/*
 *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include "api/array_view.h"

#include <array>
#include <cstddef>
#include <cstdint>
#include <span>
#include <string>
#include <utility>
#include <vector>

#include "rtc_base/buffer.h"
#include "rtc_base/checks.h"
#include "test/gmock.h"
#include "test/gtest.h"

namespace webrtc {

namespace {

using ::testing::ElementsAre;
using ::testing::IsEmpty;

template <typename T>
size_t Call(ArrayView<T> av) {
  return av.size();
}

template <typename T, size_t N>
void CallFixed(ArrayView<T, N> /* av */) {}

}  // namespace

TEST(ArrayViewDeathTest, TestConstructFromPtrAndArray) {
  char arr[] = "Arrr!";
  const char carr[] = "Carrr!";
  EXPECT_EQ(6u, Call<const char>(arr));
  EXPECT_EQ(7u, Call<const char>(carr));
  EXPECT_EQ(6u, Call<char>(arr));
  // Call<char>(carr);  // Compile error, because can't drop const.
  // Call<int>(arr);  // Compile error, because incompatible types.
  ArrayView<int*> x;
  EXPECT_EQ(0u, x.size());
  EXPECT_EQ(nullptr, x.data());
  ArrayView<char> y = arr;
  EXPECT_EQ(6u, y.size());
  EXPECT_EQ(arr, y.data());
  ArrayView<char, 6> yf = arr;
  static_assert(yf.size() == 6, "");
  EXPECT_EQ(arr, yf.data());
  ArrayView<const char> z(arr + 1, 3);
  EXPECT_EQ(3u, z.size());
  EXPECT_EQ(arr + 1, z.data());
  ArrayView<const char, 3> zf(arr + 1, 3);
  static_assert(zf.size() == 3, "");
  EXPECT_EQ(arr + 1, zf.data());
  ArrayView<const char> w(arr, 2);
  EXPECT_EQ(2u, w.size());
  EXPECT_EQ(arr, w.data());
  ArrayView<const char, 2> wf(arr, 2);
  static_assert(wf.size() == 2, "");
  EXPECT_EQ(arr, wf.data());
  ArrayView<char> q(arr, 0);
  EXPECT_EQ(0u, q.size());
  EXPECT_TRUE(q.empty());
  ArrayView<char, 0> qf(arr, 0);
  static_assert(qf.size() == 0, "");
  EXPECT_TRUE(qf.empty());
#if RTC_DCHECK_IS_ON && GTEST_HAS_DEATH_TEST && !defined(WEBRTC_ANDROID)
  // DCHECK error (nullptr with nonzero size).
  EXPECT_DEATH(ArrayView<int>(static_cast<int*>(nullptr), 5), "");
#endif
  // These are compile errors, because incompatible types.
  // ArrayView<int> m = arr;
  // ArrayView<float> n(arr + 2, 2);
}

TEST(ArrayViewTest, TestCopyConstructorVariableLvalue) {
  char arr[] = "Arrr!";
  ArrayView<char> x = arr;
  EXPECT_EQ(6u, x.size());
  EXPECT_EQ(arr, x.data());
  ArrayView<char> y = x;  // Copy non-const -> non-const.
  EXPECT_EQ(6u, y.size());
  EXPECT_EQ(arr, y.data());
  ArrayView<const char> z = x;  // Copy non-const -> const.
  EXPECT_EQ(6u, z.size());
  EXPECT_EQ(arr, z.data());
  ArrayView<const char> w = z;  // Copy const -> const.
  EXPECT_EQ(6u, w.size());
  EXPECT_EQ(arr, w.data());
  // ArrayView<char> v = z;  // Compile error, because can't drop const.
}

TEST(ArrayViewTest, TestCopyConstructorVariableRvalue) {
  char arr[] = "Arrr!";
  ArrayView<char> x = arr;
  EXPECT_EQ(6u, x.size());
  EXPECT_EQ(arr, x.data());
  ArrayView<char> y = std::move(x);  // Copy non-const -> non-const.
  EXPECT_EQ(6u, y.size());
  EXPECT_EQ(arr, y.data());
  ArrayView<const char> z = std::move(x);  // Copy non-const -> const.
  EXPECT_EQ(6u, z.size());
  EXPECT_EQ(arr, z.data());
  ArrayView<const char> w = std::move(z);  // Copy const -> const.
  EXPECT_EQ(6u, w.size());
  EXPECT_EQ(arr, w.data());
  // ArrayView<char> v = std::move(z);  // Error, because can't drop const.
}

TEST(ArrayViewTest, TestCopyConstructorFixedLvalue) {
  char arr[] = "Arrr!";
  ArrayView<char, 6> x = arr;
  static_assert(x.size() == 6, "");
  EXPECT_EQ(arr, x.data());

  // Copy fixed -> fixed.
  ArrayView<char, 6> y = x;  // Copy non-const -> non-const.
  static_assert(y.size() == 6, "");
  EXPECT_EQ(arr, y.data());
  ArrayView<const char, 6> z = x;  // Copy non-const -> const.
  static_assert(z.size() == 6, "");
  EXPECT_EQ(arr, z.data());
  ArrayView<const char, 6> w = z;  // Copy const -> const.
  static_assert(w.size() == 6, "");
  EXPECT_EQ(arr, w.data());
  // ArrayView<char, 6> v = z;  // Compile error, because can't drop const.

  // Copy fixed -> variable.
  ArrayView<char> yv = x;  // Copy non-const -> non-const.
  EXPECT_EQ(6u, yv.size());
  EXPECT_EQ(arr, yv.data());
  ArrayView<const char> zv = x;  // Copy non-const -> const.
  EXPECT_EQ(6u, zv.size());
  EXPECT_EQ(arr, zv.data());
  ArrayView<const char> wv = z;  // Copy const -> const.
  EXPECT_EQ(6u, wv.size());
  EXPECT_EQ(arr, wv.data());
  // ArrayView<char> vv = z;  // Compile error, because can't drop const.
}

TEST(ArrayViewTest, TestCopyConstructorFixedRvalue) {
  char arr[] = "Arrr!";
  ArrayView<char, 6> x = arr;
  static_assert(x.size() == 6, "");
  EXPECT_EQ(arr, x.data());

  // Copy fixed -> fixed.
  ArrayView<char, 6> y = std::move(x);  // Copy non-const -> non-const.
  static_assert(y.size() == 6, "");
  EXPECT_EQ(arr, y.data());
  ArrayView<const char, 6> z = std::move(x);  // Copy non-const -> const.
  static_assert(z.size() == 6, "");
  EXPECT_EQ(arr, z.data());
  ArrayView<const char, 6> w = std::move(z);  // Copy const -> const.
  static_assert(w.size() == 6, "");
  EXPECT_EQ(arr, w.data());
  // ArrayView<char, 6> v = std::move(z);  // Error, because can't drop const.

  // Copy fixed -> variable.
  ArrayView<char> yv = std::move(x);  // Copy non-const -> non-const.
  EXPECT_EQ(6u, yv.size());
  EXPECT_EQ(arr, yv.data());
  ArrayView<const char> zv = std::move(x);  // Copy non-const -> const.
  EXPECT_EQ(6u, zv.size());
  EXPECT_EQ(arr, zv.data());
  ArrayView<const char> wv = std::move(z);  // Copy const -> const.
  EXPECT_EQ(6u, wv.size());
  EXPECT_EQ(arr, wv.data());
  // ArrayView<char> vv = std::move(z);  // Error, because can't drop const.
}

TEST(ArrayViewTest, TestCopyAssignmentVariableLvalue) {
  char arr[] = "Arrr!";
  ArrayView<char> x(arr);
  EXPECT_EQ(6u, x.size());
  EXPECT_EQ(arr, x.data());
  ArrayView<char> y;
  y = x;  // Copy non-const -> non-const.
  EXPECT_EQ(6u, y.size());
  EXPECT_EQ(arr, y.data());
  ArrayView<const char> z;
  z = x;  // Copy non-const -> const.
  EXPECT_EQ(6u, z.size());
  EXPECT_EQ(arr, z.data());
  ArrayView<const char> w;
  w = z;  // Copy const -> const.
  EXPECT_EQ(6u, w.size());
  EXPECT_EQ(arr, w.data());
  // ArrayView<char> v;
  // v = z;  // Compile error, because can't drop const.
}

TEST(ArrayViewTest, TestCopyAssignmentVariableRvalue) {
  char arr[] = "Arrr!";
  ArrayView<char> x(arr);
  EXPECT_EQ(6u, x.size());
  EXPECT_EQ(arr, x.data());
  ArrayView<char> y;
  y = std::move(x);  // Copy non-const -> non-const.
  EXPECT_EQ(6u, y.size());
  EXPECT_EQ(arr, y.data());
  ArrayView<const char> z;
  z = std::move(x);  // Copy non-const -> const.
  EXPECT_EQ(6u, z.size());
  EXPECT_EQ(arr, z.data());
  ArrayView<const char> w;
  w = std::move(z);  // Copy const -> const.
  EXPECT_EQ(6u, w.size());
  EXPECT_EQ(arr, w.data());
  // ArrayView<char> v;
  // v = std::move(z);  // Compile error, because can't drop const.
}

TEST(ArrayViewTest, TestCopyAssignmentFixedLvalue) {
  char arr[] = "Arrr!";
  char init[] = "Init!";
  ArrayView<char, 6> x(arr);
  EXPECT_EQ(arr, x.data());

  // Copy fixed -> fixed.
  ArrayView<char, 6> y(init);
  y = x;  // Copy non-const -> non-const.
  EXPECT_EQ(arr, y.data());
  ArrayView<const char, 6> z(init);
  z = x;  // Copy non-const -> const.
  EXPECT_EQ(arr, z.data());
  ArrayView<const char, 6> w(init);
  w = z;  // Copy const -> const.
  EXPECT_EQ(arr, w.data());
  // ArrayView<char, 6> v(init);
  // v = z;  // Compile error, because can't drop const.

  // Copy fixed -> variable.
  ArrayView<char> yv;
  yv = x;  // Copy non-const -> non-const.
  EXPECT_EQ(6u, yv.size());
  EXPECT_EQ(arr, yv.data());
  ArrayView<const char> zv;
  zv = x;  // Copy non-const -> const.
  EXPECT_EQ(6u, zv.size());
  EXPECT_EQ(arr, zv.data());
  ArrayView<const char> wv;
  wv = z;  // Copy const -> const.
  EXPECT_EQ(6u, wv.size());
  EXPECT_EQ(arr, wv.data());
  // ArrayView<char> v;
  // v = z;  // Compile error, because can't drop const.
}

TEST(ArrayViewTest, TestCopyAssignmentFixedRvalue) {
  char arr[] = "Arrr!";
  char init[] = "Init!";
  ArrayView<char, 6> x(arr);
  EXPECT_EQ(arr, x.data());

  // Copy fixed -> fixed.
  ArrayView<char, 6> y(init);
  y = std::move(x);  // Copy non-const -> non-const.
  EXPECT_EQ(arr, y.data());
  ArrayView<const char, 6> z(init);
  z = std::move(x);  // Copy non-const -> const.
  EXPECT_EQ(arr, z.data());
  ArrayView<const char, 6> w(init);
  w = std::move(z);  // Copy const -> const.
  EXPECT_EQ(arr, w.data());
  // ArrayView<char, 6> v(init);
  // v = std::move(z);  // Compile error, because can't drop const.

  // Copy fixed -> variable.
  ArrayView<char> yv;
  yv = std::move(x);  // Copy non-const -> non-const.
  EXPECT_EQ(6u, yv.size());
  EXPECT_EQ(arr, yv.data());
  ArrayView<const char> zv;
  zv = std::move(x);  // Copy non-const -> const.
  EXPECT_EQ(6u, zv.size());
  EXPECT_EQ(arr, zv.data());
  ArrayView<const char> wv;
  wv = std::move(z);  // Copy const -> const.
  EXPECT_EQ(6u, wv.size());
  EXPECT_EQ(arr, wv.data());
  // ArrayView<char> v;
  // v = std::move(z);  // Compile error, because can't drop const.
}

TEST(ArrayViewTest, TestStdArray) {
  EXPECT_EQ(4u, Call<const int>(std::array<int, 4>{1, 2, 3, 4}));
  CallFixed<const int, 3>(std::array<int, 3>{2, 3, 4});
  constexpr size_t size = 5;
  std::array<float, size> arr{};
  // Fixed size view.
  ArrayView<float, size> arr_view_fixed(arr);
  EXPECT_EQ(arr.data(), arr_view_fixed.data());
  static_assert(size == arr_view_fixed.size(), "");
  // Variable size view.
  ArrayView<float> arr_view(arr);
  EXPECT_EQ(arr.data(), arr_view.data());
  EXPECT_EQ(size, arr_view.size());
}

TEST(ArrayViewTest, TestConstStdArray) {
  constexpr size_t size = 5;

  constexpr std::array<float, size> constexpr_arr{};
  ArrayView<const float, size> constexpr_arr_view(constexpr_arr);
  EXPECT_EQ(constexpr_arr.data(), constexpr_arr_view.data());
  static_assert(constexpr_arr.size() == constexpr_arr_view.size(), "");

  const std::array<float, size> const_arr{};
  ArrayView<const float, size> const_arr_view(const_arr);
  EXPECT_EQ(const_arr.data(), const_arr_view.data());
  static_assert(const_arr.size() == const_arr_view.size(), "");

  std::array<float, size> non_const_arr{};
  ArrayView<const float, size> non_const_arr_view(non_const_arr);
  EXPECT_EQ(non_const_arr.data(), non_const_arr_view.data());
  static_assert(non_const_arr.size() == non_const_arr_view.size(), "");
}

TEST(ArrayViewTest, TestStdVector) {
  EXPECT_EQ(3u, Call<const int>(std::vector<int>{4, 5, 6}));
  std::vector<int> v;
  v.push_back(3);
  v.push_back(11);
  EXPECT_EQ(2u, Call<const int>(v));
  EXPECT_EQ(2u, Call<int>(v));
  // Call<unsigned int>(v);  // Compile error, because incompatible types.
  ArrayView<int> x = v;
  EXPECT_EQ(2u, x.size());
  EXPECT_EQ(v.data(), x.data());
  ArrayView<const int> y;
  y = v;
  EXPECT_EQ(2u, y.size());
  EXPECT_EQ(v.data(), y.data());
  // ArrayView<double> d = v;  // Compile error, because incompatible types.
  const std::vector<int> cv;
  EXPECT_EQ(0u, Call<const int>(cv));
  // Call<int>(cv);  // Compile error, because can't drop const.
  ArrayView<const int> z = cv;
  EXPECT_EQ(0u, z.size());
  EXPECT_EQ(nullptr, z.data());
  // ArrayView<int> w = cv;  // Compile error, because can't drop const.
}

TEST(ArrayViewTest, TestRtcBuffer) {
  Buffer b = "so buffer";
  EXPECT_EQ(10u, Call<const uint8_t>(b));
  EXPECT_EQ(10u, Call<uint8_t>(b));
  // Call<int8_t>(b);  // Compile error, because incompatible types.
  ArrayView<uint8_t> x = b;
  EXPECT_EQ(10u, x.size());
  EXPECT_EQ(b.data(), x.data());
  ArrayView<const uint8_t> y;
  y = b;
  EXPECT_EQ(10u, y.size());
  EXPECT_EQ(b.data(), y.data());
  // ArrayView<char> d = b;  // Compile error, because incompatible types.
  const Buffer cb = "very const";
  EXPECT_EQ(11u, Call<const uint8_t>(cb));
  // Call<uint8_t>(cb);  // Compile error, because can't drop const.
  ArrayView<const uint8_t> z = cb;
  EXPECT_EQ(11u, z.size());
  EXPECT_EQ(cb.data(), z.data());
  // ArrayView<uint8_t> w = cb;  // Compile error, because can't drop const.
}

TEST(ArrayViewTest, TestSwapVariable) {
  const char arr[] = "Arrr!";
  const char aye[] = "Aye, Cap'n!";
  ArrayView<const char> x(arr);
  EXPECT_EQ(6u, x.size());
  EXPECT_EQ(arr, x.data());
  ArrayView<const char> y(aye);
  EXPECT_EQ(12u, y.size());
  EXPECT_EQ(aye, y.data());
  using std::swap;
  swap(x, y);
  EXPECT_EQ(12u, x.size());
  EXPECT_EQ(aye, x.data());
  EXPECT_EQ(6u, y.size());
  EXPECT_EQ(arr, y.data());
  // ArrayView<char> z;
  // swap(x, z);  // Compile error, because can't drop const.
}

TEST(FixArrayViewTest, TestSwapFixed) {
  const char arr[] = "Arr!";
  char aye[] = "Aye!";
  ArrayView<const char, 5> x(arr);
  EXPECT_EQ(arr, x.data());
  ArrayView<const char, 5> y(aye);
  EXPECT_EQ(aye, y.data());
  using std::swap;
  swap(x, y);
  EXPECT_EQ(aye, x.data());
  EXPECT_EQ(arr, y.data());
  // ArrayView<char, 5> z(aye);
  // swap(x, z);  // Compile error, because can't drop const.
  // ArrayView<const char, 4> w(aye, 4);
  // swap(x, w);  // Compile error, because different sizes.
}

TEST(ArrayViewDeathTest, TestIndexing) {
  char arr[] = "abcdefg";
  ArrayView<char> x(arr);
  const ArrayView<char> y(arr);
  ArrayView<const char, 8> z(arr);
  EXPECT_EQ(8u, x.size());
  EXPECT_EQ(8u, y.size());
  EXPECT_EQ(8u, z.size());
  EXPECT_EQ('b', x[1]);
  EXPECT_EQ('c', y[2]);
  EXPECT_EQ('d', z[3]);
  x[3] = 'X';
  y[2] = 'Y';
  // z[1] = 'Z';  // Compile error, because z's element type is const char.
  EXPECT_EQ('b', x[1]);
  EXPECT_EQ('Y', y[2]);
  EXPECT_EQ('X', z[3]);
#if RTC_DCHECK_IS_ON && GTEST_HAS_DEATH_TEST && !defined(WEBRTC_ANDROID)
  // DCHECK error (index out of bounds).
  EXPECT_DEATH(std::ignore = z[8], "");
#endif
}

TEST(ArrayViewTest, TestIterationEmpty) {
  // Variable-size.
  ArrayView<std::vector<std::vector<std::vector<std::string>>>> av;
  EXPECT_EQ(av.begin(), av.end());
  for (auto& e : av) {
    EXPECT_TRUE(false);
    EXPECT_EQ(42u, e.size());  // Dummy use of e to prevent unused var warning.
  }

  // Fixed-size.
  ArrayView<std::vector<std::vector<std::vector<std::string>>>, 0> af;
  EXPECT_EQ(af.begin(), af.end());
  for (auto& e : af) {
    EXPECT_TRUE(false);
    EXPECT_EQ(42u, e.size());  // Dummy use of e to prevent unused var warning.
  }
}

TEST(ArrayViewTest, TestReverseIterationEmpty) {
  // Variable-size.
  ArrayView<std::vector<std::vector<std::vector<std::string>>>> av;
  EXPECT_EQ(av.rbegin(), av.rend());
  EXPECT_TRUE(av.empty());

  // Fixed-size.
  ArrayView<std::vector<std::vector<std::vector<std::string>>>, 0> af;
  EXPECT_EQ(af.begin(), af.end());
  EXPECT_TRUE(af.empty());
}

TEST(ArrayViewTest, TestIterationVariable) {
  char arr[] = "Arrr!";
  ArrayView<char> av(arr);
  EXPECT_EQ('A', *av.begin());
  EXPECT_EQ('\0', *(av.end() - 1));
  char i = 0;
  for (auto& e : av) {
    EXPECT_EQ(arr + i, &e);
    e = 's' + i;
    ++i;
  }
  i = 0;
  for (auto& e : ArrayView<const char>(av)) {
    EXPECT_EQ(arr + i, &e);
    // e = 'q' + i;  // Compile error, because e is a const char&.
    ++i;
  }
}

TEST(ArrayViewTest, TestReverseIterationVariable) {
  char arr[] = "Arrr!";
  ArrayView<char> av(arr);
  EXPECT_EQ('\0', *av.rbegin());
  EXPECT_EQ('A', *(av.rend() - 1));

  auto it = av.end() - 1;
  for (auto rit = av.rbegin(); rit != av.rend(); ++rit, --it) {
    EXPECT_EQ(*it, *rit);
  }
}

TEST(ArrayViewTest, TestIterationFixed) {
  char arr[] = "Arrr!";
  ArrayView<char, 6> av(arr);
  EXPECT_EQ('A', *av.begin());
  EXPECT_EQ('\0', *(av.end() - 1));
  char i = 0;
  for (auto& e : av) {
    EXPECT_EQ(arr + i, &e);
    e = 's' + i;
    ++i;
  }
  i = 0;
  for (auto& e : ArrayView<const char, 6>(av)) {
    EXPECT_EQ(arr + i, &e);
    // e = 'q' + i;  // Compile error, because e is a const char&.
    ++i;
  }
}

TEST(ArrayViewTest, TestReverseIterationFixed) {
  char arr[] = "Arrr!";
  ArrayView<char, 6> av(arr);
  EXPECT_EQ('\0', *av.rbegin());
  EXPECT_EQ('A', *(av.rend() - 1));

  auto it = av.end() - 1;
  for (auto rit = av.rbegin(); rit != av.rend(); ++rit, --it) {
    EXPECT_EQ(*it, *rit);
  }
}

TEST(ArrayViewTest, TestEmpty) {
  EXPECT_TRUE(ArrayView<int>().empty());
  const int a[] = {1, 2, 3};
  EXPECT_FALSE(ArrayView<const int>(a).empty());

  static_assert(ArrayView<int, 0>().empty());
}

TEST(ArrayViewTest, TestSubSpanVariable) {
  int a[] = {1, 2, 3};
  ArrayView<int> av(a);

  EXPECT_THAT(av.subspan(0), ElementsAre(1, 2, 3));
  EXPECT_THAT(av.subspan(1), ElementsAre(2, 3));
  EXPECT_THAT(av.subspan(2), ElementsAre(3));
  EXPECT_THAT(av.subspan(3), IsEmpty());

  EXPECT_THAT(av.subspan(1, 0), IsEmpty());
  EXPECT_THAT(av.subspan(1, 1), ElementsAre(2));
  EXPECT_THAT(av.subspan(1, 2), ElementsAre(2, 3));
}

TEST(ArrayViewTest, TestSubSpanWithInvalidInput) {
  int a[] = {1, 2, 3};
  ArrayView<int> av(a);
  EXPECT_DEATH_IF_SUPPORTED(std::ignore = av.subspan(4), "");
  EXPECT_DEATH_IF_SUPPORTED(std::ignore = av.subspan(1, 3), "");
}

TEST(ArrayViewTest, SubspanFixed) {
  std::array<int, 3> a = {1, 2, 3};
  ArrayView<int, 3> av(a);

  EXPECT_THAT(av.subspan<0>(), ElementsAre(1, 2, 3));
  EXPECT_THAT(av.subspan<1>(), ElementsAre(2, 3));
  EXPECT_THAT(av.subspan<2>(), ElementsAre(3));
  EXPECT_THAT(av.subspan<3>(), IsEmpty());

  EXPECT_THAT((av.subspan<1, 0>()), IsEmpty());
  EXPECT_THAT((av.subspan<1, 1>()), ElementsAre(2));
  EXPECT_THAT((av.subspan<1, 2>()), ElementsAre(2, 3));

  EXPECT_EQ(av.subspan<1>().extent, 2u);
  EXPECT_EQ((av.subspan<1, 1>().extent), 1u);

  ArrayView<int> dynamic_av(a);
  EXPECT_THAT(dynamic_av.subspan<0>(), ElementsAre(1, 2, 3));
  EXPECT_THAT(dynamic_av.subspan<1>(), ElementsAre(2, 3));
  EXPECT_THAT(dynamic_av.subspan<2>(), ElementsAre(3));
  EXPECT_THAT(dynamic_av.subspan<3>(), IsEmpty());

  EXPECT_THAT((dynamic_av.subspan<1, 0>()), IsEmpty());
  EXPECT_THAT((dynamic_av.subspan<1, 1>()), ElementsAre(2));
  EXPECT_THAT((dynamic_av.subspan<1, 2>()), ElementsAre(2, 3));

  EXPECT_EQ(dynamic_av.subspan<1>().extent, std::dynamic_extent);
  EXPECT_EQ((dynamic_av.subspan<1, 1>()).extent, 1u);
}

TEST(ArrayViewTest, FirstFixed) {
  std::array<int, 3> a = {1, 2, 3};
  ArrayView<int> av(a);

  EXPECT_THAT(av.first<0>(), IsEmpty());
  EXPECT_THAT(av.first<1>(), ElementsAre(1));
  EXPECT_THAT(av.first<2>(), ElementsAre(1, 2));
  EXPECT_THAT(av.first<3>(), ElementsAre(1, 2, 3));

  EXPECT_EQ((av.first<0>()).extent, 0u);
  EXPECT_EQ((av.first<2>()).extent, 2u);
}

TEST(ArrayViewTest, LastFixed) {
  std::array<int, 3> a = {1, 2, 3};
  ArrayView<int> av(a);

  EXPECT_THAT(av.last<0>(), IsEmpty());
  EXPECT_THAT(av.last<1>(), ElementsAre(3));
  EXPECT_THAT(av.last<2>(), ElementsAre(2, 3));
  EXPECT_THAT(av.last<3>(), ElementsAre(1, 2, 3));

  EXPECT_EQ((av.last<0>()).extent, 0u);
  EXPECT_EQ((av.last<2>()).extent, 2u);
}

}  // namespace webrtc