// Copyright Epic Games, Inc. All Rights Reserved.

#pragma once

#include "CoreTypes.h"

#include "Async/Future.h"
#include "Containers/Array.h"
#include "Containers/StringView.h"
#include "HAL/Platform.h"
#include "Misc/AssertionMacros.h"

#ifndef WITH_ASYNCIODELETE_DEBUG
#if DO_CHECK
#define WITH_ASYNCIODELETE_DEBUG 1  // When enabled the class uses extra memory and does some tracking
#else
#define WITH_ASYNCIODELETE_DEBUG 0
#endif
#endif

// Temporarily disable AsyncIODelete on Mac until we can diagnose why it's failing
#if PLATFORM_MAC
#define ASYNCIODELETE_ASYNC_ENABLED 0
#else
#define ASYNCIODELETE_ASYNC_ENABLED 1
#endif

class FEvent;

/**
 * Helper class to asynchronously delete paths (files or directories).
 * The deleted paths are moved to a unique temporary location immediately, and then asynchronously deleted later.
 * Note that two FAsyncIODeletes (in the same process or in multiple processes) at the same with the same InOwnedTempRoot
 * is forbidden and will cause behavior errors.  Caller must ensure the machine-global uniqueness of InOwnedTempRoot.
 *
 * FAsyncIODelete's public interface is not threadsafe; all calls to the public interface must be run from the same thread.
 */
class FAsyncIODelete
{
public:
    /**
     * Quick constructor to create flags; does not take any IO action until Setup or a Delete function is used
     *
     * @param InOwnedTempRoot - The FAsyncIODelete takes ownership of this directory, and deletes it when done.
     *							It is a temporary directory used to hold the deleted directories from elsewhere.  Must not be shared with (or a parent or child of) any other FAsyncDelete's InTempRoot.
     *						    The FAsyncIODelete will not be able to delete directories until a valid TempRoot has been set, either in the constructor or in SetTempRoot
     */
    explicit FAsyncIODelete(const FStringView& InOwnedTempRoot = FStringView());

    /* Synchronously waits for all requested deletions to complete */
    ~FAsyncIODelete();

    /**
     * Set the TempRoot directory used to hold the deleted directories from elsewhere.  The FAsyncIODelete takes ownership of this directory, and deletes it when destructed or when it is changed.
     * If the FAsyncIODelete has already been used to delete files, this Set will block until all deletes are finished.
     */
    void SetTempRoot(const FStringView& InOwnedTempRoot);
    FStringView GetTempRoot() const { return TempRoot; }

    /**
     * Set whether new background deletes are paused.  If paused, paths will be moved immediately but will not be deleted from the temporary location until unpaused (or at the FAsyncIODelete's destruction).
     * Setting deletes paused does not affect deletes already in progress.
     */
    void SetDeletesPaused(bool bInPaused);
    bool GetDeletesPaused() const { return bPaused; }

    /**
     * Prepare the directory on disk.  Called OnDemand from the other interface functions.  Can also be called if desired by client code.
     * May take a long time to run if cleanup from a crashed previous process is required.
     * @return False if the TempRoot directory could not be constructed; calls to DeleteDirectory will fail in this case
     */
    bool Setup();

    /** Synchronously wait for all tasks to complete, and remove the temproot. */
    void Teardown();

    /**
     * Asynchronously delete the given directory (and all subdirs).  The directory is moved and no longer exists before returning, but the move location will be deleted from disk later.
     * The delete will fail if the given path is not a directory.
     * The delete will fail and return false if the given path is a parent directory, child directory, or is equal to TempRoot.
     * The delete can also fail due to IO Errors - insufficient permissions, device failure.
     * If the given path is on a different volume than temp root, or the move fails for other reasons, the delete will proceed synchronously but will succeed.
     * If the given path does not exist, DeleteDirectory will return true.
     *
     * @param PathToDelete - If DeleteDirectory returns true, this path has been removed from disk.
     *
     * @return Whether the requested path is no longer present on disk.
     */
    bool DeleteDirectory(const FStringView& PathToDelete)
    {
        return Delete(PathToDelete, EPathType::Directory);
    }

    /** Asynchronously delete a file.  Behavior is otherwise the same as DeleteDirectory. */
    bool DeleteFile(const FStringView& PathToDelete)
    {
        return Delete(PathToDelete, EPathType::File);
    }

    /** Synchronously wait for all deletes to complete.  */
    bool WaitForAllTasks(float TimeLimitSeconds = 0.0f);

private:
#if ASYNCIODELETE_ASYNC_ENABLED
    /** Update the ActiveTaskCount and events for a task completing */
    void OnTaskComplete();
#endif

    enum class EPathType
    {
        File,
        Directory
    };
    /** Asynchronously delete a file or directory.  We handle both in the same function, but we want the interface to be explicit. */
    bool Delete(const FStringView& PathToDelete, EPathType ExpectedType);

#if ASYNCIODELETE_ASYNC_ENABLED
    /** Create and store the task to delete the given Directory or File */
    void CreateDeleteTask(const FStringView& InDeletePath, EPathType PathType);
#endif

    /** Delete the given path synchronously; called from a task or in error fallback cases from the public thread */
    bool SynchronousDelete(const TCHAR* InDeletePath, EPathType PathType);

#if ASYNCIODELETE_ASYNC_ENABLED
    bool DeleteTempRootDirectory(uint32& OutErrorCode);
#endif

    FString TempRoot;
#if ASYNCIODELETE_ASYNC_ENABLED
    TArray<FString> PausedDeletes;
    FCriticalSection CriticalSection;  // We use a CriticalSection instead of a TAtomic ActiveTaskCount so that we can atomically { trigger TasksComplete if ActiveTaskCount == 0 }
    FEvent* TasksComplete  = nullptr;
    uint32 ActiveTaskCount = 0;
    uint32 DeleteCounter   = 0;
#endif
    bool bInitialized = false;
    bool bPaused      = false;

#if WITH_ASYNCIODELETE_DEBUG
    static TArray<FString> AllTempRoots;
    static void AddTempRoot(const FStringView& InTempRoot);
    static void RemoveTempRoot(const FStringView& InTempRoot);
#endif
};