/* Copyright (C) 2023 Wildfire Games.
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

/*
 * Win32 directory change notification
 */

#include "precompiled.h"
#include "lib/sysdep/dir_watch.h"

#include "lib/allocators/shared_ptr.h"
#include "lib/path.h"	// path_is_subpath
#include "lib/sysdep/os/win/win.h"
#include "lib/sysdep/os/win/wutil.h"
#include "lib/sysdep/os/win/wiocp.h"


//-----------------------------------------------------------------------------
// DirHandle

class DirHandle
{
public:
	DirHandle(const OsPath& path)
	{
		WinScopedPreserveLastError s;	// CreateFile
		const DWORD share = FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;
		const DWORD flags = FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED;
		m_hDir = CreateFileW(OsString(path).c_str(), FILE_LIST_DIRECTORY, share, 0, OPEN_EXISTING, flags, 0);
	}

	~DirHandle()
	{
		// contrary to MSDN, the canceled IOs do not issue a completion notification.
		// (receiving packets after (unsuccessful) cancellation would be dangerous)
		BOOL ok = CancelIo(m_hDir);
		WARN_IF_FALSE(ok);

		CloseHandle(m_hDir);
		m_hDir = INVALID_HANDLE_VALUE;
	}

	// == INVALID_HANDLE_VALUE if path doesn't exist
	operator HANDLE() const
	{
		return m_hDir;
	}

private:
	HANDLE m_hDir;
};


//-----------------------------------------------------------------------------
// DirWatchRequest

class DirWatchRequest
{
	NONCOPYABLE(DirWatchRequest);
public:
	DirWatchRequest(const OsPath& path)
		: m_path(path), m_dirHandle(path), m_data(new u8[dataSize])
	{
		m_ovl = (OVERLAPPED*)calloc(1, sizeof(OVERLAPPED));	// rationale for dynamic alloc: see decl
		ENSURE(m_ovl);

		// (hEvent is needed for the wait after CancelIo below)
		const BOOL manualReset = TRUE;
		const BOOL initialState = FALSE;
		m_ovl->hEvent = CreateEvent(0, manualReset, initialState, 0);
	}

	~DirWatchRequest()
	{
		// we need to free m_data here, so the pending IO had better
		// not write to that memory in future. therefore:
		WARN_IF_FALSE(CancelIo(m_dirHandle));
		// however, this is not synchronized with the DPC (?) that apparently
		// delivers the data - m_data is filled anyway.
		// we need to ensure that either the IO has happened or that it
		// was successfully canceled before freeing m_data and m_ovl, so wait:
		{
			WinScopedPreserveLastError s;
			// (GetOverlappedResult without a valid hEvent hangs on Vista;
			// we'll abort after a timeout to be safe.)
			const DWORD ret = WaitForSingleObject(m_ovl->hEvent, 1000);
			WARN_IF_FALSE(CloseHandle(m_ovl->hEvent));
			if(ret == WAIT_OBJECT_0 || GetLastError() == ERROR_OPERATION_ABORTED)
			{
				SetLastError(0);
				delete[] m_data;
				free(m_ovl);
			}
			else
			{
				// (this could conceivably happen if a kernel debugger
				// hangs the system during the wait duration.)
				debug_printf("WARNING: IO may still be pending; to avoid memory corruption, we won't free the buffer.\n");
				DEBUG_WARN_ERR(ERR::TIMED_OUT);
				// intentionally leak m_data and m_ovl!
			}
		}
	}

	const OsPath& Path() const
	{
		return m_path;
	}

	void AttachTo(HANDLE& hIOCP) const
	{
		AttachToCompletionPort(m_dirHandle, hIOCP, (uintptr_t)this);
	}

	// (called again after each notification, so it mustn't AttachToCompletionPort)
	Status Issue()
	{
		if(m_dirHandle == INVALID_HANDLE_VALUE)
			WARN_RETURN(ERR::PATH_NOT_FOUND);

		const BOOL watchSubtree = TRUE;	// (see IntrusiveLink comments)
		const DWORD filter = FILE_NOTIFY_CHANGE_FILE_NAME | FILE_NOTIFY_CHANGE_DIR_NAME |
			FILE_NOTIFY_CHANGE_SIZE | FILE_NOTIFY_CHANGE_LAST_WRITE |
			FILE_NOTIFY_CHANGE_CREATION;
		// not set: FILE_NOTIFY_CHANGE_ATTRIBUTES, FILE_NOTIFY_CHANGE_LAST_ACCESS, FILE_NOTIFY_CHANGE_SECURITY
		DWORD undefined = 0;	// (non-NULL pointer avoids BoundsChecker warning)
		m_ovl->Internal = 0;
		WARN_IF_FALSE(ReadDirectoryChangesW(m_dirHandle, m_data, dataSize, watchSubtree, filter, &undefined, m_ovl, 0));
		return INFO::OK;
	}

	/**
	 * (call when completion port indicates data is available)
	 **/
	void RetrieveNotifications(DirWatchNotifications& notifications) const
	{
		const FILE_NOTIFY_INFORMATION* fni = (const FILE_NOTIFY_INFORMATION*)m_data;
		for(;;)
		{
			// convert (non-zero-terminated) BSTR to Path::String
			cassert(sizeof(wchar_t) == sizeof(WCHAR));
			const size_t length = fni->FileNameLength / sizeof(WCHAR);
			Path::String name(fni->FileName, length);

			// (NB: name is actually a relative path since we watch entire subtrees)
			const OsPath pathname = m_path / name;
			const DirWatchNotification::EType type = TypeFromAction(fni->Action);
			notifications.push_back(DirWatchNotification(pathname, type));

			if(!fni->NextEntryOffset)	// this was the last entry.
				break;
			fni = (const FILE_NOTIFY_INFORMATION*)(uintptr_t(fni) + fni->NextEntryOffset);
		}
	}

private:
	static DirWatchNotification::EType TypeFromAction(const DWORD action)
	{
		switch(action)
		{
		case FILE_ACTION_ADDED:
		case FILE_ACTION_RENAMED_NEW_NAME:
			return DirWatchNotification::Created;

		case FILE_ACTION_REMOVED:
		case FILE_ACTION_RENAMED_OLD_NAME:
			return DirWatchNotification::Deleted;

		case FILE_ACTION_MODIFIED:
			return DirWatchNotification::Changed;

		default:
			DEBUG_WARN_ERR(ERR::LOGIC);
			return DirWatchNotification::Changed;
		}
	}

	OsPath m_path;
	DirHandle m_dirHandle;

	// rationale:
	// - if too small, notifications may be lost! (the CSD-poll application
	//   may be confronted with hundreds of new files in a short time frame)
	// - requests larger than 64 KiB fail on SMB due to packet restrictions.
	static const size_t dataSize = 64*KiB;

	// rationale:
	// - each instance needs their own buffer. (we can't share a central
	//   copy because the watches are independent and may be triggered
	//   'simultaneously' before the next poll.)
	// - lifetime must be managed manually (see dtor)
	u8* m_data;

	// rationale:
	// - ReadDirectoryChangesW's asynchronous mode is triggered by passing
	//   a valid OVERLAPPED parameter; notification proceeds via
	//   completion ports, but we still need hEvent - see above.
	// - this must remain valid while the IO is pending. if the wait
	//   were to fail, we must not free this memory, either.
	OVERLAPPED* m_ovl;
};

typedef std::shared_ptr<DirWatchRequest> PDirWatchRequest;


//-----------------------------------------------------------------------------
// IntrusiveLink

// using watches of entire subtrees to satisfy single-directory requests
// requires a list of existing watches. an intrusive, doubly-linked list
// is convenient because removal must occur within the DirWatch destructor.
// since boost::intrusive doesn't automatically remove objects from their
// containers when they are destroyed, we implement a simple circular list
// via sentinel. note that DirWatchManager iterates over DirWatch, not their
// embedded links. we map from link to the parent object via offsetof
// (slightly less complex than storing back pointers to the parents, and
// avoids 'this-pointer used during initialization list' warnings).

class IntrusiveLink
{
public:
	IntrusiveLink()
	{
		m_prev = m_next = this;	// sentinel
	}

	IntrusiveLink(IntrusiveLink* sentinel)
	{
		// insert after sentinel
		m_prev = sentinel;
		m_next = sentinel->m_next;
		m_next->m_prev = this;
		sentinel->m_next = this;
	}

	~IntrusiveLink()
	{
		// remove from list
		m_prev->m_next = m_next;
		m_next->m_prev = m_prev;
	}

	IntrusiveLink* Next() const
	{
		return m_next;
	}

private:
	IntrusiveLink* m_prev;
	IntrusiveLink* m_next;
};


//-----------------------------------------------------------------------------
// DirWatch

struct DirWatch
{
	DirWatch(IntrusiveLink* sentinel, const PDirWatchRequest& request)
		: link(sentinel), request(request)
	{
	}

	IntrusiveLink link;
	PDirWatchRequest request;
};


//-----------------------------------------------------------------------------
// DirWatchManager

class DirWatchManager
{
public:
	DirWatchManager()
		: hIOCP(0)	// Win32 requires 0-init; created in the first call to AttachTo
	{
	}

	~DirWatchManager()
	{
		CloseHandle(hIOCP);
	}

	Status Add(const OsPath& path, PDirWatch& dirWatch)
	{
		ENSURE(path.IsDirectory());

		// check if this is a subdirectory of a tree that's already being
		// watched (this is much faster than issuing a new watch; it also
		// prevents accidentally watching the same directory twice).
		for(IntrusiveLink* link = m_sentinel.Next(); link != &m_sentinel; link = link->Next())
		{
			DirWatch* const existingDirWatch = (DirWatch*)(uintptr_t(link) - offsetof(DirWatch, link));
			if(path_is_subpath(OsString(path).c_str(), OsString(existingDirWatch->request->Path()).c_str()))
			{
				dirWatch.reset(new DirWatch(&m_sentinel, existingDirWatch->request));
				return INFO::OK;
			}
		}

		PDirWatchRequest request(new DirWatchRequest(path));
		request->AttachTo(hIOCP);
		RETURN_STATUS_IF_ERR(request->Issue());
		dirWatch.reset(new DirWatch(&m_sentinel, request));
		return INFO::OK;
	}

	Status Poll(DirWatchNotifications& notifications)
	{
POLL_AGAIN:
		DWORD bytesTransferred; ULONG_PTR key; OVERLAPPED* ovl;
		const Status ret = PollCompletionPort(hIOCP, 0, bytesTransferred, key, ovl);
		if(ret == ERR::ABORTED)	// watch was canceled
			goto POLL_AGAIN;
		RETURN_STATUS_IF_ERR(ret);

		DirWatchRequest* request = (DirWatchRequest*)key;
		request->RetrieveNotifications(notifications);
		RETURN_STATUS_IF_ERR(request->Issue());	// re-issue
		return INFO::OK;
	}

private:
	IntrusiveLink m_sentinel;
	HANDLE hIOCP;
};

static DirWatchManager* s_dirWatchManager;


//-----------------------------------------------------------------------------

Status dir_watch_Add(const OsPath& path, PDirWatch& dirWatch)
{
	WinScopedLock lock(WDIR_WATCH_CS);
	return s_dirWatchManager->Add(path, dirWatch);
}

Status dir_watch_Poll(DirWatchNotifications& notifications)
{
	WinScopedLock lock(WDIR_WATCH_CS);
	return s_dirWatchManager->Poll(notifications);
}


//-----------------------------------------------------------------------------

Status wdir_watch_Init()
{
	s_dirWatchManager = new DirWatchManager;
	return INFO::OK;
}

Status wdir_watch_Shutdown()
{
	SAFE_DELETE(s_dirWatchManager);
	return INFO::OK;
}