Agordejo/engine/watcher.py

#! /usr/bi  n/env python3
# -*- coding: utf-8 -*-
"""
Copyright 2020, Nils Hilbricht, Germany ( https://www.hilbricht.net )

This file is part of the Laborejo Software Suite ( https://www.laborejo.org ),

This application 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 3 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.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
"""

import logging; logger = logging.getLogger(__name__); logger.info("import")

#Standard Library
from datetime import datetime
import pathlib
import os
#Our Modules
from engine.start import PATHS

def fast_scandir(dir):    
    """
    Get all subdirectories recursively.
    https://stackoverflow.com/questions/973473/getting-a-list-of-all-subdirectories-in-the-current-directory"""    
    try:
        subfolders= [f.path for f in os.scandir(dir) if f.is_dir()] 
    except PermissionError:        
        subfolders = []    
        
    for dir in list(subfolders):
        subfolders.extend(fast_scandir(dir))
    return subfolders


class Watcher(object):
    """
    Initialize with the server controller

    The watcher will should only run when the program is in the mode to choose a session.
    If a session is loaded it will technically work, but will be a waste of resources.

    The watcher will also trigger the nsmController to redundantly query for a session list,
    for example when a new empty sessions gets created or duplicated. Once because nsmd sends the
    "new" signal, and then our watcher will notice the change itself. However, this happens only so
    often and can be accepted, so the program does not need more checks and exceptions.

    Inform you via callback when:    

    a) a session dir was deleted
    b) a new directory got created.
    c) session directory renamed or moved
    d) session.nsm changed timestamp
    e) A lockfile appeared or disappeared    

    We cannot poll nsmServerControl.exportSessionsAsDicts() because that triggers an nsmd response
    including log message and will flood their console. Instead this class only offers incremental
    updates.
    Another way is to watch the dir for changes ourselves in in some cases request a new project
    list from nsmd.

    Lockfile functionality goes beyond what NSM offers. A session-daemon can open only one
    project at a time. If you try to open another project with a second GUI (but same NSM-URL)
    it goes wrong a bit, at least in the new-session-manager GUI. They will leave a zombie lockfile.
    However, it still is possible to open a second nsmd instance. In this case the lockfile prevents
    opening a session twice. And we are reflecting the opened state of the project, no matter from
    which daemon. Horray for us :)    

    Clients can only be added or removed while a session is locked. We do not check nor update
    number of clients or symlinks. Therefore we advice a GUI to deactivate the display of
    these two values while a session is locked (together with size)
    """

    def __init__(self, nsmServerControl):
        self.active = True
        
        self._nsmServerControl = nsmServerControl
        
        assert self._nsmServerControl.sessionRoot
                
        self._directories = fast_scandir(self._nsmServerControl.sessionRoot)

        logger.info("Requestion our own copy of the session list. Don't worry about the apparent redundant call :)")
        self._lastExport = self._nsmServerControl.exportSessionsAsDicts()
        self._lastTimestamp = {d["nsmSessionName"]:d["lastSavedDate"] for d in self._lastExport} #str:str        
        #Init all values with None will send the initial state via callback on program start, which is what the user wants to know. 
        self._lastLockfile = {d["nsmSessionName"]:None for d in self._lastExport} #str:bool

        self.timeStampHook = None # a single function that gets informed of changes, most likely the api callback
        self.lockFileHook = None # a single function that gets informed of changes, most likely the api callback
        self.sessionsChangedHook = None # the api callback function api.callbacks._sessionsChanged. Rarely used.

    def resume(self, *args):
        """For api callbacks"""
        self.active = True
        #If we returned from an open session that will surely have changed. Trigger a single poll
        self.process()        
        logger.info("Watcher resumed")
        
    def suspend(self, *args):
        """For api callbacks"""
        self.active = False
        logger.info("Watcher suspended")

    def process(self):
        """Add this to your event loop.
        
        We look for any changes in the directory structure.
        If we detect any we simply trigger a new NSM export and a new NSM generated project
        list via callback. We do not expect this to happen often.

        This will also trigger if we add a new session ourselves. This *is* our way to react to
        new Sessions.
        """
        if not self.active:
            return
        
        if self.sessionsChangedHook:
            current_directories = fast_scandir(self._nsmServerControl.sessionRoot)
            
            if not self._directories == current_directories:                
                self._directories = current_directories
                self._lastExport = self.sessionsChangedHook() #will gather its own data, send it to api callbacks, but also return for us.
                self._lastTimestamp = {d["nsmSessionName"]:d["lastSavedDate"] for d in self._lastExport} #str:str
                self._lastLockfile = {d["nsmSessionName"]:None for d in self._lastExport} #str:bool

        #Now check the incremental hooks.
        #No hooks, no reason to process
        if not (self.timeStampHook or self.lockFileHook): 
            logger.info("No watcher-hooks to process")
            return        

        for entry in self._lastExport:            
            nsmSessionName = entry["nsmSessionName"]

            #Timestamp of session.nsm
            if self.timeStampHook:
                timestamp = datetime.fromtimestamp(entry["sessionFile"].stat().st_mtime).isoformat(sep=" ", timespec='minutes') #same format as server control export                        
                if not timestamp == self._lastTimestamp[nsmSessionName]: #This will only trigger on a minute-based slot, which is all we want and need. This is for relaying information to the user, not for advanced processing.
                    self._lastTimestamp[nsmSessionName] = timestamp
                    self.timeStampHook(nsmSessionName, timestamp)

            #Lockfiles
            if self.lockFileHook:
                lockfileState = entry["lockFile"].is_file()
                if not self._lastLockfile[nsmSessionName] == lockfileState:
                    self._lastLockfile[nsmSessionName] = lockfileState                
                    self.lockFileHook(nsmSessionName, lockfileState)