/*
 * 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.
 */

/*
 * Copyright (C) 2015 ScyllaDB
 *
 * Modified by 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/>.
 */

#pragma once

#include <optional>

#include "bytes.hh"
#include "keys.hh"
#include "utils/UUID.hh"
#include "dht/i_partitioner.hh"
#include "db/read_repair_decision.hh"

namespace service {

namespace pager {

class paging_state final {
public:
    using replicas_per_token_range = std::unordered_map<dht::token_range, std::vector<utils::UUID>>;

private:
    partition_key _partition_key;
    std::optional<clustering_key> _clustering_key;
    uint32_t _remaining;
    utils::UUID _query_uuid;
    replicas_per_token_range _last_replicas;
    std::optional<db::read_repair_decision> _query_read_repair_decision;
    uint32_t _rows_fetched_for_last_partition;

public:
    paging_state(partition_key pk,
            std::optional<clustering_key> ck,
            uint32_t rem,
            utils::UUID reader_recall_uuid,
            replicas_per_token_range last_replicas,
            std::optional<db::read_repair_decision> query_read_repair_decision,
            uint32_t rows_fetched_for_last_partition);

    void set_partition_key(partition_key pk) {
        _partition_key = std::move(pk);
    }

    void set_clustering_key(clustering_key ck) {
        _clustering_key = std::move(ck);
    }

    void set_remaining(uint32_t remaining) {
        _remaining = remaining;
    }

    /**
     * Last processed key, i.e. where to start from in next paging round
     */
    const partition_key& get_partition_key() const {
        return _partition_key;
    }
    /**
     * Clustering key in last partition. I.e. first, next, row
     */
    const std::optional<clustering_key>& get_clustering_key() const {
        return _clustering_key;
    }
    /**
     * Max remaining rows to fetch in total.
     * I.e. initial row_limit - #rows returned so far.
     */
    uint32_t get_remaining() const {
        return _remaining;
    }

    uint32_t get_rows_fetched_for_last_partition() const {
        return _rows_fetched_for_last_partition;
    }

    /**
     * query_uuid is a unique key under which the replicas saved the
     * readers used to serve the last page. These saved readers may be
     * resumed (if not already purged from the cache) instead of opening new
     * ones - as a performance optimization.
     * If the uuid is the invalid default-constructed UUID(), it means that
     * the client got this paging_state from a coordinator running an older
     * version of Scylla.
     */
    utils::UUID get_query_uuid() const {
        return _query_uuid;
    }

    /**
     * The replicas used to serve the last page.
     *
     * Helps paged queries consistently hit the same replicas for each
     * subsequent page. Replicas that already served a page will keep
     * the readers used for filling it around in a cache. Subsequent
     * page request hitting the same replicas can reuse these readers
     * to fill the pages avoiding the work of creating these readers
     * from scratch on every page.
     * In a mixed cluster older coordinators will ignore this value.
     * Replicas are stored per token-range where the token-range
     * is some subrange of the query range that doesn't cross node
     * boundaries.
     */
    replicas_per_token_range get_last_replicas() const {
        return _last_replicas;
    }

    /**
     * The read-repair decision made for this query.
     *
     * The read-repair decision is made on the first page and is applied to
     * all subsequent pages. This way we can ensure that we consistently use
     * the same replicas on each page throughout the query. This helps
     * reader-reuse on the replicas as readers can only be reused if they're
     * used for all pages, if the replica is skipped for one or more pages the
     * saved reader has to be dropped.
     */
    std::optional<db::read_repair_decision> get_query_read_repair_decision() const {
        return _query_read_repair_decision;
    }

    static ::shared_ptr<paging_state> deserialize(bytes_opt bytes);
    bytes_opt serialize() const;
};

}

}
