package org.litesoft.encryption.symmetric;

public class AlphaNumericConstrainedSymmetricEncryptor extends AbstractSymmetricEncryptor
{
    public static final SymmetricEncryptor INSTANCE = new AlphaNumericConstrainedSymmetricEncryptor();

    public String getIdentifierAndVersion()
    {
        return "ANCE-1";
    }

    protected Helper createHelper( String pText )
    {
        return new MyHelper( pText );
    }

    private static class MyHelper extends Helper
    {
        private int mLastClearTextChar = 'M';
        private int mDeltaRunning = 0;
        private int mCharDeltasRemaining = 0;

        public MyHelper( String pText )
        {
            super( pText );
        }

        public String done()
        {
            if ( mCharDeltasRemaining != 0 )
            {
                throw new DecryptFailureException( (char) ('0' + mCharDeltasRemaining), this.getClass() );
            }
            return toString();
        }

        public void encode( int pChar )
        {
            int zDelta = pChar - mLastClearTextChar;
            if ( zDelta < 0 )
            {
                LLencode( -zDelta, 'a' );
            }
            else
            {
                LLencode( zDelta, 'A' );
            }
            mLastClearTextChar = pChar;
        }

        private void LLencode( int pDelta, int pBase )
        {
            if ( div4 <= pDelta )
            {
                mSB.append( '4' );
                pDelta = addFactor( pDelta, pBase, div4 );
                pDelta = addFactor( pDelta, pBase, div3 );
                pDelta = addFactor( pDelta, pBase, div2 );
            }
            else if ( div3 <= pDelta )
            {
                mSB.append( '3' );
                pDelta = addFactor( pDelta, pBase, div3 );
                pDelta = addFactor( pDelta, pBase, div2 );
            }
            else if ( div2 <= pDelta )
            {
                mSB.append( '2' );
                pDelta = addFactor( pDelta, pBase, div2 );
            }
            LLencodeChar( pDelta, pBase );
        }

        private int addFactor( int pDelta, int pBase, int pDivisor )
        {
            int zDelta = 0;
            while ( pDelta >= pDivisor )
            {
                zDelta++;
                pDelta -= pDivisor;
            }
            LLencodeChar( zDelta, pBase );
            return pDelta;
        }

        private void LLencodeChar( int pDelta, int pBase )
        {
            mSB.append( (pDelta == 0) ? '0' : (char) (pBase + (pDelta - 1)) );
        }

        // 0   = No Change / same letter
        // A-Z = Delta:  +1 to +26
        // a-z = Delta:  -1 to -26
        // 2-4 = Delta:  that many letters/'0' follow, witch are in base 27
        private static final int div4 = 19683; // 27 * 27 * 27;
        private static final int div3 = 729; // 27 * 27;
        private static final int div2 = 27;

        public void decode( int pChar )
        {
            if ( mCharDeltasRemaining > 0 )
            {
                int zDelta = LLdecode( pChar );
                mDeltaRunning = (mDeltaRunning * 27) + zDelta;
                if ( --mCharDeltasRemaining == 0 )
                {
                    LLdecodeChar( mDeltaRunning );
                    mDeltaRunning = 0;
                }
                return;
            }
            if ( ('2' <= pChar) && (pChar <= '4') )
            {
                mCharDeltasRemaining = pChar - '0';
                return;
            }
            LLdecodeChar( LLdecode( pChar ) );
        }

        private void LLdecodeChar( int pDelta )
        {
            mLastClearTextChar += pDelta;
            mSB.append( (char) mLastClearTextChar );
        }

        private int LLdecode( int pChar )
        {
            if ( pChar == '0' )
            {
                return 0;
            }
            if ( ('a' <= pChar) && (pChar <= 'z') )
            {
                return -(1 + (pChar - 'a'));
            }
            if ( ('A' <= pChar) && (pChar <= 'Z') )
            {
                return (1 + (pChar - 'A'));
            }
            throw new DecryptFailureException( (char) pChar, this.getClass() );
        }
    }
}