text: /*
   * Copyright (c) 2021, Krisna Pranav
   *
   * SPDX-License-Identifier: BSD-2-Clause
   */
  
  #include <base/Assertions.h>
  #include <base/Format.h>
  #include <base/Utf8View.h>
  
  namespace Base {
  
  Utf8View::Utf8View(const String& string)
      : m_string(string)
  {
  }
  
  Utf8View::Utf8View(const StringView& string)
      : m_string(string)
  {
  }
  
  Utf8View::Utf8View(const char* string)
      : m_string(string)
  {
  }
  
  const unsigned char* Utf8View::begin_ptr() const
  {
      return (const unsigned char*)m_string.characters_without_null_termination();
  }
  
  const unsigned char* Utf8View::end_ptr() const
  {
      return begin_ptr() + m_string.length();
  }
  
  Utf8CodePointIterator Utf8View::begin() const
  {
      return { begin_ptr(), m_string.length() };
  }
  
  Utf8CodePointIterator Utf8View::end() const
  {
      return { end_ptr(), 0 };
  }
  
  Utf8CodePointIterator Utf8View::iterator_at_byte_offset(size_t byte_offset) const
  {
      size_t current_offset = 0;
      for (auto iterator = begin(); !iterator.done(); ++iterator) {
          if (current_offset >= byte_offset)
              return iterator;
          current_offset += iterator.underlying_code_point_length_in_bytes();
      }
      return end();
  }
  
  size_t Utf8View::byte_offset_of(const Utf8CodePointIterator& it) const
  {
      VERIFY(it.m_ptr >= begin_ptr());
      VERIFY(it.m_ptr <= end_ptr());
  
      return it.m_ptr - begin_ptr();
  }
  
  Utf8View Utf8View::substring_view(size_t byte_offset, size_t byte_length) const
  {
      StringView string = m_string.substring_view(byte_offset, byte_length);
      return Utf8View { string };
  }
  
  Utf8View Utf8View::unicode_substring_view(size_t code_point_offset, size_t code_point_length) const
  {
      if (code_point_length == 0)
          return {};
  
      size_t code_point_index = 0, offset_in_bytes = 0;
      for (auto iterator = begin(); !iterator.done(); ++iterator) {
          if (code_point_index == code_point_offset)
              offset_in_bytes = byte_offset_of(iterator);
          if (code_point_index == code_point_offset + code_point_length - 1) {
              size_t length_in_bytes = byte_offset_of(++iterator) - offset_in_bytes;
              return substring_view(offset_in_bytes, length_in_bytes);
          }
          ++code_point_index;
      }
  
      VERIFY_NOT_REACHED();
  }
  
  static inline bool decode_first_byte(
      unsigned char byte,
      size_t& out_code_point_length_in_bytes,
      u32& out_value)
  {
      if ((byte & 128) == 0) {
          out_value = byte;
          out_code_point_length_in_bytes = 1;
          return true;
      }
      if ((byte & 64) == 0) {
          return false;
      }
      if ((byte & 32) == 0) {
          out_value = byte & 31;
          out_code_point_length_in_bytes = 2;
          return true;
      }
      if ((byte & 16) == 0) {
          out_value = byte & 15;
          out_code_point_length_in_bytes = 3;
          return true;
      }
      if ((byte & 8) == 0) {
          out_value = byte & 7;
          out_code_point_length_in_bytes = 4;
          return true;
      }
  
      return false;
  }
  
  bool Utf8View::validate(size_t& valid_bytes) const
  {
      valid_bytes = 0;
      for (auto ptr = begin_ptr(); ptr < end_ptr(); ptr++) {
          size_t code_point_length_in_bytes;
          u32 value;
          bool first_byte_makes_sense = decode_first_byte(*ptr, code_point_length_in_bytes, value);
          if (!first_byte_makes_sense)
              return false;
  
          for (size_t i = 1; i < code_point_length_in_bytes; i++) {
              ptr++;
              if (ptr >= end_ptr())
                  return false;
              if (*ptr >> 6 != 2)
                  return false;
          }
  
          valid_bytes += code_point_length_in_bytes;
      }
  
      return true;
  }
  
  size_t Utf8View::calculate_length() const
  {
      size_t length = 0;
      for ([[maybe_unused]] auto code_point : *this) {
          ++length;
      }
      return length;
  }
  
  bool Utf8View::starts_with(const Utf8View& start) const
  {
      if (start.is_empty())
          return true;
      if (is_empty())
          return false;
      if (start.length() > length())
          return false;
      if (begin_ptr() == start.begin_ptr())
          return true;
  
      for (auto k = begin(), l = start.begin(); l != start.end(); ++k, ++l) {
          if (*k != *l)
              return false;
      }
      return true;
  }
  
  bool Utf8View::contains(u32 needle) const
  {
      for (u32 code_point : *this) {
          if (code_point == needle)
              return true;
      }
      return false;
  }
  
  Utf8View Utf8View::trim(const Utf8View& characters, TrimMode mode) const
  {
      size_t substring_start = 0;
      size_t substring_length = byte_length();
  
      if (mode == TrimMode::Left || mode == TrimMode::Both) {
          for (auto code_point = begin(); code_point != end(); ++code_point) {
              if (substring_length == 0)
                  return {};
              if (!characters.contains(*code_point))
                  break;
              substring_start += code_point.underlying_code_point_length_in_bytes();
              substring_length -= code_point.underlying_code_point_length_in_bytes();
          }
      }
  
      if (mode == TrimMode::Right || mode == TrimMode::Both) {
          size_t seen_whitespace_length = 0;
          for (auto code_point = begin(); code_point != end(); ++code_point) {
              if (characters.contains(*code_point))
                  seen_whitespace_length += code_point.underlying_code_point_length_in_bytes();
              else
                  seen_whitespace_length = 0;
          }
          if (seen_whitespace_length >= substring_length)
              return {};
          substring_length -= seen_whitespace_length;
      }
  
      return substring_view(substring_start, substring_length);
  }
  
  Utf8CodePointIterator::Utf8CodePointIterator(const unsigned char* ptr, size_t length)
      : m_ptr(ptr)
      , m_length(length)
  {
  }
  
  bool Utf8CodePointIterator::operator==(const Utf8CodePointIterator& other) const
  {
      return m_ptr == other.m_ptr && m_length == other.m_length;
  }
  
  bool Utf8CodePointIterator::operator!=(const Utf8CodePointIterator& other) const
  {
      return !(*this == other);
  }
  
  Utf8CodePointIterator& Utf8CodePointIterator::operator++()
  {
      VERIFY(m_length > 0);
  
      size_t code_point_length_in_bytes = underlying_code_point_length_in_bytes();
      if (code_point_length_in_bytes > m_length) {
          // We don't have enough data for the next code point. Skip one character and try again.
          // The rest of the code will output replacement characters as needed for any eventual extension bytes we might encounter afterwards.
          dbgln("Expected code point size {} is too big for the remaining length {}. Moving forward one byte.", code_point_length_in_bytes, m_length);
          m_ptr += 1;
          m_length -= 1;
          return *this;
      }
  
      m_ptr += code_point_length_in_bytes;
      m_length -= code_point_length_in_bytes;
      return *this;
  }
  
  size_t Utf8CodePointIterator::underlying_code_point_length_in_bytes() const
  {
      VERIFY(m_length > 0);
      size_t code_point_length_in_bytes = 0;
      u32 value;
      bool first_byte_makes_sense = decode_first_byte(*m_ptr, code_point_length_in_bytes, value);
  
      // If any of these tests fail, we will output a replacement character for this byte and treat it as a code point of size 1.
      if (!first_byte_makes_sense)
          return 1;
  
      if (code_point_length_in_bytes > m_length)
          return 1;
  
      for (size_t offset = 1; offset < code_point_length_in_bytes; offset++) {
          if (m_ptr[offset] >> 6 != 2)
              return 1;
      }
  
      return code_point_length_in_bytes;
  }
  
  ReadonlyBytes Utf8CodePointIterator::underlying_code_point_bytes() const
  {
      return { m_ptr, underlying_code_point_length_in_bytes() };
  }
  
  u32 Utf8CodePointIterator::operator*() const
  {
      VERIFY(m_length > 0);
  
      u32 code_point_value_so_far = 0;
      size_t code_point_length_in_bytes = 0;
  
      bool first_byte_makes_sense = decode_first_byte(m_ptr[0], code_point_length_in_bytes, code_point_value_so_far);
  
      if (!first_byte_makes_sense) {
          // The first byte of the code point doesn't make sense: output a replacement character
          dbgln("First byte doesn't make sense: {:#02x}.", m_ptr[0]);
          return 0xFFFD;
      }
  
      if (code_point_length_in_bytes > m_length) {
          // There is not enough data left for the full code point: output a replacement character
          dbgln("Not enough bytes (need {}, have {}), first byte is: {:#02x}.", code_point_length_in_bytes, m_length, m_ptr[0]);
          return 0xFFFD;
      }
  
      for (size_t offset = 1; offset < code_point_length_in_bytes; offset++) {
          if (m_ptr[offset] >> 6 != 2) {
              // One of the extension bytes of the code point doesn't make sense: output a replacement character
              dbgln("Extension byte {:#02x} in {} position after first byte {:#02x} doesn't make sense.", m_ptr[offset], offset, m_ptr[0]);
              return 0xFFFD;
          }
  
          code_point_value_so_far <<= 6;
          code_point_value_so_far |= m_ptr[offset] & 63;
      }
  
      return code_point_value_so_far;
  }
  
  Optional<u32> Utf8CodePointIterator::peek(size_t offset) const
  {
      if (offset == 0) {
          if (this->done())
              return {};
          return this->operator*();
      }
  
      auto new_iterator = *this;
      for (size_t index = 0; index < offset; ++index) {
          ++new_iterator;
          if (new_iterator.done())
              return {};
      }
      return *new_iterator;
  }
  
  }
  