meeting_time.py

from collections import defaultdict
from datetime import datetime
import csv
import sys

__doc__ = """
This is a script that uses CSV input data (for example, collected by a Google Form) to find the acceptable times for a meeting.

The CSV columns are:

1. Timestamp (often collected by online forms; ignored)
2. Name
3. Timezone (from the table below)
4. When is the earliest time you can start work in that timezone? This is not when you start your working day; list the earliest you could wake up for and still be functional in the meeting.
5. When is the latest time you can meet until in that timezone? Again, this is not when your workday ends, but how late you can stay up before you won't be able to effectively participate.
"""

# timezone: (northern_summer_offset, northern_winter_offset, timeanddate_id)
# source: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
# and: https://dev.timeanddate.com/docs/available-locations
tzlookup = {
    "Europe/London": (1, 0, 136),
    "Europe/Berlin": (2, 1, 37),
    "Europe/Helsinki": (3, 2, 101),
    "Asia/Kolkata": (5.5, 5.5, 44),
    "Asia/Beijing": (8, 8, 33),
    "Asia/Tokyo": (9, 9, 248),
    "Australia/Melbourne": (10, 11, 152),
    "Pacific/Auckland": (12, 13, 22),
    "Pacific/Honolulu": (-10, -10, 103),
    "America/Los Angeles": (-7, -8, 137),
    "America/Denver": (-6, -7, 75),
    "America/Chicago": (-5, -6, 64),
    "America/New York": (-4, -5, 179),
}

def parse_time(instr, default):
    instr = instr.strip()
    if instr == "":
        return default
    try:
        first, second = instr.split(" ", 1)
    except ValueError:  # no AM/PM
        first = instr
        second = None
    hour = int(first.split(":", 1)[0])
    if second:
        if second.lower() == 'pm':
            hour += 12
        elif hour == 12:
            hour += 12
    else:
        if hour == 0:
            hour = 24
    return hour  # discard mins, seconds
            
def avail(start, end, offset):
    start_utc = start - offset
    end_utc = end - offset
    if start_utc < 0 or end_utc < 0:
        start_utc += 24
        end_utc += 24
    available = set()
    for h in range(start_utc, end_utc):
        available.add(h % 24)
    return available

def tzurl(cities, hour_utc, is_summer):
    if is_summer:
        date = f"month=6&day=1"
    else:
        date = f"month=12&day=1"
    time = f"hour={hour_utc}&min=0&sec=0"
    city_list = list(cities)
    city_components = []
    for i in range(len(city_list)):
        city_components.append(f"p{i}={city_list[i]}")
    city_query = "&".join(city_components)
    url = f"https://www.timeanddate.com/worldclock/meetingdetails.html?{date}&{time}&{city_query}"
    return url

with open(sys.argv[1]) as csvfile:
    reader = csv.reader(csvfile, 'excel')
    summer_candidates = set(range(0,23))
    winter_candidates = set(range(0,23))
    cities = set()
    for response in reader:
        if reader.line_num != 1:
            _, name, timezone, earliest, latest = response
            start = parse_time(earliest, 5)
            end = parse_time(latest, 24)
            summer_offset, winter_offset, tdid = tzlookup[timezone.strip()]
            cities.add(tdid)
            summer_available = avail(start, end, summer_offset)
            winter_available = avail(start, end, winter_offset)
            print(f"{name}: {start} {end} {summer_offset} {summer_available}")
            summer_candidates &= summer_available
            winter_candidates &= winter_available
    print("Agreeable (Northern) summer UTC hours:")
    for candidate in summer_candidates:
        print(f"* UTC+{candidate} - <{tzurl(cities, candidate, True)}>")
    print()
    print("Agreeable (Northern) winter UTC hours:")
    for candidate in winter_candidates:
        print(f"* UTC+{candidate} - <{tzurl(cities, candidate, False)}>")