/*
 * Copyright (C) 2011 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "third_party/blink/renderer/platform/mhtml/shared_buffer_chunk_reader.h"

#include "base/notreached.h"
#include "base/numerics/safe_conversions.h"
#include "third_party/blink/renderer/platform/wtf/shared_buffer.h"

namespace blink {

SharedBufferChunkReader::SharedBufferChunkReader(
    scoped_refptr<const SharedBuffer> buffer,
    std::string_view separator)
    : buffer_(std::move(buffer)),
      buffer_position_(0),
      segment_index_(0),
      reached_end_of_file_(false),
      separator_index_(0) {
  SetSeparator(separator);
}

void SharedBufferChunkReader::SetSeparator(std::string_view separator) {
  separator_.clear();
  separator_.append_range(separator);
}

bool SharedBufferChunkReader::NextChunk(Vector<char>& chunk,
                                        bool include_separator) {
  if (reached_end_of_file_)
    return false;

  chunk.clear();
  while (true) {
    while (segment_index_ < segment_.size()) {
      char current_character = segment_[segment_index_++];
      if (current_character != separator_[separator_index_]) {
        if (separator_index_ > 0) {
          chunk.append_range(base::span(separator_).first(separator_index_));
          separator_index_ = 0;
        }
        chunk.push_back(current_character);
        continue;
      }
      separator_index_++;
      if (separator_index_ == separator_.size()) {
        if (include_separator)
          chunk.append_range(separator_);
        separator_index_ = 0;
        return true;
      }
    }

    // Read the next segment.
    segment_index_ = 0;
    buffer_position_ += segment_.size();
    auto it = buffer_->GetIteratorAt(buffer_position_);
    if (it == buffer_->cend()) {
      segment_ = {};
      reached_end_of_file_ = true;
      if (separator_index_ > 0)
        chunk.append_range(base::span(separator_).first(separator_index_));
      return !chunk.empty();
    }
    segment_ = *it;
  }
  NOTREACHED();
}

String SharedBufferChunkReader::NextChunkAsUtf8StringWithLatin1Fallback(
    bool include_separator) {
  Vector<char> data;
  if (!NextChunk(data, include_separator))
    return String();

  return data.size()
             ? String::FromUtf8WithLatin1Fallback(base::as_byte_span(data))
             : g_empty_string;
}

size_t SharedBufferChunkReader::Peek(Vector<char>& data,
                                     size_t requested_size) {
  data.clear();
  auto data_fragment = segment_.subspan(segment_index_);
  if (requested_size <= data_fragment.size()) {
    data.append_range(data_fragment.first(requested_size));
    return requested_size;
  }

  data.append_range(data_fragment);

  for (auto it = buffer_->GetIteratorAt(buffer_position_ + segment_.size());
       it != buffer_->cend(); ++it) {
    if (requested_size <= data.size() + it->size()) {
      data.append_range((*it).first(requested_size - data.size()));
      break;
    }
    data.append_range(*it);
  }
  return data.size();
}

}  // namespace blink