tile_cache.h

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/* Copyright 2018-2019 TomTom N.V., 2014 Gareth Cross

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 <functional>
#include <limits>
#include <mutex>
#include <unordered_map>
#include <utility>

#include <QImage>

#include <boost/optional.hpp>

#include "area.h"
#include "detail/tile_downloader.h"
#include "tile_id.h"

class TileCacheGuard
{
  std::mutex& mutex;

public:
  template <typename TileCache>
  TileCacheGuard(TileCache const& cache_) : mutex(cache_.cachedTilesLock)
  {
    mutex.lock();
  }

  ~TileCacheGuard()
  {
    mutex.unlock();
  }
};

template <typename Tile>
class TileCache
{
  friend TileCacheGuard;
  std::unordered_map<TileId, Tile> cached_tiles;
  std::mutex mutable cachedTilesLock;
  detail::TileDownloader downloader;

  void loadedTile(TileId tile_id, QImage image)
  {
    TileCacheGuard guard(*this);

    if (cached_tiles.find(tile_id) == cached_tiles.end())
    {
      cached_tiles.emplace(std::make_pair(tile_id, std::move(image)));
    }
  }

public:
  TileCache()
    : downloader([this](TileId tile_id, QImage image) { loadedTile(std::move(tile_id), std::move(image)); }){};

  void request(Area const& area)
  {
    TileCacheGuard guard(*this);

    for (int x = area.left_top.x; x <= area.right_bottom.x; ++x)
    {
      for (int y = area.left_top.y; y <= area.right_bottom.y; ++y)
      {
        TileId const to_find{ area.center.tile_server, { x, y }, area.center.zoom };

        if (cached_tiles.find(to_find) == cached_tiles.end())
        {
          downloader.loadTile(to_find);
        }
      }
    }
  }

  Tile const* ready(TileId const& to_find) const
  {
    auto const it = cached_tiles.find(to_find);

    if (it == cached_tiles.cend())
    {
      return nullptr;
    }

    return &it->second;
  }

  void purge(Area const& area)
  {
    for (auto it = cached_tiles.begin(); it != cached_tiles.end();)
    {
      if (!areaContainsTile(area, it->first))
      {
        it = cached_tiles.erase(it);
      }
      else
      {
        ++it;
      }
    }
  }

  float getTileServerErrorRate(std::string const& tile_server) const
  {
    return downloader.error_rates.calculate(tile_server);
  }

protected:
  bool isAreaReady(Area const& area) const
  {
    for (int xx = area.left_top.x; xx <= area.right_bottom.x; ++xx)
    {
      for (int yy = area.left_top.y; yy <= area.right_bottom.y; ++yy)
      {
        TileId const to_find{ area.center.tile_server, { xx, yy }, area.center.zoom };

        if (cached_tiles.find(to_find) == cached_tiles.end())
        {
          return false;
        }
      }
    }
    return true;
  }
};