utils/strings/stringpiece.h

/*
 * Copyright (C) 2018 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.
 */

#ifndef LIBTEXTCLASSIFIER_UTILS_STRINGS_STRINGPIECE_H_
#define LIBTEXTCLASSIFIER_UTILS_STRINGS_STRINGPIECE_H_

#include <stddef.h>
#include <string>

#include "utils/base/logging.h"

namespace libtextclassifier3 {

// Read-only "view" of a piece of data.  Does not own the underlying data.
class StringPiece {
 public:
  StringPiece() : StringPiece(nullptr, 0) {}

  StringPiece(const char *str)  // NOLINT(runtime/explicit)
      : start_(str), size_(strlen(str)) {}

  StringPiece(const char *start, size_t size) : start_(start), size_(size) {}

  // Intentionally no "explicit" keyword: in function calls, we want strings to
  // be converted to StringPiece implicitly.
  StringPiece(const std::string &s)  // NOLINT(runtime/explicit)
      : StringPiece(s.data(), s.size()) {}

  StringPiece(const std::string &s, int offset, int len)
      : StringPiece(s.data() + offset, len) {}

  char operator[](size_t i) const { return start_[i]; }

  // Returns start address of underlying data.
  const char *data() const { return start_; }

  // Returns number of bytes of underlying data.
  size_t size() const { return size_; }
  size_t length() const { return size_; }

  bool empty() const { return size_ == 0; }

  // Returns a std::string containing a copy of the underlying data.
  std::string ToString() const { return std::string(data(), size()); }

  // Returns whether string ends with a given suffix.
  bool EndsWith(StringPiece suffix) const {
    return suffix.empty() || (size_ >= suffix.size() &&
                              memcmp(start_ + (size_ - suffix.size()),
                                     suffix.data(), suffix.size()) == 0);
  }

  // Returns whether the string begins with a given prefix.
  bool StartsWith(StringPiece prefix) const {
    return prefix.empty() ||
           (size_ >= prefix.size() &&
            memcmp(start_, prefix.data(), prefix.size()) == 0);
  }

  // Removes the first `n` characters from the string piece. Note that the
  // underlying string is not changed, only the view.
  void RemovePrefix(int n) {
    TC3_CHECK_LE(n, size_);
    start_ += n;
    size_ -= n;
  }

 private:
  const char *start_;  // Not owned.
  size_t size_;
};

inline bool EndsWith(StringPiece text, StringPiece suffix) {
  return text.EndsWith(suffix);
}

inline bool StartsWith(StringPiece text, StringPiece prefix) {
  return text.StartsWith(prefix);
}

inline bool ConsumePrefix(StringPiece *text, StringPiece prefix) {
  if (!text->StartsWith(prefix)) {
    return false;
  }
  text->RemovePrefix(prefix.size());
  return true;
}

}  // namespace libtextclassifier3

#endif  // LIBTEXTCLASSIFIER_UTILS_STRINGS_STRINGPIECE_H_