import csv
import io


# Maps our field names to possible CSV column header aliases (case-insensitive)
FIELD_ALIASES = {
    'windows_id': ['windows_id', 'employeeid', 'employee_id', 'wid', 'id', 'user_id', 'samaccountname'],
    'first_name': ['first_name', 'firstname', 'givenname', 'given_name', 'prenom'],
    'last_name':  ['last_name', 'lastname', 'surname', 'sn', 'family_name', 'nom'],
    'email':      ['email', 'mail', 'email_address', 'emailaddress'],
    'department': ['department', 'dept', 'division'],
    'job_title':  ['job_title', 'title', 'position', 'jobtitle', 'job_position'],
    'phone':      ['phone', 'telephone', 'mobile', 'phonenumber', 'telephonenumber'],
    'location':   ['location', 'office', 'site', 'physicaldeliveryofficename'],
}


def parse_users_csv(file_stream):
    """
    Parse a CSV file stream and return (users_list, errors_list).

    Accepts BOM-prefixed UTF-8 or plain UTF-8. Column headers are
    matched case-insensitively against FIELD_ALIASES.
    """
    try:
        content = file_stream.read().decode('utf-8-sig')
    except (UnicodeDecodeError, AttributeError):
        return [], ['Could not decode file. Please use UTF-8 encoding.']

    reader = csv.DictReader(io.StringIO(content))

    if not reader.fieldnames:
        return [], ['CSV file is empty or has no header row.']

    # Build a lookup: normalised header -> our field name
    norm_headers = {h.lower().strip().replace(' ', '_'): h for h in reader.fieldnames}
    col_map = {}  # our_field -> actual_csv_header
    for field, aliases in FIELD_ALIASES.items():
        for alias in aliases:
            if alias in norm_headers:
                col_map[field] = norm_headers[alias]
                break

    errors = []
    users = []

    for row_num, row in enumerate(reader, start=2):
        user = {}
        for field in FIELD_ALIASES:
            csv_col = col_map.get(field)
            user[field] = (row.get(csv_col, '') or '').strip() if csv_col else ''

        wid = user.get('windows_id', '').strip()
        if not wid:
            errors.append(f'Row {row_num}: missing windows_id — skipped.')
            continue

        users.append(user)

    return users, errors