// Copyright (c) 2011 The LevelDB Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file. See the AUTHORS file for names of contributors.

#pragma once

#include <butil/macros.h>

#include <bvar/bvar.h>

#include <glog/logging.h>

#include <gtest/gtest_prod.h>

#include <atomic>

#include <cassert>

#include <cstdint>

#include <cstdlib>

#include <cstring>

#include <functional>

#include <memory>

#include <set>

#include <string>

#include <utility>

#include "runtime/memory/lru_cache_value_base.h"

#include "util/doris_metrics.h"

#include "util/metrics.h"

namespace doris {

#include "common/compile_check_begin.h"

class Cache;

class LRUCachePolicy;

struct LRUHandle;

enum LRUCacheType {

    SIZE, // The capacity of cache is based on the memory size of cache entry, memory size = handle size + charge.

    NUMBER // The capacity of cache is based on the number of cache entry, number = charge, the weight of an entry.

};

static constexpr LRUCacheType DEFAULT_LRU_CACHE_TYPE = LRUCacheType::SIZE;

static constexpr uint32_t DEFAULT_LRU_CACHE_NUM_SHARDS = 32;

static constexpr size_t DEFAULT_LRU_CACHE_ELEMENT_COUNT_CAPACITY = 0;

static constexpr bool DEFAULT_LRU_CACHE_IS_LRU_K = false;

class CacheKey {

public:

    CacheKey() : _size(0) {}

    // Create a slice that refers to d[0,n-1].

    CacheKey(const char* d, size_t n) : _data(d), _size(n) {}

    // Create a slice that refers to the contents of "s"

    CacheKey(const std::string& s) : _data(s.data()), _size(s.size()) {}

    // Create a slice that refers to s[0,strlen(s)-1]

    CacheKey(const char* s) : _data(s), _size(strlen(s)) {}

    ~CacheKey() = default;

    // Return a pointer to the beginning of the referenced data

    const char* data() const { return _data; }

    // Return the length (in bytes) of the referenced data

    size_t size() const { return _size; }

    // Return true if the length of the referenced data is zero

    bool empty() const { return _size == 0; }

    // Return the ith byte in the referenced data.

    // REQUIRES: n < size()

    char operator[](size_t n) const {

        assert(n < size());

        return _data[n];

    }

    // Change this slice to refer to an empty array

    void clear() {

        _data = nullptr;

        _size = 0;

    }

    // Drop the first "n" bytes from this slice.

    void remove_prefix(size_t n) {

        assert(n <= size());

        _data += n;

        _size -= n;

    }

    // Return a string that contains the copy of the referenced data.

    std::string to_string() const { return {_data, _size}; }

    bool operator==(const CacheKey& other) const {

        return ((size() == other.size()) && (memcmp(data(), other.data(), size()) == 0));

    }

    bool operator!=(const CacheKey& other) const { return !(*this == other); }

    int compare(const CacheKey& b) const {

        const size_t min_len = (_size < b._size) ? _size : b._size;

        int r = memcmp(_data, b._data, min_len);

        if (r == 0) {

            if (_size < b._size) {

                r = -1;

            } else if (_size > b._size) {

                r = +1;

            }

        }

        return r;

    }

    uint32_t hash(const char* data, size_t n, uint32_t seed) const;

    // Return true if "x" is a prefix of "*this"

    bool starts_with(const CacheKey& x) const {

        return ((_size >= x._size) && (memcmp(_data, x._data, x._size) == 0));

    }

private:

    uint32_t _decode_fixed32(const char* ptr) const {

        // Load the raw bytes

        uint32_t result;

        memcpy(&result, ptr, sizeof(result)); // gcc optimizes this to a plain load

        return result;

    }

    const char* _data = nullptr;

    size_t _size;

};

// The entry with smaller CachePriority will evict firstly

enum class CachePriority { NORMAL = 0, DURABLE = 1 };

using CachePrunePredicate = std::function<bool(const LRUHandle*)>;

// CacheValueTimeExtractor can extract timestamp

// in cache value through the specified function,

// such as last_visit_time in InvertedIndexSearcherCache::CacheValue

using CacheValueTimeExtractor = std::function<int64_t(const void*)>;

struct PrunedInfo {

    int64_t pruned_count = 0;

    int64_t pruned_size = 0;

};

class Cache {

public:

    Cache() = default;

    // Destroys all existing entries by calling the "deleter"

    // function that was passed to the constructor.

    virtual ~Cache() = default;

    // Opaque handle to an entry stored in the cache.

    struct Handle {};

    // Insert a mapping from key->value into the cache and assign it

    // the specified charge against the total cache capacity.

    //

    // Returns a handle that corresponds to the mapping.  The caller

    // must call this->release(handle) when the returned mapping is no

    // longer needed.

    //

    // When the inserted entry is no longer needed, the key and

    // value will be passed to "deleter".

    //

    // if cache is lru k and cache is full, first insert of key will not succeed.

    //

    // Note: if is ShardedLRUCache, cache capacity = ShardedLRUCache_capacity / num_shards.

    virtual Handle* insert(const CacheKey& key, void* value, size_t charge,

                           CachePriority priority = CachePriority::NORMAL) = 0;

    // If the cache has no mapping for "key", returns nullptr.

    //

    // Else return a handle that corresponds to the mapping.  The caller

    // must call this->release(handle) when the returned mapping is no

    // longer needed.

    virtual Handle* lookup(const CacheKey& key) = 0;

    // Release a mapping returned by a previous Lookup().

    // REQUIRES: handle must not have been released yet.

    // REQUIRES: handle must have been returned by a method on *this.

    virtual void release(Handle* handle) = 0;

    // Return the value encapsulated in a handle returned by a

    // successful lookup().

    // REQUIRES: handle must not have been released yet.

    // REQUIRES: handle must have been returned by a method on *this.

    virtual void* value(Handle* handle) = 0;

    // If the cache contains entry for key, erase it.  Note that the

    // underlying entry will be kept around until all existing handles

    // to it have been released.

    virtual void erase(const CacheKey& key) = 0;

    // Return a new numeric id.  May be used by multiple clients who are

    // sharing the same cache to partition the key space.  Typically the

    // client will allocate a new id at startup and prepend the id to

    // its cache keys.

    virtual uint64_t new_id() = 0;

    // Remove all cache entries that are not actively in use.  Memory-constrained

    // applications may wish to call this method to reduce memory usage.

    // Default implementation of Prune() does nothing.  Subclasses are strongly

    // encouraged to override the default implementation.  A future release of

    // leveldb may change prune() to a pure abstract method.

    // return num of entries being pruned.

    virtual PrunedInfo prune() { return {0, 0}; }

    // Same as prune(), but the entry will only be pruned if the predicate matched.

    // NOTICE: the predicate should be simple enough, or the prune_if() function

    // may hold lock for a long time to execute predicate.

    virtual PrunedInfo prune_if(CachePrunePredicate pred, bool lazy_mode = false) { return {0, 0}; }

    virtual int64_t get_usage() = 0;

    virtual PrunedInfo set_capacity(size_t capacity) = 0;

    virtual size_t get_capacity() = 0;

    virtual size_t get_element_count() = 0;

private:

    DISALLOW_COPY_AND_ASSIGN(Cache);

};

// An entry is a variable length heap-allocated structure.  Entries

// are kept in a circular doubly linked list ordered by access time.

// Note: member variables can only be POD types and raw pointer,

// cannot be class objects or smart pointers, because LRUHandle will be created using malloc.

struct LRUHandle {

    void* value = nullptr;

    struct LRUHandle* next_hash = nullptr; // next entry in hash table

    struct LRUHandle* next = nullptr;      // next entry in lru list

    struct LRUHandle* prev = nullptr;      // previous entry in lru list

    size_t charge;

    size_t key_length;

    size_t total_size; // Entry charge, used to limit cache capacity, LRUCacheType::SIZE including key length.

    bool in_cache; // Whether entry is in the cache.

    uint32_t refs;

    uint32_t hash; // Hash of key(); used for fast sharding and comparisons

    CachePriority priority = CachePriority::NORMAL;

    LRUCacheType type;

    int64_t last_visit_time; // Save the last visit time of this cache entry.

    char key_data[1];        // Beginning of key

    // Note! key_data must be at the end.

    CacheKey key() const {

        // For cheaper lookups, we allow a temporary Handle object

        // to store a pointer to a key in "value".

        if (next == this) {

            return *(reinterpret_cast<CacheKey*>(value));

        } else {

            return {key_data, key_length};

        }

    }

    void free() {

        if (value != nullptr) { // value allows null pointer.

            delete (LRUCacheValueBase*)value;

        }

        ::free(this);

    }

};

// We provide our own simple hash tablet since it removes a whole bunch

// of porting hacks and is also faster than some of the built-in hash

// tablet implementations in some of the compiler/runtime combinations

// we have tested.  E.g., readrandom speeds up by ~5% over the g++

// 4.4.3's builtin hashtable.

class HandleTable {

public:

    HandleTable() { _resize(); }

    ~HandleTable();

    LRUHandle* lookup(const CacheKey& key, uint32_t hash);

    LRUHandle* insert(LRUHandle* h);

    // Remove element from hash table by "key" and "hash".

    LRUHandle* remove(const CacheKey& key, uint32_t hash);

    // Remove element from hash table by "h", it would be faster

    // than the function above.

    // Return whether h is found and removed.

    bool remove(const LRUHandle* h);

    uint32_t element_count() const;

private:

    FRIEND_TEST(CacheTest, HandleTableTest);

    // The tablet consists of an array of buckets where each bucket is

    // a linked list of cache entries that hash into the bucket.

    uint32_t _length {};

    uint32_t _elems {};

    LRUHandle** _list = nullptr;

    // Return a pointer to slot that points to a cache entry that

    // matches key/hash.  If there is no such cache entry, return a

    // pointer to the trailing slot in the corresponding linked list.

    LRUHandle** _find_pointer(const CacheKey& key, uint32_t hash);

    void _resize();

};

// pair first is timestatmp, put <timestatmp, LRUHandle*> into asc set,

// when need to free space, can first evict the begin of the set,

// because the begin element's timestamp is the oldest.

using LRUHandleSortedSet = std::set<std::pair<int64_t, LRUHandle*>>;

// A single shard of sharded cache.

class LRUCache {

public:

    LRUCache(LRUCacheType type, bool is_lru_k = DEFAULT_LRU_CACHE_IS_LRU_K);

    ~LRUCache();

    // visits_lru_cache_key is the hash value of CacheKey.

    // If there is a hash conflict, a cache entry may be inserted early

    // and another cache entry with the same key hash may be inserted later.

    // Otherwise, this does not affect the correctness of the cache.

    using visits_lru_cache_key = uint32_t;

    using visits_lru_cache_pair = std::pair<visits_lru_cache_key, size_t>;

    // Separate from constructor so caller can easily make an array of LRUCache

    PrunedInfo set_capacity(size_t capacity);

    void set_element_count_capacity(uint32_t element_count_capacity) {

        _element_count_capacity = element_count_capacity;

    }

    // Like Cache methods, but with an extra "hash" parameter.

    // Must call release on the returned handle pointer.

    Cache::Handle* insert(const CacheKey& key, uint32_t hash, void* value, size_t charge,

                          CachePriority priority = CachePriority::NORMAL);

    Cache::Handle* lookup(const CacheKey& key, uint32_t hash);

    void release(Cache::Handle* handle);

    void erase(const CacheKey& key, uint32_t hash);

    PrunedInfo prune();

    PrunedInfo prune_if(CachePrunePredicate pred, bool lazy_mode = false);

    void set_cache_value_time_extractor(CacheValueTimeExtractor cache_value_time_extractor);

    void set_cache_value_check_timestamp(bool cache_value_check_timestamp);

    uint64_t get_lookup_count();

    uint64_t get_hit_count();

    uint64_t get_miss_count();

    uint64_t get_stampede_count();

    size_t get_usage();

    size_t get_capacity();

    size_t get_element_count();

private:

    void _lru_remove(LRUHandle* e);

    void _lru_append(LRUHandle* list, LRUHandle* e);

    bool _unref(LRUHandle* e);

    void _evict_from_lru(size_t total_size, LRUHandle** to_remove_head);

    void _evict_from_lru_with_time(size_t total_size, LRUHandle** to_remove_head);

    void _evict_one_entry(LRUHandle* e);

    bool _check_element_count_limit();

    bool _lru_k_insert_visits_list(size_t total_size, visits_lru_cache_key visits_key);

private:

    LRUCacheType _type;

    // Initialized before use.

    size_t _capacity = 0;

    // _mutex protects the following state.

    std::mutex _mutex;

    size_t _usage = 0;

    // Dummy head of LRU list.

    // Entries have refs==1 and in_cache==true.

    // _lru_normal.prev is newest entry, _lru_normal.next is oldest entry.

    LRUHandle _lru_normal;

    // _lru_durable.prev is newest entry, _lru_durable.next is oldest entry.

    LRUHandle _lru_durable;

    HandleTable _table;

    uint64_t _lookup_count = 0; // number of cache lookups

    uint64_t _hit_count = 0;    // number of cache hits

    uint64_t _miss_count = 0;   // number of cache misses

    uint64_t _stampede_count = 0;

    CacheValueTimeExtractor _cache_value_time_extractor;

    bool _cache_value_check_timestamp = false;

    LRUHandleSortedSet _sorted_normal_entries_with_timestamp;

    LRUHandleSortedSet _sorted_durable_entries_with_timestamp;

    uint32_t _element_count_capacity = 0;

    bool _is_lru_k = false; // LRU-K algorithm, K=2

    std::list<visits_lru_cache_pair> _visits_lru_cache_list;

    std::unordered_map<visits_lru_cache_key, std::list<visits_lru_cache_pair>::iterator>

            _visits_lru_cache_map;

    size_t _visits_lru_cache_usage = 0;

};

class ShardedLRUCache : public Cache {

public:

    ~ShardedLRUCache() override;

    Handle* insert(const CacheKey& key, void* value, size_t charge,

                   CachePriority priority = CachePriority::NORMAL) override;

    Handle* lookup(const CacheKey& key) override;

    void release(Handle* handle) override;

    void erase(const CacheKey& key) override;

    void* value(Handle* handle) override;

    uint64_t new_id() override;

    PrunedInfo prune() override;

    PrunedInfo prune_if(CachePrunePredicate pred, bool lazy_mode = false) override;

    int64_t get_usage() override;

    size_t get_element_count() override;

    PrunedInfo set_capacity(size_t capacity) override;

    size_t get_capacity() override;

private:

    // LRUCache can only be created and managed with LRUCachePolicy.

    friend class LRUCachePolicy;

    explicit ShardedLRUCache(const std::string& name, size_t capacity, LRUCacheType type,

                             uint32_t num_shards, uint32_t element_count_capacity, bool is_lru_k);

    explicit ShardedLRUCache(const std::string& name, size_t capacity, LRUCacheType type,

                             uint32_t num_shards,

                             CacheValueTimeExtractor cache_value_time_extractor,

                             bool cache_value_check_timestamp, uint32_t element_count_capacity,

                             bool is_lru_k);

    void update_cache_metrics() const;

private:

    static uint32_t _hash_slice(const CacheKey& s);

    uint32_t _shard(uint32_t hash) const {

        return _num_shard_bits > 0 ? (hash >> (32 - _num_shard_bits)) : 0;

    }

    std::string _name;

    const int _num_shard_bits;

    const uint32_t _num_shards;

    LRUCache** _shards = nullptr;

    std::atomic<uint64_t> _last_id;

    std::mutex _mutex;

    size_t _capacity {0};

    std::shared_ptr<MetricEntity> _entity;

    IntGauge* cache_capacity = nullptr;

    IntGauge* cache_usage = nullptr;

    IntGauge* cache_element_count = nullptr;

    DoubleGauge* cache_usage_ratio = nullptr;

    IntCounter* cache_lookup_count = nullptr;

    IntCounter* cache_hit_count = nullptr;

    IntCounter* cache_miss_count = nullptr;

    IntCounter* cache_stampede_count = nullptr;

    DoubleGauge* cache_hit_ratio = nullptr;

    // bvars

    std::unique_ptr<bvar::Adder<uint64_t>> _hit_count_bvar;

    std::unique_ptr<bvar::PerSecond<bvar::Adder<uint64_t>>> _hit_count_per_second;

    std::unique_ptr<bvar::Adder<uint64_t>> _lookup_count_bvar;

    std::unique_ptr<bvar::PerSecond<bvar::Adder<uint64_t>>> _lookup_count_per_second;

};

// Compatible with ShardedLRUCache usage, but will not actually cache.

class DummyLRUCache : public Cache {

public:

    // Must call release on the returned handle pointer.

    Handle* insert(const CacheKey& key, void* value, size_t charge,

                   CachePriority priority = CachePriority::NORMAL) override;

    Handle* lookup(const CacheKey& key) override { return nullptr; };

    void release(Handle* handle) override;

    void erase(const CacheKey& key) override {};

    void* value(Handle* handle) override;

    uint64_t new_id() override { return 0; };

    PrunedInfo prune() override { return {0, 0}; };

    PrunedInfo prune_if(CachePrunePredicate pred, bool lazy_mode = false) override {

        return {0, 0};

    };

    int64_t get_usage() override { return 0; };

    PrunedInfo set_capacity(size_t capacity) override { return {0, 0}; };

    size_t get_capacity() override { return 0; };

    size_t get_element_count() override { return 0; };

};

} // namespace doris

#include "common/compile_check_end.h"