import sys as trans
import csv
import pprint

def main():
    if len(trans.argv) != 2:
        print("Requires exactly one argument: the CSV to process.")
        trans.exit(1)

    filename = trans.argv[1]

    # data we will parse from the CSV
    # we assume that participant IDs and event names are unique
    participants = {}
    events = {}

    # the docs say we must use newline='' if passing in a file-like object
    with open(filename, newline='') as file:
        # deduce the format of the CSV file by looking at the first
        #   kilobyte of data
        dialect = csv.Sniffer().sniff(file.read(1024))
        # rewind the file to its start
        file.seek(0)
        reader = csv.DictReader(file, dialect=dialect)

        for row in reader:
            # grap all the data from the row. this makes the code below less
            # verbose and also ensures all data is present - "fail fast"
            participant_id = row['Participant ID']
            participant_name = row['Participant Name']
            event_name = row['Event Name']
            event_type = row['Event Type']

            # if this participant has not yet been seen, record them
            if participant_id not in participants:
                participants[participant_id] = {
                    'name': participant_name,
                    'events': []
                }

            # if this event has not yet been seen, record it
            # note that we trust the event type from the first occurrance
            if event_name not in events:
                events[event_name] = {
                    'type': event_type,
                    'participants': []
                }

            # record this attendance on both the participant and event
            participants[participant_id]['events'] += [event_name]
            events[event_name]['participants'] += [participant_name]

    # print all the data
    pprint.pp(participants)
    pprint.pp(events)

    print()

    # print attendee stats
    for pid in participants.keys():
        name = participants[pid]['name']
        num_events = len(participants[pid]['events'])
        print(f"{name} ({pid}) attended {num_events} events")

    print()

    # print attendance stats
    for event_name in events.keys():
        num_participants = len(events[event_name]['participants'])
        print(f"{event_name} had {num_participants} attendees")

if __name__ == "__main__":
    main()