// This file Copyright © Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.

#pragma once

#ifndef LIBTRANSMISSION_PEER_MODULE
#error only the libtransmission peer module should #include this header.
#endif

#include <cstddef> // size_t
#include <functional>
#include <memory>
#include <vector>

#include "libtransmission/transmission.h"

#include "libtransmission/observable.h"
#include "libtransmission/utils.h"

class tr_bitfield;

/**
 * Figures out what blocks we want to request next.
 */
class Wishlist
{
public:
    static auto constexpr EndgameMaxPeers = size_t{ 2U };
    static auto constexpr NormalMaxPeers = size_t{ 1U };

    struct Mediator
    {
        [[nodiscard]] virtual bool client_has_block(tr_block_index_t block) const = 0;
        [[nodiscard]] virtual bool client_wants_piece(tr_piece_index_t piece) const = 0;
        [[nodiscard]] virtual bool is_endgame() const = 0;
        [[nodiscard]] virtual bool is_sequential_download() const = 0;
        [[nodiscard]] virtual size_t count_active_requests(tr_block_index_t block) const = 0;
        [[nodiscard]] virtual size_t count_missing_blocks(tr_piece_index_t piece) const = 0;
        [[nodiscard]] virtual size_t count_piece_replication(tr_piece_index_t piece) const = 0;
        [[nodiscard]] virtual tr_block_span_t block_span(tr_piece_index_t piece) const = 0;
        [[nodiscard]] virtual tr_piece_index_t piece_count() const = 0;
        [[nodiscard]] virtual tr_priority_t priority(tr_piece_index_t piece) const = 0;

        [[nodiscard]] virtual libtransmission::ObserverTag observe_peer_disconnect(
            libtransmission::SimpleObservable<tr_torrent*, tr_bitfield const&>::Observer observer) = 0;
        [[nodiscard]] virtual libtransmission::ObserverTag observe_got_bitfield(
            libtransmission::SimpleObservable<tr_torrent*, tr_bitfield const&>::Observer observer) = 0;
        [[nodiscard]] virtual libtransmission::ObserverTag observe_got_block(
            libtransmission::SimpleObservable<tr_torrent*, tr_piece_index_t, tr_block_index_t>::Observer observer) = 0;
        [[nodiscard]] virtual libtransmission::ObserverTag observe_got_have(
            libtransmission::SimpleObservable<tr_torrent*, tr_piece_index_t>::Observer observer) = 0;
        [[nodiscard]] virtual libtransmission::ObserverTag observe_got_have_all(
            libtransmission::SimpleObservable<tr_torrent*>::Observer observer) = 0;
        [[nodiscard]] virtual libtransmission::ObserverTag observe_piece_completed(
            libtransmission::SimpleObservable<tr_torrent*, tr_piece_index_t>::Observer observer) = 0;
        [[nodiscard]] virtual libtransmission::ObserverTag observe_priority_changed(
            libtransmission::SimpleObservable<tr_torrent*, tr_file_index_t const*, tr_file_index_t, tr_priority_t>::Observer
                observer) = 0;
        [[nodiscard]] virtual libtransmission::ObserverTag observe_sequential_download_changed(
            libtransmission::SimpleObservable<tr_torrent*, bool>::Observer observer) = 0;

        virtual ~Mediator() = default;
    };

    explicit Wishlist(std::unique_ptr<Mediator> mediator_in);
    ~Wishlist();

    // the next blocks that we should request from a peer
    [[nodiscard]] std::vector<tr_block_span_t> next(
        size_t n_wanted_blocks,
        std::function<bool(tr_piece_index_t)> const& peer_has_piece,
        std::function<bool(tr_block_index_t)> const& has_active_pending_to_peer);

private:
    class Impl;
    std::unique_ptr<Impl> impl_;
};