#include "cache.h"
#include "config.h"
#include "fsmonitor.h"
#include "fsm-listen.h"
#include "fsmonitor--daemon.h"

/*
 * The documentation of ReadDirectoryChangesW() states that the maximum
 * buffer size is 64K when the monitored directory is remote.
 *
 * Larger buffers may be used when the monitored directory is local and
 * will help us receive events faster from the kernel and avoid dropped
 * events.
 *
 * So we try to use a very large buffer and silently fallback to 64K if
 * we get an error.
 */
#define MAX_RDCW_BUF_FALLBACK (65536)
#define MAX_RDCW_BUF          (65536 * 8)

struct one_watch
{
	char buffer[MAX_RDCW_BUF];
	DWORD buf_len;
	DWORD count;

	struct strbuf path;
	HANDLE hDir;
	HANDLE hEvent;
	OVERLAPPED overlapped;

	/*
	 * Is there an active ReadDirectoryChangesW() call pending.  If so, we
	 * need to later call GetOverlappedResult() and possibly CancelIoEx().
	 */
	BOOL is_active;
};

struct fsmonitor_daemon_backend_data
{
	struct one_watch *watch_worktree;
	struct one_watch *watch_gitdir;

	HANDLE hEventShutdown;

	HANDLE hListener[3]; /* we don't own these handles */
#define LISTENER_SHUTDOWN 0
#define LISTENER_HAVE_DATA_WORKTREE 1
#define LISTENER_HAVE_DATA_GITDIR 2
	int nr_listener_handles;
};

/*
 * Convert the WCHAR path from the notification into UTF8 and
 * then normalize it.
 */
static int normalize_path_in_utf8(FILE_NOTIFY_INFORMATION *info,
				  struct strbuf *normalized_path)
{
	int reserve;
	int len = 0;

	strbuf_reset(normalized_path);
	if (!info->FileNameLength)
		goto normalize;

	/*
	 * Pre-reserve enough space in the UTF8 buffer for
	 * each Unicode WCHAR character to be mapped into a
	 * sequence of 2 UTF8 characters.  That should let us
	 * avoid ERROR_INSUFFICIENT_BUFFER 99.9+% of the time.
	 */
	reserve = info->FileNameLength + 1;
	strbuf_grow(normalized_path, reserve);

	for (;;) {
		len = WideCharToMultiByte(CP_UTF8, 0, info->FileName,
					  info->FileNameLength / sizeof(WCHAR),
					  normalized_path->buf,
					  strbuf_avail(normalized_path) - 1,
					  NULL, NULL);
		if (len > 0)
			goto normalize;
		if (GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
			error(_("[GLE %ld] could not convert path to UTF-8: '%.*ls'"),
			      GetLastError(),
			      (int)(info->FileNameLength / sizeof(WCHAR)),
			      info->FileName);
			return -1;
		}

		strbuf_grow(normalized_path,
			    strbuf_avail(normalized_path) + reserve);
	}

normalize:
	strbuf_setlen(normalized_path, len);
	return strbuf_normalize_path(normalized_path);
}

void fsm_listen__stop_async(struct fsmonitor_daemon_state *state)
{
	SetEvent(state->backend_data->hListener[LISTENER_SHUTDOWN]);
}

static struct one_watch *create_watch(struct fsmonitor_daemon_state *state,
				      const char *path)
{
	struct one_watch *watch = NULL;
	DWORD desired_access = FILE_LIST_DIRECTORY;
	DWORD share_mode =
		FILE_SHARE_WRITE | FILE_SHARE_READ | FILE_SHARE_DELETE;
	HANDLE hDir;
	wchar_t wpath[MAX_PATH];

	if (xutftowcs_path(wpath, path) < 0) {
		error(_("could not convert to wide characters: '%s'"), path);
		return NULL;
	}

	hDir = CreateFileW(wpath,
			   desired_access, share_mode, NULL, OPEN_EXISTING,
			   FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED,
			   NULL);
	if (hDir == INVALID_HANDLE_VALUE) {
		error(_("[GLE %ld] could not watch '%s'"),
		      GetLastError(), path);
		return NULL;
	}

	CALLOC_ARRAY(watch, 1);

	watch->buf_len = sizeof(watch->buffer); /* assume full MAX_RDCW_BUF */

	strbuf_init(&watch->path, 0);
	strbuf_addstr(&watch->path, path);

	watch->hDir = hDir;
	watch->hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

	return watch;
}

static void destroy_watch(struct one_watch *watch)
{
	if (!watch)
		return;

	strbuf_release(&watch->path);
	if (watch->hDir != INVALID_HANDLE_VALUE)
		CloseHandle(watch->hDir);
	if (watch->hEvent != INVALID_HANDLE_VALUE)
		CloseHandle(watch->hEvent);

	free(watch);
}

static int start_rdcw_watch(struct fsmonitor_daemon_backend_data *data,
			    struct one_watch *watch)
{
	DWORD dwNotifyFilter =
		FILE_NOTIFY_CHANGE_FILE_NAME |
		FILE_NOTIFY_CHANGE_DIR_NAME |
		FILE_NOTIFY_CHANGE_ATTRIBUTES |
		FILE_NOTIFY_CHANGE_SIZE |
		FILE_NOTIFY_CHANGE_LAST_WRITE |
		FILE_NOTIFY_CHANGE_CREATION;

	ResetEvent(watch->hEvent);

	memset(&watch->overlapped, 0, sizeof(watch->overlapped));
	watch->overlapped.hEvent = watch->hEvent;

	/*
	 * Queue an async call using Overlapped IO.  This returns immediately.
	 * Our event handle will be signalled when the real result is available.
	 *
	 * The return value here just means that we successfully queued it.
	 * We won't know if the Read...() actually produces data until later.
	 */
	watch->is_active = ReadDirectoryChangesW(
		watch->hDir, watch->buffer, watch->buf_len, TRUE,
		dwNotifyFilter, &watch->count, &watch->overlapped, NULL);

	if (watch->is_active)
		return 0;

	error(_("ReadDirectoryChangedW failed on '%s' [GLE %ld]"),
	      watch->path.buf, GetLastError());
	return -1;
}

static int recv_rdcw_watch(struct one_watch *watch)
{
	DWORD gle;

	watch->is_active = FALSE;

	/*
	 * The overlapped result is ready.  If the Read...() was successful
	 * we finally receive the actual result into our buffer.
	 */
	if (GetOverlappedResult(watch->hDir, &watch->overlapped, &watch->count,
				TRUE))
		return 0;

	gle = GetLastError();
	if (gle == ERROR_INVALID_PARAMETER &&
	    /*
	     * The kernel throws an invalid parameter error when our
	     * buffer is too big and we are pointed at a remote
	     * directory (and possibly for other reasons).  Quietly
	     * set it down and try again.
	     *
	     * See note about MAX_RDCW_BUF at the top.
	     */
	    watch->buf_len > MAX_RDCW_BUF_FALLBACK) {
		watch->buf_len = MAX_RDCW_BUF_FALLBACK;
		return -2;
	}

	/*
	 * NEEDSWORK: If an external <gitdir> is deleted, the above
	 * returns an error.  I'm not sure that there's anything that
	 * we can do here other than failing -- the <worktree>/.git
	 * link file would be broken anyway.  We might try to check
	 * for that and return a better error message, but I'm not
	 * sure it is worth it.
	 */

	error(_("GetOverlappedResult failed on '%s' [GLE %ld]"),
	      watch->path.buf, gle);
	return -1;
}

static void cancel_rdcw_watch(struct one_watch *watch)
{
	DWORD count;

	if (!watch || !watch->is_active)
		return;

	/*
	 * The calls to ReadDirectoryChangesW() and GetOverlappedResult()
	 * form a "pair" (my term) where we queue an IO and promise to
	 * hang around and wait for the kernel to give us the result.
	 *
	 * If for some reason after we queue the IO, we have to quit
	 * or otherwise not stick around for the second half, we must
	 * tell the kernel to abort the IO.  This prevents the kernel
	 * from writing to our buffer and/or signalling our event
	 * after we free them.
	 *
	 * (Ask me how much fun it was to track that one down).
	 */
	CancelIoEx(watch->hDir, &watch->overlapped);
	GetOverlappedResult(watch->hDir, &watch->overlapped, &count, TRUE);
	watch->is_active = FALSE;
}

/*
 * Process filesystem events that happen anywhere (recursively) under the
 * <worktree> root directory.  For a normal working directory, this includes
 * both version controlled files and the contents of the .git/ directory.
 *
 * If <worktree>/.git is a file, then we only see events for the file
 * itself.
 */
static int process_worktree_events(struct fsmonitor_daemon_state *state)
{
	struct fsmonitor_daemon_backend_data *data = state->backend_data;
	struct one_watch *watch = data->watch_worktree;
	struct strbuf path = STRBUF_INIT;
	struct string_list cookie_list = STRING_LIST_INIT_DUP;
	struct fsmonitor_batch *batch = NULL;
	const char *p = watch->buffer;

	/*
	 * If the kernel gets more events than will fit in the kernel
	 * buffer associated with our RDCW handle, it drops them and
	 * returns a count of zero.
	 *
	 * Yes, the call returns WITHOUT error and with length zero.
	 * This is the documented behavior.  (My testing has confirmed
	 * that it also sets the last error to ERROR_NOTIFY_ENUM_DIR,
	 * but we do not rely on that since the function did not
	 * return an error and it is not documented.)
	 *
	 * (The "overflow" case is not ambiguous with the "no data" case
	 * because we did an INFINITE wait.)
	 *
	 * This means we have a gap in coverage.  Tell the daemon layer
	 * to resync.
	 */
	if (!watch->count) {
		trace2_data_string("fsmonitor", NULL, "fsm-listen/kernel",
				   "overflow");
		fsmonitor_force_resync(state);
		return LISTENER_HAVE_DATA_WORKTREE;
	}

	/*
	 * On Windows, `info` contains an "array" of paths that are
	 * relative to the root of whichever directory handle received
	 * the event.
	 */
	for (;;) {
		FILE_NOTIFY_INFORMATION *info = (void *)p;
		const char *slash;
		enum fsmonitor_path_type t;

		strbuf_reset(&path);
		if (normalize_path_in_utf8(info, &path) == -1)
			goto skip_this_path;

		t = fsmonitor_classify_path_workdir_relative(path.buf);

		switch (t) {
		case IS_INSIDE_DOT_GIT_WITH_COOKIE_PREFIX:
			/* special case cookie files within .git */

			/* Use just the filename of the cookie file. */
			slash = find_last_dir_sep(path.buf);
			string_list_append(&cookie_list,
					   slash ? slash + 1 : path.buf);
			break;

		case IS_INSIDE_DOT_GIT:
			/* ignore everything inside of "<worktree>/.git/" */
			break;

		case IS_DOT_GIT:
			/* "<worktree>/.git" was deleted (or renamed away) */
			if ((info->Action == FILE_ACTION_REMOVED) ||
			    (info->Action == FILE_ACTION_RENAMED_OLD_NAME)) {
				trace2_data_string("fsmonitor", NULL,
						   "fsm-listen/dotgit",
						   "removed");
				goto force_shutdown;
			}
			break;

		case IS_WORKDIR_PATH:
			/* queue normal pathname */
			if (!batch)
				batch = fsmonitor_batch__new();
			fsmonitor_batch__add_path(batch, path.buf);
			break;

		case IS_GITDIR:
		case IS_INSIDE_GITDIR:
		case IS_INSIDE_GITDIR_WITH_COOKIE_PREFIX:
		default:
			BUG("unexpected path classification '%d' for '%s'",
			    t, path.buf);
		}

skip_this_path:
		if (!info->NextEntryOffset)
			break;
		p += info->NextEntryOffset;
	}

	fsmonitor_publish(state, batch, &cookie_list);
	batch = NULL;
	string_list_clear(&cookie_list, 0);
	strbuf_release(&path);
	return LISTENER_HAVE_DATA_WORKTREE;

force_shutdown:
	fsmonitor_batch__free_list(batch);
	string_list_clear(&cookie_list, 0);
	strbuf_release(&path);
	return LISTENER_SHUTDOWN;
}

/*
 * Process filesystem events that happened anywhere (recursively) under the
 * external <gitdir> (such as non-primary worktrees or submodules).
 * We only care about cookie files that our client threads created here.
 *
 * Note that we DO NOT get filesystem events on the external <gitdir>
 * itself (it is not inside something that we are watching).  In particular,
 * we do not get an event if the external <gitdir> is deleted.
 */
static int process_gitdir_events(struct fsmonitor_daemon_state *state)
{
	struct fsmonitor_daemon_backend_data *data = state->backend_data;
	struct one_watch *watch = data->watch_gitdir;
	struct strbuf path = STRBUF_INIT;
	struct string_list cookie_list = STRING_LIST_INIT_DUP;
	const char *p = watch->buffer;

	if (!watch->count) {
		trace2_data_string("fsmonitor", NULL, "fsm-listen/kernel",
				   "overflow");
		fsmonitor_force_resync(state);
		return LISTENER_HAVE_DATA_GITDIR;
	}

	for (;;) {
		FILE_NOTIFY_INFORMATION *info = (void *)p;
		const char *slash;
		enum fsmonitor_path_type t;

		strbuf_reset(&path);
		if (normalize_path_in_utf8(info, &path) == -1)
			goto skip_this_path;

		t = fsmonitor_classify_path_gitdir_relative(path.buf);

		switch (t) {
		case IS_INSIDE_GITDIR_WITH_COOKIE_PREFIX:
			/* special case cookie files within gitdir */

			/* Use just the filename of the cookie file. */
			slash = find_last_dir_sep(path.buf);
			string_list_append(&cookie_list,
					   slash ? slash + 1 : path.buf);
			break;

		case IS_INSIDE_GITDIR:
			goto skip_this_path;

		default:
			BUG("unexpected path classification '%d' for '%s'",
			    t, path.buf);
		}

skip_this_path:
		if (!info->NextEntryOffset)
			break;
		p += info->NextEntryOffset;
	}

	fsmonitor_publish(state, NULL, &cookie_list);
	string_list_clear(&cookie_list, 0);
	strbuf_release(&path);
	return LISTENER_HAVE_DATA_GITDIR;
}

void fsm_listen__loop(struct fsmonitor_daemon_state *state)
{
	struct fsmonitor_daemon_backend_data *data = state->backend_data;
	DWORD dwWait;
	int result;

	state->error_code = 0;

	if (start_rdcw_watch(data, data->watch_worktree) == -1)
		goto force_error_stop;

	if (data->watch_gitdir &&
	    start_rdcw_watch(data, data->watch_gitdir) == -1)
		goto force_error_stop;

	for (;;) {
		dwWait = WaitForMultipleObjects(data->nr_listener_handles,
						data->hListener,
						FALSE, INFINITE);

		if (dwWait == WAIT_OBJECT_0 + LISTENER_HAVE_DATA_WORKTREE) {
			result = recv_rdcw_watch(data->watch_worktree);
			if (result == -1) {
				/* hard error */
				goto force_error_stop;
			}
			if (result == -2) {
				/* retryable error */
				if (start_rdcw_watch(data, data->watch_worktree) == -1)
					goto force_error_stop;
				continue;
			}

			/* have data */
			if (process_worktree_events(state) == LISTENER_SHUTDOWN)
				goto force_shutdown;
			if (start_rdcw_watch(data, data->watch_worktree) == -1)
				goto force_error_stop;
			continue;
		}

		if (dwWait == WAIT_OBJECT_0 + LISTENER_HAVE_DATA_GITDIR) {
			result = recv_rdcw_watch(data->watch_gitdir);
			if (result == -1) {
				/* hard error */
				goto force_error_stop;
			}
			if (result == -2) {
				/* retryable error */
				if (start_rdcw_watch(data, data->watch_gitdir) == -1)
					goto force_error_stop;
				continue;
			}

			/* have data */
			if (process_gitdir_events(state) == LISTENER_SHUTDOWN)
				goto force_shutdown;
			if (start_rdcw_watch(data, data->watch_gitdir) == -1)
				goto force_error_stop;
			continue;
		}

		if (dwWait == WAIT_OBJECT_0 + LISTENER_SHUTDOWN)
			goto clean_shutdown;

		error(_("could not read directory changes [GLE %ld]"),
		      GetLastError());
		goto force_error_stop;
	}

force_error_stop:
	state->error_code = -1;

force_shutdown:
	/*
	 * Tell the IPC thead pool to stop (which completes the await
	 * in the main thread (which will also signal this thread (if
	 * we are still alive))).
	 */
	ipc_server_stop_async(state->ipc_server_data);

clean_shutdown:
	cancel_rdcw_watch(data->watch_worktree);
	cancel_rdcw_watch(data->watch_gitdir);
}

int fsm_listen__ctor(struct fsmonitor_daemon_state *state)
{
	struct fsmonitor_daemon_backend_data *data;

	CALLOC_ARRAY(data, 1);

	data->hEventShutdown = CreateEvent(NULL, TRUE, FALSE, NULL);

	data->watch_worktree = create_watch(state,
					    state->path_worktree_watch.buf);
	if (!data->watch_worktree)
		goto failed;

	if (state->nr_paths_watching > 1) {
		data->watch_gitdir = create_watch(state,
						  state->path_gitdir_watch.buf);
		if (!data->watch_gitdir)
			goto failed;
	}

	data->hListener[LISTENER_SHUTDOWN] = data->hEventShutdown;
	data->nr_listener_handles++;

	data->hListener[LISTENER_HAVE_DATA_WORKTREE] =
		data->watch_worktree->hEvent;
	data->nr_listener_handles++;

	if (data->watch_gitdir) {
		data->hListener[LISTENER_HAVE_DATA_GITDIR] =
			data->watch_gitdir->hEvent;
		data->nr_listener_handles++;
	}

	state->backend_data = data;
	return 0;

failed:
	CloseHandle(data->hEventShutdown);
	destroy_watch(data->watch_worktree);
	destroy_watch(data->watch_gitdir);

	return -1;
}

void fsm_listen__dtor(struct fsmonitor_daemon_state *state)
{
	struct fsmonitor_daemon_backend_data *data;

	if (!state || !state->backend_data)
		return;

	data = state->backend_data;

	CloseHandle(data->hEventShutdown);
	destroy_watch(data->watch_worktree);
	destroy_watch(data->watch_gitdir);

	FREE_AND_NULL(state->backend_data);
}