars = (ushort)(password.ToCharArray(i,1)[0]);
                y = RotateBit(chars, (ushort)(i+1));
                hash ^= y;
            }
            return (ushort)(hash ^ char_count ^ 0xCE4B);
        }


        private ushort RotateBit(ushort Value, ushort bit)
        {
            int temp = Value;
            ushort result;

            // Bit shift the value to the left
            temp <<= bit;

            //  if any of the bits from 15 upwards are set
            //  rotate them back to the start of the value
            for (int i = 15; i <= 30; i++)
            {
                //if ((temp & (1 << i)) == (1<<i))
                if ((temp & (1<<i)) != 0)
                {
                    temp = (temp & (~(1 << i)));
                    temp = (temp | (1 << (i - 15) ));
                }
            }

            // copy the first 2 bytes of the long value
            //result = BitConverter.ToInt16(BitConverter.GetBytes(temp), 0);
            result = BitConverter.ToUInt16(BitConverter.GetBytes(temp), 0);

            return result;
        }

        public SheetProtection()
        {
            m_password = new Biff8Excel.Records.Password();
            m_protect = new Biff8Excel.Records.Protect();
            m_objProtect = new Biff8Excel.Records.ObjectProtection();
            m_scenProtect = new Biff8Excel.Records.ScenProtect();
        }

        #region IDisposable ³ΙΤ±

        public void Dispose()
        {
            m_password = null;
            m_protect = null;
            m_objProtect = null;
            m_scenProtect = null;
        }

        #endregion
    }
}