tile_cache_delay.h

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/* Copyright 2018-2019 TomTom N.V.

Licensed 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 <vector>

#include <QTimer>

#include "tile_cache.h"

template <typename Tile>
class TileCacheDelay;

namespace detail
{
struct ExpiringArea
{
  QTimer timer;
  Area area;

  ExpiringArea(Area area) : area(std::move(area))
  {
    timer.setSingleShot(true);
    int constexpr timeout = 2000;  // in ms
    timer.start(timeout);
  }

  ExpiringArea(ExpiringArea&&) = default;
  ExpiringArea(ExpiringArea const& p) : area(p.area)
  {
    *this = p;
  }

  template <typename Tile>
  bool ready(TileCacheDelay<Tile> const& cache) const
  {
    if (!timer.isActive())
    {
      return true;
    }

    return cache.isAreaReady(area);
  }

  ExpiringArea& operator=(ExpiringArea&&) = default;

  ExpiringArea& operator=(ExpiringArea const& p)
  {
    area = p.area;

    // QTimer has no copy operator
    if (p.timer.isActive())
    {
      timer.start(p.timer.remainingTime());
    }
    return *this;
  }
};

class AreaHistory
{
  std::vector<ExpiringArea> history_;

public:
  void fit(Area const& area)
  {
    history_.erase(std::remove_if(history_.begin(), history_.end(),
                                  [&area](ExpiringArea const& p) { return !areaContainsTile(p.area, area.center); }),
                   history_.end());
  }

  void add(Area const& area)
  {
    auto const it =
        std::find_if(history_.begin(), history_.end(), [&area](ExpiringArea const& p) { return p.area == area; });
    if (it == history_.end())
    {
      history_.emplace_back(area);
    }
  };

  template <typename Tile>
  bool ready(TileCacheDelay<Tile> const& cache, TileId const& to_find) const
  {
    return std::any_of(history_.begin(), history_.end(), [&to_find, &cache](ExpiringArea const& ea) {
      return areaContainsTile(ea.area, to_find) && ea.ready(cache);
    });
  }
};
}  // namespace detail

template <typename Tile>
class TileCacheDelay : public TileCache<Tile>
{
  detail::AreaHistory history_;
  friend detail::ExpiringArea;

public:
  void request(Area const& area)
  {
    TileCache<Tile>::request(area);

    history_.fit(area);
    history_.add(area);
  }

  Tile const* ready(TileId const& to_find) const
  {
    Tile const* tile = TileCache<Tile>::ready(to_find);
    if (tile && history_.ready(*this, to_find))
    {
      return tile;
    }

    return nullptr;
  }
};