"""
DynamoDB Client
=============

Provides dynamodb_resource attribute for connection to AWS DynamDB service.

https://aws.amazon.com/documentation/dynamodb/
"""

from copy import deepcopy

import boto3
from boto3.dynamodb import conditions
from botocore.client import Config
from oto import response

from masters_registry import config
from masters_registry import utils
from masters_registry.constant import field_const


dynamodb_resource = boto3.resource(
    'dynamodb', 'us-east-1', config=Config(max_pool_connections=1000))
client = dynamodb_resource.meta.client

ITEM_FIELD = 'Item'


def batch_update_item_fields(
        table, key, verb, expressions, attribute_names, attribute_values,
        batch_size=4000, force=False):
    """Util to update several fields within an item."""
    update_expression = '{} {}'.format(verb, ', '.join(expressions))
    if not expressions or batch_size > len(update_expression) and not force:
        return False
    update_item = getattr(table, 'update_item')

    kwargs = {
        'Key': key,
        'UpdateExpression': update_expression,
        'ExpressionAttributeNames': attribute_names,
    }
    if attribute_values:
        kwargs['ExpressionAttributeValues'] = attribute_values

    update_item(**kwargs)
    log_updated_timestamp(table, key)
    return True


def update_isrc_item_field(isrc, field_name, new_value):
    """Update field in entry in masters-active table with provided data.

    This function also updates `updated_timestamp` field so that
    Snowflake could correctly process data from DynamoDB.
    For details refer to MR-3000 ticket.

    Args:
        isrc (str): ISRC (Key in masters-active table)
        field_name (str): Name of field in isrc entry, e.g. territories
        new_value (object): Value to save into given field

    Returns:
        response.Response: dict with updated info
    """
    kwargs = {
        'TableName': config.DYNAMODB_MASTERS_ACTIVE,
        'Key': {field_const.ISRC: isrc},
        # Condition ensures that update will happen only if ISRC exists
        'ConditionExpression': conditions.Key(field_const.ISRC).eq(isrc),
        'UpdateExpression': 'SET {} = :new_value'.format(field_name),
        'ExpressionAttributeValues': {':new_value': new_value},
    }
    kwargs = _add_updated_timestamp_to_kwargs(kwargs)
    client.update_item(**kwargs)

    response_payload = {
        'isrc': isrc,
        'field_name': field_name,
        'saved_value': new_value
    }
    return response.Response(message=response_payload)


def _add_updated_timestamp_to_kwargs(update_kwargs):
    """Add expression to update `updated_timestamp` field of ISRC item.

    When performing update of ISRC item we want to log timestamp when
    given item was changed.

    Args:
          update_kwargs (dict): Kwargs for dynamo_client.update_item func

    Returns:
        dict: kwargs with added expression that updates timestamp field
    """
    update_timestamp_expression = 'updated_timestamp = :new_timestamp'
    timestamp_attribute_value = {
        ':new_timestamp': utils.get_timestamp_for_dynamo()
    }
    new_kwargs = deepcopy(update_kwargs)
    new_kwargs['UpdateExpression'] = ', '.join(
        [new_kwargs['UpdateExpression'], update_timestamp_expression])
    new_kwargs['ExpressionAttributeValues'].update(timestamp_attribute_value)
    return new_kwargs


def log_updated_timestamp(table, isrc):
    """Write updated_timestamp field for given isrc.

    Supposed to be used when performing actions with masters_active table.

    Args:
        table (object): DynamoDB table
        isrc (str): ISRC to update
    """
    kwargs = {
        'Key': isrc,
        'UpdateExpression': 'SET updated_timestamp = :r',
        'ExpressionAttributeValues': {':r': utils.get_timestamp_for_dynamo()},
    }
    table.update_item(**kwargs)
    return True


def update_isrc(isrc):
    """Replace or create an ISRC item in DynamoDB active table.

    Args:
        isrc (dict): ISRC item to be written

    Returns:
        response.Response: response object, containing an updated item
    """
    isrc[field_const.UPDATED_TIMESTAMP] = utils.get_timestamp_for_dynamo()

    kwargs = {
        'TableName': config.DYNAMODB_MASTERS_ACTIVE,
        'Item': isrc
    }
    client.put_item(**kwargs)
    return response.Response(isrc)