//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// <string>

// void push_back(charT c) // constexpr since C++20

#include <string>
#include <algorithm>
#include <cassert>

#include "test_macros.h"
#include "min_allocator.h"

struct VeryLarge {
  long long a;
  char b;
};

namespace std {
  template <>
  struct char_traits<VeryLarge> {
    using char_type           = VeryLarge;
    using int_type            = int;
    using off_type            = streamoff;
    using pos_type            = streampos;
    using state_type          = mbstate_t;

    static TEST_CONSTEXPR_CXX20 void assign(char_type& c1, const char_type& c2) { c1 = c2; }
    static bool eq(char_type c1, char_type c2);
    static bool lt(char_type c1, char_type c2);

    static int compare(const char_type* s1, const char_type* s2, std::size_t n);
    static std::size_t length(const char_type* s);
    static const char_type* find(const char_type* s, std::size_t n, const char_type& a);
    static char_type* move(char_type* s1, const char_type* s2, std::size_t n);
    static TEST_CONSTEXPR_CXX20 char_type* copy(char_type* s1, const char_type* s2, std::size_t n) {
      std::copy_n(s2, n, s1);
      return s1;
    }
    static TEST_CONSTEXPR_CXX20 char_type* assign(char_type* s, std::size_t n, char_type a) {
      std::fill_n(s, n, a);
      return s;
    }

    static int_type not_eof(int_type c);
    static char_type to_char_type(int_type c);
    static int_type to_int_type(char_type c);
    static bool eq_int_type(int_type c1, int_type c2);
    static int_type eof();
  };
} // end namespace std

template <class S>
TEST_CONSTEXPR_CXX20 void
test(S s, typename S::value_type c, S expected)
{
    s.push_back(c);
    LIBCPP_ASSERT(s.__invariants());
    assert(s == expected);
}

TEST_CONSTEXPR_CXX20 bool test() {
  {
    typedef std::string S;
    test(S(), 'a', S(1, 'a'));
    test(S("12345"), 'a', S("12345a"));
    test(S("12345678901234567890"), 'a', S("12345678901234567890a"));
  }
#if TEST_STD_VER >= 11
  {
    typedef std::basic_string<char, std::char_traits<char>, min_allocator<char>> S;
    test(S(), 'a', S(1, 'a'));
    test(S("12345"), 'a', S("12345a"));
    test(S("12345678901234567890"), 'a', S("12345678901234567890a"));
  }
#endif

  {
    // https://llvm.org/PR31454
    std::basic_string<VeryLarge> s;
    VeryLarge vl = {};
    s.push_back(vl);
    s.push_back(vl);
    s.push_back(vl);
  }

  return true;
}

int main(int, char**)
{
  test();
#if TEST_STD_VER > 17
  static_assert(test());
#endif

  return 0;
}