smartselect/tokenizer.cc

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * 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.
 */

#include "smartselect/tokenizer.h"

#include <algorithm>

#include "util/strings/utf8.h"
#include "util/utf8/unicodetext.h"

namespace libtextclassifier {

Tokenizer::Tokenizer(
    const std::vector<TokenizationCodepointRange>& codepoint_ranges)
    : codepoint_ranges_(codepoint_ranges) {
  std::sort(codepoint_ranges_.begin(), codepoint_ranges_.end(),
            [](const TokenizationCodepointRange& a,
               const TokenizationCodepointRange& b) {
              return a.start() < b.start();
            });
}

TokenizationCodepointRange::Role Tokenizer::FindTokenizationRole(
    int codepoint) const {
  auto it = std::lower_bound(
      codepoint_ranges_.begin(), codepoint_ranges_.end(), codepoint,
      [](const TokenizationCodepointRange& range, int codepoint) {
        // This function compares range with the codepoint for the purpose of
        // finding the first greater or equal range. Because of the use of
        // std::lower_bound it needs to return true when range < codepoint;
        // the first time it will return false the lower bound is found and
        // returned.
        //
        // It might seem weird that the condition is range.end <= codepoint
        // here but when codepoint == range.end it means it's actually just
        // outside of the range, thus the range is less than the codepoint.
        return range.end() <= codepoint;
      });
  if (it != codepoint_ranges_.end() && it->start() <= codepoint &&
      it->end() > codepoint) {
    return it->role();
  } else {
    return TokenizationCodepointRange::DEFAULT_ROLE;
  }
}

std::vector<Token> Tokenizer::Tokenize(const std::string& utf8_text) const {
  UnicodeText context_unicode = UTF8ToUnicodeText(utf8_text, /*do_copy=*/false);

  std::vector<Token> result;
  Token new_token("", 0, 0);
  int codepoint_index = 0;
  for (auto it = context_unicode.begin(); it != context_unicode.end();
       ++it, ++codepoint_index) {
    TokenizationCodepointRange::Role role = FindTokenizationRole(*it);
    if (role & TokenizationCodepointRange::SPLIT_BEFORE) {
      if (!new_token.value.empty()) {
        result.push_back(new_token);
      }
      new_token = Token("", codepoint_index, codepoint_index);
    }
    if (!(role & TokenizationCodepointRange::DISCARD_CODEPOINT)) {
      new_token.value += std::string(
          it.utf8_data(),
          it.utf8_data() + GetNumBytesForNonZeroUTF8Char(it.utf8_data()));
      ++new_token.end;
    }
    if (role & TokenizationCodepointRange::SPLIT_AFTER) {
      if (!new_token.value.empty()) {
        result.push_back(new_token);
      }
      new_token = Token("", codepoint_index + 1, codepoint_index + 1);
    }
  }
  if (!new_token.value.empty()) {
    result.push_back(new_token);
  }

  return result;
}

}  // namespace libtextclassifier