import re
from datetime import datetime, timedelta
from icalendar import Calendar, Event, Timezone, TimezoneStandard, TimezoneDaylight, vRecur
import pytz
import uuid
import gradio as gr
import os

# Define the shift pattern to match: DD.MM. Day ShiftCode HH.MM - HH.MM
shift_pattern = re.compile(
    r'(\d{2}\.\d{2})\.?\s+'  # Date (DD.MM or DD.MM.)
    r'[A-Za-z]{2}\s+'       # Day abbreviation (ignored)
    r'([A-Za-z0-9]+)\s+'       # Shift code (allow lowercase)
    r'(\d{2}\.\d{2})\s+-\s+(\d{2}\.\d{2})'  # Time range
)

def create_shift_calendar(shift_data, year=datetime.now().year):
    # Split data into lines and remove empty lines
    lines = [line.strip() for line in shift_data.split('\n') if line.strip()]

    # Create a new calendar with specified format
    cal = Calendar()
    cal.add('prodid', '-//Gemini AI//Google Calendar Creator//EN')
    cal.add('version', '2.0')
    cal.add('calscale', 'GREGORIAN')
    cal.add('method', 'PUBLISH')
    cal.add('x-wr-calname', 'Work Shifts')
    cal.add('x-wr-timezone', 'Europe/Helsinki')

    # Add timezone component for Europe/Helsinki
    tz = Timezone()
    tz.add('tzid', 'Europe/Helsinki')
    
    # Standard time (UTC+2)
    std = TimezoneStandard()
    std.add('tzname', 'EET')
    std.add('dtstart', datetime(1970, 10, 25, 3, 0, 0))
    std.add('tzoffsetto', timedelta(hours=2))
    std.add('tzoffsetfrom', timedelta(hours=3))
    std.add('rrule', vRecur(freq='YEARLY', bymonth=10, byweekday=['SU'], bysetpos=-1))
    tz.add_component(std)
    
    # Daylight saving time (UTC+3)
    dst = TimezoneDaylight()
    dst.add('tzname', 'EEST')
    dst.add('dtstart', datetime(1970, 3, 29, 2, 0, 0))
    dst.add('tzoffsetto', timedelta(hours=3))
    dst.add('tzoffsetfrom', timedelta(hours=2))
    dst.add('rrule', vRecur(freq='YEARLY', bymonth=3, byweekday=['SU'], bysetpos=-1))
    tz.add_component(dst)
    
    cal.add_component(tz)

    # Get the timezone object
    helsinki_tz = pytz.timezone('Europe/Helsinki')

    for line in lines:
        match = shift_pattern.match(line)
        if not match:
            print(f"Warning: Could not parse line '{line}'")
            continue

        try:
            # Extract components from the match groups
            date_str = match.group(1)  # First group: date (DD.MM)
            shift_code = match.group(2)  # Second group: shift code
            start_time_str = match.group(3)  # Third group: start time
            end_time_str = match.group(4)  # Fourth group: end time
            
            # Create datetime objects and localize to Helsinki time
            start_dt_naive = datetime.strptime(
                f"{date_str}.{year} {start_time_str.replace('.', ':')}",
                "%d.%m.%Y %H:%M"
            )
            end_dt_naive = datetime.strptime(
                f"{date_str}.{year} {end_time_str.replace('.', ':')}",
                "%d.%m.%Y %H:%M"
            )

            # Localize to Helsinki timezone and convert to UTC
            start_dt_helsinki = helsinki_tz.localize(start_dt_naive)
            end_dt_helsinki = helsinki_tz.localize(end_dt_naive)
            start_dt_utc = start_dt_helsinki.astimezone(pytz.utc)
            end_dt_utc = end_dt_helsinki.astimezone(pytz.utc)

            # Create event with UTC times
            event = Event()
            event.add('summary', f'Work Shift: {shift_code}')
            event.add('dtstart', start_dt_utc)
            event.add('dtend', end_dt_utc)
            event.add('description', f'Shift code: {shift_code}')
            event.add('uid', str(uuid.uuid4()))
            event.add('dtstamp', datetime.utcnow())
            
            # Add event to calendar
            cal.add_component(event)
            
        except ValueError as e:
            print(f"Warning: Could not parse date/time on line '{line}'. Error: {e}")
            continue

    return cal.to_ical()  # Return the calendar data

def generate_ical(shift_data):
    """
    Takes raw shift data, generates an iCalendar file, and returns the path to the file.
    """
    if not shift_data:
        # Gradio needs a file path to be returned, so create an empty file.
        with open("shifts_empty.ics", "w") as f:
            pass
        return "shifts_empty.ics"

    ics_data = create_shift_calendar(shift_data)
    
    # Define the output file path
    file_path = "shifts.ics"
    
    # Write the iCalendar data to the file
    with open(file_path, 'wb') as f:
        f.write(ics_data)
        
    return file_path

# Create the Gradio interface
demo = gr.Interface(
    fn=generate_ical,
    inputs=gr.Textbox(
        lines=15, 
        label="Paste Shift Data Here", 
        placeholder="Example:\n01.07.\tTi\tA5\t07.30 - 15.42\n02.07.\tKe\tI2\t13.00 - 21.00\n..."
    ),
    outputs=gr.File(label="Download iCalendar File"),
    title="Shift to iCalendar Converter",
    description="Paste your shift data in the format 'DD.MM. Day ShiftCode HH.MM - HH.MM' (one shift per line). The script will generate a downloadable .ics file that you can import into your calendar application.",
    allow_flagging="never",
)

if __name__ == "__main__":
    demo.launch()