// 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 <iterator>

#include <list>

#include <unordered_map>

namespace doris {

template <typename Key, typename Value>

class LruCache {

public:

    typedef typename std::pair<Key, Value> KeyValuePair;

    typedef typename std::list<KeyValuePair>::iterator ListIterator;

    class Iterator {

    public:

        using iterator_category = std::input_iterator_tag;

        using value_type = KeyValuePair;

        using difference_type = ptrdiff_t;

        using pointer = KeyValuePair*;

        using reference = KeyValuePair&;

        Iterator(typename std::unordered_map<Key, ListIterator>::iterator it) : _it(it) {}

        Iterator& operator++() {

            ++_it;

            return *this;

        }

        bool operator==(const Iterator& rhs) const { return _it == rhs._it; }

        bool operator!=(const Iterator& rhs) const { return _it != rhs._it; }

        KeyValuePair* operator->() { return _it->second.operator->(); }

        KeyValuePair& operator*() { return *_it->second; }

    private:

        typename std::unordered_map<Key, ListIterator>::iterator _it;

    };

    LruCache(size_t max_size) : _max_size(max_size) {}

    void put(const Key& key, const Value& value) {

        auto it = _cache_items_map.find(key);

        if (it != _cache_items_map.end()) {

            _cache_items_list.erase(it->second);

            _cache_items_map.erase(it);

        }

        _cache_items_list.push_front(KeyValuePair(key, value));

        _cache_items_map[key] = _cache_items_list.begin();

        if (_cache_items_map.size() > _max_size) {

            auto last = _cache_items_list.end();

            last--;

            _cache_items_map.erase(last->first);

            _cache_items_list.pop_back();

        }

    }

    void erase(const Key& key) {

        auto it = _cache_items_map.find(key);

        if (it != _cache_items_map.end()) {

            _cache_items_list.erase(it->second);

            _cache_items_map.erase(it);

        }

    }

    // Must copy value, because value maybe released when caller used

    bool get(const Key& key, Value* value) {

        auto it = _cache_items_map.find(key);

        if (it == _cache_items_map.end()) {

            return false;

        }

        _cache_items_list.splice(_cache_items_list.begin(), _cache_items_list, it->second);

        *value = it->second->second;

        return true;

    }

    bool exists(const Key& key) const {

        return _cache_items_map.find(key) != _cache_items_map.end();

    }

    size_t size() const { return _cache_items_map.size(); }

    Iterator begin() { return Iterator(_cache_items_map.begin()); }

    Iterator end() { return Iterator(_cache_items_map.end()); }

private:

    std::list<KeyValuePair> _cache_items_list;

    std::unordered_map<Key, ListIterator> _cache_items_map;

    size_t _max_size;

};

} // namespace doris