icing/util/i18n-utils.h

// 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_UTIL_I18N_UTILS_H_
#define ICING_UTIL_I18N_UTILS_H_

#include <string>
#include <string_view>

#include "icing/text_classifier/lib3/utils/base/statusor.h"
#include "unicode/umachine.h"

namespace icing {
namespace lib {

// Internationalization utils that use standard utilities or custom code. Does
// not require any special dependencies, such as data files for ICU.
namespace i18n_utils {

// An invalid value defined by Unicode.
static constexpr UChar32 kInvalidUChar32 = 0xFFFD;

// Converts a UTF16 string to a UTF8 string.
//
// Returns:
//   A UTF8 string on success
//   INTERNAL_ERROR on any failures
libtextclassifier3::StatusOr<std::string> Utf16ToUtf8(
    const std::u16string& utf16_string);

// Converts a UTF8 string to a UTF16 string.
//
// Returns:
//   A UTF16 string on success
//   INTERNAL_ERROR on any failures
libtextclassifier3::StatusOr<std::u16string> Utf8ToUtf16(
    std::string_view utf8_string);

// Returns the char at the given position.
UChar32 GetUChar32At(const char* data, int length, int position);

// Returns the safe position to truncate a UTF8 string at so that multi-byte
// UTF8 characters are not cut in the middle. The returned value will always be
// 0 <= val <= desired_length.
//
// REQUIRES: 0 <= desired_length < strlen(str)
int SafeTruncateUtf8Length(const char* str, int desired_length);

// Safely truncates a UTF8 string so that multi-byte UTF8 characters are not cut
// in the middle. The string will be truncated in place.
void SafeTruncateUtf8(std::string* str, int truncate_to_length);

// Checks if the single char is within ASCII range.
bool IsAscii(char c);

// Checks if the Unicode char is within ASCII range.
bool IsAscii(UChar32 c);

// Checks if the Unicode char is alphanumeric.
bool IsAlphaNumeric(UChar32 c);

// Returns how many code units (char) are used for the UTF-8 encoding of this
// Unicode character. Returns 0 if not valid.
int GetUtf8Length(UChar32 c);

// Returns how many code units (char16_t) are used for the UTF-16 encoding of
// this Unicode character. Returns 0 if not valid.
int GetUtf16Length(UChar32 c);

// Checks if the single char is the first byte of a UTF8 character, note
// that a single ASCII char is also considered a lead byte.
bool IsLeadUtf8Byte(char c);

// Checks if the character at position is punctuation. Assigns the length of the
// character at position to *char_len_out if the character at position is valid
// punctuation and char_len_out is not null.
bool IsPunctuationAt(std::string_view input, int position,
                     int* char_len_out = nullptr);

// Checks if the character at position is a whitespace.
bool IsWhitespaceAt(std::string_view input, int position);

// Checks if the character at position is a whitespace.
bool IsAlphabeticAt(std::string_view input, int position);

void AppendUchar32ToUtf8(std::string* utf8_string, UChar32 uchar);

}  // namespace i18n_utils
}  // namespace lib
}  // namespace icing

#endif  // ICING_UTIL_I18N_UTILS_H_