/*
 * Copyright (C) 2017-present ScyllaDB
 */

/*
 * This file is part of Scylla.
 *
 * Scylla is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Scylla is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Scylla.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <boost/test/unit_test.hpp>
#include "utils/loading_shared_values.hh"
#include "utils/loading_cache.hh"
#include <seastar/core/aligned_buffer.hh>
#include <seastar/core/file.hh>
#include <seastar/core/thread.hh>
#include <seastar/core/sstring.hh>
#include <seastar/core/seastar.hh>
#include <seastar/core/sleep.hh>
#include <seastar/util/defer.hh>


#include "seastarx.hh"
#include "test/lib/eventually.hh"
#include <seastar/testing/test_case.hh>
#include <seastar/testing/thread_test_case.hh>
#include "test/lib/tmpdir.hh"
#include "test/lib/log.hh"
#include "test/lib/random_utils.hh"

#include <vector>
#include <numeric>
#include <random>

/// Get a random integer in the [0, max) range.
/// \param max bound of the random value range
/// \return The uniformly distributed random integer from the [0, \ref max) range.
static int rand_int(int max) {
    return tests::random::get_int(max - 1);
}

static const sstring test_file_name = "loading_cache_test.txt";
static const sstring test_string = "1";
static bool file_prepared = false;
static constexpr int num_loaders = 1000;

static thread_local int load_count;
static const tmpdir& get_tmpdir() {
    static thread_local tmpdir tmp;
    return tmp;
}

static future<> prepare() {
    if (file_prepared) {
        return make_ready_future<>();
    }

    return open_file_dma((get_tmpdir().path() / test_file_name.c_str()).c_str(), open_flags::create | open_flags::wo).then([] (file f) {
        return do_with(std::move(f), [] (file& f) {
            auto size = test_string.size() + 1;
            auto aligned_size = align_up(size, f.disk_write_dma_alignment());
            auto buf = allocate_aligned_buffer<char>(aligned_size, f.disk_write_dma_alignment());
            auto wbuf = buf.get();
            std::copy_n(test_string.c_str(), size, wbuf);
            return f.dma_write(0, wbuf, aligned_size).then([aligned_size, buf = std::move(buf)] (size_t s) {
                BOOST_REQUIRE_EQUAL(s, aligned_size);
                file_prepared = true;
            }).finally([&f] () mutable {
                return f.close();
            });
        });
    });
}

static future<sstring> loader(const int& k) {
    return open_file_dma((get_tmpdir().path() / test_file_name.c_str()).c_str(), open_flags::ro).then([] (file f) -> future<sstring> {
        return do_with(std::move(f), [] (file& f) -> future<sstring> {
            auto size = align_up(test_string.size() + 1, f.disk_read_dma_alignment());
            return f.dma_read_exactly<char>(0, size).then([] (auto buf) {
                sstring str(buf.get());
                BOOST_REQUIRE_EQUAL(str, test_string);
                ++load_count;
                return make_ready_future<sstring>(std::move(str));
            }).finally([&f] () mutable {
                return f.close();
            });
        });
    });
}

SEASTAR_TEST_CASE(test_loading_shared_values_parallel_loading_same_key) {
    return seastar::async([] {
        std::vector<int> ivec(num_loaders);
        load_count = 0;
        utils::loading_shared_values<int, sstring> shared_values;
        std::list<typename utils::loading_shared_values<int, sstring>::entry_ptr> anchors_list;

        prepare().get();

        std::fill(ivec.begin(), ivec.end(), 0);

        parallel_for_each(ivec, [&] (int& k) {
            return shared_values.get_or_load(k, loader).then([&] (auto entry_ptr) {
                anchors_list.emplace_back(std::move(entry_ptr));
            });
        }).get();

        // "loader" must be called exactly once
        BOOST_REQUIRE_EQUAL(load_count, 1);
        BOOST_REQUIRE_EQUAL(shared_values.size(), 1);
        anchors_list.clear();
    });
}

SEASTAR_TEST_CASE(test_loading_shared_values_parallel_loading_different_keys) {
    return seastar::async([] {
        std::vector<int> ivec(num_loaders);
        load_count = 0;
        utils::loading_shared_values<int, sstring> shared_values;
        std::list<typename utils::loading_shared_values<int, sstring>::entry_ptr> anchors_list;

        prepare().get();

        std::iota(ivec.begin(), ivec.end(), 0);

        parallel_for_each(ivec, [&] (int& k) {
            return shared_values.get_or_load(k, loader).then([&] (auto entry_ptr) {
                anchors_list.emplace_back(std::move(entry_ptr));
            });
        }).get();

        // "loader" must be called once for each key
        BOOST_REQUIRE_EQUAL(load_count, num_loaders);
        BOOST_REQUIRE_EQUAL(shared_values.size(), num_loaders);
        anchors_list.clear();
    });
}

SEASTAR_TEST_CASE(test_loading_shared_values_rehash) {
    return seastar::async([] {
        std::vector<int> ivec(num_loaders);
        load_count = 0;
        utils::loading_shared_values<int, sstring> shared_values;
        std::list<typename utils::loading_shared_values<int, sstring>::entry_ptr> anchors_list;

        prepare().get();

        std::iota(ivec.begin(), ivec.end(), 0);

        // verify that load factor is always in the (0.25, 0.75) range
        for (int k = 0; k < num_loaders; ++k) {
            shared_values.get_or_load(k, loader).then([&] (auto entry_ptr) {
                anchors_list.emplace_back(std::move(entry_ptr));
            }).get();
            BOOST_REQUIRE_LE(shared_values.size(), 3 * shared_values.buckets_count() / 4);
        }

        BOOST_REQUIRE_GE(shared_values.size(), shared_values.buckets_count() / 4);

        // minimum buckets count (by default) is 16, so don't check for less than 4 elements
        for (int k = 0; k < num_loaders - 4; ++k) {
            anchors_list.pop_back();
            shared_values.rehash();
            BOOST_REQUIRE_GE(shared_values.size(), shared_values.buckets_count() / 4);
        }

        anchors_list.clear();
    });
}

SEASTAR_TEST_CASE(test_loading_shared_values_parallel_loading_explicit_eviction) {
    return seastar::async([] {
        std::vector<int> ivec(num_loaders);
        load_count = 0;
        utils::loading_shared_values<int, sstring> shared_values;
        std::vector<typename utils::loading_shared_values<int, sstring>::entry_ptr> anchors_vec(num_loaders);

        prepare().get();

        std::iota(ivec.begin(), ivec.end(), 0);

        parallel_for_each(ivec, [&] (int& k) {
            return shared_values.get_or_load(k, loader).then([&] (auto entry_ptr) {
                anchors_vec[k] = std::move(entry_ptr);
            });
        }).get();

        int rand_key = rand_int(num_loaders);
        BOOST_REQUIRE(shared_values.find(rand_key) != nullptr);
        anchors_vec[rand_key] = nullptr;
        BOOST_REQUIRE_MESSAGE(shared_values.find(rand_key) == nullptr, format("explicit removal for key {} failed", rand_key));
        anchors_vec.clear();
    });
}

SEASTAR_TEST_CASE(test_loading_cache_loading_same_key) {
    return seastar::async([] {
        using namespace std::chrono;
        std::vector<int> ivec(num_loaders);
        load_count = 0;
        utils::loading_cache<int, sstring> loading_cache(num_loaders, 1s, testlog);
        auto stop_cache_reload = seastar::defer([&loading_cache] { loading_cache.stop().get(); });

        prepare().get();

        std::fill(ivec.begin(), ivec.end(), 0);

        parallel_for_each(ivec, [&] (int& k) {
            return loading_cache.get_ptr(k, loader).discard_result();
        }).get();

        // "loader" must be called exactly once
        BOOST_REQUIRE_EQUAL(load_count, 1);
        BOOST_REQUIRE_EQUAL(loading_cache.size(), 1);
    });
}

SEASTAR_THREAD_TEST_CASE(test_loading_cache_removing_key) {
    using namespace std::chrono;
    load_count = 0;
    utils::loading_cache<int, sstring> loading_cache(num_loaders, 100s, testlog);
    auto stop_cache_reload = seastar::defer([&loading_cache] { loading_cache.stop().get(); });

    prepare().get();

    loading_cache.get_ptr(0, loader).discard_result().get();
    BOOST_REQUIRE_EQUAL(load_count, 1);
    BOOST_REQUIRE(loading_cache.find(0) != nullptr);

    loading_cache.remove(0);
    BOOST_REQUIRE(loading_cache.find(0) == nullptr);
}

SEASTAR_TEST_CASE(test_loading_cache_loading_different_keys) {
    return seastar::async([] {
        using namespace std::chrono;
        std::vector<int> ivec(num_loaders);
        load_count = 0;
        utils::loading_cache<int, sstring> loading_cache(num_loaders, 1h, testlog);
        auto stop_cache_reload = seastar::defer([&loading_cache] { loading_cache.stop().get(); });

        prepare().get();

        std::iota(ivec.begin(), ivec.end(), 0);

        parallel_for_each(ivec, [&] (int& k) {
            return loading_cache.get_ptr(k, loader).discard_result();
        }).get();

        BOOST_REQUIRE_EQUAL(load_count, num_loaders);
        BOOST_REQUIRE_EQUAL(loading_cache.size(), num_loaders);
    });
}

SEASTAR_TEST_CASE(test_loading_cache_loading_expiry_eviction) {
    return seastar::async([] {
        using namespace std::chrono;
        utils::loading_cache<int, sstring> loading_cache(num_loaders, 20ms, testlog);
        auto stop_cache_reload = seastar::defer([&loading_cache] { loading_cache.stop().get(); });

        prepare().get();

        loading_cache.get_ptr(0, loader).discard_result().get();

        BOOST_REQUIRE(loading_cache.find(0) != nullptr);

        sleep(20ms).get();
        REQUIRE_EVENTUALLY_EQUAL(loading_cache.find(0), nullptr);
    });
}

SEASTAR_TEST_CASE(test_loading_cache_loading_expiry_reset_on_sync_op) {
    return seastar::async([] {
        using namespace std::chrono;
        utils::loading_cache<int, sstring> loading_cache(num_loaders, 30ms, testlog);
        auto stop_cache_reload = seastar::defer([&loading_cache] { loading_cache.stop().get(); });

        prepare().get();

        loading_cache.get_ptr(0, loader).discard_result().get();
        auto vp = loading_cache.find(0);
        auto load_time = steady_clock::now();

        // Check that the expiration timer is reset every time we call a find()
        for (int i = 0; i < 10; ++i) {
            // seastar::lowres_clock has 10ms resolution. This means that we should use 10ms threshold to compensate.
            if (steady_clock::now() <= load_time + 20ms) {
                BOOST_REQUIRE(vp != nullptr);
            } else {
                // If there was a delay and we weren't able to execute the next loop iteration during 20ms let's repopulate
                // the cache.
                loading_cache.get_ptr(0, loader).discard_result().get();
                BOOST_TEST_MESSAGE("Test " << i << " was skipped. Repopulating...");
            }
            vp = loading_cache.find(0);
            load_time = steady_clock::now();
            sleep(10ms).get();
        }

        sleep(30ms).get();
        REQUIRE_EVENTUALLY_EQUAL(loading_cache.size(), 0);
    });
}

SEASTAR_TEST_CASE(test_loading_cache_move_item_to_mru_list_front_on_sync_op) {
    return seastar::async([] {
        using namespace std::chrono;
        utils::loading_cache<int, sstring> loading_cache(2, 1h, testlog);
        auto stop_cache_reload = seastar::defer([&loading_cache] { loading_cache.stop().get(); });

        prepare().get();

        for (int i = 0; i < 2; ++i) {
            loading_cache.get_ptr(i, loader).discard_result().get();
        }

        auto vp0 = loading_cache.find(0);
        BOOST_REQUIRE(vp0 != nullptr);

        loading_cache.get_ptr(2, loader).discard_result().get();

        // "0" should be at the beginning of the list and "1" right after it before we try to add a new entry to the
        // cache ("2"). And hence "1" should get evicted.
        vp0 = loading_cache.find(0);
        auto vp1 = loading_cache.find(1);
        BOOST_REQUIRE(vp0 != nullptr);
        BOOST_REQUIRE(vp1 == nullptr);
    });
}

SEASTAR_TEST_CASE(test_loading_cache_loading_reloading) {
    return seastar::async([] {
        using namespace std::chrono;
        load_count = 0;
        utils::loading_cache<int, sstring, utils::loading_cache_reload_enabled::yes> loading_cache(num_loaders, 100ms, 20ms, testlog, loader);
        auto stop_cache_reload = seastar::defer([&loading_cache] { loading_cache.stop().get(); });
        prepare().get();
        loading_cache.get_ptr(0, loader).discard_result().get();
        sleep(60ms).get();
        BOOST_REQUIRE(eventually_true([&] { return load_count >= 2; }));
    });
}

SEASTAR_TEST_CASE(test_loading_cache_max_size_eviction) {
    return seastar::async([] {
        using namespace std::chrono;
        load_count = 0;
        utils::loading_cache<int, sstring> loading_cache(1, 1s, testlog);
        auto stop_cache_reload = seastar::defer([&loading_cache] { loading_cache.stop().get(); });

        prepare().get();

        for (int i = 0; i < num_loaders; ++i) {
            loading_cache.get_ptr(i % 2, loader).discard_result().get();
        }

        BOOST_REQUIRE_EQUAL(load_count, num_loaders);
        BOOST_REQUIRE_EQUAL(loading_cache.size(), 1);
    });
}

SEASTAR_TEST_CASE(test_loading_cache_reload_during_eviction) {
    return seastar::async([] {
        using namespace std::chrono;
        load_count = 0;
        utils::loading_cache<int, sstring, utils::loading_cache_reload_enabled::yes> loading_cache(1, 100ms, 10ms, testlog, loader);
        auto stop_cache_reload = seastar::defer([&loading_cache] { loading_cache.stop().get(); });

        prepare().get();

        auto curr_time = lowres_clock::now();
        int i = 0;

        // this will cause reloading when values are being actively evicted due to the limited cache size
        do_until(
            [&] { return lowres_clock::now() - curr_time > 1s; },
            [&] { return loading_cache.get_ptr(i++ % 2).discard_result(); }
        ).get();

        BOOST_REQUIRE_EQUAL(loading_cache.size(), 1);
    });
}