// 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.

#include "absl/strings/str_cat.h"

#include <assert.h>

#include <cstddef>

#include <cstdint>

#include <cstring>

#include <initializer_list>

#include <limits>

#include <string>

#include "absl/base/config.h"

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

#include "absl/base/nullability.h"

#include "absl/base/optimization.h"

#include "absl/base/throw_delegate.h"

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

#include "absl/strings/resize_and_overwrite.h"

#include "absl/strings/string_view.h"

namespace absl {

ABSL_NAMESPACE_BEGIN

// ----------------------------------------------------------------------

// StrCat()

//    This merges the given strings or integers, with no delimiter. This

//    is designed to be the fastest possible way to construct a string out

//    of a mix of raw C strings, string_views, strings, and integer values.

// ----------------------------------------------------------------------

namespace {

// Append is merely a version of memcpy that returns the address of the byte

// after the area just overwritten.

inline char* absl_nonnull Append(char* absl_nonnull out, const AlphaNum& x) {

  // memcpy is allowed to overwrite arbitrary memory, so doing this after the

  // call would force an extra fetch of x.size().

  char* after = out + x.size();

  if (x.size() != 0) {

    memcpy(out, x.data(), x.size());

  }

  return after;

}

// Safely adds size_t values, throwing std::length_error if overflow occurs.

inline size_t SafeAdd(size_t a, size_t b) {

  const uint64_t sum = static_cast<uint64_t>(a) + b;

  if (ABSL_PREDICT_FALSE(sum > (std::numeric_limits<size_t>::max)())) {

    ThrowStdLengthError("absl string append length overflow");

  }

  return static_cast<size_t>(sum);

}

inline size_t SafeAdd(std::initializer_list<size_t> sizes) {

  uint64_t sum = 0;

  for (size_t size : sizes) {

    sum += size;

  }

  if (ABSL_PREDICT_FALSE(sum > (std::numeric_limits<size_t>::max)())) {

    ThrowStdLengthError("absl string append length overflow");

  }

  return static_cast<size_t>(sum);

}

}  // namespace

std::string StrCat(const AlphaNum& a, const AlphaNum& b) {

  std::string result;

  // Use uint64_t to prevent size_t overflow. We assume it is not possible for

  // in memory strings to overflow a uint64_t.

  constexpr uint64_t kMaxSize = uint64_t{std::numeric_limits<size_t>::max()};

  const uint64_t result_size =

      static_cast<uint64_t>(a.size()) + static_cast<uint64_t>(b.size());

  ABSL_INTERNAL_CHECK(result_size <= kMaxSize, "size_t overflow");

  absl::StringResizeAndOverwrite(result, static_cast<size_t>(result_size),

                                 [&a, &b](char* const begin, size_t buf_size) {

                                   char* out = begin;

                                   out = Append(out, a);

                                   out = Append(out, b);

                                   assert(out == begin + buf_size);

                                   return buf_size;

                                 });

  return result;

}

std::string StrCat(const AlphaNum& a, const AlphaNum& b, const AlphaNum& c) {

  std::string result;

  // Use uint64_t to prevent size_t overflow. We assume it is not possible for

  // in memory strings to overflow a uint64_t.

  constexpr uint64_t kMaxSize = uint64_t{std::numeric_limits<size_t>::max()};

  const uint64_t result_size = static_cast<uint64_t>(a.size()) +

                               static_cast<uint64_t>(b.size()) +

                               static_cast<uint64_t>(c.size());

  ABSL_INTERNAL_CHECK(result_size <= kMaxSize, "size_t overflow");

  absl::StringResizeAndOverwrite(

      result, static_cast<size_t>(result_size),

      [&a, &b, &c](char* const begin, size_t buf_size) {

        char* out = begin;

        out = Append(out, a);

        out = Append(out, b);

        out = Append(out, c);

        assert(out == begin + buf_size);

        return buf_size;

      });

  return result;

}

std::string StrCat(const AlphaNum& a, const AlphaNum& b, const AlphaNum& c,

                   const AlphaNum& d) {

  std::string result;

  // Use uint64_t to prevent size_t overflow. We assume it is not possible for

  // in memory strings to overflow a uint64_t.

  constexpr uint64_t kMaxSize = uint64_t{std::numeric_limits<size_t>::max()};

  const uint64_t result_size =

      static_cast<uint64_t>(a.size()) + static_cast<uint64_t>(b.size()) +

      static_cast<uint64_t>(c.size()) + static_cast<uint64_t>(d.size());

  ABSL_INTERNAL_CHECK(result_size <= kMaxSize, "size_t overflow");

  absl::StringResizeAndOverwrite(

      result, static_cast<size_t>(result_size),

      [&a, &b, &c, &d](char* const begin, size_t buf_size) {

        char* out = begin;

        out = Append(out, a);

        out = Append(out, b);

        out = Append(out, c);

        out = Append(out, d);

        assert(out == begin + buf_size);

        return buf_size;

      });

  return result;

}

namespace strings_internal {

// Do not call directly - these are not part of the public API.

std::string CatPieces(std::initializer_list<absl::string_view> pieces) {

  std::string result;

  // Use uint64_t to prevent size_t overflow. We assume it is not possible for

  // in memory strings to overflow a uint64_t.

  constexpr uint64_t kMaxSize = uint64_t{std::numeric_limits<size_t>::max()};

  uint64_t total_size = 0;

  for (absl::string_view piece : pieces) {

    total_size += piece.size();

  }

  ABSL_INTERNAL_CHECK(total_size <= kMaxSize, "size_t overflow");

  absl::StringResizeAndOverwrite(result, static_cast<size_t>(total_size),

                                 [&pieces](char* const begin, size_t buf_size) {

                                   char* out = begin;

                                   for (absl::string_view piece : pieces) {

                                     const size_t this_size = piece.size();

                                     if (this_size != 0) {

                                       memcpy(out, piece.data(), this_size);

                                       out += this_size;

                                     }

                                   }

                                   assert(out == begin + buf_size);

                                   return buf_size;

                                 });

  return result;

}

// It's possible to call StrAppend with an absl::string_view that is itself a

// fragment of the string we're appending to.  However the results of this are

// random. Therefore, check for this in debug mode.  Use unsigned math so we

// only have to do one comparison. Note, there's an exception case: appending an

// empty string is always allowed.

#define ASSERT_NO_OVERLAP(dest, src) \

  assert(((src).size() == 0) ||      \

         (uintptr_t((src).data() - (dest).data()) > uintptr_t((dest).size())))

void AppendPieces(std::string* absl_nonnull dest,

                  std::initializer_list<absl::string_view> pieces) {

  size_t to_append = 0;

  for (absl::string_view piece : pieces) {

    ASSERT_NO_OVERLAP(*dest, piece);

    to_append = SafeAdd(to_append, piece.size());

  }

  StringAppendAndOverwrite(*dest, to_append,

                           [&pieces](char* const buf, size_t buf_size) {

                             char* out = buf;

                             for (absl::string_view piece : pieces) {

                               const size_t this_size = piece.size();

                               if (this_size != 0) {

                                 memcpy(out, piece.data(), this_size);

                                 out += this_size;

                               }

                             }

                             assert(out == buf + buf_size);

                             return buf_size;

                           });

}

}  // namespace strings_internal

void StrAppend(std::string* absl_nonnull dest, const AlphaNum& a) {

  ASSERT_NO_OVERLAP(*dest, a);

  strings_internal::StringAppendAndOverwrite(

      *dest, a.size(), [&a](char* const buf, size_t buf_size) {

        char* out = buf;

        out = Append(out, a);

        assert(out == buf + buf_size);

        return buf_size;

      });

}

void StrAppend(std::string* absl_nonnull dest, const AlphaNum& a,

               const AlphaNum& b) {

  ASSERT_NO_OVERLAP(*dest, a);

  ASSERT_NO_OVERLAP(*dest, b);

  strings_internal::StringAppendAndOverwrite(

      *dest, SafeAdd(a.size(), b.size()),

      [&a, &b](char* const buf, size_t buf_size) {

        char* out = buf;

        out = Append(out, a);

        out = Append(out, b);

        assert(out == buf + buf_size);

        return buf_size;

      });

}

void StrAppend(std::string* absl_nonnull dest, const AlphaNum& a,

               const AlphaNum& b, const AlphaNum& c) {

  ASSERT_NO_OVERLAP(*dest, a);

  ASSERT_NO_OVERLAP(*dest, b);

  ASSERT_NO_OVERLAP(*dest, c);

  strings_internal::StringAppendAndOverwrite(

      *dest, SafeAdd({a.size(), b.size(), c.size()}),

      [&a, &b, &c](char* const buf, size_t buf_size) {

        char* out = buf;

        out = Append(out, a);

        out = Append(out, b);

        out = Append(out, c);

        assert(out == buf + buf_size);

        return buf_size;

      });

}

void StrAppend(std::string* absl_nonnull dest, const AlphaNum& a,

               const AlphaNum& b, const AlphaNum& c, const AlphaNum& d) {

  ASSERT_NO_OVERLAP(*dest, a);

  ASSERT_NO_OVERLAP(*dest, b);

  ASSERT_NO_OVERLAP(*dest, c);

  ASSERT_NO_OVERLAP(*dest, d);

  strings_internal::StringAppendAndOverwrite(

      *dest, SafeAdd({a.size(), b.size(), c.size(), d.size()}),

      [&a, &b, &c, &d](char* const buf, size_t buf_size) {

        char* out = buf;

        out = Append(out, a);

        out = Append(out, b);

        out = Append(out, c);

        out = Append(out, d);

        assert(out == buf + buf_size);

        return buf_size;

      });

}

ABSL_NAMESPACE_END

}  // namespace absl