/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Mozilla Communicator client code.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1998
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
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 * ***** END LICENSE BLOCK ***** */

#include "nsUCConstructors.h"
#include "nsUCS2BEToUnicode.h"
#include "nsUCvLatinDll.h"
#include "nsCharTraits.h"
#include <string.h>
#include "prtypes.h"

#define STATE_NORMAL          0
#define STATE_HALF_CODE_POINT 1
#define STATE_FIRST_CALL      2
#define STATE_FOUND_BOM       3

static nsresult
UTF16ConvertToUnicode(PRUint8& aState, PRUint8& aOddByte,
                      PRUnichar& aOddHighSurrogate, const char * aSrc,
                      PRInt32 * aSrcLength, PRUnichar * aDest,
                      PRInt32 * aDestLength,
                      PRBool aSwapBytes)
{
  const char* src = aSrc;
  const char* srcEnd = aSrc + *aSrcLength;
  PRUnichar* dest = aDest;
  PRUnichar* destEnd = aDest + *aDestLength;

  if(STATE_FOUND_BOM == aState) // caller found a BOM
  {
    if (*aSrcLength < 2)
      return NS_ERROR_ILLEGAL_INPUT;
    src+=2;
    aState = STATE_NORMAL;
  } else if(STATE_FIRST_CALL == aState) { // first time called
    if (*aSrcLength < 2)
      return NS_ERROR_ILLEGAL_INPUT;

    // Eliminate BOM (0xFEFF). Note that different endian case is taken care of
    // in |Convert| of LE and BE converters. Here, we only have to
    // deal with the same endian case. That is, 0xFFFE (byte-swapped BOM) is
    // illegal.
    if(0xFEFF == *((PRUnichar*)src)) {
      src+=2;
    } else if(0xFFFE == *((PRUnichar*)src)) {
      *aSrcLength=0;
      *aDestLength=0;
      return NS_ERROR_ILLEGAL_INPUT;
    }  
    aState = STATE_NORMAL;
  }

  if (src == srcEnd) {
    *aDestLength = 0;
    return NS_OK;
  }

  PRUnichar oddHighSurrogate = aOddHighSurrogate;

  const char* srcEvenEnd;

  PRUnichar u;
  if (aState == STATE_HALF_CODE_POINT) {
    // the 1st byte of a 16-bit code unit was stored in |aOddByte| in the
    // previous run while the 2nd byte has to come from |*src|.
    aState = STATE_NORMAL;
#ifdef IS_BIG_ENDIAN
    u = (aOddByte << 8) | *src++; // safe, we know we have at least one byte.
#else
    u = (*src++ << 8) | aOddByte; // safe, we know we have at least one byte.
#endif
    srcEvenEnd = src + ((srcEnd - src) & ~1); // handle even number of bytes in main loop
    goto have_codepoint;
  } else {
    srcEvenEnd = src + ((srcEnd - src) & ~1); // handle even number of bytes in main loop
  }

  while (src != srcEvenEnd) {
    if (dest == destEnd)
      goto error;

    u = *(const PRUnichar*)src;
    src += 2;

have_codepoint:
    if (aSwapBytes)
      u = u << 8 | u >> 8;

    if (!IS_SURROGATE(u)) {
      if (oddHighSurrogate) {
        *dest++ = UCS2_REPLACEMENT_CHAR;
        if (dest == destEnd)
          goto error;
        oddHighSurrogate = 0;
      }
      *dest++ = u;
    } else if (IS_HIGH_SURROGATE(u)) {
      if (oddHighSurrogate) {
        *dest++ = UCS2_REPLACEMENT_CHAR;
        if (dest == destEnd)
          goto error;
      }
      oddHighSurrogate = u;
    }
    else /* if (IS_LOW_SURROGATE(u)) */ {
      if (oddHighSurrogate) {
        if (dest == destEnd - 1) {
          *dest++ = UCS2_REPLACEMENT_CHAR;
          goto error;
        }
        *dest++ = oddHighSurrogate;
        *dest++ = u;
        oddHighSurrogate = 0;
      } else {
        *dest++ = UCS2_REPLACEMENT_CHAR;
      }
    }
  }
  if (src != srcEnd) {
    // store the lead byte of a 16-bit unit for the next run.
    aOddByte = *src++;
    aState = STATE_HALF_CODE_POINT;
  }

  aOddHighSurrogate = oddHighSurrogate;

  *aDestLength = dest - aDest;
  *aSrcLength =  src  - aSrc; 
  return NS_OK;

error:
  *aDestLength = dest - aDest;
  *aSrcLength =  src  - aSrc; 
  return  NS_OK_UDEC_MOREOUTPUT;
}

NS_IMETHODIMP
nsUTF16ToUnicodeBase::Reset()
{
  mState = STATE_FIRST_CALL;
  mOddByte = 0;
  mOddHighSurrogate = 0;
  return NS_OK;
}

NS_IMETHODIMP
nsUTF16ToUnicodeBase::GetMaxLength(const char * aSrc, PRInt32 aSrcLength, 
                                   PRInt32 * aDestLength)
{
  // the left-over data of the previous run have to be taken into account.
  *aDestLength = (aSrcLength +
                    ((STATE_HALF_CODE_POINT == mState) ? 1 : 0)) / 2 +
                 ((mOddHighSurrogate != 0) ? 1 : 0);
  return NS_OK;
}


NS_IMETHODIMP
nsUTF16BEToUnicode::Convert(const char * aSrc, PRInt32 * aSrcLength,
                            PRUnichar * aDest, PRInt32 * aDestLength)
{
#ifdef IS_LITTLE_ENDIAN
    // Remove the BOM if we're little-endian. The 'same endian' case with the
    // leading BOM will be taken care of by |UTF16ConvertToUnicode|.
    if(STATE_FIRST_CALL == mState) // Called for the first time.
    {
      mState = STATE_NORMAL;
      if (*aSrcLength < 2)
        return NS_ERROR_ILLEGAL_INPUT;
      if(0xFFFE == *((PRUnichar*)aSrc)) {
        // eliminate BOM (on LE machines, BE BOM is 0xFFFE)
        mState = STATE_FOUND_BOM;
      } else if(0xFEFF == *((PRUnichar*)aSrc)) {
        *aSrcLength=0;
        *aDestLength=0;
        return NS_ERROR_ILLEGAL_INPUT;
      }
    }
#endif

  nsresult rv = UTF16ConvertToUnicode(mState, mOddByte, mOddHighSurrogate,
                                      aSrc, aSrcLength, aDest, aDestLength,
#ifdef IS_LITTLE_ENDIAN
                                      PR_TRUE
#else
                                      PR_FALSE
#endif
                                      );
  return rv;
}

NS_IMETHODIMP
nsUTF16LEToUnicode::Convert(const char * aSrc, PRInt32 * aSrcLength,
                            PRUnichar * aDest, PRInt32 * aDestLength)
{
#ifdef IS_BIG_ENDIAN
    // Remove the BOM if we're big-endian. The 'same endian' case with the
    // leading BOM will be taken care of by |UTF16ConvertToUnicode|.
    if(STATE_FIRST_CALL == mState) // first time called
    {
      mState = STATE_NORMAL;
      if (*aSrcLength < 2)
        return NS_ERROR_ILLEGAL_INPUT;
      if(0xFFFE == *((PRUnichar*)aSrc)) {
        // eliminate BOM (on BE machines, LE BOM is 0xFFFE)
        mState = STATE_FOUND_BOM;
      } else if(0xFEFF == *((PRUnichar*)aSrc)) {
        *aSrcLength=0;
        *aDestLength=0;
        return NS_ERROR_ILLEGAL_INPUT;
      }
    }
#endif
    
  nsresult rv = UTF16ConvertToUnicode(mState, mOddByte, mOddHighSurrogate,
                                      aSrc, aSrcLength, aDest, aDestLength,
#ifdef IS_BIG_ENDIAN
                                      PR_TRUE
#else
                                      PR_FALSE
#endif
                                      );
  return rv;
}

NS_IMETHODIMP
nsUTF16ToUnicode::Reset()
{
  mEndian = kUnknown;
  mFoundBOM = PR_FALSE;
  return nsUTF16ToUnicodeBase::Reset();
}

NS_IMETHODIMP
nsUTF16ToUnicode::Convert(const char * aSrc, PRInt32 * aSrcLength,
                          PRUnichar * aDest, PRInt32 * aDestLength)
{
    if(STATE_FIRST_CALL == mState) // first time called
    {
      mState = STATE_NORMAL;
      if (*aSrcLength < 2)
        return NS_ERROR_ILLEGAL_INPUT;

      // check if BOM (0xFEFF) is at the beginning, remove it if found, and
      // set mEndian accordingly.
      if(0xFF == PRUint8(aSrc[0]) && 0xFE == PRUint8(aSrc[1])) {
        mState = STATE_FOUND_BOM;
        mEndian = kLittleEndian;
        mFoundBOM = PR_TRUE;
      }
      else if(0xFE == PRUint8(aSrc[0]) && 0xFF == PRUint8(aSrc[1])) {
        mState = STATE_FOUND_BOM;
        mEndian = kBigEndian;
        mFoundBOM = PR_TRUE;
      }
      // BOM is not found, but we can use a simple heuristic to determine
      // the endianness. Assume the first character is [U+0001, U+00FF].
      // Not always valid, but it's very likely to hold for html/xml/css. 
      else if(!aSrc[0] && aSrc[1]) {  // 0x00 0xhh (hh != 00)
        mEndian = kBigEndian;
      }
      else if(aSrc[0] && !aSrc[1]) {  // 0xhh 0x00 (hh != 00)
        mEndian = kLittleEndian;
      }
      else { // Neither BOM nor 'plausible' byte patterns at the beginning.
             // Just assume it's BE (following Unicode standard)
             // and let the garbage show up in the browser. (security concern?)
             // (bug 246194)
        mEndian = kBigEndian;
      }
    }
    
    nsresult rv = UTF16ConvertToUnicode(mState, mOddByte, mOddHighSurrogate,
                                        aSrc, aSrcLength, aDest, aDestLength,
#ifdef IS_BIG_ENDIAN
                                        (mEndian == kLittleEndian)
#elif defined(IS_LITTLE_ENDIAN)
                                        (mEndian == kBigEndian)
#else
    #error "Unknown endianness"
#endif
                                        );

    // If BOM is not found and we're to return NS_OK, signal that BOM
    // is not found. Otherwise, return |rv| from |UTF16ConvertToUnicode|
    return (rv == NS_OK && !mFoundBOM) ? NS_OK_UDEC_NOBOMFOUND : rv;
}