// Copyright 2023 PingCAP, Inc.
//
// 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
//
//     http://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 <Common/TiFlashMetrics.h>
#include <Storages/DeltaMerge/File/ColumnCache.h>

namespace DB::DM
{

RangeWithStrategys ColumnCache::getReadStrategyImpl(
    size_t start_pack_idx,
    size_t pack_count,
    ColId column_id,
    std::function<bool(size_t, ColId)> is_hit)
{
    PackRange target_range{start_pack_idx, start_pack_idx + pack_count};

    RangeWithStrategys range_and_strategys;
    range_and_strategys.reserve(pack_count);
    auto strategy = Strategy::Unknown;
    size_t range_start = 0;
    for (size_t cursor = target_range.first; cursor < target_range.second; ++cursor)
    {
        if (is_hit(cursor, column_id))
        {
            if (strategy == Strategy::Memory)
            {
                continue;
            }
            else if (strategy == Strategy::Disk)
            {
                range_and_strategys.emplace_back(PackRange{range_start, cursor}, Strategy::Disk);
            }
            range_start = cursor;
            strategy = Strategy::Memory;
        }
        else
        {
            if (strategy == Strategy::Memory)
            {
                range_and_strategys.emplace_back(PackRange{range_start, cursor}, Strategy::Memory);
            }
            else if (strategy == Strategy::Disk)
            {
                continue;
            }
            range_start = cursor;
            strategy = Strategy::Disk;
        }
    }
    range_and_strategys.emplace_back(PackRange{range_start, target_range.second}, strategy);
    range_and_strategys.shrink_to_fit();
    return range_and_strategys;
}

RangeWithStrategys ColumnCache::getReadStrategy(size_t start_pack_idx, size_t pack_count, ColId column_id)
{
    const auto strategies
        = getReadStrategyImpl(start_pack_idx, pack_count, column_id, [this](size_t pack_id, ColId column_id) {
              return isPackInCache(pack_id, column_id);
          });
    for (const auto & [range, strategy] : strategies)
    {
        switch (strategy)
        {
        case Strategy::Memory:
            if (type == ColumnCacheType::ExtraColumnCache)
                GET_METRIC(tiflash_storage_column_cache_packs, type_extra_column_hit)
                    .Increment(range.second - range.first);
            else
                GET_METRIC(tiflash_storage_column_cache_packs, type_data_sharing_hit)
                    .Increment(range.second - range.first);
            break;
        case Strategy::Disk:
            if (type == ColumnCacheType::ExtraColumnCache)
                GET_METRIC(tiflash_storage_column_cache_packs, type_extra_column_miss)
                    .Increment(range.second - range.first);
            else
                GET_METRIC(tiflash_storage_column_cache_packs, type_data_sharing_miss)
                    .Increment(range.second - range.first);
            break;
        default:
            break;
        }
    }
    return strategies;
}

RangeWithStrategys ColumnCache::getCleanReadStrategy(
    size_t start_pack_idx,
    size_t pack_count,
    const std::vector<size_t> & clean_read_pack_idx)
{
    return getReadStrategyImpl(start_pack_idx, pack_count, 0, [&clean_read_pack_idx](size_t pack_id, ColId) {
        return std::find(clean_read_pack_idx.cbegin(), clean_read_pack_idx.cend(), pack_id)
            != clean_read_pack_idx.cend();
    });
}

void ColumnCache::tryPutColumn(
    size_t pack_id,
    ColId column_id,
    const ColumnPtr & column,
    size_t rows_offset,
    size_t rows_count)
{
    column_caches.withExclusive([&](auto & column_caches) {
        if (auto iter = column_caches.find(pack_id); iter != column_caches.end())
        {
            auto & column_cache_entry = iter->second;
            if (column_cache_entry.columns.find(column_id) != column_cache_entry.columns.end())
            {
                return;
            }
            if (column_cache_entry.rows_offset != rows_offset || column_cache_entry.rows_count != rows_count)
            {
                return;
            }

            column_cache_entry.columns.emplace(column_id, column);
        }
        else
        {
            ColumnCache::ColumnCacheEntry column_cache_entry;
            column_cache_entry.columns.emplace(column_id, column);
            column_cache_entry.rows_offset = rows_offset;
            column_cache_entry.rows_count = rows_count;

            column_caches.emplace(pack_id, column_cache_entry);
        }
    });
}

ColumnCacheElement ColumnCache::getColumn(size_t pack_id, ColId column_id)
{
    return column_caches.withShared([&](auto & column_caches) {
        if (auto iter = column_caches.find(pack_id); iter != column_caches.end())
        {
            auto & column_cache_entry = iter->second;
            auto & columns = column_cache_entry.columns;
            if (auto column_iter = columns.find(column_id); column_iter != columns.end())
            {
                return std::make_pair(
                    column_iter->second,
                    std::make_pair(column_cache_entry.rows_offset, column_cache_entry.rows_count));
            }
        }
        throw Exception(
            ErrorCodes::LOGICAL_ERROR,
            "Cannot find column in cache for pack id: {}, column id: {}",
            pack_id,
            column_id);
    });
}

void ColumnCache::delColumn(ColId column_id, size_t upper_pack_id)
{
    column_caches.withExclusive([&](auto & column_caches) {
        for (auto iter = column_caches.begin(); iter != column_caches.end();)
        {
            auto & columns = iter->second.columns;
            if (iter->first < upper_pack_id)
                columns.erase(column_id);

            if (columns.empty())
            {
                iter = column_caches.erase(iter);
            }
            else
            {
                ++iter;
            }
        }
    });
}

bool ColumnCache::isPackInCache(PackId pack_id, ColId column_id)
{
    return column_caches.withShared([&](auto & column_caches) {
        if (auto iter = column_caches.find(pack_id); iter != column_caches.end())
        {
            auto & columns = iter->second.columns;
            if (columns.find(column_id) != columns.end())
            {
                return true;
            }
        }
        return false;
    });
}

} // namespace DB::DM