// Copyright 2021 The Pigweed 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 "pw_multisink/multisink.h"

#include <array>
#include <cstdint>
#include <cstring>
#include <optional>
#include <string_view>

#include "pw_function/function.h"
#include "pw_span/span.h"
#include "pw_status/status.h"
#include "pw_unit_test/framework.h"

namespace pw::multisink {
using Drain = MultiSink::Drain;
using Listener = MultiSink::Listener;

class CountingListener : public Listener {
 public:
  void OnNewEntryAvailable() override { notification_count_++; }

  size_t GetNotificationCount() { return notification_count_; }

  void ResetNotificationCount() { notification_count_ = 0; }

 private:
  size_t notification_count_ = 0;
};

class EntriesSizeMonitorListener : public Listener {
 public:
  EntriesSizeMonitorListener(pw::multisink::MultiSink::Drain& drain)
      : last_seen_unread_size_(0u), drain_(drain) {}
  void OnNewEntryAvailable() override {
    last_seen_unread_size_ = drain_.UnsafeGetUnreadEntriesSize();
  }

  size_t GetLastSeenUnreadEntriesSize() const { return last_seen_unread_size_; }

 private:
  size_t last_seen_unread_size_;
  pw::multisink::MultiSink::Drain& drain_;
};

class MultiSinkTest : public ::testing::Test {
 protected:
  static constexpr std::byte kMessage[] = {
      (std::byte)0xDE, (std::byte)0xAD, (std::byte)0xBE, (std::byte)0xEF};
  static constexpr std::byte kMessageOther[] = {
      (std::byte)0x12, (std::byte)0x34, (std::byte)0x56, (std::byte)0x78};
  static constexpr size_t kMaxDrains = 3;
  static constexpr size_t kMaxListeners = 3;
  static constexpr size_t kEntryBufferSize = 1024;
  static constexpr size_t kBufferSize = 5 * kEntryBufferSize;

  MultiSinkTest() : buffer_{}, multisink_(buffer_) {}

  // Expects the peeked or popped message to equal the provided non-empty
  // message, and the drop count to match. If `expected_message` is empty, the
  // Pop call status expected is OUT_OF_RANGE.
  void ExpectMessageAndDropCounts(Result<ConstByteSpan>& result,
                                  uint32_t result_drop_count,
                                  uint32_t result_ingress_drop_count,
                                  std::optional<ConstByteSpan> expected_message,
                                  uint32_t expected_drop_count,
                                  uint32_t expected_ingress_drop_count) {
    if (!expected_message.has_value()) {
      EXPECT_EQ(Status::OutOfRange(), result.status());
    } else {
      ASSERT_EQ(result.status(), OkStatus());
      if (!expected_message.value().empty()) {
        ASSERT_FALSE(result.value().empty());
        ASSERT_EQ(result.value().size_bytes(),
                  expected_message.value().size_bytes());
        EXPECT_EQ(memcmp(result.value().data(),
                         expected_message.value().data(),
                         expected_message.value().size_bytes()),
                  0);
      }
    }
    EXPECT_EQ(result_drop_count, expected_drop_count);
    EXPECT_EQ(result_ingress_drop_count, expected_ingress_drop_count);
  }

  void VerifyPopEntry(Drain& drain,
                      std::optional<ConstByteSpan> expected_message,
                      uint32_t expected_drop_count,
                      uint32_t expected_ingress_drop_count) {
    uint32_t drop_count = 0;
    uint32_t ingress_drop_count = 0;
    Result<ConstByteSpan> result =
        drain.PopEntry(entry_buffer_, drop_count, ingress_drop_count);
    ExpectMessageAndDropCounts(result,
                               drop_count,
                               ingress_drop_count,
                               expected_message,
                               expected_drop_count,
                               expected_ingress_drop_count);
  }

  void VerifyPeekResult(const Result<Drain::PeekedEntry>& peek_result,
                        uint32_t result_drop_count,
                        uint32_t result_ingress_drop_count,
                        std::optional<ConstByteSpan> expected_message,
                        uint32_t expected_drop_count,
                        uint32_t expected_ingress_drop_count) {
    if (peek_result.ok()) {
      ASSERT_FALSE(peek_result.value().entry().empty());
      Result<ConstByteSpan> verify_result(peek_result.value().entry());
      ExpectMessageAndDropCounts(verify_result,
                                 result_drop_count,
                                 result_ingress_drop_count,
                                 expected_message,
                                 expected_drop_count,
                                 expected_ingress_drop_count);
      return;
    }
    if (expected_message.has_value()) {
      // Fail since we expected OkStatus.
      ASSERT_EQ(peek_result.status(), OkStatus());
    }
    EXPECT_EQ(Status::OutOfRange(), peek_result.status());
  }

  void ExpectNotificationCount(CountingListener& listener,
                               size_t expected_notification_count) {
    EXPECT_EQ(listener.GetNotificationCount(), expected_notification_count);
    listener.ResetNotificationCount();
  }

  std::byte buffer_[kBufferSize];
  std::byte entry_buffer_[kEntryBufferSize];
  CountingListener listeners_[kMaxListeners];
  Drain drains_[kMaxDrains];
  MultiSink multisink_;
};

TEST_F(MultiSinkTest, SingleDrain) {
  multisink_.AttachDrain(drains_[0]);
  multisink_.AttachListener(listeners_[0]);
  ExpectNotificationCount(listeners_[0], 1u);
  multisink_.HandleEntry(kMessage);

  // Single entry push and pop.
  ExpectNotificationCount(listeners_[0], 1u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 0u);
  // Single empty entry push and pop.
  multisink_.HandleEntry(ConstByteSpan());
  ExpectNotificationCount(listeners_[0], 1u);
  VerifyPopEntry(drains_[0], ConstByteSpan(), 0u, 0u);

  // Multiple entries with intermittent drops.
  multisink_.HandleEntry(kMessage);
  multisink_.HandleDropped();
  multisink_.HandleEntry(kMessage);
  ExpectNotificationCount(listeners_[0], 3u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 0u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 1u);

  // Send drops only.
  multisink_.HandleDropped();
  ExpectNotificationCount(listeners_[0], 1u);
  VerifyPopEntry(drains_[0], std::nullopt, 0u, 1u);

  // Confirm out-of-range if no entries are expected.
  ExpectNotificationCount(listeners_[0], 0u);
  VerifyPopEntry(drains_[0], std::nullopt, 0u, 0u);
}

TEST_F(MultiSinkTest, MultipleDrain) {
  multisink_.AttachDrain(drains_[0]);
  multisink_.AttachDrain(drains_[1]);
  multisink_.AttachListener(listeners_[0]);
  multisink_.AttachListener(listeners_[1]);
  ExpectNotificationCount(listeners_[0], 1u);
  ExpectNotificationCount(listeners_[1], 1u);

  multisink_.HandleEntry(kMessage);
  multisink_.HandleEntry(kMessage);
  multisink_.HandleDropped();
  multisink_.HandleEntry(kMessage);
  multisink_.HandleDropped();

  // Drain one drain entirely.
  ExpectNotificationCount(listeners_[0], 5u);
  ExpectNotificationCount(listeners_[1], 5u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 0u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 0u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 1u);
  VerifyPopEntry(drains_[0], std::nullopt, 0u, 1u);
  VerifyPopEntry(drains_[0], std::nullopt, 0u, 0u);

  // Confirm the other drain can be drained separately.
  ExpectNotificationCount(listeners_[0], 0u);
  ExpectNotificationCount(listeners_[1], 0u);
  VerifyPopEntry(drains_[1], kMessage, 0u, 0u);
  VerifyPopEntry(drains_[1], kMessage, 0u, 0u);
  VerifyPopEntry(drains_[1], kMessage, 0u, 1u);
  VerifyPopEntry(drains_[1], std::nullopt, 0u, 1u);
  VerifyPopEntry(drains_[1], std::nullopt, 0u, 0u);
}

TEST_F(MultiSinkTest, LateDrainRegistration) {
  // Drains attached after entries are pushed should still observe those entries
  // if they have not been evicted from the ring buffer.
  multisink_.HandleEntry(kMessage);

  multisink_.AttachDrain(drains_[0]);
  multisink_.AttachListener(listeners_[0]);
  ExpectNotificationCount(listeners_[0], 1u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 0u);
  VerifyPopEntry(drains_[0], std::nullopt, 0u, 0u);

  multisink_.HandleEntry(kMessage);
  ExpectNotificationCount(listeners_[0], 1u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 0u);
  VerifyPopEntry(drains_[0], std::nullopt, 0u, 0u);
}

TEST_F(MultiSinkTest, DynamicDrainRegistration) {
  multisink_.AttachDrain(drains_[0]);
  multisink_.AttachListener(listeners_[0]);
  ExpectNotificationCount(listeners_[0], 1u);

  multisink_.HandleDropped();
  multisink_.HandleEntry(kMessage);
  multisink_.HandleDropped();
  multisink_.HandleEntry(kMessage);

  // Drain out one message and detach it.
  ExpectNotificationCount(listeners_[0], 4u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 1u);
  multisink_.DetachDrain(drains_[0]);
  multisink_.DetachListener(listeners_[0]);

  // Re-attaching the drain should reproduce the last observed message. Note
  // that notifications are not expected, nor are drops observed before the
  // first valid message in the buffer.
  multisink_.AttachDrain(drains_[0]);
  multisink_.AttachListener(listeners_[0]);
  ExpectNotificationCount(listeners_[0], 1u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 1u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 1u);
  VerifyPopEntry(drains_[0], std::nullopt, 0u, 0u);

  multisink_.HandleEntry(kMessage);
  ExpectNotificationCount(listeners_[0], 1u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 0u);
  VerifyPopEntry(drains_[0], std::nullopt, 0u, 0u);
}

TEST_F(MultiSinkTest, TooSmallBuffer) {
  multisink_.AttachDrain(drains_[0]);

  // Insert an entry and a drop, then try to read into an insufficient buffer.
  uint32_t drop_count = 0;
  uint32_t ingress_drop_count = 0;
  multisink_.HandleDropped();
  multisink_.HandleEntry(kMessage);

  // Attempting to acquire an entry with a small buffer should result in
  // RESOURCE_EXHAUSTED and remove it.
  Result<ConstByteSpan> result = drains_[0].PopEntry(
      span(entry_buffer_, 1), drop_count, ingress_drop_count);
  EXPECT_EQ(result.status(), Status::ResourceExhausted());

  VerifyPopEntry(drains_[0], std::nullopt, 1u, 1u);
}

TEST_F(MultiSinkTest, Iterator) {
  multisink_.AttachDrain(drains_[0]);

  // Insert entries and consume them all.
  multisink_.HandleEntry(kMessage);
  multisink_.HandleEntry(kMessage);
  multisink_.HandleEntry(kMessage);

  VerifyPopEntry(drains_[0], kMessage, 0u, 0u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 0u);
  VerifyPopEntry(drains_[0], kMessage, 0u, 0u);

  // Confirm that the iterator still observes the messages in the ring buffer.
  size_t iterated_entries = 0;
  for (ConstByteSpan entry : multisink_.UnsafeIteration()) {
    EXPECT_EQ(memcmp(entry.data(), kMessage, sizeof(kMessage)), 0);
    iterated_entries++;
  }
  EXPECT_EQ(iterated_entries, 3u);
}

TEST_F(MultiSinkTest, IteratorNoDrains) {
  // Insert entries with no drains attached. Even though there are no consumers,
  // iterators should still walk from the oldest entry.
  multisink_.HandleEntry(kMessage);
  multisink_.HandleEntry(kMessage);
  multisink_.HandleEntry(kMessage);

  // Confirm that the iterator still observes the messages in the ring buffer.
  size_t iterated_entries = 0;
  for (ConstByteSpan entry : multisink_.UnsafeIteration()) {
    EXPECT_EQ(memcmp(entry.data(), kMessage, sizeof(kMessage)), 0);
    iterated_entries++;
  }
  EXPECT_EQ(iterated_entries, 3u);
}

TEST_F(MultiSinkTest, IteratorNoEntries) {
  // Attach a drain, but don't add any entries.
  multisink_.AttachDrain(drains_[0]);
  // Confirm that the iterator has no entries.
  MultiSink::UnsafeIterationWrapper unsafe_iterator =
      multisink_.UnsafeIteration();
  EXPECT_EQ(unsafe_iterator.begin(), unsafe_iterator.end());
}

TEST_F(MultiSinkTest, PeekEntryNoEntries) {
  multisink_.AttachDrain(drains_[0]);

  // Peek empty multisink.
  uint32_t drop_count = 0;
  uint32_t ingress_drop_count = 0;
  auto peek_result =
      drains_[0].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  VerifyPeekResult(peek_result, 0, drop_count, std::nullopt, 0, 0);
}

TEST_F(MultiSinkTest, PeekAndPop) {
  multisink_.AttachDrain(drains_[0]);
  multisink_.AttachDrain(drains_[1]);

  // Peek entry after multisink has some entries.
  multisink_.HandleEntry(kMessage);
  multisink_.HandleEntry(kMessageOther);
  uint32_t drop_count = 0;
  uint32_t ingress_drop_count = 0;
  auto first_peek_result =
      drains_[0].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  VerifyPeekResult(
      first_peek_result, drop_count, ingress_drop_count, kMessage, 0, 0);

  // Multiple peeks must return the front message.
  auto peek_duplicate =
      drains_[0].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  VerifyPeekResult(
      peek_duplicate, drop_count, ingress_drop_count, kMessage, 0, 0);
  // A second drain must peek the front message.
  auto peek_other_drain =
      drains_[1].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  VerifyPeekResult(
      peek_other_drain, drop_count, ingress_drop_count, kMessage, 0, 0);

  // After a drain pops a peeked entry, the next peek call must return the next
  // message.
  ASSERT_EQ(drains_[0].PopEntry(first_peek_result.value()), OkStatus());
  auto second_peek_result =
      drains_[0].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  VerifyPeekResult(
      second_peek_result, drop_count, ingress_drop_count, kMessageOther, 0, 0);
  // Slower readers must be unchanged.
  auto peek_other_drain_duplicate =
      drains_[1].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  VerifyPeekResult(peek_other_drain_duplicate,
                   drop_count,
                   ingress_drop_count,
                   kMessage,
                   0,
                   0);

  // PopEntry prior to popping the previously peeked entry.
  VerifyPopEntry(drains_[0], kMessageOther, 0, 0);
  // Popping an entry already handled must not trigger errors.
  ASSERT_EQ(drains_[0].PopEntry(second_peek_result.value()), OkStatus());
  // Popping with an old peek context must not trigger errors.
  ASSERT_EQ(drains_[0].PopEntry(first_peek_result.value()), OkStatus());

  // Multisink is empty, pops and peeks should trigger OUT_OF_RANGE.
  VerifyPopEntry(drains_[0], std::nullopt, 0, 0);
  auto empty_peek_result =
      drains_[0].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  VerifyPeekResult(
      empty_peek_result, drop_count, ingress_drop_count, std::nullopt, 0, 0);

  // // Slower readers must be unchanged.
  auto peek_other_drain_unchanged =
      drains_[1].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  VerifyPeekResult(peek_other_drain_unchanged,
                   drop_count,
                   ingress_drop_count,
                   kMessage,
                   0,
                   0);
}

TEST_F(MultiSinkTest, PeekReportsIngressDropCount) {
  multisink_.AttachDrain(drains_[0]);

  // Peek entry after multisink has some entries.
  multisink_.HandleEntry(kMessage);
  const uint32_t ingress_drops = 10;
  multisink_.HandleDropped(ingress_drops);

  uint32_t drop_count = 0;
  uint32_t ingress_drop_count = 0;
  auto peek_result1 =
      drains_[0].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  // No drops reported until the drain finds a gap in the sequence IDs.
  VerifyPeekResult(
      peek_result1, drop_count, ingress_drop_count, kMessage, 0, 0);

  // Popping the peeked entry advances the drain, and a new peek will find the
  // gap in sequence IDs.
  ASSERT_EQ(drains_[0].PopEntry(peek_result1.value()), OkStatus());
  auto peek_result2 =
      drains_[0].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  ASSERT_EQ(peek_result2.status(), Status::OutOfRange());
  EXPECT_EQ(drop_count, 0u);
  EXPECT_EQ(ingress_drop_count, ingress_drops);
}

TEST_F(MultiSinkTest, PeekReportsSlowDrainDropCount) {
  multisink_.AttachDrain(drains_[0]);

  // Add entries until buffer is full and drain has to be advanced.
  // The sequence ID takes 1 byte when less than 128.
  const size_t max_multisink_messages = 128;
  const size_t buffer_entry_size = kBufferSize / max_multisink_messages;
  // Account for 1 byte of preamble (sequnce ID) and 1 byte of data size.
  const size_t message_size = buffer_entry_size - 2;
  std::array<std::byte, message_size> message;
  std::memset(message.data(), 'a', message.size());
  for (size_t i = 0; i < max_multisink_messages; ++i) {
    message[0] = static_cast<std::byte>(i);
    multisink_.HandleEntry(message);
  }

  // At this point the buffer is full, but the sequence ID will take 1 more byte
  // in the preamble, meaning that adding N new entries, drops N + 1 entries.
  // Account for that offset.
  const size_t expected_drops = 5;
  for (size_t i = 1; i < expected_drops; ++i) {
    message[0] = static_cast<std::byte>(200 + i);
    multisink_.HandleEntry(message);
  }

  uint32_t drop_count = 0;
  uint32_t ingress_drop_count = 0;

  auto peek_result =
      drains_[0].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  // The message peeked is the 6th message added.
  message[0] = static_cast<std::byte>(5);
  VerifyPeekResult(
      peek_result, drop_count, ingress_drop_count, message, expected_drops, 0);

  // Add 3 more messages since we peeked the multisink, generating 2 more drops.
  const size_t expected_drops2 = 2;
  for (size_t i = 0; i < expected_drops2 + 1; ++i) {
    message[0] = static_cast<std::byte>(220 + i);
    multisink_.HandleEntry(message);
  }

  // Pop the 6th message now, even though it was already dropped.
  EXPECT_EQ(drains_[0].PopEntry(peek_result.value()), OkStatus());

  // A new peek would get the 9th message because two more messages were
  // dropped. Given that PopEntry() was called with peek_result, all the dropped
  // messages before peek_result should be considered handled and only the two
  // new drops should be reported here.
  auto peek_result2 =
      drains_[0].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  message[0] = static_cast<std::byte>(8);  // 9th message
  VerifyPeekResult(peek_result2,
                   drop_count,
                   ingress_drop_count,
                   message,
                   expected_drops2,
                   0);
}

TEST_F(MultiSinkTest, IngressDropCountOverflow) {
  multisink_.AttachDrain(drains_[0]);

  // Make drain's last handled drop larger than multisink drop count, which
  // overflowed.
  const uint32_t drop_count_close_to_overflow =
      std::numeric_limits<uint32_t>::max() - 3;
  multisink_.HandleDropped(drop_count_close_to_overflow);
  multisink_.HandleEntry(kMessage);

  // Catch up drain's drop count.
  uint32_t drop_count = 0;
  uint32_t ingress_drop_count = 0;
  auto peek_result1 =
      drains_[0].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  VerifyPeekResult(peek_result1,
                   drop_count,
                   ingress_drop_count,
                   kMessage,
                   0,
                   drop_count_close_to_overflow);
  // Popping the peeked entry advances the drain, and a new peek will find the
  // gap in sequence IDs.
  ASSERT_EQ(drains_[0].PopEntry(peek_result1.value()), OkStatus());

  // Overflow multisink's drop count.
  const uint32_t expected_ingress_drop_count = 10;
  multisink_.HandleDropped(expected_ingress_drop_count);

  auto peek_result2 =
      drains_[0].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  ASSERT_EQ(peek_result2.status(), Status::OutOfRange());
  EXPECT_EQ(drop_count, 0u);
  EXPECT_EQ(ingress_drop_count, expected_ingress_drop_count);

  multisink_.HandleEntry(kMessage);
  auto peek_result3 =
      drains_[0].PeekEntry(entry_buffer_, drop_count, ingress_drop_count);
  VerifyPeekResult(
      peek_result3, drop_count, ingress_drop_count, kMessage, 0, 0);
}

TEST_F(MultiSinkTest, DetachedDrainReportsDropCount) {
  multisink_.AttachDrain(drains_[0]);

  const uint32_t ingress_drops = 10;
  multisink_.HandleDropped(ingress_drops);
  multisink_.HandleEntry(kMessage);
  VerifyPopEntry(drains_[0], kMessage, 0, ingress_drops);

  // Detaching and attaching drain should report the same drops.
  multisink_.DetachDrain(drains_[0]);
  multisink_.AttachDrain(drains_[0]);
  VerifyPopEntry(drains_[0], kMessage, 0, ingress_drops);
}

TEST_F(MultiSinkTest, DrainUnreadEntriesSize) {
  multisink_.AttachDrain(drains_[0]);

  EXPECT_EQ(drains_[0].GetUnreadEntriesSize(), 0u);
  multisink_.HandleEntry(kMessage);
  multisink_.HandleEntry(kMessage);
  const size_t unread_entries_size = drains_[0].GetUnreadEntriesSize();
  EXPECT_GT(unread_entries_size, 0u);

  // Attach another drain, it sees the same unread entriess size as the first
  // drain.
  multisink_.AttachDrain(drains_[1]);
  EXPECT_EQ(drains_[1].GetUnreadEntriesSize(), unread_entries_size);

  // Pop entries from the first drain.
  VerifyPopEntry(drains_[0],
                 /*expected_message=*/kMessage,
                 /*expected_drop_count=*/0,
                 /*expected_ingress_drop_count=*/0);
  VerifyPopEntry(drains_[0],
                 /*expected_message=*/kMessage,
                 /*expected_drop_count=*/0,
                 /*expected_ingress_drop_count=*/0);
  EXPECT_EQ(drains_[0].GetUnreadEntriesSize(), 0u);
  EXPECT_EQ(drains_[1].GetUnreadEntriesSize(), unread_entries_size);
}

TEST(UnsafeGetUnreadEntriesSize, ReadFromListener) {
  std::array<std::byte, 32> buffer;
  MultiSink multisink(buffer);

  pw::multisink::MultiSink::Drain drain;
  multisink.AttachDrain(drain);

  EntriesSizeMonitorListener listener(drain);
  multisink.AttachListener(listener);

  ASSERT_EQ(listener.GetLastSeenUnreadEntriesSize(), 0u);

  constexpr std::string_view kEntryToPush = "one";
  multisink.HandleEntry(as_bytes(span<const char>(kEntryToPush)));

  EXPECT_EQ(listener.GetLastSeenUnreadEntriesSize(),
            drain.GetUnreadEntriesSize());
}

TEST(UnsafeIteration, NoLimit) {
  constexpr std::array<std::string_view, 5> kExpectedEntries{
      "one", "two", "three", "four", "five"};
  std::array<std::byte, 32> buffer;
  MultiSink multisink(buffer);

  for (std::string_view entry : kExpectedEntries) {
    multisink.HandleEntry(as_bytes(span<const char>(entry)));
  }

  size_t entry_count = 0;
  struct {
    size_t& entry_count;
    span<const std::string_view> expected_results;
  } ctx{entry_count, kExpectedEntries};
  auto cb = [&ctx](ConstByteSpan data) {
    std::string_view expected_entry = ctx.expected_results[ctx.entry_count];
    EXPECT_EQ(data.size(), expected_entry.size());
    const int result =
        memcmp(data.data(), expected_entry.data(), expected_entry.size());
    EXPECT_EQ(0, result);
    ctx.entry_count++;
  };

  EXPECT_EQ(OkStatus(), multisink.UnsafeForEachEntry(cb));
  EXPECT_EQ(kExpectedEntries.size(), entry_count);
}

TEST(UnsafeIteration, Subset) {
  constexpr std::array<std::string_view, 5> kExpectedEntries{
      "one", "two", "three", "four", "five"};
  constexpr size_t kStartOffset = 3;
  constexpr size_t kExpectedEntriesMaxEntries =
      kExpectedEntries.size() - kStartOffset;
  std::array<std::byte, 32> buffer;
  MultiSink multisink(buffer);

  for (std::string_view entry : kExpectedEntries) {
    multisink.HandleEntry(as_bytes(span<const char>(entry)));
  }

  size_t entry_count = 0;
  struct {
    size_t& entry_count;
    span<const std::string_view> expected_results;
  } ctx{entry_count, kExpectedEntries};
  auto cb = [&ctx](ConstByteSpan data) {
    std::string_view expected_entry =
        ctx.expected_results[ctx.entry_count + kStartOffset];
    EXPECT_EQ(data.size(), expected_entry.size());
    const int result =
        memcmp(data.data(), expected_entry.data(), expected_entry.size());
    EXPECT_EQ(0, result);
    ctx.entry_count++;
  };

  EXPECT_EQ(
      OkStatus(),
      multisink.UnsafeForEachEntry(cb, kExpectedEntries.size() - kStartOffset));
  EXPECT_EQ(kExpectedEntriesMaxEntries, entry_count);
}

}  // namespace pw::multisink