/**
 * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010  Free Software Foundation, Inc.
 *
 * Author: Oliver Hitz
 *
 * This file is part of GNU Libidn.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
 * USA
 */

package gnu.inet.encoding;

/**
 * This class offers static methods for Unicode NFKC string normalization.
 */
public class NFKC
{
  /**
   * Applies NFKC normalization to a string.
   *
   * @param in The string to normalize.
   * @return An NFKC normalized string.
   */
  public static String normalizeNFKC(String in)
  {
    StringBuffer out = new StringBuffer();

    for (int i = 0; i < in.length(); i++) {
      char code = in.charAt(i);

      // In Unicode 3.0, Hangul was defined as the block from U+AC00
      // to U+D7A3, however, since Unicode 3.2 the block extends until
      // U+D7AF. The decomposeHangul function only decomposes until
      // U+D7A3. Should this be changed?
      if (code >= 0xAC00 && code <= 0xD7AF) {
	out.append(decomposeHangul(code));
      } else {
	int index = decomposeIndex(code);
	if (index == -1) {
	  out.append(code);
	} else {
	  out.append(DecompositionMappings.m[index]);
	}
      }
    }

    // Bring the stringbuffer into canonical order.
    canonicalOrdering(out);

    // Do the canonical composition.
    int last_cc = 0;
    int last_start = 0;

    for (int i = 0; i < out.length(); i++) {
      int cc = combiningClass(out.charAt(i));

      if (i > 0 && (last_cc == 0 || last_cc != cc)) {
	  // Try to combine characters
	  char a = out.charAt(last_start);
	  char b = out.charAt(i);

	  int c = compose(a, b);

	  if (c != -1) {
	      out.setCharAt(last_start, (char) c);
	      out.deleteCharAt(i);
	      i--;

	  if (i == last_start) {
	    last_cc = 0;
	  } else {
	    last_cc = combiningClass(out.charAt(i-1));
	  }
	  continue;
	}
      }

      if (cc == 0) {
	  last_start = i;
      }

      last_cc = cc;
    }

    return out.toString();
  }


  /**
   * Returns the index inside the decomposition table, implemented
   * using a binary search.
   *
   * @param c Character to look up.
   * @return Index if found, -1 otherwise.
   */
  static int decomposeIndex(char c)
  {
    int start = 0;
    int end = DecompositionKeys.k.length/2;

    while (true) {
      int half = (start + end) / 2;
      int code = DecompositionKeys.k[half*2];

      if (c == code) {
	return DecompositionKeys.k[half*2 + 1];
      }
      if (half == start) {
	// Character not found
	return -1;
      } else if (c > code) {
	start = half;
      } else {
	end = half;
      }
    }
  }

  /**
   * Returns the combining class of a given character.
   *
   * @param c The character.
   * @return The combining class.
   */
  static int combiningClass(char c)
  {
    int h = c >> 8;
    int l = c & 0xff;

    int i = CombiningClass.i[h];
    if (i > -1) {
      return CombiningClass.c[i][l];
    } else {
      return 0;
    }
  }

  /**
   * Rearranges characters in a stringbuffer in order to respect the
   * canonical ordering properties.
   *
   * @param The StringBuffer to rearrange.
   */
  static void canonicalOrdering(StringBuffer in)
  {
    boolean isOrdered = false;

    while (!isOrdered) {
      isOrdered = true;

      int lastCC = combiningClass(in.charAt(0));

      for (int i = 0; i < in.length()-1; i++) {
	int nextCC = combiningClass(in.charAt(i+1));
	if (nextCC != 0 && lastCC > nextCC) {
	  for (int j = i+1; j > 0; j--) {
	    if (combiningClass(in.charAt(j-1)) <= nextCC) {
	      break;
	    }
	    char t = in.charAt(j);
	    in.setCharAt(j, in.charAt(j-1));
	    in.setCharAt(j-1, t);
	    isOrdered = false;
	  }
	  nextCC = lastCC;
	}
	lastCC = nextCC;
      }
    }
  }

  /**
   * Returns the index inside the composition table.
   *
   * @param a Character to look up.
   * @return Index if found, -1 otherwise.
   */
  static int composeIndex(char a)
  {
    if (a>>8 >= Composition.composePage.length) {
      return -1;
    }
    int ap = Composition.composePage[a>>8];
    if (ap == -1) {
      return -1;
    }
    return Composition.composeData[ap][a & 0xff];
  }

  /**
   * Tries to compose two characters canonically.
   *
   * @param a First character.
   * @param b Second character.
   * @return The composed character or -1 if no composition could be
   * found.
   */
  static int compose(char a, char b)
  {
    int h = composeHangul(a, b);
    if (h != -1) {
      return h;
    }

    int ai = composeIndex(a);

    if (ai >= Composition.singleFirstStart && ai < Composition.singleSecondStart) {
      if (b == Composition.singleFirst[ai - Composition.singleFirstStart][0]) {
	return Composition.singleFirst[ai - Composition.singleFirstStart][1];
      } else {
	return -1;
      }
    }

    int bi = composeIndex(b);

    if (bi >= Composition.singleSecondStart) {
      if (a == Composition.singleSecond[bi - Composition.singleSecondStart][0]) {
	return Composition.singleSecond[bi - Composition.singleSecondStart][1];
      } else {
	return -1;
      }
    }

    if (ai >= 0 && ai < Composition.multiSecondStart &&
	bi >= Composition.multiSecondStart && bi < Composition.singleFirstStart) {
      char[] f = Composition.multiFirst[ai];

      if (bi - Composition.multiSecondStart < f.length) {
	char r = f[bi - Composition.multiSecondStart];
	if (r == 0) {
	  return -1;
	} else {
	  return r;
	}
      }
    }


    return -1;
  }

  /**
   * Entire hangul code copied from:
   * http://www.unicode.org/unicode/reports/tr15/
   *
   * Several hangul specific constants
   */
  static final int SBase = 0xAC00;
  static final int LBase = 0x1100;
  static final int VBase = 0x1161;
  static final int TBase = 0x11A7;
  static final int LCount = 19;
  static final int VCount = 21;
  static final int TCount = 28;
  static final int NCount = VCount * TCount;
  static final int SCount = LCount * NCount;

  /**
   * Decomposes a hangul character.
   *
   * @param s A character to decompose.
   * @return A string containing the hangul decomposition of the input
   * character. If no hangul decomposition can be found, a string
   * containing the character itself is returned.
   */
  static String decomposeHangul(char s)
  {
    int SIndex = s - SBase;
    if (SIndex < 0 || SIndex >= SCount) {
      return String.valueOf(s);
    }
    StringBuffer result = new StringBuffer();
    int L = LBase + SIndex / NCount;
    int V = VBase + (SIndex % NCount) / TCount;
    int T = TBase + SIndex % TCount;
    result.append((char)L);
    result.append((char)V);
    if (T != TBase) result.append((char)T);
    return result.toString();
  }

  /**
   * Composes two hangul characters.
   *
   * @param a First character.
   * @param b Second character.
   * @return Returns the composed character or -1 if the two
   * characters cannot be composed.
   */
  static int composeHangul(char a, char b)
  {
    // 1. check to see if two current characters are L and V
    int LIndex = a - LBase;
    if (0 <= LIndex && LIndex < LCount) {
      int VIndex = b - VBase;
      if (0 <= VIndex && VIndex < VCount) {
	// make syllable of form LV
	return SBase + (LIndex * VCount + VIndex) * TCount;
      }
    }
    
    // 2. check to see if two current characters are LV and T
    int SIndex = a - SBase;
    if (0 <= SIndex && SIndex < SCount && (SIndex % TCount) == 0) {
      int TIndex = b - TBase;
      if (0 <= TIndex && TIndex <= TCount) {
	// make syllable of form LVT
	return a+TIndex;
      }
    }
    return -1;
  }

}