/*
 * Copyright 2023 jacqueline <me@jacqueline.id.au>
 *
 * SPDX-License-Identifier: GPL-3.0-only
 */

#pragma once

#include <list>
#include <memory>
#include <mutex>
#include <shared_mutex>
#include <vector>

#include "database.hpp"
#include "tasks.hpp"
#include "track.hpp"

namespace audio {

/*
 * Owns and manages a complete view of the playback queue. Includes the
 * currently playing track, a truncated list of previously played tracks, and
 * all future tracks that have been queued.
 *
 * In order to not use all of our memory, this class deals strictly with track
 * ids. Consumers that need more data than this should fetch it from the
 * database.
 *
 * Instances of this class are broadly safe to use from multiple tasks; each
 * method represents an atomic operation. No guarantees are made about
 * consistency between calls however.
 */
class TrackQueue {
 public:
  TrackQueue(tasks::Worker& bg_worker);

  /* Returns the currently playing track. */
  auto current() const -> std::optional<database::TrackId>;

  /* Returns, in order, tracks that have been queued to be played next. */
  auto peekNext(std::size_t limit) const -> std::vector<database::TrackId>;

  /*
   * Returns the tracks in the queue that have already been played, ordered
   * most recently played first.
   */
  auto peekPrevious(std::size_t limit) const -> std::vector<database::TrackId>;

  auto currentPosition() const -> size_t;
  auto totalSize() const -> size_t;

  using Item = std::variant<database::TrackId, database::TrackIterator>;
  auto insert(Item) -> void;
  auto append(Item i) -> void;

  /*
   * Advances to the next track in the queue, placing the current track at the
   * front of the 'played' queue.
   */
  auto next() -> void;
  auto previous() -> void;

  auto skipTo(database::TrackId) -> void;

  /*
   * Removes all tracks from all queues, and stops any currently playing track.
   */
  auto clear() -> void;

  // Cannot be copied or moved.
  TrackQueue(const TrackQueue&) = delete;
  TrackQueue& operator=(const TrackQueue&) = delete;

 private:
  mutable std::shared_mutex mutex_;

  tasks::Worker& bg_worker_;

  size_t pos_;
  std::pmr::vector<database::TrackId> tracks_;
};

}  // namespace audio