remindme_caldav/remindme_caldav.py

from pathlib import Path
from icalendar import Calendar, Event
import toml, argparse, os, sys, hashlib, json, pytz, os, time
from dateutil.relativedelta import relativedelta
from dateutil.rrule import rrulestr
import datetime as dt
import time
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler
import humanfriendly
from pathlib import Path
import argparse, textwrap, logging
from alert_processor import AlertProcessor

logger = logging.getLogger()

def setup_log_location(logdir):
    if not Path.is_dir(logdir):
        raise FileNotFoundError(f"Log dir '{logdir}' does not exist. Be sure to create it first.")
    log_location = os.path.join(logdir, "log")
    status_location = os.path.join(logdir, "status")
    alert_history_location = os.path.join(logdir, "alert_history")
    return log_location, status_location, alert_history_location

def setup_logging(log_location):
    log_format='[%(levelname)s] %(asctime)s %(message)s'
    logging.basicConfig(filename = log_location, format=log_format, level=logging.INFO)

def parse_args():
    """Parse command line arguments."""
    parser = argparse.ArgumentParser(description="A simple calendar alerting daemon written in Python")
    parser.add_argument('--config', type=str, help='Path to config file. Must be .toml')
    parser.add_argument('--logdir', type=str, help='Path to logfile directory', default = "logs")
    parser.add_argument('--loglevel', help="Set the log level (DEBUG, INFO, WARNING, ERROR, CRITICAL)", 
                        type=str, choices=['DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL'])
    args = parser.parse_args()
    if args.config is None:
        logger.error("No config file provided. Please use --config path_to_config.toml")
        sys.exit(1)
    return args

def read_file(filename):                                       
    try:                                                       
        return Path(filename).read_text()                      
    except FileNotFoundError:                             
        raise FileNotFoundError("Error: The specified file does not exist.")
                                                               
def parse_toml(content):                                       
    try:                                                       
        config = toml.loads(content)                             
        if config is None:
            logging.error("Invalid config")
            sys.exit(1)
        return config
    except Exception:                                     
        raise RuntimeError("Error: Failed to parse TOML file.")             

def get_calendar_dir(config):
    cal_dir = Path(config["app"]["calendar_dir"])
    if not cal_dir.is_dir():                                                  
        logger.error(f"The provided path to .ics files does not exist: '{cal_dir}'") 
        sys.exit(1)
    return cal_dir

def parse_calendar_files(cal_dir):
    files = []
    no_files_detected = True
    logger.info(f"Looking for calendar files in {cal_dir}...")
    while no_files_detected is True:
        files = list(cal_dir.glob('*.ics'))                        
        if len(files) != 0:
            logger.info("Calendar files detected in sync location!")
            no_files_detected = False
    return files

def construct_initial_event_dict(cal_dir):
    files = parse_calendar_files(cal_dir)
    calendar_parser = CalendarParser()
    event_list = []
    for file in files:
        with open(file, 'r') as f:
            cal_str = f.read()
        try:
            event_dict = calendar_parser.parse_calendar(cal_str)
        except Exception as e:
            logger.warning(f"Error parsing event, skipping. {file}. Error message {e}")
            continue
        event_list.append(event_dict)
    return event_list

def calculate_event_hash(event):
    return hashlib.md5(json.dumps(event, sort_keys=True, cls=DateTimeEncoder).encode()).hexdigest()

class DateTimeEncoder(json.JSONEncoder):
    def default(self, o):
        if isinstance(o, (dt.datetime, dt.timedelta)):
            return str(o)  # Convert the datetime or timedelta object to a string
        return super().default(o)

class FileChangeHandler(FileSystemEventHandler):
    """
    `FileChangeHandler` is a custom event handler for the
    `watchdog.observers.Observer` class that handles file system events such as
    file modifications, deletions and creations.
    """
    def __init__(self, event_list):
        self.calendar_parser = CalendarParser()
        self.event_list = event_list   

    def on_modified(self, event):
        logger.info(f"File modified: {event.src_path}")
        if not event.is_directory:    
            try:
                with open(event.src_path, 'r') as f:
                    cal_str = f.read()
            except Exception as e:
                logger.error(f"Not a valid file: {event.src_path}. Error: {e}")
                return
            try:
                event_dict = self.calendar_parser.parse_calendar(cal_str)  # Use the instance to call parse_calendar method
            except Exception as e:
                logger.error(f"Failed to parse calendar event at: {event.src_path}. Error: {e}")
                return
            self.handle_modified(old_event=None, event_dict=event_dict)

    def on_deleted(self, event):
        logger.info(f"File deleted: {event.src_path}")
        if not event.is_directory:    
            uid = os.path.splitext(os.path.basename(event.src_path))[0]    # Get the UID from the file path without extension
            self.handle_modified(old_event=None, event_dict={"uid": uid}, remove=True)
    
    def on_created(self, event):
        logger.info(f"File created: {event.src_path}")
        if not event.is_directory:    
            try:
                with open(event.src_path, 'r') as f:
                    cal_str = f.read()
            except Exception as e:
                logger.warning(f"Not a valid file: {event.src_path}. Error: {e}")
                return
            try:
                event_dict = self.calendar_parser.parse_calendar(cal_str)  # Use the instance to call parse_calendar method
            except Exception as e:
                logger.warning(f"Failed to parse calendar event at: {event.src_path}. Error: {e}")
                return
            self.handle_modified(old_event=None, event_dict=event_dict)
    
    def handle_modified(self, old_event, event_dict, remove=False):
        if not remove:
            for i, old_event in enumerate(self.event_list):
                if old_event["uid"] == event_dict["uid"]:  
                    old_hash = old_event["hash"]
                    new_hash = calculate_event_hash(event_dict)
                    if new_hash != old_hash:    
                        logger.info(f"Event with UID {old_event['uid']} has been modified or deleted")
                        self.event_list[i] = event_dict
                    break
            else:    
                self.event_list.append(event_dict)
        else:   # If remove is True, remove the event from the list
            for i, old_event in enumerate(self.event_list):
                if old_event["uid"] == event_dict["uid"]:   
                    logger.info(f"Event with UID {old_event['uid']} has been deleted")
                    
                    del self.event_list[i]
                    break

class RecurringEventGenerator:
    """
    A class to generate recurring events based on a start date and a recurrence rule.
    """
    def __init__(self, dtstart, rrule):
        self.dtstart = dtstart
        self.rrule = rrule
        self.recur_info = {
            "recur_dates": [dtstart], 
            "infinite_recur": False,
            "recur_freq": None,
            "recur_interval": None,
            "n_recur_dates_left": 1
        }
        
    def generate(self):
        """
        """
        if self.rrule is None:
            return self.recur_info
            
        rule_str = "RRULE:{}".format(self.rrule.to_ical().decode('utf-8'))
        start_date = self.dtstart
        infinite_recur = False
        freq = self.rrule.get('FREQ')[0]
        count = self.rrule.get("COUNT")
        interval = self.rrule.get('INTERVAL')[0]
        until = self.rrule.get('UNTIL')
        current_date = dt.datetime.now().replace(tzinfo=pytz.UTC)
        
        if count is None or until is not None:
        # If there is no COUNT value in RRULE, we need to manually calculate
        # the dates else rrulestr method will return a very large number of
        # values. Here we iterate from the start_date to the current_date based
        # on the interval, then add an arbitrary number of days to that (here
        # it's 10).

            delta = None
            
            if freq == "DAILY":
                delta = relativedelta(days=interval)
            elif freq == "MONTHLY":
                delta = relativedelta(months=interval)
            elif freq == "YEARLY":
                delta = relativedelta(years=interval)
                
            count = 0
            origin_date = start_date
            while origin_date < current_date:
                count += interval
                origin_date += delta*interval
            
            rule_str += ";COUNT={}".format(count+10)
            infinite_recur = True
        
        ruleset = rrulestr(rule_str, dtstart=start_date)
        
        recur_dates = [None]
        n_recur = None
        dates = list(ruleset) # Generate future dates according to the rules
        recur_dates = [i for i in dates if i >= current_date]
        n_recur = "inf" if infinite_recur is True else len(recur_dates) 
        
        self.recur_info["recur_dates"] = recur_dates
        self.recur_info["infinite_recur"] = infinite_recur
        self.recur_info["recur_freq"] = freq
        self.recur_info["recur_interval"] = interval
        self.recur_info["n_recur_dates_left"] = n_recur
        
        return self.recur_info

class CalendarParser:
    def parse_calendar(self, cal_str):
        """
        Parse a calendar string and process each event. 
        """
        # Parse the calendar
        cal = self.parse_icalendar(cal_str)
        
        # Iterate over each event in the calendar
        for event in cal.walk('vevent'):
            event_dict = self.process_event(event)
            dtstart = self.dtstart_to_datetime(event_dict["dtstart"].dt)
            
            generator = RecurringEventGenerator(dtstart, event_dict["rrule"])
            recur_info = generator.generate() 
            event_dates = self.remove_exdates(event_dict["exdate"], recur_info["recur_dates"])
            if len(event_dates) == 0:
                logging.warning(f"No event dates for event: '{event['summary']}'")

            valarms = self.process_valarm(event)
            
            event_dict = {
                "uid": str(event_dict["uid"]), 
                "dtstart": dtstart,
                "summary": event_dict["summary"],
                "description": event_dict["description"],
                "location": event_dict["location"],
                "event_dates": event_dates,
                "recur_info": "Recur freq: {}, Recur interval: {}, N dates left: {}".format(
                    recur_info["recur_freq"], 
                    recur_info["recur_interval"], 
                    recur_info["n_recur_dates_left"]
                ),
                "valarms": valarms,
                "alert_history": []
            }
            try:
                new_hash = calculate_event_hash(event_dict)  # Calculate the hash of the event dictionary
            except Exception:
                raise RuntimeError("Error calculating event hash")
            event_dict["hash"] = new_hash  # Store the hash in the event dictionary
            return event_dict
    
    def parse_icalendar(self, cal_str):
        """
        Parse a calendar string into an iCalendar object. 
        """
        try:
            return Calendar.from_ical(cal_str)
        except Exception:
            raise RuntimeError("Error parsing icalendar.")
            
    def process_event(self, event):
        """
        Process an event from a parsed calendar and extract relevant information. 
        """
        event_info = {
                 "uid": None,
                 "dtstart": "",
                 "exdate": [],
                 "summary": None,
                 "description": None,
                 "location": None,
                 "rrule": None
         }
         
        # Catch errors for missing components
        for info in event_info:
            try:
                event_info[info] = event[info]
            except Exception:
                logging.info(f"CalDav componant '{info}' missing for event {event['summary']}")
        return event_info
    
    def dtstart_to_datetime(self, dtstart):
        """
        Convert a date or datetime object into a datetime object with UTC timezone. 
        """
        # Ensure dates are always as datetime
        try:
            if isinstance(dtstart, dt.datetime): 
                return dtstart.replace(tzinfo=pytz.UTC)
            else:
                return dt.datetime.combine(dtstart, dt.time.min).replace(tzinfo=pytz.UTC)
        except Exception:
            raise RuntimeError("Error converting dtstart to datetime.")

    def remove_exdates(self, exdates, recur_dates):
        """
        Remove dates from a list of recurring event dates that are in the exdate list. 
        """
        if exdates != []:
            try:
                if isinstance(exdates, list):
                    exdates = [i.dts[0].dt.replace(tzinfo=pytz.UTC) for i in exdates]
                else:
                    exdates = [exdates.dts[0].dt.replace(tzinfo=pytz.UTC)]
                return [i for i in recur_dates if i not in exdates]
            except Exception:
                raise RuntimeError("Error processing exdates.")
        else: 
            return recur_dates

    def process_valarm(self, event):
        """
        Process VALARM components from an iCalendar event and extract trigger times. 
        """
        valarms = []
        for subcomponent in event.walk("valarm"):
            valarm = Event.from_ical(subcomponent.to_ical())
            timedelta = valarm["trigger"].dt
            valarms.append(timedelta)
            if len(valarms) == 0:
                logging.info(f"No reminders for event: {event['summary']}")
        return valarms

def get_next_alert(event, current_time):
    """
    Returns the next alert that should be processed based on the current time.
    """
    event_dates = event["event_dates"]
    valarm_deltas = event["valarms"]
    if event_dates == [] or event_dates is None or current_time > event_dates[-1]:
        return None, None
    next_event = [i for i in event_dates if i >= current_time][0]
    next_alert_list = [next_event + i for i in valarm_deltas if next_event + i >= current_time]
    if len(next_alert_list) == 0:
        next_alert = next_event
    else:
        next_alert = min(next_alert_list)
    return next_alert - dt.timedelta(seconds=5), next_event

def process_alert(current_time, next_alert, next_event, event, config, alert_history_location):
    """
    Processes a given alert and passes it to a messaging client.
    """
    if current_time >= next_alert and current_time < next_alert + dt.timedelta(seconds=15):
        if len(event["alert_history"]) == 0:
            logger.info(f"First alert for '{event['summary']}' detected")
            event["alert_history"] = [{"timestamp_alert_triggered": current_time, "alert_defintition_time": next_alert}]
        elif next_alert in [i["alert_defintition_time"] for i in event["alert_history"]]:
            return
        else:
            logger.info(f"Posting alert for {event['summary']}!")
            event["alert_history"].append({"timestamp_alert_triggered": current_time, "alert_defintition_time": next_alert})
        try:
            processor = AlertProcessor(config)
            processor.send_email(event, next_alert, next_event)
        except Exception as e:
            raise RuntimeError(f"Error sending alert for event. {e}")
        with open(alert_history_location, 'a') as f:
            f.write(str(event))
        return

def daemon(status_location, alert_history_location, config, event_list):
    with open(status_location, 'w') as f:
        f.write("") # Refresh the status file
    current_time = dt.datetime.now().replace(tzinfo=pytz.UTC)
    for event in event_list:
        try:
            next_alert, next_event = get_next_alert(event, current_time)
        except RuntimeError as e:
            logger.warning(f"Error getting next alert for {event['summary']}, skipping event. Error message {e}")
            continue
        if next_alert == None:
            continue
        event_delta = next_alert-current_time
        total_seconds = event_delta.total_seconds()
        human_readable_time = humanfriendly.format_timespan(total_seconds)
        monitor_status = f"""\
            Current time: {current_time}
            Monitoring: {event["summary"]}
            Event date: {next_event}
            Recur Dates: {[str(i) for i in event["event_dates"]]}
            Next alert on: {next_alert} in {human_readable_time}
            Recur info: {event["recur_info"]}
            Alert history: {event["alert_history"]}\n"""
        monitor_status = textwrap.dedent(monitor_status)
        with open(status_location, 'a') as f:
            f.write(monitor_status) # Write the output to the file
            f.write("\n")
        try:
            process_alert(current_time, next_alert, next_event, event, config, alert_history_location)
        except RuntimeError as e:
            logger.warning(f"Error processing alert for event {event['summary']}. Error message: {e}")
    return

def main():
    # Parse args and initiate logging
    args = parse_args()
    log_location, status_location, alert_history_location = setup_log_location(args.logdir)
    setup_logging(log_location)
    logger = logging.getLogger()

    # Redefine log level if args passed
    if args.loglevel is not None:
        numeric_level = getattr(logging, args.loglevel.upper(), None)   # Convert string to integer
        if isinstance(numeric_level, int):
            logger = logging.getLogger()
            logger.setLevel(numeric_level) # Set the log level

    # Setup initial event_list
    config_file = read_file(args.config)
    config = parse_toml(config_file)
    cal_dir = get_calendar_dir(config)
    event_list = construct_initial_event_dict(cal_dir)

    # Start file handler to detect changes to calendar dir
    observer = Observer()
    handler = FileChangeHandler(event_list)
    observer.schedule(handler, cal_dir, recursive=True)
    observer.start()

    # Start main loop
    try:
        while True:
            daemon(status_location, alert_history_location, config, event_list)
            time.sleep(1)
    except KeyboardInterrupt:
        observer.stop()
        observer.join()

if __name__ == "__main__":
    main()