package au.gov.amsa.util;
   
   public final class SixBit {
   
   	/** Precompiled list of int to six bit mappings. */
   	private static final int[] INT_TO_SIX_BIT = createIntToSixBit();
   
   	private static int[] createIntToSixBit() {
   		int[] toSixbit = new int[256 * 256]; // we actually only use 256, but we
  		                                     // parse chars around instead of
  		                                     // bytes
  		for (int chr = 0; chr < toSixbit.length; chr++) {
  			if (chr < 48 || chr > 119 || chr > 87 && chr < 96) {
  				toSixbit[chr] = -1;
  			} else if (chr < 0x60) {
  				toSixbit[chr] = chr - 48 & 0x3F;
  			} else {
  				toSixbit[chr] = chr - 56 & 0x3F;
  			}
  		}
  		return toSixbit;
  	}
  
  	/**
  	 * Converts sixBit string characters to bits (boolean values in the array
  	 * bitSet) but just between the bit range {@code from} to {@code to}
  	 * exclusive.
  	 * 
  	 * @param str
  	 * @param padBits
  	 * @param bitSet
  	 * @param calculated
  	 * @param from
  	 * @param to
  	 */
  	public static void convertSixBitToBits(String str, int padBits, boolean bitSet[],
  	        boolean[] calculated, int from, int to) {
  		if (str.length() == 0)
  			return;
  		int index = from - from % 6;
  		int strFrom = from / 6;
  		int slen = str.length() - 1;
  		int strTo = to / 6 + 1;
  		for (int i = strFrom; i < Math.min(strTo, slen); i++) {
  			if (!calculated[i]) {
  				char chr = str.charAt(i);
  				int binVal = INT_TO_SIX_BIT[chr];
  				if (binVal == -1) {
  					throw new SixBitException("Illegal sixbit ascii char: " + chr);
  				}
  				bitSet[index] = (binVal & 32) > 0;
  				bitSet[index + 1] = (binVal & 16) > 0;
  				bitSet[index + 2] = (binVal & 8) > 0;
  				bitSet[index + 3] = (binVal & 4) > 0;
  				bitSet[index + 4] = (binVal & 2) > 0;
  				bitSet[index + 5] = (binVal & 1) > 0;
  
  				calculated[i] = true;
  			}
  
  			index += 6;
  		}
  		if (strTo > slen) {
  			// Process the last char which might be padded
  			char chr = str.charAt(slen);
  			int binVal = INT_TO_SIX_BIT[chr];
  			if (binVal == -1) {
  				throw new SixBitException("Illegal sixbit ascii char: " + chr);
  			}
  			int bits = 6 - padBits;
  
  			switch (bits) {
  			case 6:
  				bitSet[index + 5] = (binVal & 1) > 0;
  			case 5:
  				bitSet[index + 4] = (binVal & 2) > 0;
  			case 4:
  				bitSet[index + 3] = (binVal & 4) > 0;
  			case 3:
  				bitSet[index + 2] = (binVal & 8) > 0;
  			case 2:
  				bitSet[index + 1] = (binVal & 16) > 0;
  			case 1:
  				bitSet[index] = (binVal & 32) > 0;
  			}
  
  			calculated[slen] = true;
  		}
  	}
  
  	public static long getValue(int from, int to, boolean[] bitSet) {
  		if (to > bitSet.length) {
  			throw new SixBitException(bitSet.length + " is not enough bits. At least " + to
  			        + " expected.");
  		}
  		long val = 0;
  		long powMask = 1;
  		for (int i = to - 1; i >= from; i--) {
  			if (bitSet[i]) {
 				val += powMask;
 			}
 			powMask <<= 1;
 		}
 		return val;
 	}
 
 	public static long getSignedValue(int from, int to, boolean[] bitSet) {
 		if (to > bitSet.length) {
 			throw new SixBitException(bitSet.length + " is not enough bits. At least " + to
 			        + " expected.");
 		}
 		long val = 0;
 		long powMask = 1;
 
 		for (int i = to - 1; i >= from; i--) {
 			if (bitSet[i]) {
 				val += powMask;
 			}
 			powMask <<= 1;
 		}
 		if (bitSet[from]) {
 			val = val - powMask;
 		}
 		return val;
 	}
 
 	public static String getString(int from, int to, boolean[] bitSet) {
 		int len = (to - from) / 6;
 		char[] resStr = new char[len];
 		int pos = from;
 		int i;
 		for (i = 0; i < len; i++) {
 			// Note that SixBit.getValue() should never return a value > 63
 			// because it is only using 6 bits so intToAscii should never throw
 			// a SixBitException.
 			char ch = (char) intToAscii((char) SixBit.getValue(pos, pos + 6, bitSet));
 			// stops at the first instance of @ character
 			if (ch == '@') {
 				len = i;
 				break;
 			}
 			resStr[i] = ch;
 			pos += 6;
 		}
 		// remove trailing @ characters and spaces
 		while (len > 0 && (resStr[len - 1] == ' '))
 			len -= 1;
 		return new String(resStr, 0, len);
 	}
 
 	/**
 	 * Convert six bit int value to character
 	 *
 	 * @param val
 	 * @return
 	 */
 	private static int intToAscii(int val) {
 		if (val > 63) {
 			throw new SixBitException("Char value " + val + " not allowed");
 		} else if (val < 32) {
 			return val + 64;
 		} else {
 			return val;
 		}
 	}
 
 }