"""Lambda function module."""

import os

import common_config
import sns  # noqa
import util  # noqa

from constants import common
from constants import general
from constants import error


def validate_size(size):
    """Validate file size.

    Args:
        size (int): S3 file size

    Returns:
        bool: validation result

    """
    return size <= general.MAX_ALLOWED_FILE_SIZE


def validate_extension(extension):
    """Validate file extension.

    Args:
        extension (str): S3 file extension

    Returns:
        bool: validation result

    """
    return extension.lower() in general.ALLOWED_FILE_EXTENSIONS


def validate_path(key):
    """Validate file path.

    Args:
        key (str): S3 file key

    Returns:
        bool: validation result

    """
    head, tail = os.path.split(key)
    return head == common_config.S3_BUCKET_FOLDER


def validate_file(s3_object):
    """Validate file attributes.

    Args:
        s3_object (dict): Attributes of the file (s3.object)

    Returns:
        str: Error message or empty string (in case of success)

    """
    if not validate_path(s3_object['key']):
        return error.INVALID_PATH_MSG

    if not validate_size(s3_object['size']):
        return error.INVALID_SIZE_MSG

    parsed_attrs = util.parse_file_key(s3_object['key'])
    if not parsed_attrs:
        return error.INVALID_NAME_MSG

    if not validate_extension(parsed_attrs['extension']):
        return error.INVALID_EXTENSION_MSG
    return ''


def handler(event, context):
    """Lambda entry point."""
    if common_config.IGNORE_ALL_EVENTS is not None:
        common_config.logger.warning(common.IGNORE_MESSAGE)
        return
    s3_object = event['Records'][0]['s3']['object']
    key = s3_object.get('key')
    common_config.logger.info(
        'Starting verification process for {}'.format(key))
    validation_result = validate_file(s3_object)
    message = {
        's3_event': event,
        'attachment_attrs': util.parse_file_key(s3_object['key'])
    }
    if validation_result:
        error_message = 'Verification error: {} {}'.format(
            key, validation_result)
        common_config.logger.info(error_message)
        message.update({
            'status': 'ERROR',
            'detailed': error_message})
        sns.send_notification(
            common_config.SNS_ARN_FAIL, message)
    else:
        common_config.logger.info('Verification successfully finished.')
        sns.send_notification(
            common_config.SNS_ARN_SUCCESS, message)