////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Dr. Frank Celler
////////////////////////////////////////////////////////////////////////////////

#include "tri-strings.h"
#include "Basics/conversions.h"
#include "Basics/Utf8Helper.h"

#include <openssl/sha.h>

////////////////////////////////////////////////////////////////////////////////
/// @brief escapes UTF-8 range U+0000 to U+007F
////////////////////////////////////////////////////////////////////////////////

static void EscapeUtf8Range0000T007F(char** dst, char const** src) {
  uint8_t c;
  uint16_t i1;
  uint16_t i2;

  c = (uint8_t) * (*src);

  i1 = (((uint16_t)c) & 0xF0) >> 4;
  i2 = (((uint16_t)c) & 0x0F);

  *(*dst)++ = '\\';
  *(*dst)++ = 'u';
  *(*dst)++ = '0';
  *(*dst)++ = '0';

  *(*dst)++ = (i1 < 10) ? ('0' + i1) : ('A' + i1 - 10);
  *(*dst) = (i2 < 10) ? ('0' + i2) : ('A' + i2 - 10);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief escapes UTF-8 range U+0080 to U+07FF
////////////////////////////////////////////////////////////////////////////////

static void EscapeUtf8Range0080T07FF(char** dst, char const** src) {
  uint8_t c;
  uint8_t d;

  c = (uint8_t) * ((*src) + 0);
  d = (uint8_t) * ((*src) + 1);

  // correct UTF-8
  if ((d & 0xC0) == 0x80) {
    uint16_t n;

    uint16_t i1;
    uint16_t i2;
    uint16_t i3;
    uint16_t i4;

    n = ((c & 0x1F) << 6) | (d & 0x3F);
    TRI_ASSERT(n >= 128);

    i1 = (n & 0xF000) >> 12;
    i2 = (n & 0x0F00) >> 8;
    i3 = (n & 0x00F0) >> 4;
    i4 = (n & 0x000F);

    *(*dst)++ = '\\';
    *(*dst)++ = 'u';

    *(*dst)++ = (i1 < 10) ? ('0' + i1) : ('A' + i1 - 10);
    *(*dst)++ = (i2 < 10) ? ('0' + i2) : ('A' + i2 - 10);
    *(*dst)++ = (i3 < 10) ? ('0' + i3) : ('A' + i3 - 10);
    *(*dst) = (i4 < 10) ? ('0' + i4) : ('A' + i4 - 10);

    (*src) += 1;
  }

  // corrupted UTF-8
  else {
    *(*dst) = *(*src);
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief escapes UTF-8 range U+0800 to U+D7FF and U+E000 to U+FFFF
////////////////////////////////////////////////////////////////////////////////

static void EscapeUtf8Range0800TFFFF(char** dst, char const** src) {
  uint8_t c;
  uint8_t d;
  uint8_t e;

  c = (uint8_t) * ((*src) + 0);
  d = (uint8_t) * ((*src) + 1);
  e = (uint8_t) * ((*src) + 2);

  // correct UTF-8 (3-byte sequence UTF-8 1110xxxx 10xxxxxx)
  if ((d & 0xC0) == 0x80 && (e & 0xC0) == 0x80) {
    uint16_t n;

    uint16_t i1;
    uint16_t i2;
    uint16_t i3;
    uint16_t i4;

    n = ((c & 0x0F) << 12) | ((d & 0x3F) << 6) | (e & 0x3F);

    TRI_ASSERT(n >= 2048 && (n < 55296 || n > 57343));

    i1 = (n & 0xF000) >> 12;
    i2 = (n & 0x0F00) >> 8;
    i3 = (n & 0x00F0) >> 4;
    i4 = (n & 0x000F);

    *(*dst)++ = '\\';
    *(*dst)++ = 'u';

    *(*dst)++ = (i1 < 10) ? ('0' + i1) : ('A' + i1 - 10);
    *(*dst)++ = (i2 < 10) ? ('0' + i2) : ('A' + i2 - 10);
    *(*dst)++ = (i3 < 10) ? ('0' + i3) : ('A' + i3 - 10);
    *(*dst) = (i4 < 10) ? ('0' + i4) : ('A' + i4 - 10);

    (*src) += 2;
  }

  // corrupted UTF-8
  else {
    *(*dst) = *(*src);
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief escapes UTF-8 range U+10000 to U+10FFFF
////////////////////////////////////////////////////////////////////////////////

static void EscapeUtf8Range10000T10FFFF(char** dst, char const** src) {
  uint8_t c;
  uint8_t d;
  uint8_t e;
  uint8_t f;

  c = (uint8_t) * ((*src) + 0);
  d = (uint8_t) * ((*src) + 1);
  e = (uint8_t) * ((*src) + 2);
  f = (uint8_t) * ((*src) + 3);

  // correct UTF-8 (4-byte sequence UTF-8 1110xxxx 10xxxxxx 10xxxxxx)
  if ((d & 0xC0) == 0x80 && (e & 0xC0) == 0x80 && (f & 0xC0) == 0x80) {
    uint32_t n;

    uint32_t s1;
    uint32_t s2;

    uint16_t i1;
    uint16_t i2;
    uint16_t i3;
    uint16_t i4;

    n = ((c & 0x0F) << 18) | ((d & 0x3F) << 12) | ((e & 0x3F) << 6) |
        (f & 0x3F);
    TRI_ASSERT(n >= 65536 && n <= 1114111);

    // construct the surrogate pairs
    n -= 0x10000;

    s1 = ((n & 0xFFC00) >> 10) + 0xD800;
    s2 = (n & 0x3FF) + 0xDC00;

    // encode high surrogate
    i1 = (s1 & 0xF000) >> 12;
    i2 = (s1 & 0x0F00) >> 8;
    i3 = (s1 & 0x00F0) >> 4;
    i4 = (s1 & 0x000F);

    *(*dst)++ = '\\';
    *(*dst)++ = 'u';

    *(*dst)++ = (i1 < 10) ? ('0' + i1) : ('A' + i1 - 10);
    *(*dst)++ = (i2 < 10) ? ('0' + i2) : ('A' + i2 - 10);
    *(*dst)++ = (i3 < 10) ? ('0' + i3) : ('A' + i3 - 10);
    *(*dst)++ = (i4 < 10) ? ('0' + i4) : ('A' + i4 - 10);

    // encode low surrogate
    i1 = (s2 & 0xF000) >> 12;
    i2 = (s2 & 0x0F00) >> 8;
    i3 = (s2 & 0x00F0) >> 4;
    i4 = (s2 & 0x000F);

    *(*dst)++ = '\\';
    *(*dst)++ = 'u';

    *(*dst)++ = (i1 < 10) ? ('0' + i1) : ('A' + i1 - 10);
    *(*dst)++ = (i2 < 10) ? ('0' + i2) : ('A' + i2 - 10);
    *(*dst)++ = (i3 < 10) ? ('0' + i3) : ('A' + i3 - 10);
    *(*dst) = (i4 < 10) ? ('0' + i4) : ('A' + i4 - 10);

    // advance src
    (*src) += 3;
  }

  // corrupted UTF-8
  else {
    *(*dst) = *(*src);
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief decodes a unicode escape sequence
////////////////////////////////////////////////////////////////////////////////

static void DecodeUnicodeEscape(char** dst, char const* src) {
  int i1;
  int i2;
  int i3;
  int i4;
  uint16_t n;

  i1 = TRI_IntHex(src[0], 0);
  i2 = TRI_IntHex(src[1], 0);
  i3 = TRI_IntHex(src[2], 0);
  i4 = TRI_IntHex(src[3], 0);

  n = ((i1 & 0xF) << 12) | ((i2 & 0xF) << 8) | ((i3 & 0xF) << 4) | (i4 & 0xF);

  if (n <= 0x7F) {
    *(*dst) = n & 0x7F;
  } else if (n <= 0x7FF) {
    *(*dst)++ = 0xC0 + (n >> 6);
    *(*dst) = 0x80 + (n & 0x3F);

  } else {
    *(*dst)++ = 0xE0 + (n >> 12);
    *(*dst)++ = 0x80 + ((n >> 6) & 0x3F);
    *(*dst) = 0x80 + (n & 0x3F);
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief decodes a unicode surrogate pair
////////////////////////////////////////////////////////////////////////////////

static void DecodeSurrogatePair(char** dst, char const* src1,
                                char const* src2) {
  int i1;
  int i2;
  int i3;
  int i4;
  uint32_t n1;
  uint32_t n2;
  uint32_t n;

  i1 = TRI_IntHex(src1[0], 0);
  i2 = TRI_IntHex(src1[1], 0);
  i3 = TRI_IntHex(src1[2], 0);
  i4 = TRI_IntHex(src1[3], 0);

  n1 = ((i1 & 0xF) << 12) | ((i2 & 0xF) << 8) | ((i3 & 0xF) << 4) | (i4 & 0xF);
  n1 -= 0xD800;

  i1 = TRI_IntHex(src2[0], 0);
  i2 = TRI_IntHex(src2[1], 0);
  i3 = TRI_IntHex(src2[2], 0);
  i4 = TRI_IntHex(src2[3], 0);

  n2 = ((i1 & 0xF) << 12) | ((i2 & 0xF) << 8) | ((i3 & 0xF) << 4) | (i4 & 0xF);
  n2 -= 0xDC00;

  n = 0x10000 + ((n1 << 10) | n2);

  if (n <= 0x7F) {
    *(*dst) = n & 0x7F;
  } else if (n <= 0x7FF) {
    *(*dst)++ = 0xC0 + (n >> 6);
    *(*dst) = 0x80 + (n & 0x3F);
  } else if (n <= 0xFFFF) {
    *(*dst)++ = 0xE0 + (n >> 12);
    *(*dst)++ = 0x80 + ((n >> 6) & 0x3F);
    *(*dst) = 0x80 + (n & 0x3F);
  } else {
    *(*dst)++ = 0xF0 + (n >> 18);
    *(*dst)++ = 0x80 + ((n >> 12) & 0x3F);
    *(*dst)++ = 0x80 + ((n >> 6) & 0x3F);
    *(*dst) = 0x80 + (n & 0x3F);
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief convert a string to lower case
////////////////////////////////////////////////////////////////////////////////

char* TRI_LowerAsciiString(char const* value) {
  size_t length;
  char* buffer;
  char* p;
  char* out;
  char c;

  if (value == nullptr) {
    return nullptr;
  }

  length = strlen(value);

  buffer = static_cast<char*>(
      TRI_Allocate((sizeof(char) * length) + 1));

  if (buffer == nullptr) {
    return nullptr;
  }

  p = (char*)value;
  out = buffer;

  while ((c = *p++)) {
    if (c >= 'A' && c <= 'Z') {
      *out++ = c + 32;
    } else {
      *out++ = c;
    }
  }

  *out = '\0';

  return buffer;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief convert a string to upper case
////////////////////////////////////////////////////////////////////////////////

char* TRI_UpperAsciiString(char const* value) {
  size_t length;
  char* buffer;
  char* p;
  char* out;
  char c;

  if (value == nullptr) {
    return nullptr;
  }

  length = strlen(value);

  buffer = static_cast<char*>(
      TRI_Allocate((sizeof(char) * length) + 1));

  if (buffer == nullptr) {
    return nullptr;
  }

  p = (char*)value;
  out = buffer;

  while ((c = *p++)) {
    if (c >= 'a' && c <= 'z') {
      *out++ = c - 32;
    } else {
      *out++ = c;
    }
  }

  *out = '\0';

  return buffer;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief tests if strings are equal
////////////////////////////////////////////////////////////////////////////////

bool TRI_EqualString(char const* left, char const* right) {
  return strcmp(left, right) == 0;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief tests if strings are equal
////////////////////////////////////////////////////////////////////////////////

bool TRI_EqualString(char const* left, char const* right, size_t n) {
  return strncmp(left, right, n) == 0;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief tests if ASCII strings are equal ignoring case
////////////////////////////////////////////////////////////////////////////////

bool TRI_CaseEqualString(char const* left, char const* right) {
  return strcasecmp(left, right) == 0;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief tests if ASCII strings are equal ignoring case
////////////////////////////////////////////////////////////////////////////////

bool TRI_CaseEqualString(char const* left, char const* right, size_t n) {
  return strncasecmp(left, right, n) == 0;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief tests if second string is prefix of the first
////////////////////////////////////////////////////////////////////////////////

bool TRI_IsPrefixString(char const* full, char const* prefix) {
  return strncmp(full, prefix, strlen(prefix)) == 0;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief tests if second string is contained in the first, byte-safe
////////////////////////////////////////////////////////////////////////////////

char* TRI_IsContainedMemory(char const* full, size_t fullLength,
                            char const* part, size_t partLength) {
  if (fullLength == 0 || partLength == 0 || fullLength < partLength) {
    return nullptr;
  }

  if (partLength == 1) {
    return static_cast<char*>(const_cast<void*>(
        memchr(static_cast<void const*>(full), (int)*part, fullLength)));
  }

  char const* end = full + fullLength - partLength;

  for (char const* p = full; p <= end; ++p) {
    if (*p == *part &&
        memcmp(static_cast<void const*>(p), static_cast<void const*>(part),
               partLength) == 0) {
      return const_cast<char*>(p);
    }
  }

  return nullptr;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief duplicates a string
////////////////////////////////////////////////////////////////////////////////

char* TRI_DuplicateString(char const* value) {
  size_t n = strlen(value) + 1;
  char* result = static_cast<char*>(TRI_Allocate(n));

  if (result != nullptr) {
    memcpy(result, value, n);
  }

  return result;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief duplicates a string of given length
////////////////////////////////////////////////////////////////////////////////

char* TRI_DuplicateString(char const* value,
                          size_t length) {
  char* result = static_cast<char*>(TRI_Allocate(length + 1));

  if (result != nullptr) {
    memcpy(result, value, length);
    result[length] = '\0';
  }

  return result;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief copies a string
////////////////////////////////////////////////////////////////////////////////

void TRI_CopyString(char* dst, char const* src, size_t length) {
  *dst = '\0';
  strncat(dst, src, length);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief concatenate three strings using a memory zone
////////////////////////////////////////////////////////////////////////////////

char* TRI_Concatenate3String(char const* a,
                             char const* b, char const* c) {
  size_t na = strlen(a);
  size_t nb = strlen(b);
  size_t nc = strlen(c);

  char* result =
      static_cast<char*>(TRI_Allocate(na + nb + nc + 1));

  if (result != nullptr) {
    memcpy(result, a, na);
    memcpy(result + na, b, nb);
    memcpy(result + na + nb, c, nc);

    result[na + nb + nc] = '\0';
  }

  return result;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief frees a string
////////////////////////////////////////////////////////////////////////////////

void TRI_FreeString(char* value) {
  TRI_Free(value);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief sha256 of a string
////////////////////////////////////////////////////////////////////////////////

char* TRI_SHA256String(char const* source, size_t sourceLen, size_t* dstLen) {
  unsigned char* dst = static_cast<unsigned char*>(
      TRI_Allocate(SHA256_DIGEST_LENGTH));
  if (dst == nullptr) {
    return nullptr;
  }
  *dstLen = SHA256_DIGEST_LENGTH;

  SHA256((unsigned char const*)source, sourceLen, dst);

  return (char*)dst;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief escapes special characters using C escapes
////////////////////////////////////////////////////////////////////////////////

char* TRI_EscapeControlsCString(char const* in,
                                size_t inLength, size_t* outLength,
                                bool appendNewline) {
  char* buffer = static_cast<char*>(
      TRI_Allocate(TRI_MaxLengthEscapeControlsCString(inLength)));

  return TRI_EscapeControlsCString(in, inLength, buffer, outLength, appendNewline);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief escapes special characters using C escapes
/// the target buffer must have been allocated already and big enough to hold
/// the result of at most (4 * inLength) + 2 bytes!
////////////////////////////////////////////////////////////////////////////////

char* TRI_EscapeControlsCString(char const* in, size_t inLength, 
                                char* out, size_t* outLength,
                                bool appendNewline) {
  if (out == nullptr) {
    return nullptr;
  }

  char* qtr = out;
  char const* ptr;
  char const* end;

  for (ptr = in, end = ptr + inLength; ptr < end; ptr++, qtr++) {
    uint8_t n;

    switch (*ptr) {
      case '\n':
        *qtr++ = '\\';
        *qtr = 'n';
        break;

      case '\r':
        *qtr++ = '\\';
        *qtr = 'r';
        break;
      
      case '\t':
        *qtr++ = '\\';
        *qtr = 't';
        break;

      default:
        n = (uint8_t)(*ptr);

        if (n < 32) {
          uint8_t n1 = n >> 4;
          uint8_t n2 = n & 0x0F;

          *qtr++ = '\\';
          *qtr++ = 'x';
          *qtr++ = (n1 < 10) ? ('0' + n1) : ('A' + n1 - 10);
          *qtr = (n2 < 10) ? ('0' + n2) : ('A' + n2 - 10);
        } else {
          *qtr = *ptr;
        }

        break;
    }
  }

  if (appendNewline) {
    *qtr++ = '\n';
  }

  *qtr = '\0';
  *outLength = static_cast<size_t>(qtr - out);
  return out;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief escapes special characters using unicode escapes
////////////////////////////////////////////////////////////////////////////////

char* TRI_EscapeUtf8String(char const* in,
                           size_t inLength, bool escapeSlash, size_t* outLength,
                           bool compactResult) {
  char* buffer = (char*)TRI_Allocate(6 * inLength + 1);

  if (buffer == nullptr) {
    return nullptr;
  }

  char* qtr = buffer;
  char const* ptr;
  char const* end;

  for (ptr = in, end = ptr + inLength; ptr < end; ++ptr, ++qtr) {
    switch (*ptr) {
      case '/':
        if (escapeSlash) {
          *qtr++ = '\\';
        }

        *qtr = *ptr;
        break;

      case '\\':
      case '"':
        *qtr++ = '\\';
        *qtr = *ptr;
        break;

      case '\b':
        *qtr++ = '\\';
        *qtr = 'b';
        break;

      case '\f':
        *qtr++ = '\\';
        *qtr = 'f';
        break;

      case '\n':
        *qtr++ = '\\';
        *qtr = 'n';
        break;

      case '\r':
        *qtr++ = '\\';
        *qtr = 'r';
        break;

      case '\t':
        *qtr++ = '\\';
        *qtr = 't';
        break;

      case '\0':
        *qtr++ = '\\';
        *qtr++ = 'u';
        *qtr++ = '0';
        *qtr++ = '0';
        *qtr++ = '0';
        *qtr = '0';
        break;

      default: {
        uint8_t c;

        // next character as unsigned char
        c = (uint8_t)*ptr;

        // character is in the normal latin1 range
        if ((c & 0x80) == 0) {
          // special character, escape
          if (c < 32) {
            EscapeUtf8Range0000T007F(&qtr, &ptr);
          }

          // normal latin1
          else {
            *qtr = *ptr;
          }
        }

        // unicode range 0080 - 07ff (2-byte sequence UTF-8)
        else if ((c & 0xE0) == 0xC0) {
          // hopefully correct UTF-8
          if (ptr + 1 < end) {
            EscapeUtf8Range0080T07FF(&qtr, &ptr);
          }

          // corrupted UTF-8
          else {
            *qtr = *ptr;
          }
        }

        // unicode range 0800 - ffff (3-byte sequence UTF-8)
        else if ((c & 0xF0) == 0xE0) {
          // hopefully correct UTF-8
          if (ptr + 2 < end) {
            EscapeUtf8Range0800TFFFF(&qtr, &ptr);
          }

          // corrupted UTF-8
          else {
            *qtr = *ptr;
          }
        }

        // unicode range 10000 - 10ffff (4-byte sequence UTF-8)
        else if ((c & 0xF8) == 0xF0) {
          // hopefully correct UTF-8
          if (ptr + 3 < end) {
            EscapeUtf8Range10000T10FFFF(&qtr, &ptr);
          }

          // corrupted UTF-8
          else {
            *qtr = *ptr;
          }
        }

        // unicode range above 10ffff -- NOT IMPLEMENTED
        else {
          *qtr = *ptr;
        }
      }

      break;
    }
  }

  *qtr = '\0';
  *outLength = (size_t)(qtr - buffer);

  if (!compactResult) {
    return buffer;
  }

  qtr = static_cast<char*>(TRI_Allocate(*outLength + 1));

  if (qtr != nullptr) {
    memcpy(qtr, buffer, *outLength + 1);
  }

  TRI_Free(buffer);

  return qtr;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief unescapes unicode escape sequences
////////////////////////////////////////////////////////////////////////////////

char* TRI_UnescapeUtf8String(char const* in,
                             size_t inLength, size_t* outLength, bool normalize) {
  char const* ptr;
  char const* end;
  size_t tmpLength = 0;

  char* buffer = static_cast<char*>(TRI_Allocate(inLength + 1));

  if (buffer == nullptr) {
    return nullptr;
  }

  char* qtr = buffer;

  for (ptr = in, end = ptr + inLength; ptr < end; ++ptr, ++qtr) {
    if (*ptr == '\\' && ptr + 1 < end) {
      ++ptr;

      switch (*ptr) {
        case 'b':
          *qtr = '\b';
          break;

        case 'f':
          *qtr = '\f';
          break;

        case 'n':
          *qtr = '\n';
          break;

        case 'r':
          *qtr = '\r';
          break;

        case 't':
          *qtr = '\t';
          break;

        case 'u':
          // expecting at least 6 characters: \uXXXX
          if (ptr + 4 < end) {
            // check, if we have a surrogate pair
            if (ptr + 10 < end) {
              bool sp;
              char c1 = ptr[1];

              sp = (c1 == 'd' || c1 == 'D');

              if (sp) {
                char c2 = ptr[2];
                sp &= (c2 == '8' || c2 == '9' || c2 == 'A' || c2 == 'a' ||
                       c2 == 'B' || c2 == 'b');
              }

              if (sp) {
                char c3 = ptr[7];

                sp &= (ptr[5] == '\\' && ptr[6] == 'u');
                sp &= (c3 == 'd' || c3 == 'D');
              }

              if (sp) {
                char c4 = ptr[8];
                sp &= (c4 == 'C' || c4 == 'c' || c4 == 'D' || c4 == 'd' ||
                       c4 == 'E' || c4 == 'e' || c4 == 'F' || c4 == 'f');
              }

              if (sp) {
                DecodeSurrogatePair(&qtr, ptr + 1, ptr + 7);
                ptr += 10;
              } else {
                DecodeUnicodeEscape(&qtr, ptr + 1);
                ptr += 4;
              }
            } else {
              DecodeUnicodeEscape(&qtr, ptr + 1);
              ptr += 4;
            }
          }
          // ignore wrong format
          else {
            *qtr = *ptr;
          }
          break;

        default:
          // this includes cases \/, \\, and \"
          *qtr = *ptr;
          break;
      }

      continue;
    }

    *qtr = *ptr;
  }

  *qtr = '\0';
  *outLength = (size_t)(qtr - buffer);

  if (normalize && *outLength > 0) {
    char* utf8_nfc =
        TRI_normalize_utf8_to_NFC(buffer, *outLength, &tmpLength);

    if (utf8_nfc != nullptr) {
      *outLength = tmpLength;
      TRI_Free(buffer);
      return utf8_nfc;
    }
    // intentionally falls through
  }

  return buffer;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief determine the number of characters in a UTF-8 string
////////////////////////////////////////////////////////////////////////////////

size_t TRI_CharLengthUtf8String(char const* in, size_t length) {
  unsigned char const* p = reinterpret_cast<unsigned char const*>(in);
  unsigned char const* e = p + length;
  size_t chars = 0;

  while (p < e) {
    unsigned char c = *p;

    if (c < 128) {
      // single byte
      p++;
    } else if (c < 224) {
      p += 2;
    } else if (c < 240) {
      p += 3;
    } else if (c < 248) {
      p += 4;
    } else {
      // invalid UTF-8 sequence
      break;
    }

    ++chars;
  }

  return chars;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief get the string end position for a leftmost prefix of a UTF-8 string
/// eg. when specifying (müller, 2), the return value will be a pointer to the
/// first "l".
/// the UTF-8 string must be well-formed and end with a NUL terminator
////////////////////////////////////////////////////////////////////////////////

char* TRI_PrefixUtf8String(char const* in, const uint32_t maximumLength) {
  uint32_t length;
  unsigned char* p;

  p = (unsigned char*)in;
  length = 0;

  while (*p && length < maximumLength) {
    unsigned char c = *p;

    if (c < 128) {
      // single byte
      p++;
    } else if (c < 224) {
      p += 2;
    } else if (c < 240) {
      p += 3;
    } else if (c < 248) {
      p += 4;
    } else {
      // invalid UTF-8 sequence
      break;
    }

    ++length;
  }

  return (char*)p;
}