moto/moto/dynamodb/models/__init__.py

from collections import defaultdict
import copy
import datetime
import decimal
import json
import re
import uuid

from collections import OrderedDict
from moto.core import BaseBackend, BaseModel, CloudFormationModel
from moto.core.utils import unix_time, unix_time_millis, BackendDict
from moto.core.exceptions import JsonRESTError
from moto.dynamodb.comparisons import get_filter_expression
from moto.dynamodb.comparisons import get_expected
from moto.dynamodb.exceptions import (
    InvalidIndexNameError,
    ItemSizeTooLarge,
    ItemSizeToUpdateTooLarge,
    HashKeyTooLong,
    RangeKeyTooLong,
    ConditionalCheckFailed,
    TransactionCanceledException,
    EmptyKeyAttributeException,
    InvalidAttributeTypeError,
    MultipleTransactionsException,
    TooManyTransactionsException,
    TableNotFoundException,
    ResourceNotFoundException,
    SourceTableNotFoundException,
    TableAlreadyExistsException,
    BackupNotFoundException,
    ResourceInUseException,
    StreamAlreadyEnabledException,
    MockValidationException,
    InvalidConversion,
)
from moto.dynamodb.models.utilities import bytesize
from moto.dynamodb.models.dynamo_type import DynamoType
from moto.dynamodb.parsing.executors import UpdateExpressionExecutor
from moto.dynamodb.parsing.expressions import UpdateExpressionParser
from moto.dynamodb.parsing.validators import UpdateExpressionValidator
from moto.dynamodb.limits import HASH_KEY_MAX_LENGTH, RANGE_KEY_MAX_LENGTH


class DynamoJsonEncoder(json.JSONEncoder):
    def default(self, o):
        if hasattr(o, "to_json"):
            return o.to_json()


def dynamo_json_dump(dynamo_object):
    return json.dumps(dynamo_object, cls=DynamoJsonEncoder)


# https://github.com/spulec/moto/issues/1874
# Ensure that the total size of an item does not exceed 400kb
class LimitedSizeDict(dict):
    def __init__(self, *args, **kwargs):
        self.update(*args, **kwargs)

    def __setitem__(self, key, value):
        current_item_size = sum(
            [
                item.size() if type(item) == DynamoType else bytesize(str(item))
                for item in (list(self.keys()) + list(self.values()))
            ]
        )
        new_item_size = bytesize(key) + (
            value.size() if type(value) == DynamoType else bytesize(str(value))
        )
        # Official limit is set to 400000 (400KB)
        # Manual testing confirms that the actual limit is between 409 and 410KB
        # We'll set the limit to something in between to be safe
        if (current_item_size + new_item_size) > 405000:
            raise ItemSizeTooLarge
        super().__setitem__(key, value)


class Item(BaseModel):
    def __init__(self, hash_key, range_key, attrs):
        self.hash_key = hash_key
        self.range_key = range_key

        self.attrs = LimitedSizeDict()
        for key, value in attrs.items():
            self.attrs[key] = DynamoType(value)

    def __eq__(self, other):
        return all(
            [
                self.hash_key == other.hash_key,
                self.range_key == other.range_key,
                self.attrs == other.attrs,
            ]
        )

    def __repr__(self):
        return "Item: {0}".format(self.to_json())

    def size(self):
        return sum(bytesize(key) + value.size() for key, value in self.attrs.items())

    def to_json(self):
        attributes = {}
        for attribute_key, attribute in self.attrs.items():
            attributes[attribute_key] = {attribute.type: attribute.value}

        return {"Attributes": attributes}

    def describe_attrs(self, attributes):
        if attributes:
            included = {}
            for key, value in self.attrs.items():
                if key in attributes:
                    included[key] = value
        else:
            included = self.attrs
        return {"Item": included}

    def validate_no_empty_key_values(self, attribute_updates, key_attributes):
        for attribute_name, update_action in attribute_updates.items():
            action = update_action.get("Action") or "PUT"  # PUT is default
            if action == "DELETE":
                continue
            new_value = next(iter(update_action["Value"].values()))
            if action == "PUT" and new_value == "" and attribute_name in key_attributes:
                raise EmptyKeyAttributeException

    def update_with_attribute_updates(self, attribute_updates):
        for attribute_name, update_action in attribute_updates.items():
            # Use default Action value, if no explicit Action is passed.
            # Default value is 'Put', according to
            # Boto3 DynamoDB.Client.update_item documentation.
            action = update_action.get("Action", "PUT")
            if action == "DELETE" and "Value" not in update_action:
                if attribute_name in self.attrs:
                    del self.attrs[attribute_name]
                continue
            new_value = list(update_action["Value"].values())[0]
            if action == "PUT":
                # TODO deal with other types
                if set(update_action["Value"].keys()) == set(["SS"]):
                    self.attrs[attribute_name] = DynamoType({"SS": new_value})
                elif isinstance(new_value, list):
                    self.attrs[attribute_name] = DynamoType({"L": new_value})
                elif isinstance(new_value, dict):
                    self.attrs[attribute_name] = DynamoType({"M": new_value})
                elif set(update_action["Value"].keys()) == set(["N"]):
                    self.attrs[attribute_name] = DynamoType({"N": new_value})
                elif set(update_action["Value"].keys()) == set(["NULL"]):
                    if attribute_name in self.attrs:
                        del self.attrs[attribute_name]
                else:
                    self.attrs[attribute_name] = DynamoType({"S": new_value})
            elif action == "ADD":
                if set(update_action["Value"].keys()) == set(["N"]):
                    existing = self.attrs.get(attribute_name, DynamoType({"N": "0"}))
                    self.attrs[attribute_name] = DynamoType(
                        {
                            "N": str(
                                decimal.Decimal(existing.value)
                                + decimal.Decimal(new_value)
                            )
                        }
                    )
                elif set(update_action["Value"].keys()) == set(["SS"]):
                    existing = self.attrs.get(attribute_name, DynamoType({"SS": {}}))
                    new_set = set(existing.value).union(set(new_value))
                    self.attrs[attribute_name] = DynamoType({"SS": list(new_set)})
                elif set(update_action["Value"].keys()) == {"L"}:
                    existing = self.attrs.get(attribute_name, DynamoType({"L": []}))
                    new_list = existing.value + new_value
                    self.attrs[attribute_name] = DynamoType({"L": new_list})
                else:
                    # TODO: implement other data types
                    raise NotImplementedError(
                        "ADD not supported for %s"
                        % ", ".join(update_action["Value"].keys())
                    )
            elif action == "DELETE":
                if set(update_action["Value"].keys()) == set(["SS"]):
                    existing = self.attrs.get(attribute_name, DynamoType({"SS": {}}))
                    new_set = set(existing.value).difference(set(new_value))
                    self.attrs[attribute_name] = DynamoType({"SS": list(new_set)})
                else:
                    raise NotImplementedError(
                        "ADD not supported for %s"
                        % ", ".join(update_action["Value"].keys())
                    )
            else:
                raise NotImplementedError(
                    "%s action not support for update_with_attribute_updates" % action
                )

    # Filter using projection_expression
    # Ensure a deep copy is used to filter, otherwise actual data will be removed
    def filter(self, projection_expression):
        expressions = [x.strip() for x in projection_expression.split(",")]
        top_level_expressions = [
            expr[0 : expr.index(".")] for expr in expressions if "." in expr
        ]
        for attr in list(self.attrs):
            if attr not in expressions and attr not in top_level_expressions:
                self.attrs.pop(attr)
            if attr in top_level_expressions:
                relevant_expressions = [
                    expr[len(attr + ".") :]
                    for expr in expressions
                    if expr.startswith(attr + ".")
                ]
                self.attrs[attr].filter(relevant_expressions)


class StreamRecord(BaseModel):
    def __init__(self, table, stream_type, event_name, old, new, seq):
        old_a = old.to_json()["Attributes"] if old is not None else {}
        new_a = new.to_json()["Attributes"] if new is not None else {}

        rec = old if old is not None else new
        keys = {table.hash_key_attr: rec.hash_key.to_json()}
        if table.range_key_attr is not None:
            keys[table.range_key_attr] = rec.range_key.to_json()

        self.record = {
            "eventID": uuid.uuid4().hex,
            "eventName": event_name,
            "eventSource": "aws:dynamodb",
            "eventVersion": "1.0",
            "awsRegion": "us-east-1",
            "dynamodb": {
                "StreamViewType": stream_type,
                "ApproximateCreationDateTime": datetime.datetime.utcnow().isoformat(),
                "SequenceNumber": str(seq),
                "SizeBytes": 1,
                "Keys": keys,
            },
        }

        if stream_type in ("NEW_IMAGE", "NEW_AND_OLD_IMAGES"):
            self.record["dynamodb"]["NewImage"] = new_a
        if stream_type in ("OLD_IMAGE", "NEW_AND_OLD_IMAGES"):
            self.record["dynamodb"]["OldImage"] = old_a

        # This is a substantial overestimate but it's the easiest to do now
        self.record["dynamodb"]["SizeBytes"] = len(
            dynamo_json_dump(self.record["dynamodb"])
        )

    def to_json(self):
        return self.record


class StreamShard(BaseModel):
    def __init__(self, account_id, table):
        self.account_id = account_id
        self.table = table
        self.id = "shardId-00000001541626099285-f35f62ef"
        self.starting_sequence_number = 1100000000017454423009
        self.items = []
        self.created_on = datetime.datetime.utcnow()

    def to_json(self):
        return {
            "ShardId": self.id,
            "SequenceNumberRange": {
                "StartingSequenceNumber": str(self.starting_sequence_number)
            },
        }

    def add(self, old, new):
        t = self.table.stream_specification["StreamViewType"]
        if old is None:
            event_name = "INSERT"
        elif new is None:
            event_name = "REMOVE"
        else:
            event_name = "MODIFY"
        seq = len(self.items) + self.starting_sequence_number
        self.items.append(StreamRecord(self.table, t, event_name, old, new, seq))
        result = None
        from moto.awslambda import lambda_backends

        for arn, esm in self.table.lambda_event_source_mappings.items():
            region = arn[
                len("arn:aws:lambda:") : arn.index(":", len("arn:aws:lambda:"))
            ]

            result = lambda_backends[self.account_id][region].send_dynamodb_items(
                arn, self.items, esm.event_source_arn
            )

        if result:
            self.items = []

    def get(self, start, quantity):
        start -= self.starting_sequence_number
        assert start >= 0
        end = start + quantity
        return [i.to_json() for i in self.items[start:end]]


class SecondaryIndex(BaseModel):
    def project(self, item):
        """
        Enforces the ProjectionType of this Index (LSI/GSI)
        Removes any non-wanted attributes from the item
        :param item:
        :return:
        """
        if self.projection:
            projection_type = self.projection.get("ProjectionType", None)
            key_attributes = self.table_key_attrs + [
                key["AttributeName"] for key in self.schema
            ]

            if projection_type == "KEYS_ONLY":
                item.filter(",".join(key_attributes))
            elif projection_type == "INCLUDE":
                allowed_attributes = key_attributes + self.projection.get(
                    "NonKeyAttributes", []
                )
                item.filter(",".join(allowed_attributes))
            # ALL is handled implicitly by not filtering
        return item


class LocalSecondaryIndex(SecondaryIndex):
    def __init__(self, index_name, schema, projection, table_key_attrs):
        self.name = index_name
        self.schema = schema
        self.projection = projection
        self.table_key_attrs = table_key_attrs

    def describe(self):
        return {
            "IndexName": self.name,
            "KeySchema": self.schema,
            "Projection": self.projection,
        }

    @staticmethod
    def create(dct, table_key_attrs):
        return LocalSecondaryIndex(
            index_name=dct["IndexName"],
            schema=dct["KeySchema"],
            projection=dct["Projection"],
            table_key_attrs=table_key_attrs,
        )


class GlobalSecondaryIndex(SecondaryIndex):
    def __init__(
        self,
        index_name,
        schema,
        projection,
        table_key_attrs,
        status="ACTIVE",
        throughput=None,
    ):
        self.name = index_name
        self.schema = schema
        self.projection = projection
        self.table_key_attrs = table_key_attrs
        self.status = status
        self.throughput = throughput or {
            "ReadCapacityUnits": 0,
            "WriteCapacityUnits": 0,
        }

    def describe(self):
        return {
            "IndexName": self.name,
            "KeySchema": self.schema,
            "Projection": self.projection,
            "IndexStatus": self.status,
            "ProvisionedThroughput": self.throughput,
        }

    @staticmethod
    def create(dct, table_key_attrs):
        return GlobalSecondaryIndex(
            index_name=dct["IndexName"],
            schema=dct["KeySchema"],
            projection=dct["Projection"],
            table_key_attrs=table_key_attrs,
            throughput=dct.get("ProvisionedThroughput", None),
        )

    def update(self, u):
        self.name = u.get("IndexName", self.name)
        self.schema = u.get("KeySchema", self.schema)
        self.projection = u.get("Projection", self.projection)
        self.throughput = u.get("ProvisionedThroughput", self.throughput)


class Table(CloudFormationModel):
    def __init__(
        self,
        table_name,
        account_id,
        region,
        schema=None,
        attr=None,
        throughput=None,
        billing_mode=None,
        indexes=None,
        global_indexes=None,
        streams=None,
        sse_specification=None,
        tags=None,
    ):
        self.name = table_name
        self.account_id = account_id
        self.attr = attr
        self.schema = schema
        self.range_key_attr = None
        self.hash_key_attr = None
        self.range_key_type = None
        self.hash_key_type = None
        for elem in schema:
            attr_type = [
                a["AttributeType"]
                for a in attr
                if a["AttributeName"] == elem["AttributeName"]
            ][0]
            if elem["KeyType"] == "HASH":
                self.hash_key_attr = elem["AttributeName"]
                self.hash_key_type = attr_type
            else:
                self.range_key_attr = elem["AttributeName"]
                self.range_key_type = attr_type
        self.table_key_attrs = [
            key for key in (self.hash_key_attr, self.range_key_attr) if key
        ]
        self.billing_mode = billing_mode
        if throughput is None:
            self.throughput = {"WriteCapacityUnits": 0, "ReadCapacityUnits": 0}
        else:
            self.throughput = throughput
        self.throughput["NumberOfDecreasesToday"] = 0
        self.indexes = [
            LocalSecondaryIndex.create(i, self.table_key_attrs)
            for i in (indexes if indexes else [])
        ]
        self.global_indexes = [
            GlobalSecondaryIndex.create(i, self.table_key_attrs)
            for i in (global_indexes if global_indexes else [])
        ]
        self.created_at = datetime.datetime.utcnow()
        self.items = defaultdict(dict)
        self.table_arn = self._generate_arn(table_name)
        self.tags = tags or []
        self.ttl = {
            "TimeToLiveStatus": "DISABLED"  # One of 'ENABLING'|'DISABLING'|'ENABLED'|'DISABLED',
            # 'AttributeName': 'string'  # Can contain this
        }
        self.stream_specification = {"StreamEnabled": False}
        self.latest_stream_label = None
        self.stream_shard = None
        self.set_stream_specification(streams)
        self.lambda_event_source_mappings = {}
        self.continuous_backups = {
            "ContinuousBackupsStatus": "ENABLED",  # One of 'ENABLED'|'DISABLED', it's enabled by default
            "PointInTimeRecoveryDescription": {
                "PointInTimeRecoveryStatus": "DISABLED"  # One of 'ENABLED'|'DISABLED'
            },
        }
        self.sse_specification = sse_specification
        if sse_specification and "KMSMasterKeyId" not in self.sse_specification:
            self.sse_specification["KMSMasterKeyId"] = self._get_default_encryption_key(
                account_id, region
            )

    def _get_default_encryption_key(self, account_id, region):
        from moto.kms import kms_backends

        # https://aws.amazon.com/kms/features/#AWS_Service_Integration
        # An AWS managed CMK is created automatically when you first create
        # an encrypted resource using an AWS service integrated with KMS.
        kms = kms_backends[account_id][region]
        ddb_alias = "alias/aws/dynamodb"
        if not kms.alias_exists(ddb_alias):
            key = kms.create_key(
                policy="",
                key_usage="ENCRYPT_DECRYPT",
                key_spec="SYMMETRIC_DEFAULT",
                description="Default master key that protects my DynamoDB table storage",
                tags=None,
            )
            kms.add_alias(key.id, ddb_alias)
        ebs_key = kms.describe_key(ddb_alias)
        return ebs_key.arn

    @classmethod
    def has_cfn_attr(cls, attr):
        return attr in ["Arn", "StreamArn"]

    def get_cfn_attribute(self, attribute_name):
        from moto.cloudformation.exceptions import UnformattedGetAttTemplateException

        if attribute_name == "Arn":
            return self.table_arn
        elif attribute_name == "StreamArn" and self.stream_specification:
            return self.describe()["TableDescription"]["LatestStreamArn"]

        raise UnformattedGetAttTemplateException()

    @property
    def physical_resource_id(self):
        return self.name

    @property
    def attribute_keys(self):
        # A set of all the hash or range attributes for all indexes
        def keys_from_index(idx):
            schema = idx.schema
            return [attr["AttributeName"] for attr in schema]

        fieldnames = copy.copy(self.table_key_attrs)
        for idx in self.indexes + self.global_indexes:
            fieldnames += keys_from_index(idx)
        return fieldnames

    @staticmethod
    def cloudformation_name_type():
        return "TableName"

    @staticmethod
    def cloudformation_type():
        # https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-dynamodb-table.html
        return "AWS::DynamoDB::Table"

    @classmethod
    def create_from_cloudformation_json(
        cls, resource_name, cloudformation_json, account_id, region_name, **kwargs
    ):
        properties = cloudformation_json["Properties"]
        params = {}

        if "KeySchema" in properties:
            params["schema"] = properties["KeySchema"]
        if "AttributeDefinitions" in properties:
            params["attr"] = properties["AttributeDefinitions"]
        if "GlobalSecondaryIndexes" in properties:
            params["global_indexes"] = properties["GlobalSecondaryIndexes"]
        if "ProvisionedThroughput" in properties:
            params["throughput"] = properties["ProvisionedThroughput"]
        if "LocalSecondaryIndexes" in properties:
            params["indexes"] = properties["LocalSecondaryIndexes"]
        if "StreamSpecification" in properties:
            params["streams"] = properties["StreamSpecification"]

        table = dynamodb_backends[account_id][region_name].create_table(
            name=resource_name, **params
        )
        return table

    @classmethod
    def delete_from_cloudformation_json(
        cls, resource_name, cloudformation_json, account_id, region_name
    ):
        table = dynamodb_backends[account_id][region_name].delete_table(
            name=resource_name
        )
        return table

    def _generate_arn(self, name):
        return f"arn:aws:dynamodb:us-east-1:{self.account_id}:table/{name}"

    def set_stream_specification(self, streams):
        self.stream_specification = streams
        if streams and (streams.get("StreamEnabled") or streams.get("StreamViewType")):
            self.stream_specification["StreamEnabled"] = True
            self.latest_stream_label = datetime.datetime.utcnow().isoformat()
            self.stream_shard = StreamShard(self.account_id, self)
        else:
            self.stream_specification = {"StreamEnabled": False}

    def describe(self, base_key="TableDescription"):
        results = {
            base_key: {
                "AttributeDefinitions": self.attr,
                "ProvisionedThroughput": self.throughput,
                "BillingModeSummary": {"BillingMode": self.billing_mode},
                "TableSizeBytes": 0,
                "TableName": self.name,
                "TableStatus": "ACTIVE",
                "TableArn": self.table_arn,
                "KeySchema": self.schema,
                "ItemCount": len(self),
                "CreationDateTime": unix_time(self.created_at),
                "GlobalSecondaryIndexes": [
                    index.describe() for index in self.global_indexes
                ],
                "LocalSecondaryIndexes": [index.describe() for index in self.indexes],
            }
        }
        if self.latest_stream_label:
            results[base_key]["LatestStreamLabel"] = self.latest_stream_label
            results[base_key][
                "LatestStreamArn"
            ] = f"{self.table_arn}/stream/{self.latest_stream_label}"
        if self.stream_specification and self.stream_specification["StreamEnabled"]:
            results[base_key]["StreamSpecification"] = self.stream_specification
        if self.sse_specification and self.sse_specification.get("Enabled") is True:
            results[base_key]["SSEDescription"] = {
                "Status": "ENABLED",
                "SSEType": "KMS",
                "KMSMasterKeyArn": self.sse_specification.get("KMSMasterKeyId"),
            }
        return results

    def __len__(self):
        return sum(
            [(len(value) if self.has_range_key else 1) for value in self.items.values()]
        )

    @property
    def hash_key_names(self):
        keys = [self.hash_key_attr]
        for index in self.global_indexes:
            hash_key = None
            for key in index.schema:
                if key["KeyType"] == "HASH":
                    hash_key = key["AttributeName"]
            keys.append(hash_key)
        return keys

    @property
    def range_key_names(self):
        keys = [self.range_key_attr]
        for index in self.global_indexes:
            range_key = None
            for key in index.schema:
                if key["KeyType"] == "RANGE":
                    range_key = keys.append(key["AttributeName"])
            keys.append(range_key)
        return keys

    def _validate_key_sizes(self, item_attrs):
        for hash_name in self.hash_key_names:
            hash_value = item_attrs.get(hash_name)
            if hash_value:
                if DynamoType(hash_value).size() > HASH_KEY_MAX_LENGTH:
                    raise HashKeyTooLong
        for range_name in self.range_key_names:
            range_value = item_attrs.get(range_name)
            if range_value:
                if DynamoType(range_value).size() > RANGE_KEY_MAX_LENGTH:
                    raise RangeKeyTooLong

    def _validate_item_types(self, item_attrs):
        for key, value in item_attrs.items():
            if type(value) == dict:
                self._validate_item_types(value)
            elif type(value) == int and key == "N":
                raise InvalidConversion

    def put_item(
        self,
        item_attrs,
        expected=None,
        condition_expression=None,
        expression_attribute_names=None,
        expression_attribute_values=None,
        overwrite=False,
    ):
        if self.hash_key_attr not in item_attrs.keys():
            raise MockValidationException(
                "One or more parameter values were invalid: Missing the key "
                + self.hash_key_attr
                + " in the item"
            )
        hash_value = DynamoType(item_attrs.get(self.hash_key_attr))
        if self.has_range_key:
            if self.range_key_attr not in item_attrs.keys():
                raise MockValidationException(
                    "One or more parameter values were invalid: Missing the key "
                    + self.range_key_attr
                    + " in the item"
                )
            range_value = DynamoType(item_attrs.get(self.range_key_attr))
        else:
            range_value = None

        if hash_value.type != self.hash_key_type:
            raise InvalidAttributeTypeError(
                self.hash_key_attr,
                expected_type=self.hash_key_type,
                actual_type=hash_value.type,
            )
        if range_value and range_value.type != self.range_key_type:
            raise InvalidAttributeTypeError(
                self.range_key_attr,
                expected_type=self.range_key_type,
                actual_type=range_value.type,
            )

        self._validate_key_sizes(item_attrs)

        self._validate_item_types(item_attrs)

        if expected is None:
            expected = {}
            lookup_range_value = range_value
        else:
            expected_range_value = expected.get(self.range_key_attr, {}).get("Value")
            if expected_range_value is None:
                lookup_range_value = range_value
            else:
                lookup_range_value = DynamoType(expected_range_value)
        current = self.get_item(hash_value, lookup_range_value)
        item = Item(hash_value, range_value, item_attrs)

        if not overwrite:
            if not get_expected(expected).expr(current):
                raise ConditionalCheckFailed
            condition_op = get_filter_expression(
                condition_expression,
                expression_attribute_names,
                expression_attribute_values,
            )
            if not condition_op.expr(current):
                raise ConditionalCheckFailed

        if range_value:
            self.items[hash_value][range_value] = item
        else:
            self.items[hash_value] = item

        if self.stream_shard is not None:
            self.stream_shard.add(current, item)

        return item

    def __nonzero__(self):
        return True

    def __bool__(self):
        return self.__nonzero__()

    @property
    def has_range_key(self):
        return self.range_key_attr is not None

    def get_item(self, hash_key, range_key=None, projection_expression=None):
        if self.has_range_key and not range_key:
            raise MockValidationException(
                "Table has a range key, but no range key was passed into get_item"
            )
        try:
            result = None

            if range_key:
                result = self.items[hash_key][range_key]
            elif hash_key in self.items:
                result = self.items[hash_key]

            if projection_expression and result:
                result = copy.deepcopy(result)
                result.filter(projection_expression)

            if not result:
                raise KeyError

            return result
        except KeyError:
            return None

    def delete_item(self, hash_key, range_key):
        try:
            if range_key:
                item = self.items[hash_key].pop(range_key)
            else:
                item = self.items.pop(hash_key)

            if self.stream_shard is not None:
                self.stream_shard.add(item, None)

            return item
        except KeyError:
            return None

    def query(
        self,
        hash_key,
        range_comparison,
        range_objs,
        limit,
        exclusive_start_key,
        scan_index_forward,
        projection_expression,
        index_name=None,
        filter_expression=None,
        **filter_kwargs,
    ):
        results = []

        if index_name:
            all_indexes = self.all_indexes()
            indexes_by_name = dict((i.name, i) for i in all_indexes)
            if index_name not in indexes_by_name:
                raise MockValidationException(
                    "Invalid index: %s for table: %s. Available indexes are: %s"
                    % (index_name, self.name, ", ".join(indexes_by_name.keys()))
                )

            index = indexes_by_name[index_name]
            try:
                index_hash_key = [
                    key for key in index.schema if key["KeyType"] == "HASH"
                ][0]
            except IndexError:
                raise MockValidationException(
                    "Missing Hash Key. KeySchema: %s" % index.name
                )

            try:
                index_range_key = [
                    key for key in index.schema if key["KeyType"] == "RANGE"
                ][0]
            except IndexError:
                index_range_key = None

            possible_results = []
            for item in self.all_items():
                if not isinstance(item, Item):
                    continue
                item_hash_key = item.attrs.get(index_hash_key["AttributeName"])
                if index_range_key is None:
                    if item_hash_key and item_hash_key == hash_key:
                        possible_results.append(item)
                else:
                    item_range_key = item.attrs.get(index_range_key["AttributeName"])
                    if item_hash_key and item_hash_key == hash_key and item_range_key:
                        possible_results.append(item)
        else:
            possible_results = [
                item
                for item in list(self.all_items())
                if isinstance(item, Item) and item.hash_key == hash_key
            ]

        if range_comparison:
            if index_name and not index_range_key:
                raise ValueError(
                    "Range Key comparison but no range key found for index: %s"
                    % index_name
                )

            elif index_name:
                for result in possible_results:
                    if result.attrs.get(index_range_key["AttributeName"]).compare(
                        range_comparison, range_objs
                    ):
                        results.append(result)
            else:
                for result in possible_results:
                    if result.range_key.compare(range_comparison, range_objs):
                        results.append(result)

        if filter_kwargs:
            for result in possible_results:
                for field, value in filter_kwargs.items():
                    dynamo_types = [
                        DynamoType(ele) for ele in value["AttributeValueList"]
                    ]
                    if result.attrs.get(field).compare(
                        value["ComparisonOperator"], dynamo_types
                    ):
                        results.append(result)

        if not range_comparison and not filter_kwargs:
            # If we're not filtering on range key or on an index return all
            # values
            results = possible_results

        if index_name:

            if index_range_key:

                # Convert to float if necessary to ensure proper ordering
                def conv(x):
                    return float(x.value) if x.type == "N" else x.value

                results.sort(
                    key=lambda item: conv(item.attrs[index_range_key["AttributeName"]])
                    if item.attrs.get(index_range_key["AttributeName"])
                    else None
                )
        else:
            results.sort(key=lambda item: item.range_key)

        if scan_index_forward is False:
            results.reverse()

        scanned_count = len(list(self.all_items()))

        results = copy.deepcopy(results)
        if index_name:
            index = self.get_index(index_name)
            for result in results:
                index.project(result)

        results, last_evaluated_key = self._trim_results(
            results, limit, exclusive_start_key, scanned_index=index_name
        )

        if filter_expression is not None:
            results = [item for item in results if filter_expression.expr(item)]

        if projection_expression:
            for result in results:
                result.filter(projection_expression)

        return results, scanned_count, last_evaluated_key

    def all_items(self):
        for hash_set in self.items.values():
            if self.range_key_attr:
                for item in hash_set.values():
                    yield item
            else:
                yield hash_set

    def all_indexes(self):
        return (self.global_indexes or []) + (self.indexes or [])

    def get_index(self, index_name, error_if_not=False):
        all_indexes = self.all_indexes()
        indexes_by_name = dict((i.name, i) for i in all_indexes)
        if error_if_not and index_name not in indexes_by_name:
            raise InvalidIndexNameError(
                "The table does not have the specified index: %s" % index_name
            )
        return indexes_by_name[index_name]

    def has_idx_items(self, index_name):

        idx = self.get_index(index_name)
        idx_col_set = set([i["AttributeName"] for i in idx.schema])

        for hash_set in self.items.values():
            if self.range_key_attr:
                for item in hash_set.values():
                    if idx_col_set.issubset(set(item.attrs)):
                        yield item
            else:
                if idx_col_set.issubset(set(hash_set.attrs)):
                    yield hash_set

    def scan(
        self,
        filters,
        limit,
        exclusive_start_key,
        filter_expression=None,
        index_name=None,
        projection_expression=None,
    ):
        results = []
        scanned_count = 0

        if index_name:
            self.get_index(index_name, error_if_not=True)
            items = self.has_idx_items(index_name)
        else:
            items = self.all_items()

        for item in items:
            scanned_count += 1
            passes_all_conditions = True
            for (
                attribute_name,
                (comparison_operator, comparison_objs),
            ) in filters.items():
                attribute = item.attrs.get(attribute_name)

                if attribute:
                    # Attribute found
                    if not attribute.compare(comparison_operator, comparison_objs):
                        passes_all_conditions = False
                        break
                elif comparison_operator == "NULL":
                    # Comparison is NULL and we don't have the attribute
                    continue
                else:
                    # No attribute found and comparison is no NULL. This item
                    # fails
                    passes_all_conditions = False
                    break

            if passes_all_conditions:
                results.append(item)

        results, last_evaluated_key = self._trim_results(
            results, limit, exclusive_start_key, scanned_index=index_name
        )

        if filter_expression is not None:
            results = [item for item in results if filter_expression.expr(item)]

        if projection_expression:
            results = copy.deepcopy(results)
            for result in results:
                result.filter(projection_expression)

        return results, scanned_count, last_evaluated_key

    def _trim_results(self, results, limit, exclusive_start_key, scanned_index=None):
        if exclusive_start_key is not None:
            hash_key = DynamoType(exclusive_start_key.get(self.hash_key_attr))
            range_key = exclusive_start_key.get(self.range_key_attr)
            if range_key is not None:
                range_key = DynamoType(range_key)
            for i in range(len(results)):
                if (
                    results[i].hash_key == hash_key
                    and results[i].range_key == range_key
                ):
                    results = results[i + 1 :]
                    break

        last_evaluated_key = None
        size_limit = 1000000  # DynamoDB has a 1MB size limit
        item_size = sum(res.size() for res in results)
        if item_size > size_limit:
            item_size = idx = 0
            while item_size + results[idx].size() < size_limit:
                item_size += results[idx].size()
                idx += 1
            limit = min(limit, idx) if limit else idx
        if limit and len(results) > limit:
            results = results[:limit]
            last_evaluated_key = {self.hash_key_attr: results[-1].hash_key}
            if results[-1].range_key is not None:
                last_evaluated_key[self.range_key_attr] = results[-1].range_key

            if scanned_index:
                idx = self.get_index(scanned_index)
                idx_col_list = [i["AttributeName"] for i in idx.schema]
                for col in idx_col_list:
                    last_evaluated_key[col] = results[-1].attrs[col]

        return results, last_evaluated_key

    def delete(self, account_id, region_name):
        dynamodb_backends[account_id][region_name].delete_table(self.name)


class RestoredTable(Table):
    def __init__(self, name, account_id, region, backup):
        params = self._parse_params_from_backup(backup)
        super().__init__(name, account_id=account_id, region=region, **params)
        self.indexes = copy.deepcopy(backup.table.indexes)
        self.global_indexes = copy.deepcopy(backup.table.global_indexes)
        self.items = copy.deepcopy(backup.table.items)
        # Restore Attrs
        self.source_backup_arn = backup.arn
        self.source_table_arn = backup.table.table_arn
        self.restore_date_time = self.created_at

    @staticmethod
    def _parse_params_from_backup(backup):
        params = {
            "schema": copy.deepcopy(backup.table.schema),
            "attr": copy.deepcopy(backup.table.attr),
            "throughput": copy.deepcopy(backup.table.throughput),
        }
        return params

    def describe(self, base_key="TableDescription"):
        result = super().describe(base_key=base_key)
        result[base_key]["RestoreSummary"] = {
            "SourceBackupArn": self.source_backup_arn,
            "SourceTableArn": self.source_table_arn,
            "RestoreDateTime": unix_time(self.restore_date_time),
            "RestoreInProgress": False,
        }
        return result


class RestoredPITTable(Table):
    def __init__(self, name, account_id, region, source):
        params = self._parse_params_from_table(source)
        super().__init__(name, account_id=account_id, region=region, **params)
        self.indexes = copy.deepcopy(source.indexes)
        self.global_indexes = copy.deepcopy(source.global_indexes)
        self.items = copy.deepcopy(source.items)
        # Restore Attrs
        self.source_table_arn = source.table_arn
        self.restore_date_time = self.created_at

    @staticmethod
    def _parse_params_from_table(table):
        params = {
            "schema": copy.deepcopy(table.schema),
            "attr": copy.deepcopy(table.attr),
            "throughput": copy.deepcopy(table.throughput),
        }
        return params

    def describe(self, base_key="TableDescription"):
        result = super().describe(base_key=base_key)
        result[base_key]["RestoreSummary"] = {
            "SourceTableArn": self.source_table_arn,
            "RestoreDateTime": unix_time(self.restore_date_time),
            "RestoreInProgress": False,
        }
        return result


class Backup(object):
    def __init__(self, backend, name, table, status=None, type_=None):
        self.backend = backend
        self.name = name
        self.table = copy.deepcopy(table)
        self.status = status or "AVAILABLE"
        self.type = type_ or "USER"
        self.creation_date_time = datetime.datetime.utcnow()
        self.identifier = self._make_identifier()

    def _make_identifier(self):
        timestamp = int(unix_time_millis(self.creation_date_time))
        timestamp_padded = str("0" + str(timestamp))[-16:16]
        guid = str(uuid.uuid4())
        guid_shortened = guid[:8]
        return "{}-{}".format(timestamp_padded, guid_shortened)

    @property
    def arn(self):
        return "arn:aws:dynamodb:{region}:{account}:table/{table_name}/backup/{identifier}".format(
            region=self.backend.region_name,
            account=self.backend.account_id,
            table_name=self.table.name,
            identifier=self.identifier,
        )

    @property
    def details(self):
        details = {
            "BackupArn": self.arn,
            "BackupName": self.name,
            "BackupSizeBytes": 123,
            "BackupStatus": self.status,
            "BackupType": self.type,
            "BackupCreationDateTime": unix_time(self.creation_date_time),
        }
        return details

    @property
    def summary(self):
        summary = {
            "TableName": self.table.name,
            # 'TableId': 'string',
            "TableArn": self.table.table_arn,
            "BackupArn": self.arn,
            "BackupName": self.name,
            "BackupCreationDateTime": unix_time(self.creation_date_time),
            # 'BackupExpiryDateTime': datetime(2015, 1, 1),
            "BackupStatus": self.status,
            "BackupType": self.type,
            "BackupSizeBytes": 123,
        }
        return summary

    @property
    def description(self):
        source_table_details = self.table.describe()["TableDescription"]
        source_table_details["TableCreationDateTime"] = source_table_details[
            "CreationDateTime"
        ]
        description = {
            "BackupDetails": self.details,
            "SourceTableDetails": source_table_details,
        }
        return description


class DynamoDBBackend(BaseBackend):
    def __init__(self, region_name, account_id):
        super().__init__(region_name, account_id)
        self.tables = OrderedDict()
        self.backups = OrderedDict()

    @staticmethod
    def default_vpc_endpoint_service(service_region, zones):
        """Default VPC endpoint service."""
        # No 'vpce' in the base endpoint DNS name
        return BaseBackend.default_vpc_endpoint_service_factory(
            service_region,
            zones,
            "dynamodb",
            "Gateway",
            private_dns_names=False,
            base_endpoint_dns_names=[f"dynamodb.{service_region}.amazonaws.com"],
        )

    def create_table(self, name, **params):
        if name in self.tables:
            raise ResourceInUseException
        table = Table(
            name, account_id=self.account_id, region=self.region_name, **params
        )
        self.tables[name] = table
        return table

    def delete_table(self, name):
        if name not in self.tables:
            raise ResourceNotFoundException
        return self.tables.pop(name, None)

    def describe_endpoints(self):
        return [
            {
                "Address": "dynamodb.{}.amazonaws.com".format(self.region_name),
                "CachePeriodInMinutes": 1440,
            }
        ]

    def tag_resource(self, table_arn, tags):
        for table in self.tables:
            if self.tables[table].table_arn == table_arn:
                self.tables[table].tags.extend(tags)

    def untag_resource(self, table_arn, tag_keys):
        for table in self.tables:
            if self.tables[table].table_arn == table_arn:
                self.tables[table].tags = [
                    tag for tag in self.tables[table].tags if tag["Key"] not in tag_keys
                ]

    def list_tags_of_resource(self, table_arn):
        for table in self.tables:
            if self.tables[table].table_arn == table_arn:
                return self.tables[table].tags
        raise ResourceNotFoundException

    def list_tables(self, limit, exclusive_start_table_name):
        all_tables = list(self.tables.keys())

        if exclusive_start_table_name:
            try:
                last_table_index = all_tables.index(exclusive_start_table_name)
            except ValueError:
                start = len(all_tables)
            else:
                start = last_table_index + 1
        else:
            start = 0

        if limit:
            tables = all_tables[start : start + limit]
        else:
            tables = all_tables[start:]

        if limit and len(all_tables) > start + limit:
            return tables, tables[-1]
        return tables, None

    def describe_table(self, name):
        table = self.get_table(name)
        return table.describe(base_key="Table")

    def update_table(
        self,
        name,
        attr_definitions,
        global_index,
        throughput,
        billing_mode,
        stream_spec,
    ):
        table = self.get_table(name)
        if attr_definitions:
            table.attr = attr_definitions
        if global_index:
            table = self.update_table_global_indexes(name, global_index)
        if throughput:
            table = self.update_table_throughput(name, throughput)
        if billing_mode:
            table = self.update_table_billing_mode(name, billing_mode)
        if stream_spec:
            table = self.update_table_streams(name, stream_spec)
        return table

    def update_table_throughput(self, name, throughput):
        table = self.tables[name]
        table.throughput = throughput
        return table

    def update_table_billing_mode(self, name, billing_mode):
        table = self.tables[name]
        table.billing_mode = billing_mode
        return table

    def update_table_streams(self, name, stream_specification):
        table = self.tables[name]
        if (
            stream_specification.get("StreamEnabled")
            or stream_specification.get("StreamViewType")
        ) and table.latest_stream_label:
            raise StreamAlreadyEnabledException
        table.set_stream_specification(stream_specification)
        return table

    def update_table_global_indexes(self, name, global_index_updates):
        table = self.tables[name]
        gsis_by_name = dict((i.name, i) for i in table.global_indexes)
        for gsi_update in global_index_updates:
            gsi_to_create = gsi_update.get("Create")
            gsi_to_update = gsi_update.get("Update")
            gsi_to_delete = gsi_update.get("Delete")

            if gsi_to_delete:
                index_name = gsi_to_delete["IndexName"]
                if index_name not in gsis_by_name:
                    raise ValueError(
                        "Global Secondary Index does not exist, but tried to delete: %s"
                        % gsi_to_delete["IndexName"]
                    )

                del gsis_by_name[index_name]

            if gsi_to_update:
                index_name = gsi_to_update["IndexName"]
                if index_name not in gsis_by_name:
                    raise ValueError(
                        "Global Secondary Index does not exist, but tried to update: %s"
                        % index_name
                    )
                gsis_by_name[index_name].update(gsi_to_update)

            if gsi_to_create:
                if gsi_to_create["IndexName"] in gsis_by_name:
                    raise ValueError(
                        "Global Secondary Index already exists: %s"
                        % gsi_to_create["IndexName"]
                    )

                gsis_by_name[gsi_to_create["IndexName"]] = GlobalSecondaryIndex.create(
                    gsi_to_create, table.table_key_attrs
                )

        # in python 3.6, dict.values() returns a dict_values object, but we expect it to be a list in other
        # parts of the codebase
        table.global_indexes = list(gsis_by_name.values())
        return table

    def put_item(
        self,
        table_name,
        item_attrs,
        expected=None,
        condition_expression=None,
        expression_attribute_names=None,
        expression_attribute_values=None,
        overwrite=False,
    ):
        table = self.get_table(table_name)
        return table.put_item(
            item_attrs,
            expected,
            condition_expression,
            expression_attribute_names,
            expression_attribute_values,
            overwrite,
        )

    def get_table_keys_name(self, table_name, keys):
        """
        Given a set of keys, extracts the key and range key
        """
        table = self.tables.get(table_name)
        if not table:
            return None, None
        else:
            if len(keys) == 1:
                for key in keys:
                    if key in table.hash_key_names:
                        return key, None
            # for potential_hash, potential_range in zip(table.hash_key_names, table.range_key_names):
            #     if set([potential_hash, potential_range]) == set(keys):
            #         return potential_hash, potential_range
            potential_hash, potential_range = None, None
            for key in set(keys):
                if key in table.hash_key_names:
                    potential_hash = key
                elif key in table.range_key_names:
                    potential_range = key
            return potential_hash, potential_range

    def get_keys_value(self, table, keys):
        if table.hash_key_attr not in keys or (
            table.has_range_key and table.range_key_attr not in keys
        ):
            # "Table has a range key, but no range key was passed into get_item"
            raise MockValidationException("Validation Exception")
        hash_key = DynamoType(keys[table.hash_key_attr])
        range_key = (
            DynamoType(keys[table.range_key_attr]) if table.has_range_key else None
        )
        return hash_key, range_key

    def get_schema(self, table_name, index_name):
        table = self.get_table(table_name)
        if index_name:
            all_indexes = (table.global_indexes or []) + (table.indexes or [])
            indexes_by_name = dict((i.name, i) for i in all_indexes)
            if index_name not in indexes_by_name:
                raise ResourceNotFoundException(
                    "Invalid index: {} for table: {}. Available indexes are: {}".format(
                        index_name, table_name, ", ".join(indexes_by_name.keys())
                    )
                )

            return indexes_by_name[index_name].schema
        else:
            return table.schema

    def get_table(self, table_name):
        if table_name not in self.tables:
            raise ResourceNotFoundException()
        return self.tables.get(table_name)

    def get_item(self, table_name, keys, projection_expression=None):
        table = self.get_table(table_name)
        hash_key, range_key = self.get_keys_value(table, keys)
        return table.get_item(hash_key, range_key, projection_expression)

    def query(
        self,
        table_name,
        hash_key_dict,
        range_comparison,
        range_value_dicts,
        limit,
        exclusive_start_key,
        scan_index_forward,
        projection_expression,
        index_name=None,
        expr_names=None,
        expr_values=None,
        filter_expression=None,
        **filter_kwargs,
    ):
        table = self.get_table(table_name)

        hash_key = DynamoType(hash_key_dict)
        range_values = [DynamoType(range_value) for range_value in range_value_dicts]

        filter_expression = get_filter_expression(
            filter_expression, expr_names, expr_values
        )

        return table.query(
            hash_key,
            range_comparison,
            range_values,
            limit,
            exclusive_start_key,
            scan_index_forward,
            projection_expression,
            index_name,
            filter_expression,
            **filter_kwargs,
        )

    def scan(
        self,
        table_name,
        filters,
        limit,
        exclusive_start_key,
        filter_expression,
        expr_names,
        expr_values,
        index_name,
        projection_expression,
    ):
        table = self.get_table(table_name)

        scan_filters = {}
        for key, (comparison_operator, comparison_values) in filters.items():
            dynamo_types = [DynamoType(value) for value in comparison_values]
            scan_filters[key] = (comparison_operator, dynamo_types)

        filter_expression = get_filter_expression(
            filter_expression, expr_names, expr_values
        )

        return table.scan(
            scan_filters,
            limit,
            exclusive_start_key,
            filter_expression,
            index_name,
            projection_expression,
        )

    def update_item(
        self,
        table_name,
        key,
        update_expression,
        expression_attribute_names,
        expression_attribute_values,
        attribute_updates=None,
        expected=None,
        condition_expression=None,
    ):
        table = self.get_table(table_name)

        # Support spaces between operators in an update expression
        # E.g. `a = b + c` -> `a=b+c`
        if update_expression:
            # Parse expression to get validation errors
            update_expression_ast = UpdateExpressionParser.make(update_expression)
            update_expression = re.sub(r"\s*([=\+-])\s*", "\\1", update_expression)
            update_expression_ast.validate()

        if all([table.hash_key_attr in key, table.range_key_attr in key]):
            # Covers cases where table has hash and range keys, ``key`` param
            # will be a dict
            hash_value = DynamoType(key[table.hash_key_attr])
            range_value = DynamoType(key[table.range_key_attr])
        elif table.hash_key_attr in key:
            # Covers tables that have a range key where ``key`` param is a dict
            hash_value = DynamoType(key[table.hash_key_attr])
            range_value = None
        else:
            # Covers other cases
            hash_value = DynamoType(key)
            range_value = None

        item = table.get_item(hash_value, range_value)
        orig_item = copy.deepcopy(item)

        if not expected:
            expected = {}

        if not get_expected(expected).expr(item):
            raise ConditionalCheckFailed
        condition_op = get_filter_expression(
            condition_expression,
            expression_attribute_names,
            expression_attribute_values,
        )
        if not condition_op.expr(item):
            raise ConditionalCheckFailed

        # Update does not fail on new items, so create one
        if item is None:
            if update_expression:
                # Validate AST before creating anything
                item = Item(hash_value, range_value, attrs={})
                UpdateExpressionValidator(
                    update_expression_ast,
                    expression_attribute_names=expression_attribute_names,
                    expression_attribute_values=expression_attribute_values,
                    item=item,
                    table=table,
                ).validate()
            data = {table.hash_key_attr: {hash_value.type: hash_value.value}}
            if range_value:
                data.update(
                    {table.range_key_attr: {range_value.type: range_value.value}}
                )

            table.put_item(data)
            item = table.get_item(hash_value, range_value)

        if attribute_updates:
            item.validate_no_empty_key_values(attribute_updates, table.attribute_keys)

        if update_expression:
            validator = UpdateExpressionValidator(
                update_expression_ast,
                expression_attribute_names=expression_attribute_names,
                expression_attribute_values=expression_attribute_values,
                item=item,
                table=table,
            )
            validated_ast = validator.validate()
            try:
                UpdateExpressionExecutor(
                    validated_ast, item, expression_attribute_names
                ).execute()
            except ItemSizeTooLarge:
                raise ItemSizeToUpdateTooLarge()
        else:
            item.update_with_attribute_updates(attribute_updates)
        if table.stream_shard is not None:
            table.stream_shard.add(orig_item, item)
        return item

    def delete_item(
        self,
        table_name,
        key,
        expression_attribute_names=None,
        expression_attribute_values=None,
        condition_expression=None,
    ):
        table = self.get_table(table_name)

        hash_value, range_value = self.get_keys_value(table, key)
        item = table.get_item(hash_value, range_value)

        condition_op = get_filter_expression(
            condition_expression,
            expression_attribute_names,
            expression_attribute_values,
        )
        if not condition_op.expr(item):
            raise ConditionalCheckFailed

        return table.delete_item(hash_value, range_value)

    def update_time_to_live(self, table_name, ttl_spec):
        table = self.tables.get(table_name)
        if table is None:
            raise JsonRESTError("ResourceNotFound", "Table not found")

        if "Enabled" not in ttl_spec or "AttributeName" not in ttl_spec:
            raise JsonRESTError(
                "InvalidParameterValue",
                "TimeToLiveSpecification does not contain Enabled and AttributeName",
            )

        if ttl_spec["Enabled"]:
            table.ttl["TimeToLiveStatus"] = "ENABLED"
        else:
            table.ttl["TimeToLiveStatus"] = "DISABLED"
        table.ttl["AttributeName"] = ttl_spec["AttributeName"]

    def describe_time_to_live(self, table_name):
        table = self.tables.get(table_name)
        if table is None:
            raise JsonRESTError("ResourceNotFound", "Table not found")

        return table.ttl

    def transact_write_items(self, transact_items):
        if len(transact_items) > 25:
            raise TooManyTransactionsException()
        # Create a backup in case any of the transactions fail
        original_table_state = copy.deepcopy(self.tables)
        target_items = set()

        def check_unicity(table_name, key):
            item = (str(table_name), str(key))
            if item in target_items:
                raise MultipleTransactionsException()
            target_items.add(item)

        errors = []
        for item in transact_items:
            try:
                if "ConditionCheck" in item:
                    item = item["ConditionCheck"]
                    key = item["Key"]
                    table_name = item["TableName"]
                    check_unicity(table_name, key)
                    condition_expression = item.get("ConditionExpression", None)
                    expression_attribute_names = item.get(
                        "ExpressionAttributeNames", None
                    )
                    expression_attribute_values = item.get(
                        "ExpressionAttributeValues", None
                    )
                    current = self.get_item(table_name, key)

                    condition_op = get_filter_expression(
                        condition_expression,
                        expression_attribute_names,
                        expression_attribute_values,
                    )
                    if not condition_op.expr(current):
                        raise ConditionalCheckFailed()
                elif "Put" in item:
                    item = item["Put"]
                    attrs = item["Item"]
                    table_name = item["TableName"]
                    condition_expression = item.get("ConditionExpression", None)
                    expression_attribute_names = item.get(
                        "ExpressionAttributeNames", None
                    )
                    expression_attribute_values = item.get(
                        "ExpressionAttributeValues", None
                    )
                    self.put_item(
                        table_name,
                        attrs,
                        condition_expression=condition_expression,
                        expression_attribute_names=expression_attribute_names,
                        expression_attribute_values=expression_attribute_values,
                    )
                elif "Delete" in item:
                    item = item["Delete"]
                    key = item["Key"]
                    table_name = item["TableName"]
                    check_unicity(table_name, key)
                    condition_expression = item.get("ConditionExpression", None)
                    expression_attribute_names = item.get(
                        "ExpressionAttributeNames", None
                    )
                    expression_attribute_values = item.get(
                        "ExpressionAttributeValues", None
                    )
                    self.delete_item(
                        table_name,
                        key,
                        condition_expression=condition_expression,
                        expression_attribute_names=expression_attribute_names,
                        expression_attribute_values=expression_attribute_values,
                    )
                elif "Update" in item:
                    item = item["Update"]
                    key = item["Key"]
                    table_name = item["TableName"]
                    check_unicity(table_name, key)
                    update_expression = item["UpdateExpression"]
                    condition_expression = item.get("ConditionExpression", None)
                    expression_attribute_names = item.get(
                        "ExpressionAttributeNames", None
                    )
                    expression_attribute_values = item.get(
                        "ExpressionAttributeValues", None
                    )
                    self.update_item(
                        table_name,
                        key,
                        update_expression=update_expression,
                        condition_expression=condition_expression,
                        expression_attribute_names=expression_attribute_names,
                        expression_attribute_values=expression_attribute_values,
                    )
                else:
                    raise ValueError
                errors.append((None, None))
            except MultipleTransactionsException:
                # Rollback to the original state, and reraise the error
                self.tables = original_table_state
                raise MultipleTransactionsException()
            except Exception as e:  # noqa: E722 Do not use bare except
                errors.append((type(e).__name__, e.message))
        if set(errors) != set([(None, None)]):
            # Rollback to the original state, and reraise the errors
            self.tables = original_table_state
            raise TransactionCanceledException(errors)

    def describe_continuous_backups(self, table_name):
        try:
            table = self.get_table(table_name)
        except ResourceNotFoundException:
            raise TableNotFoundException(table_name)

        return table.continuous_backups

    def update_continuous_backups(self, table_name, point_in_time_spec):
        try:
            table = self.get_table(table_name)
        except ResourceNotFoundException:
            raise TableNotFoundException(table_name)

        if (
            point_in_time_spec["PointInTimeRecoveryEnabled"]
            and table.continuous_backups["PointInTimeRecoveryDescription"][
                "PointInTimeRecoveryStatus"
            ]
            == "DISABLED"
        ):
            table.continuous_backups["PointInTimeRecoveryDescription"] = {
                "PointInTimeRecoveryStatus": "ENABLED",
                "EarliestRestorableDateTime": unix_time(),
                "LatestRestorableDateTime": unix_time(),
            }
        elif not point_in_time_spec["PointInTimeRecoveryEnabled"]:
            table.continuous_backups["PointInTimeRecoveryDescription"] = {
                "PointInTimeRecoveryStatus": "DISABLED"
            }

        return table.continuous_backups

    def get_backup(self, backup_arn):
        if backup_arn not in self.backups:
            raise BackupNotFoundException(backup_arn)
        return self.backups.get(backup_arn)

    def list_backups(self, table_name):
        backups = list(self.backups.values())
        if table_name is not None:
            backups = [backup for backup in backups if backup.table.name == table_name]
        return backups

    def create_backup(self, table_name, backup_name):
        try:
            table = self.get_table(table_name)
        except ResourceNotFoundException:
            raise TableNotFoundException(table_name)
        backup = Backup(self, backup_name, table)
        self.backups[backup.arn] = backup
        return backup

    def delete_backup(self, backup_arn):
        backup = self.get_backup(backup_arn)
        if backup is None:
            raise KeyError()
        backup_deleted = self.backups.pop(backup_arn)
        backup_deleted.status = "DELETED"
        return backup_deleted

    def describe_backup(self, backup_arn):
        backup = self.get_backup(backup_arn)
        if backup is None:
            raise KeyError()
        return backup

    def restore_table_from_backup(self, target_table_name, backup_arn):
        backup = self.get_backup(backup_arn)
        if target_table_name in self.tables:
            raise TableAlreadyExistsException(target_table_name)
        new_table = RestoredTable(
            target_table_name,
            account_id=self.account_id,
            region=self.region_name,
            backup=backup,
        )
        self.tables[target_table_name] = new_table
        return new_table

    def restore_table_to_point_in_time(self, target_table_name, source_table_name):
        """
        Currently this only accepts the source and target table elements, and will
        copy all items from the source without respect to other arguments.
        """

        try:
            source = self.get_table(source_table_name)
        except ResourceNotFoundException:
            raise SourceTableNotFoundException(source_table_name)
        if target_table_name in self.tables:
            raise TableAlreadyExistsException(target_table_name)
        new_table = RestoredPITTable(
            target_table_name,
            account_id=self.account_id,
            region=self.region_name,
            source=source,
        )
        self.tables[target_table_name] = new_table
        return new_table

    ######################
    # LIST of methods where the logic completely resides in responses.py
    # Duplicated here so that the implementation coverage script is aware
    # TODO: Move logic here
    ######################

    def batch_get_item(self):
        pass

    def batch_write_item(self):
        pass

    def transact_get_items(self):
        pass


dynamodb_backends = BackendDict(DynamoDBBackend, "dynamodb")