#pragma once

#include <mbgl/actor/actor_ref.hpp>
#include <mbgl/storage/file_source.hpp>
#include <mbgl/storage/offline.hpp>
#include <mbgl/util/constants.hpp>
#include <mbgl/util/optional.hpp>
#include <mbgl/util/expected.hpp>

#include <vector>
#include <mutex>

namespace mbgl {

namespace util {
template <typename T> class Thread;
} // namespace util

class ResourceTransform;

// TODO: the callback should include a potential error info when https://github.com/mapbox/mapbox-gl-native/issues/14759 is resolved
using PathChangeCallback = std::function<void ()>;

class DefaultFileSource : public FileSource {
public:
    /*
     * The maximumCacheSize parameter is a limit applied to non-offline resources only,
     * i.e. resources added to the database for the "ambient use" caching functionality.
     * There is no size limit for offline resources. If a user never creates any offline
     * regions, we want the database to remain fairly small (order tens or low hundreds
     * of megabytes).
     */
    DefaultFileSource(const std::string& cachePath, const std::string& assetPath);
    DefaultFileSource(const std::string& cachePath, std::unique_ptr<FileSource>&& assetFileSource);
    ~DefaultFileSource() override;

    bool supportsCacheOnlyRequests() const override {
        return true;
    }

    void setAPIBaseURL(const std::string&);
    std::string getAPIBaseURL();

    void setAccessToken(const std::string&);
    std::string getAccessToken();

    void setResourceTransform(optional<ActorRef<ResourceTransform>>&&);

    void setResourceCachePath(const std::string&, optional<ActorRef<PathChangeCallback>>&&);

    std::unique_ptr<AsyncRequest> request(const Resource&, Callback) override;

    /*
     * Retrieve all regions in the offline database.
     *
     * The query will be executed asynchronously and the results passed to the given
     * callback, which will be executed on the database thread; it is the responsibility
     * of the SDK bindings to re-execute a user-provided callback on the main thread.
     */
    void listOfflineRegions(std::function<void (expected<OfflineRegions, std::exception_ptr>)>);

    /*
     * Create an offline region in the database.
     *
     * When the initial database queries have completed, the provided callback will be
     * executed on the database thread; it is the responsibility of the SDK bindings
     * to re-execute a user-provided callback on the main thread.
     *
     * Note that the resulting region will be in an inactive download state; to begin
     * downloading resources, call `setOfflineRegionDownloadState(OfflineRegionDownloadState::Active)`,
     * optionally registering an `OfflineRegionObserver` beforehand.
     */
    void createOfflineRegion(const OfflineRegionDefinition& definition,
                             const OfflineRegionMetadata& metadata,
                             std::function<void (expected<OfflineRegion, std::exception_ptr>)>);

    /*
     * Update an offline region metadata in the database.
     */
    void updateOfflineMetadata(const int64_t regionID,
                               const OfflineRegionMetadata& metadata,
                               std::function<void (expected<OfflineRegionMetadata, std::exception_ptr>)>);
    /*
     * Register an observer to be notified when the state of the region changes.
     */
    void setOfflineRegionObserver(OfflineRegion&, std::unique_ptr<OfflineRegionObserver>);

    /*
     * Pause or resume downloading of regional resources.
     */
    void setOfflineRegionDownloadState(OfflineRegion&, OfflineRegionDownloadState);

    /*
     * Retrieve the current status of the region. The query will be executed
     * asynchronously and the results passed to the given callback, which will be
     * executed on the database thread; it is the responsibility of the SDK bindings
     * to re-execute a user-provided callback on the main thread.
     */
    void getOfflineRegionStatus(
        OfflineRegion&,
        std::function<void (expected<OfflineRegionStatus, std::exception_ptr>)>) const;

    /*
     * Merge offline regions from a secondary database into the main offline database.
     *
     * When the database merge is completed, the provided callback will be
     * executed on the database thread; it is the responsibility of the SDK bindings
     * to re-execute a user-provided callback on the main thread.
     *
     * The secondary database may need to be upgraded to the latest schema. This is done
     * in-place and requires write-access to `sideDatabasePath`; it is the
     * responsibility of the SDK bindings to ensure that this path is writeable.
     *
     * Only resources and tiles that belong to a region will be copied over. Identical
     * regions will be flattened into a single new region in the main database.
     *
     * Invokes the callback with a `MapboxOfflineTileCountExceededException` error if
     * the merge operation would result in the offline tile count limit being exceeded.
     *
     * Merged regions may not be in a completed status if the secondary database
     * does not contain all the tiles or resources required by the region definition.
     */
    void mergeOfflineRegions(const std::string& sideDatabasePath,
                            std::function<void (expected<OfflineRegions, std::exception_ptr>)>);

    /*
     * Remove an offline region from the database and perform any resources evictions
     * necessary as a result.
     *
     * Eviction works by removing the least-recently requested resources not also required
     * by other regions, until the database shrinks below a certain size.
     *
     * Note that this method takes ownership of the input, reflecting the fact that once
     * region deletion is initiated, it is not legal to perform further actions with the
     * region.
     *
     * When the operation is complete or encounters an error, the given callback will be
     * executed on the database thread; it is the responsibility of the SDK bindings
     * to re-execute a user-provided callback on the main thread.
     */
    void deleteOfflineRegion(OfflineRegion&&, std::function<void (std::exception_ptr)>);

    /*
     * Invalidate all the tiles from an offline region forcing Mapbox GL to revalidate
     * the tiles with the server before using. This is more efficient than deleting the
     * offline region and downloading it again because if the data on the cache matches
     * the server, no new data gets transmitted.
     */
    void invalidateOfflineRegion(OfflineRegion&, std::function<void (std::exception_ptr)>);

    /*
     * Changing or bypassing this limit without permission from Mapbox is prohibited
     * by the Mapbox Terms of Service.
     */
    void setOfflineMapboxTileCountLimit(uint64_t) const;

    /*
     * Pause file request activity.
     *
     * If pause is called then no revalidation or network request activity
     * will occur.
     */
    void pause();

    /*
     * Resume file request activity.
     *
     * Calling resume will unpause the file source and process any tasks that
     * expired while the file source was paused.
     */
    void resume();
    
    /*
     * Insert the provided resource into the ambient cache
     *
     * Consumers of the resource will expect the uncompressed version; the
     * OfflineDatabase will determine whether to compress the data on disk.
     * This call is asynchronous: the data may not be immediately available
     * for in-progress requests, although subsequent requests should have
     * access to the cached data.
     */
    void put(const Resource&, const Response&);

    /*
     * Delete existing database and re-initialize.
     *
     * When the operation is complete or encounters an error, the given callback will be
     * executed on the database thread; it is the responsibility of the SDK bindings
     * to re-execute a user-provided callback on the main thread.
     */
    void resetDatabase(std::function<void (std::exception_ptr)>);

    /*
     * Forces revalidation of the ambient cache.
     *
     * Forces Mapbox GL Native to revalidate resources stored in the ambient
     * cache with the tile server before using them, making sure they
     * are the latest version. This is more efficient than cleaning the
     * cache because if the resource is considered valid after the server
     * lookup, it will not get downloaded again.
     *
     * Resources overlapping with offline regions will not be affected
     * by this call.
     */
    void invalidateAmbientCache(std::function<void (std::exception_ptr)>);

    /*
     * Erase resources from the ambient cache, freeing storage space.
     *
     * Erases the ambient cache, freeing resources. This operation can be
     * potentially slow because it will trigger a VACUUM on SQLite,
     * forcing the database to move pages on the filesystem.
     *
     * Resources overlapping with offline regions will not be affected
     * by this call.
     */
    void clearAmbientCache(std::function<void (std::exception_ptr)>);

    /*
     * Sets the maximum size in bytes for the ambient cache.
     *
     * This call is potentially expensive because it will try
     * to trim the data in case the database is larger than the
     * size defined. The size of offline regions are not affected
     * by this settings, but the ambient cache will always try
     * to not exceed the maximum size defined, taking into account
     * the current size for the offline regions.
     *
     * If the maximum size is set to 50 MB and 40 MB are already
     * used by offline regions, the cache size will be effectively
     * 10 MB.
     *
     * Setting the size to 0 will disable the cache if there is no
     * offline region on the database.
     *
     * This method should always be called before using the database,
     * otherwise the default maximum size will be used.
     */
    void setMaximumAmbientCacheSize(uint64_t size, std::function<void (std::exception_ptr)> callback);

    // For testing only.
    void setOnlineStatus(bool);

    class Impl;

private:
    // Shared so destruction is done on this thread
    const std::shared_ptr<FileSource> assetFileSource;
    const std::unique_ptr<util::Thread<Impl>> impl;

    std::mutex cachedBaseURLMutex;
    std::string cachedBaseURL = mbgl::util::API_BASE_URL;

    std::mutex cachedAccessTokenMutex;
    std::string cachedAccessToken;
};

} // namespace mbgl