"""DynamoDB utils."""

import json

from boto3.dynamodb.types import TypeSerializer
from src.aws_utils import parse_arn
from src.models import DownloadRequest


def get_table_name_from_arn(arn):
    """Extract DynamoDB table name from arn."""
    return parse_arn(arn)['resource'].split('/')[0]


def extract_download_request_from_dynamodb_item(
        dynamodb_item) -> (DownloadRequest, dict):
    """Parse dynamodb event record."""
    dynamodb_key = dynamodb_item['Keys']
    download_request_payload = dynamodb_item['NewImage']['request']['S']
    taskId = dynamodb_item['NewImage']['taskId']['S']
    download_request_dict = json.loads(download_request_payload)
    download_request_dict['tasksMessageId'] = taskId
    download_request = DownloadRequest(**download_request_dict)
    return download_request, dynamodb_key


type_serializer = TypeSerializer()


def build_update_item_expression_kwargs(to_update: dict):
    """Build kwargs for boto3 dynamodb update_item method."""
    keys = {}
    values = {}
    expressions = []
    for count, key_value in enumerate(to_update.items(), start=1):
        key, value = key_value
        key_name = f'#v{count}'
        value_name = f':v{count}'
        expressions.append(f'{key_name} = {value_name}')
        keys[key_name] = key
        values[value_name] = type_serializer.serialize(value)
    return dict(
        UpdateExpression=f'set {", ".join(expressions)}',
        ExpressionAttributeValues=values,
        ExpressionAttributeNames=keys
    )