import csv

from ywalk.types import Connection, Mode, Place

FIELD_NAMES = ['Origin', 'Destination', 'Mode', 'Time']

class InputError(Exception):
    def __init__(self, message, file, line, context):
        super().__init__(message)
        self.message = message
        self.file = file
        self.line = line
        self.context = context

    def __str__(self):
        return f'{self.file}:{self.line}: {self.message}\n {self.context}'

def parse_row(row):
    for field in FIELD_NAMES:
        if row[field] is None:
            raise ValueError(f'Empty field \'{field}\'')

    # This is an enum lookup, not a creation. The Enum class replaces a custom
    # __new__ after class creation with one that only does lookups.
    # pylint: disable=no-value-for-parameter
    mode = Mode(row['Mode'])
    time = int(row['Time'])

    if time < 0:
        raise ValueError('Negative travel time')

    return Connection(Place(row['Origin']), Place(row['Destination']), mode, time)

def check_fieldnames(names):
    for name in FIELD_NAMES:
        if name not in names:
            raise ValueError(f'Missing field \'{name}\' in {names}')

def parse_tsv(path):
    with open(path, encoding='utf-8', newline='') as file:
        reader = csv.DictReader(file, dialect=csv.excel_tab)
        check_fieldnames(reader.fieldnames)
        for line, row in enumerate(reader):
            try:
                yield parse_row(row)
            except ValueError as err:
                raise InputError(err, path, line + 1, row) from err