// Copyright 2020 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.

#include "absl/strings/internal/escaping.h"

#include <limits>

#include "absl/base/internal/endian.h"

#include "absl/base/internal/raw_logging.h"

namespace absl {

ABSL_NAMESPACE_BEGIN

namespace strings_internal {

size_t CalculateBase64EscapedLenInternal(size_t input_len, bool do_padding) {

  // Base64 encodes three bytes of input at a time. If the input is not

  // divisible by three, we pad as appropriate.

  //

  // Base64 encodes each three bytes of input into four bytes of output.

  constexpr size_t kMaxSize = (std::numeric_limits<size_t>::max() - 1) / 4 * 3;

  ABSL_INTERNAL_CHECK(input_len <= kMaxSize,

                      "CalculateBase64EscapedLenInternal() overflow");

  size_t len = (input_len / 3) * 4;

  // Since all base 64 input is an integral number of octets, only the following

  // cases can arise:

  if (input_len % 3 == 0) {

    // (from https://tools.ietf.org/html/rfc3548)

    // (1) the final quantum of encoding input is an integral multiple of 24

    // bits; here, the final unit of encoded output will be an integral

    // multiple of 4 characters with no "=" padding,

  } else if (input_len % 3 == 1) {

    // (from https://tools.ietf.org/html/rfc3548)

    // (2) the final quantum of encoding input is exactly 8 bits; here, the

    // final unit of encoded output will be two characters followed by two

    // "=" padding characters, or

    len += 2;

    if (do_padding) {

      len += 2;

    }

  } else {  // (input_len % 3 == 2)

    // (from https://tools.ietf.org/html/rfc3548)

    // (3) the final quantum of encoding input is exactly 16 bits; here, the

    // final unit of encoded output will be three characters followed by one

    // "=" padding character.

    len += 3;

    if (do_padding) {

      len += 1;

    }

  }

  return len;

}

}  // namespace strings_internal

ABSL_NAMESPACE_END

}  // namespace absl