// Licensed to the Apache Software Foundation (ASF) under one

// or more contributor license agreements.  See the NOTICE file

// distributed with this work for additional information

// regarding copyright ownership.  The ASF licenses this file

// to you 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.

#pragma once

#include <butil/macros.h>

#include <glog/logging.h>

#include <stddef.h>

#include <stdint.h>

#include <atomic>

#include <memory>

#include <ostream>

#include <string>

#include <utility>

#include <vector>

#include "common/status.h"

#include "olap/lru_cache.h"

#include "olap/olap_common.h" // for rowset id

#include "olap/rowset/segment_v2/segment.h"

#include "runtime/memory/lru_cache_policy.h"

#include "util/time.h"

namespace doris {

class SegmentCacheHandle;

class BetaRowset;

// SegmentLoader is used to load the Segment of BetaRowset.

// An LRUCache is encapsulated inside it, which is used to cache the opened segments.

// The caller should use the following method to load and obtain

// the segments of a specified rowset:

//

//  SegmentCacheHandle cache_handle;

//  RETURN_IF_ERROR(SegmentCache::instance()->load_segments(_rowset, &cache_handle));

//  for (auto& seg_ptr : cache_handle.value()->segments) {

//      ... visit segment ...

//  }

//

// Make sure that cache_handle is valid during the segment usage period.

using BetaRowsetSharedPtr = std::shared_ptr<BetaRowset>;

class SegmentCache : public LRUCachePolicy {

public:

    using LRUCachePolicy::insert;

    // The cache key or segment lru cache

    struct CacheKey {

        CacheKey(RowsetId rowset_id_, int64_t segment_id_)

                : rowset_id(rowset_id_), segment_id(segment_id_) {}

        RowsetId rowset_id;

        int64_t segment_id;

        // Encode to a flat binary which can be used as LRUCache's key

        [[nodiscard]] std::string encode() const {

            return rowset_id.to_string() + std::to_string(segment_id);

        }

    };

    // The cache value of segment lru cache.

    // Holding all opened segments of a rowset.

    class CacheValue : public LRUCacheValueBase {

    public:

        ~CacheValue() override { segment.reset(); }

        segment_v2::SegmentSharedPtr segment;

    };

    SegmentCache(size_t memory_bytes_limit, size_t segment_num_limit)

            : LRUCachePolicy(CachePolicy::CacheType::SEGMENT_CACHE, memory_bytes_limit,

                             LRUCacheType::SIZE, config::tablet_rowset_stale_sweep_time_sec,

                             DEFAULT_LRU_CACHE_NUM_SHARDS * 2, segment_num_limit) {}

    // Lookup the given segment in the cache.

    // If the segment is found, the cache entry will be written into handle.

    // Return true if entry is found, otherwise return false.

    bool lookup(const SegmentCache::CacheKey& key, SegmentCacheHandle* handle);

    // Insert a cache entry by key.

    // And the cache entry will be returned in handle.

    // This function is thread-safe.

    void insert(const SegmentCache::CacheKey& key, CacheValue& value, SegmentCacheHandle* handle);

    void erase(const SegmentCache::CacheKey& key);

};

class SegmentLoader {

public:

    static SegmentLoader* instance();

    // Create global instance of this class.

    // "capacity" is the capacity of lru cache.

    // TODO: Currently we use the number of rowset as the cache capacity.

    // That is, the limit of cache is the number of rowset.

    // This is because currently we cannot accurately estimate the memory occupied by a segment.

    // After the estimation of segment memory usage is provided later, it is recommended

    // to use Memory as the capacity limit of the cache.

    SegmentLoader(size_t memory_limit_bytes, size_t segment_num_count) {

        _segment_cache = std::make_unique<SegmentCache>(memory_limit_bytes, segment_num_count);

    }

    // Load segments of "rowset", return the "cache_handle" which contains segments.

    // If use_cache is true, it will be loaded from _cache.

    Status load_segments(const BetaRowsetSharedPtr& rowset, SegmentCacheHandle* cache_handle,

                         bool use_cache = false, bool need_load_pk_index_and_bf = false,

                         OlapReaderStatistics* index_load_stats = nullptr);

    void erase_segment(const SegmentCache::CacheKey& key);

    void erase_segments(const RowsetId& rowset_id, int64_t num_segments);

    // Just used for BE UT

    int64_t cache_mem_usage() const { return _cache_mem_usage; }

private:

    SegmentLoader();

    std::unique_ptr<SegmentCache> _segment_cache;

    // Just used for BE UT

    int64_t _cache_mem_usage = 0;

};

// A handle for a single rowset from segment lru cache.

// The handle can ensure that the segment is valid

// and will not be closed while the holder of the handle is accessing the segment.

// The handle will automatically release the cache entry when it is destroyed.

// So the caller need to make sure the handle is valid in lifecycle.

class SegmentCacheHandle {

public:

    SegmentCacheHandle() = default;

    ~SegmentCacheHandle() = default;

    void push_segment(LRUCachePolicy* cache, Cache::Handle* handle) {

        segments.push_back(((SegmentCache::CacheValue*)cache->value(handle))->segment);

        cache->release(handle);

    }

    void push_segment(segment_v2::SegmentSharedPtr segment) {

        segments.push_back(std::move(segment));

    }

    std::vector<segment_v2::SegmentSharedPtr>& get_segments() { return segments; }

    [[nodiscard]] bool is_inited() const { return _init; }

    void set_inited() {

        DCHECK(!_init);

        _init = true;

    }

    segment_v2::SegmentSharedPtr pop_unhealthy_segment() {

        if (segments.empty()) {

            return nullptr;

        }

        segment_v2::SegmentSharedPtr last_segment = segments.back();

        if (last_segment->healthy_status().ok()) {

            return nullptr;

        }

        segments.pop_back();

        return last_segment;

    }

private:

    std::vector<segment_v2::SegmentSharedPtr> segments;

    bool _init {false};

    // Don't allow copy and assign

    DISALLOW_COPY_AND_ASSIGN(SegmentCacheHandle);

};

} // namespace doris