// Copyright 2017 The Abseil Authors.
//
// 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
//
//      https://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.
//
// UTF8 utilities, implemented to reduce dependencies.

#ifndef ABSL_STRINGS_INTERNAL_UTF8_H_
#define ABSL_STRINGS_INTERNAL_UTF8_H_

#include <cstddef>
#include <cstdint>

#include "absl/base/config.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace strings_internal {

// For Unicode code points 0 through 0x10FFFF, EncodeUTF8Char writes
// out the UTF-8 encoding into buffer, and returns the number of chars
// it wrote.
//
// As described in https://tools.ietf.org/html/rfc3629#section-3 , the encodings
// are:
//    00 -     7F : 0xxxxxxx
//    80 -    7FF : 110xxxxx 10xxxxxx
//   800 -   FFFF : 1110xxxx 10xxxxxx 10xxxxxx
// 10000 - 10FFFF : 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
//
// Values greater than 0x10FFFF are not supported and may or may not write
// characters into buffer, however never will more than kMaxEncodedUTF8Size
// bytes be written, regardless of the value of utf8_char.
enum { kMaxEncodedUTF8Size = 4 };
size_t EncodeUTF8Char(char* buffer, char32_t utf8_char);

struct ShiftState {
  bool saw_high_surrogate = false;
  unsigned char bits = 0;
};

// Converts `wc` from UTF-16 or UTF-32 to UTF-8 and writes to `buf`. `buf` is
// assumed to have enough space for the output. `s` is used to carry state
// between successive calls with a UTF-16 surrogate pair. Returns the number of
// chars written, or `static_cast<size_t>(-1)` on failure.
//
// This is basically std::wcrtomb(), but always outputting UTF-8 instead of
// respecting the current locale.
size_t WideToUtf8(wchar_t wc, char* buf, ShiftState& s);

}  // namespace strings_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_STRINGS_INTERNAL_UTF8_H_