// 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/base/internal/strerror.h"

#include <array>

#include <cerrno>

#include <cstddef>

#include <cstdio>

#include <cstring>

#include <string>

#include <type_traits>

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

namespace absl {

ABSL_NAMESPACE_BEGIN

namespace base_internal {

namespace {

const char* StrErrorAdaptor(int errnum, char* buf, size_t buflen) {

#if defined(_WIN32)

  int rc = strerror_s(buf, buflen, errnum);

  buf[buflen - 1] = '\0';  // guarantee NUL termination

  if (rc == 0 && strncmp(buf, "Unknown error", buflen) == 0) *buf = '\0';

  return buf;

#else

  // The type of `ret` is platform-specific; both of these branches must compile

  // either way but only one will execute on any given platform:

  auto ret = strerror_r(errnum, buf, buflen);

  if (std::is_same<decltype(ret), int>::value) {

    // XSI `strerror_r`; `ret` is `int`:

    if (ret) *buf = '\0';

    return buf;

  } else {

    // GNU `strerror_r`; `ret` is `char *`:

    return reinterpret_cast<const char*>(ret);

  }

#endif

}

std::string StrErrorInternal(int errnum) {

  char buf[100];

  const char* str = StrErrorAdaptor(errnum, buf, sizeof buf);

  if (*str == '\0') {

    snprintf(buf, sizeof buf, "Unknown error %d", errnum);

    str = buf;

  }

  return str;

}

// kSysNerr is the number of errors from a recent glibc. `StrError()` falls back

// to `StrErrorAdaptor()` if the value is larger than this.

constexpr int kSysNerr = 135;

std::array<std::string, kSysNerr>* NewStrErrorTable() {

  auto* table = new std::array<std::string, kSysNerr>;

  for (size_t i = 0; i < table->size(); ++i) {

    (*table)[i] = StrErrorInternal(static_cast<int>(i));

  }

  return table;

}

}  // namespace

std::string StrError(int errnum) {

  absl::base_internal::ErrnoSaver errno_saver;

  static const auto* table = NewStrErrorTable();

  if (errnum >= 0 && static_cast<size_t>(errnum) < table->size()) {

    return (*table)[static_cast<size_t>(errnum)];

  }

  return StrErrorInternal(errnum);

}

}  // namespace base_internal

ABSL_NAMESPACE_END

}  // namespace absl