ins_compl_prep(int c)
{
    int		retval = FALSE;
    int		prev_mode = ctrl_x_mode;

    // Forget any previous 'special' messages if this is actually
    // a ^X mode key - bar ^R, in which case we wait to see what it gives us.
    if (c != Ctrl_R && vim_is_ctrl_x_key(c))
	edit_submode_extra = NULL;

    // Ignore end of Select mode mapping and mouse scroll buttons.
    if (c == K_SELECT || c == K_MOUSEDOWN || c == K_MOUSEUP
	    || c == K_MOUSELEFT || c == K_MOUSERIGHT
	    || c == K_COMMAND || c == K_SCRIPT_COMMAND)
	return retval;

#ifdef FEAT_PROP_POPUP
    // Ignore mouse events in a popup window
    if (is_mouse_key(c))
    {
	// Ignore drag and release events, the position does not need to be in
	// the popup and it may have just closed.
	if (c == K_LEFTRELEASE
		|| c == K_LEFTRELEASE_NM
		|| c == K_MIDDLERELEASE
		|| c == K_RIGHTRELEASE
		|| c == K_X1RELEASE
		|| c == K_X2RELEASE
		|| c == K_LEFTDRAG
		|| c == K_MIDDLEDRAG
		|| c == K_RIGHTDRAG
		|| c == K_X1DRAG
		|| c == K_X2DRAG)
	    return retval;
	if (popup_visible)
	{
	    int	    row = mouse_row;
	    int	    col = mouse_col;
	    win_T   *wp = mouse_find_win(&row, &col, FIND_POPUP);

	    if (wp != NULL && WIN_IS_POPUP(wp))
		return retval;
	}
    }
#endif

    if (ctrl_x_mode == CTRL_X_CMDLINE_CTRL_X && c != Ctrl_X)
    {
	if (c == Ctrl_V || c == Ctrl_Q || c == Ctrl_Z || ins_compl_pum_key(c)
		|| !vim_is_ctrl_x_key(c))
	{
	    // Not starting another completion mode.
	    ctrl_x_mode = CTRL_X_CMDLINE;

	    // CTRL-X CTRL-Z should stop completion without inserting anything
	    if (c == Ctrl_Z)
		retval = TRUE;
	}
	else
	{
	    ctrl_x_mode = CTRL_X_CMDLINE;

	    // Other CTRL-X keys first stop completion, then start another
	    // completion mode.
	    ins_compl_prep(' ');
	    ctrl_x_mode = CTRL_X_NOT_DEFINED_YET;
	}
    }

    // Set "compl_get_longest" when finding the first matches.
    if (ctrl_x_mode_not_defined_yet()
			   || (ctrl_x_mode_normal() && !compl_started))
    {
	compl_get_longest = compl_longest;
	compl_used_match = TRUE;

    }

    if (ctrl_x_mode_not_defined_yet())
	// We have just typed CTRL-X and aren't quite sure which CTRL-X mode
	// it will be yet.  Now we decide.
	retval = set_ctrl_x_mode(c);
    else if (ctrl_x_mode_not_default())
    {
	// We're already in CTRL-X mode, do we stay in it?
	if (!vim_is_ctrl_x_key(c))
	{
	    if (ctrl_x_mode_scroll())
		ctrl_x_mode = CTRL_X_NORMAL;
	    else
		ctrl_x_mode = CTRL_X_FINISHED;
	    edit_submode = NULL;
	}
	showmode();
    }

    if (compl_started || ctrl_x_mode == CTRL_X_FINISHED)
    {
	// Show error message from attempted keyword completion (probably
	// 'Pattern not found') until another key is hit, then go back to
	// showing what mode we are in.
	showmode();
	if ((ctrl_x_mode_normal() && c != Ctrl_N && c != Ctrl_P
				       && c != Ctrl_R && !ins_compl_pum_key(c))
		|| ctrl_x_mode == CTRL_X_FINISHED)
	    retval = ins_compl_stop(c, prev_mode, retval);
    }
    else if (ctrl_x_mode == CTRL_X_LOCAL_MSG)
	// Trigger the CompleteDone event to give scripts a chance to act
	// upon the (possibly failed) completion.
	ins_apply_autocmds(EVENT_COMPLETEDONE);

    may_trigger_modechanged();

    // reset continue_* if we left expansion-mode, if we stay they'll be
    // (re)set properly in ins_complete()
    if (!vim_is_ctrl_x_key(c))
    {
	compl_cont_status = 0;
	compl_cont_mode = 0;
    }

    return retval;
}