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// Copyright (C) 2019 Google LLC
//
// 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 ICING_TOKENIZATION_LANGUAGE_SEGMENTER_H_
#define ICING_TOKENIZATION_LANGUAGE_SEGMENTER_H_
#include <cstdint>
#include <memory>
#include <string_view>
#include <vector>
#include "icing/text_classifier/lib3/utils/base/statusor.h"
#include "icing/absl_ports/canonical_errors.h"
#include "icing/util/character-iterator.h"
namespace icing {
namespace lib {
// A base class that all other LanguageSegmenters should inherit from. It
// provides interfaces that allow callers to segment text. The return value
// could be an iterator or a list of tokens. Example usage:
//
// std::unique_ptr<LanguageSegmenter> segmenter = GetSegmenter();
// ICING_ASSIGN_OR_RETURN(std::unique_ptr<LanguageSegmenter::Iterator> iter,
// segmenter->Segment(text));
// ICING_ASSIGN_OR_RETURN(std::vector<std::string_view> segments,
// segmenter->GetAllTerms(text));
class LanguageSegmenter {
public:
virtual ~LanguageSegmenter() = default;
// An iterator helping to find terms in the input text.
// Example usage:
//
// while (iterator.Advance()) {
// const std::string_view term = iterator.GetTerm();
// // Do something
// }
class Iterator {
public:
virtual ~Iterator() = default;
// Advances to the next term. Returns false if it has reached the end.
virtual bool Advance() = 0;
// Returns the current term. It can be called only when Advance() returns
// true.
virtual std::string_view GetTerm() const = 0;
// RETURNS:
// On success, a CharacterIterator pointing to the beginning of the
// current term.
// ABORTED if an invalid unicode character is encountered while
// calculating the term start.
virtual libtextclassifier3::StatusOr<CharacterIterator>
CalculateTermStart() {
return absl_ports::UnimplementedError("");
}
// RETURNS:
// On success, a CharacterIterator pointing just past the end of the
// current term.
// ABORTED if an invalid unicode character is encountered while
// calculating the term end.
virtual libtextclassifier3::StatusOr<CharacterIterator>
CalculateTermEndExclusive() {
return absl_ports::UnimplementedError("");
}
// Resets the iterator to point to the first term that starts after UTF-32
// offset.
// GetTerm will now return that term. For example:
//
// language_segmenter = language_segmenter_factory::Create(type);
// iterator = language_segmenter->Segment("foo bar baz");
// iterator.ResetToTermStartingAfterUtf32(4);
// iterator.GetTerm() // returns "baz";
//
// Return types of OK and NOT_FOUND indicate that the function call was
// valid and the state of the iterator has changed. Return type of
// INVALID_ARGUMENT will leave the iterator unchanged. Lastly, a return type
// of ABORTED means that the iterator may be left in an undefined state and
// no longer be usable.
//
// Returns:
// On success, the UTF-32 offset of the first term that starts after
// offset.
// NOT_FOUND if an error occurred or there are no terms that start after
// offset.
// INVALID_ARGUMENT if offset is beyond the end of the text.
// ABORTED if an invalid unicode character is encountered while
// traversing the text.
virtual libtextclassifier3::StatusOr<int32_t> ResetToTermStartingAfterUtf32(
int32_t offset) {
return absl_ports::UnimplementedError("");
}
// Resets the iterator to point to the first term that ends before UTF-32
// offset.
// GetTerm will now return that term. For example:
//
// language_segmenter = language_segmenter_factory::Create(type);
// iterator = language_segmenter->Segment("foo bar baz");
// iterator.ResetToTermEndingBeforeUtf32(7);
// iterator.GetTerm() // returns "bar";
//
// Return types of OK and NOT_FOUND indicate that the function call was
// valid and the state of the iterator has changed. Return type of
// INVALID_ARGUMENT will leave the iterator unchanged. Lastly, a return type
// of ABORTED means that the iterator may be left in an undefined state and
// no longer be usable.
//
// Returns:
// On success, the UTF-32 offset of the first term that ends before
// offset.
// NOT_FOUND if an error occurred or there are no terms that ends before
// offset.
// INVALID_ARGUMENT if offset is negative
// ABORTED if an invalid unicode character is encountered while
// traversing the text.
virtual libtextclassifier3::StatusOr<int32_t> ResetToTermEndingBeforeUtf32(
int32_t offset) {
return absl_ports::UnimplementedError("");
}
// Resets the iterator to point to the first term.
// GetTerm will now return that term. For example:
//
// language_segmenter = language_segmenter_factory::Create(type);
// iterator = language_segmenter->Segment("foo bar baz");
// iterator.Advance();
// iterator.ResetToStartUtf32();
// iterator.GetTerm() // returns "foo";
//
// Return types of OK and NOT_FOUND indicate that the function call was
// valid and the state of the iterator has changed.
//
// Returns:
// On success, the starting position of the first term.
// NOT_FOUND if an error occurred or there are no valid terms in the text.
// ABORTED if an invalid unicode character is encountered while
// traversing the text.
virtual libtextclassifier3::StatusOr<int32_t> ResetToStartUtf32() = 0;
};
// Segments the input text into terms.
//
// Returns:
// An iterator of terms on success
// INTERNAL_ERROR if any error occurs
//
// Note: The underlying char* data of the input string won't be copied but
// shared with the return strings, so please make sure the input string
// outlives the returned iterator.
virtual libtextclassifier3::StatusOr<
std::unique_ptr<LanguageSegmenter::Iterator>>
Segment(std::string_view text) const = 0;
// Segments and returns all terms in the input text.
//
// Returns:
// A list of terms on success
// INTERNAL_ERROR if any error occurs
//
// Note: The underlying char* data of the input string won't be copied but
// shared with the return strings, so please make sure the input string
// outlives the returned terms.
virtual libtextclassifier3::StatusOr<std::vector<std::string_view>>
GetAllTerms(std::string_view text) const = 0;
};
} // namespace lib
} // namespace icing
#endif // ICING_TOKENIZATION_LANGUAGE_SEGMENTER_H_
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