/*
 * Copyright (C) by Christian Kamm <mail@ckamm.de>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 * for more details.
 */
#pragma once

// if this is included, to support a qpointer on the account, all hell breaks loose wrt endless "cannot open include file: 'owncloudlib.h'
// No such file or directory" which is fundamental to the libsync exports
// so unfortunately we can't make a qpointer for the account here - do the update described below asap to get rid of the dependency
// #include "libsync/account.h"
#include "assert.h"
#include "csync/csync.h"
#include "ocsynclib.h"
#include "pinstate.h"
#include "result.h"
#include "syncfilestatus.h"
#include "utility.h"

#include <QObject>
#include <QUrl>
#include <QVersionNumber>

#include <memory>


namespace OCC {

class Account;

class SyncJournalDb;
class SyncFileItem;
class SyncEngine;

/** Collection of parameters for initializing a Vfs instance. */
struct OCSYNC_EXPORT VfsSetupParams
{
    explicit VfsSetupParams(Account *account, const QUrl &baseUrl, SyncEngine *syncEngine);
    /** The full path to the folder on the local filesystem
     *
     * Always ends with /.
     */
    QString filesystemPath;

    /** The path to the synced folder on the account
     *
     * Always ends with /.
     */
    QString remotePath;

    /// Account url, credentials etc. for network calls
    Account *account;

    /** Access to the sync folder's database.
     *
     * Note: The journal must live at least until the Vfs::stop() call.
     */
    SyncJournalDb *journal = nullptr;

    /// Strings potentially passed on to the platform
    QString providerDisplayName;
    QString providerName;
    QVersionNumber providerVersion;

    /** when registering with the system we might use
     *  a different presentation to identify the accounts
     */
    bool multipleAccountsRegistered = false;

    const QUrl &baseUrl() const
    {
        return _baseUrl;
    }

    // sync engine is only used by win vfs impl
    SyncEngine *syncEngine() const;

private:
    QUrl _baseUrl;
    // this should be a QPointer but when I try to make it so, I get compile errors because std::isConvertible<SyncEngine *, QObject *> fails
    // no freaking idea but I'll figure it out later
    // update: nope! due to our "creative" splitting into libs I can't actually include sync engine to make a qpointer to it possible :D
    // too bad. See comment on include of account.h above - we have the same problem if we try to include SyncEngine
    SyncEngine *_syncEngine;
};

/** Interface describing how to deal with virtual/placeholder files.
 *
 * There are different ways of representing files locally that will only
 * be filled with data (hydrated) on demand. One such way would be suffixed
 * files, others could be FUSE based or use Windows CfAPI.
 *
 * This interface intends to decouple the sync algorithm and Folder from
 * the details of how a particular VFS solution works.
 *
 * An instance is usually created through a plugin via the createVfsFromPlugin()
 * function.
 */
class OCSYNC_EXPORT Vfs : public QObject
{
    Q_OBJECT

public:
    /** The kind of VFS in use (or no-VFS)
     *
     * Currently plugins and modes are one-to-one but that's not required.
     */
    enum Mode { Off, WindowsCfApi };
    Q_ENUM(Mode)
    enum class ConvertToPlaceholderResult {
        Ok,
        Locked
    };
    Q_ENUM(ConvertToPlaceholderResult)

    static Mode modeFromString(const QString &str);

    /**
     * @brief pathSupportDetail - needs a better name but the concept is that this function checks to see if the path is supported for vfs.
     * if it is not supported the return string contains the "reason" it's not supported.
     * @param path to check to for support
     * @param mode which we want to check - note that the only arg that makes sense here at all is Vfs::WindowsCfApi
     * @return empty string if the mode is supported on the given path. If the string is not empty, it contains a string explaining the
     * reason the mode is not supported.
     *
     * as of this writing, the possible root reasons are: path is a drive, path is on a network drive, path fs is not ntfs.
     */
    static QString pathSupportDetail(const QString &path, OCC::Vfs::Mode mode);

    enum class AvailabilityError
    {
        // Availability can't be retrieved due to db error
        DbError,
        // Availability not available since the item doesn't exist
        NoSuchItem,
    };
    using AvailabilityResult = Result<VfsItemAvailability, AvailabilityError>;

public:
    explicit Vfs(QObject *parent);
    ~Vfs() override;

    virtual Mode mode() const = 0;

    /// Access to the parameters the instance was start()ed with.
    const VfsSetupParams &params() const { return *_setupParams.get(); }

    /** Initializes interaction with the VFS provider.
     *
     * The plugin-specific work is done in startImpl().
     *
     * \warning Please read the comments to \a startImpl() about the
     *          asynchronous behaviour!
     */
    void start(const VfsSetupParams &params);

    /// Stop interaction with VFS provider. Like when the client application quits.
    virtual void stop() = 0;

    /// Deregister the folder with the sync provider, like when a folder is removed.
    virtual void unregisterFolder() = 0;


    /** Whether the socket api should show pin state options
     *
     * Some plugins might provide alternate shell integration, making the normal
     * context menu actions redundant.
     */
    virtual bool socketApiPinStateActionsShown() const = 0;

    /// Create a new dehydrated placeholder. Called from PropagateDownload.
    [[nodiscard]] virtual Result<void, QString> createPlaceholder(const SyncFileItem &item) = 0;

    /** Discovery hook: even unchanged files may need UPDATE_METADATA.
     *
     * For instance cfapi vfs wants local hydrated non-placeholder files to
     * become hydrated placeholder files.
     */
    [[nodiscard]] virtual bool needsMetadataUpdate(const SyncFileItem &item) = 0;

    /// Determine whether the file at the given absolute path is a dehydrated placeholder.
    [[nodiscard]] virtual bool isDehydratedPlaceholder(const QString &filePath) = 0;

    /** Similar to isDehydratedPlaceholder() but used from sync discovery.
     *
     * This function shall set stat->type if appropriate.
     * It may rely on stat->path and stat_data (platform specific data).
     *
     * Returning true means that type was fully determined.
     */
    [[nodiscard]] virtual bool statTypeVirtualFile(csync_file_stat_t *stat, void *stat_data) = 0;

    /** Sets the pin state for the item at a path.
     *
     * The pin state is set on the item and for all items below it.
     *
     * Usually this would forward to setting the pin state flag in the db table,
     * but some vfs plugins will store the pin state in file attributes instead.
     *
     * relFilePath is relative to the sync folder. Can be "" for root folder.
     */
    [[nodiscard]] virtual bool setPinState(const QString &relFilePath, PinState state) = 0;

    /** Returns the pin state of an item at a path.
     *
     * Usually backed by the db's effectivePinState() function but some vfs
     * plugins will override it to retrieve the state from elsewhere.
     *
     * relFilePath is relative to the sync folder. Can be "" for root folder.
     *
     * Returns none on retrieval error.
     */
    [[nodiscard]] virtual Optional<PinState> pinState(const QString &relFilePath) = 0;

    /** Returns availability status of an item at a path.
     *
     * The availability is a condensed user-facing version of PinState. See
     * VfsItemAvailability for details.
     *
     * folderPath is relative to the sync folder. Can be "" for root folder.
     */
    [[nodiscard]] virtual AvailabilityResult availability(const QString &folderPath) = 0;

    /** Removes all virtual file db entries and dehydrated local placeholders.
     *
     * Particularly useful when switching off vfs mode or switching to a
     * different kind of vfs.
     */
    void wipeDehydratedVirtualFiles();

public Q_SLOTS:
    /** Update in-sync state based on SyncFileStatusTracker signal.
     *
     * For some vfs plugins the icons aren't based on SocketAPI but rather on data shared
     * via the vfs plugin. The connection to SyncFileStatusTracker allows both to be based
     * on the same data.
     */
    virtual void onFileStatusChanged(const QString &systemFileName, SyncFileStatus fileStatus) = 0;

Q_SIGNALS:
    /// start complete
    void started();

    /// we encountered an error
    void error(const QString &error);

    /// The vfs plugin detected that the metadata are out of sync and requests a sync with the server
    void needSync();

protected:
    /** Update placeholder metadata during discovery.
     *
     * If the remote metadata changes, the local placeholder's metadata should possibly
     * change as well.
     */
    [[nodiscard]] virtual Result<ConvertToPlaceholderResult, QString> updateMetadata(const SyncFileItem &item, const QString &filePath, const QString &replacesFile) = 0;

    /** Set up the plugin for the folder.
     *
     * For example, the VFS provider might monitor files to be able to start a file
     * hydration (download of a file's remote contents) when the user wants to open
     * it.
     *
     * Usually some registration needs to be done with the backend. This function
     * should take care of it if necessary.
     *
     * \note The implementation is allowed to run asynchronously, meaning the method
     *       can return before the start is fully complete. On completion, the
     *       \a started() signal is emitted.
     * \warning For VFS implementations: the rest of the code in the client assumes
     *          that it is safe to do multiple calls to this method, EVEN IF A PREVIOUS
     *          START IS NOT FULLY FINISHED. If ANY synchronization needs to be done
     *          (e.g. reading/writing to the Windows registry, or searching for
     *          StorageProvider information), this has to be implemented in the
     *          plugin itself.
     */
    virtual void startImpl(const VfsSetupParams &params) = 0;

    // Db-backed pin state handling. Derived classes may use it to implement pin states.
    bool setPinStateInDb(const QString &folderPath, PinState state);
    Optional<PinState> pinStateInDb(const QString &folderPath);
    AvailabilityResult availabilityInDb(const QString &folderPath);

private:
    // the parameters passed to start()
    std::unique_ptr<VfsSetupParams> _setupParams;

    friend class OwncloudPropagator;
};

class OCSYNC_EXPORT VfsPluginManager
{
public:
    /// Check whether the plugin for the mode is available.
    bool isVfsPluginAvailable(Vfs::Mode mode) const;

    /// Return the best available VFS mode.
    Vfs::Mode bestAvailableVfsMode() const;

    /// Create a VFS instance for the mode, returns nullptr on failure.
    Vfs *createVfsFromPlugin(Vfs::Mode mode, QObject *parent) const;

    static const VfsPluginManager &instance();

protected:
    VfsPluginManager() = default;

private:
    static VfsPluginManager *_instance;

    mutable QMap<Vfs::Mode, bool> _pluginCache;
};

template <>
OCSYNC_EXPORT QString Utility::enumToString(Vfs::Mode mode);

} // namespace OCC
