from __future__ import unicode_literals
from collections import defaultdict
import copy
import datetime
import decimal
import json
import re
import uuid
import six

import boto3
from moto.compat import OrderedDict
from moto.core import BaseBackend, BaseModel
from moto.core.utils import unix_time
from moto.core.exceptions import JsonRESTError
from .comparisons import get_comparison_func
from .comparisons import get_filter_expression
from .comparisons import get_expected
from .exceptions import InvalidIndexNameError


class DynamoJsonEncoder(json.JSONEncoder):

    def default(self, obj):
        if hasattr(obj, 'to_json'):
            return obj.to_json()


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


class DynamoType(object):
    """
    http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DataModel.html#DataModelDataTypes
    """

    def __init__(self, type_as_dict):
        self.type = list(type_as_dict)[0]
        self.value = list(type_as_dict.values())[0]

    def __hash__(self):
        return hash((self.type, self.value))

    def __eq__(self, other):
        return (
            self.type == other.type and
            self.value == other.value
        )

    def __lt__(self, other):
        return self.value < other.value

    def __le__(self, other):
        return self.value <= other.value

    def __gt__(self, other):
        return self.value > other.value

    def __ge__(self, other):
        return self.value >= other.value

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

    @property
    def cast_value(self):
        if self.is_number():
            try:
                return int(self.value)
            except ValueError:
                return float(self.value)
        elif self.is_set():
            sub_type = self.type[0]
            return set([DynamoType({sub_type: v}).cast_value
                        for v in self.value])
        elif self.is_list():
            return [DynamoType(v).cast_value for v in self.value]
        elif self.is_map():
            return dict([
                (k, DynamoType(v).cast_value)
                for k, v in self.value.items()])
        else:
            return self.value

    def child_attr(self, key):
        """
        Get Map or List children by key. str for Map, int for List.

        Returns DynamoType or None.
        """
        if isinstance(key, six.string_types) and self.is_map() and key in self.value:
            return DynamoType(self.value[key])

        if isinstance(key, int) and self.is_list():
            idx = key
            if idx >= 0 and idx < len(self.value):
                return DynamoType(self.value[idx])

        return None

    def to_json(self):
        return {self.type: self.value}

    def compare(self, range_comparison, range_objs):
        """
        Compares this type against comparison filters
        """
        range_values = [obj.cast_value for obj in range_objs]
        comparison_func = get_comparison_func(range_comparison)
        return comparison_func(self.cast_value, *range_values)

    def is_number(self):
        return self.type == 'N'

    def is_set(self):
        return self.type == 'SS' or self.type == 'NS' or self.type == 'BS'

    def is_list(self):
        return self.type == 'L'

    def is_map(self):
        return self.type == 'M'

    def same_type(self, other):
        return self.type == other.type


class Item(BaseModel):

    def __init__(self, hash_key, hash_key_type, range_key, range_key_type, attrs):
        self.hash_key = hash_key
        self.hash_key_type = hash_key_type
        self.range_key = range_key
        self.range_key_type = range_key_type

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

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

    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 update(self, update_expression, expression_attribute_names, expression_attribute_values):
        # Update subexpressions are identifiable by the operator keyword, so split on that and
        # get rid of the empty leading string.
        parts = [p for p in re.split(r'\b(SET|REMOVE|ADD|DELETE)\b', update_expression, flags=re.I) if p]
        # make sure that we correctly found only operator/value pairs
        assert len(parts) % 2 == 0, "Mismatched operators and values in update expression: '{}'".format(update_expression)
        for action, valstr in zip(parts[:-1:2], parts[1::2]):
            action = action.upper()

            # "Should" retain arguments in side (...)
            values = re.split(r',(?![^(]*\))', valstr)
            for value in values:
                # A Real value
                value = value.lstrip(":").rstrip(",").strip()
                for k, v in expression_attribute_names.items():
                    value = re.sub(r'{0}\b'.format(k), v, value)

                if action == "REMOVE":
                    self.attrs.pop(value, None)
                elif action == 'SET':
                    key, value = value.split("=", 1)
                    key = key.strip()
                    value = value.strip()

                    # If not exists, changes value to a default if needed, else its the same as it was
                    if value.startswith('if_not_exists'):
                        # Function signature
                        match = re.match(r'.*if_not_exists\s*\((?P<path>.+),\s*(?P<default>.+)\).*', value)
                        if not match:
                            raise TypeError

                        path, value = match.groups()

                        # If it already exists, get its value so we dont overwrite it
                        if path in self.attrs:
                            value = self.attrs[path]

                    if type(value) != DynamoType:
                        if value in expression_attribute_values:
                            value = DynamoType(expression_attribute_values[value])
                        else:
                            value = DynamoType({"S": value})

                    if '.' not in key:
                        self.attrs[key] = value
                    else:
                        # Handle nested dict updates
                        key_parts = key.split('.')
                        attr = key_parts.pop(0)
                        if attr not in self.attrs:
                            raise ValueError

                        last_val = self.attrs[attr].value
                        for key_part in key_parts:
                            # Hack but it'll do, traverses into a dict
                            last_val_type = list(last_val.keys())
                            if last_val_type and last_val_type[0] == 'M':
                                    last_val = last_val['M']

                            if key_part not in last_val:
                                last_val[key_part] = {'M': {}}

                            last_val = last_val[key_part]

                        # We have reference to a nested object but we cant just assign to it
                        current_type = list(last_val.keys())[0]
                        if current_type == value.type:
                            last_val[current_type] = value.value
                        else:
                            last_val[value.type] = value.value
                            del last_val[current_type]

                elif action == 'ADD':
                    key, value = value.split(" ", 1)
                    key = key.strip()
                    value_str = value.strip()
                    if value_str in expression_attribute_values:
                        dyn_value = DynamoType(expression_attribute_values[value])
                    else:
                        raise TypeError

                    # Handle adding numbers - value gets added to existing value,
                    # or added to 0 if it doesn't exist yet
                    if dyn_value.is_number():
                        existing = self.attrs.get(key, DynamoType({"N": '0'}))
                        if not existing.same_type(dyn_value):
                            raise TypeError()
                        self.attrs[key] = DynamoType({"N": str(
                            decimal.Decimal(existing.value) +
                            decimal.Decimal(dyn_value.value)
                        )})

                    # Handle adding sets - value is added to the set, or set is
                    # created with only this value if it doesn't exist yet
                    # New value must be of same set type as previous value
                    elif dyn_value.is_set():
                        existing = self.attrs.get(key, DynamoType({dyn_value.type: {}}))
                        if not existing.same_type(dyn_value):
                            raise TypeError()
                        new_set = set(existing.value).union(dyn_value.value)
                        self.attrs[key] = DynamoType({existing.type: list(new_set)})
                    else:  # Number and Sets are the only supported types for ADD
                        raise TypeError

                elif action == 'DELETE':
                    key, value = value.split(" ", 1)
                    key = key.strip()
                    value_str = value.strip()
                    if value_str in expression_attribute_values:
                        dyn_value = DynamoType(expression_attribute_values[value])
                    else:
                        raise TypeError

                    if not dyn_value.is_set():
                        raise TypeError
                    existing = self.attrs.get(key, None)
                    if existing:
                        if not existing.same_type(dyn_value):
                            raise TypeError
                        new_set = set(existing.value).difference(dyn_value.value)
                        self.attrs[key] = DynamoType({existing.type: list(new_set)})
                else:
                    raise NotImplementedError('{} update action not yet supported'.format(action))

    def update_with_attribute_updates(self, attribute_updates):
        for attribute_name, update_action in attribute_updates.items():
            action = update_action['Action']
            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 isinstance(new_value, list):
                    self.attrs[attribute_name] = DynamoType({"L": new_value})
                elif isinstance(new_value, set):
                    self.attrs[attribute_name] = DynamoType({"SS": 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)
                    })
                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)


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': 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(
            json.dumps(self.record['dynamodb']))

    def to_json(self):
        return self.record


class StreamShard(BaseModel):
    def __init__(self, table):
        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 = 'DELETE'
        else:
            event_name = 'MODIFY'
        seq = len(self.items) + self.starting_sequence_number
        self.items.append(
            StreamRecord(self.table, t, event_name, old, new, seq))

    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 Table(BaseModel):

    def __init__(self, table_name, schema=None, attr=None, throughput=None, indexes=None, global_indexes=None, streams=None):
        self.name = table_name
        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:
            if elem["KeyType"] == "HASH":
                self.hash_key_attr = elem["AttributeName"]
                self.hash_key_type = elem["KeyType"]
            else:
                self.range_key_attr = elem["AttributeName"]
                self.range_key_type = elem["KeyType"]
        if throughput is None:
            self.throughput = {
                'WriteCapacityUnits': 10, 'ReadCapacityUnits': 10}
        else:
            self.throughput = throughput
        self.throughput["NumberOfDecreasesToday"] = 0
        self.indexes = indexes
        self.global_indexes = 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 = []
        self.ttl = {
            'TimeToLiveStatus': 'DISABLED'  # One of 'ENABLING'|'DISABLING'|'ENABLED'|'DISABLED',
            # 'AttributeName': 'string'  # Can contain this
        }
        self.set_stream_specification(streams)

    @classmethod
    def create_from_cloudformation_json(cls, resource_name, cloudformation_json, region_name):
        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']

        table = dynamodb_backends[region_name].create_table(name=properties['TableName'], **params)
        return table

    def _generate_arn(self, name):
        return 'arn:aws:dynamodb:us-east-1:123456789011: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)
        else:
            self.stream_specification = {'StreamEnabled': False}
            self.latest_stream_label = None
            self.stream_shard = None

    def describe(self, base_key='TableDescription'):
        results = {
            base_key: {
                'AttributeDefinitions': self.attr,
                'ProvisionedThroughput': self.throughput,
                '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 for index in self.global_indexes],
                'LocalSecondaryIndexes': [index for index in self.indexes],
            }
        }
        if self.stream_specification and self.stream_specification['StreamEnabled']:
            results[base_key]['StreamSpecification'] = self.stream_specification
            if self.latest_stream_label:
                results[base_key]['LatestStreamLabel'] = self.latest_stream_label
                results[base_key]['LatestStreamArn'] = self.table_arn + '/stream/' + self.latest_stream_label
        return results

    def __len__(self):
        count = 0
        for key, value in self.items.items():
            if self.has_range_key:
                count += len(value)
            else:
                count += 1
        return count

    @property
    def hash_key_names(self):
        keys = [self.hash_key_attr]
        for index in self.global_indexes:
            hash_key = None
            for key in index['KeySchema']:
                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['KeySchema']:
                if key['KeyType'] == 'RANGE':
                    range_key = keys.append(key['AttributeName'])
            keys.append(range_key)
        return keys

    def put_item(self, item_attrs, expected=None, condition_expression=None,
                 expression_attribute_names=None,
                 expression_attribute_values=None, overwrite=False):
        hash_value = DynamoType(item_attrs.get(self.hash_key_attr))
        if self.has_range_key:
            range_value = DynamoType(item_attrs.get(self.range_key_attr))
        else:
            range_value = None

        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, self.hash_key_type, range_value,
                    self.range_key_type, item_attrs)

        if not overwrite:
            if not get_expected(expected).expr(current):
                raise ValueError('The conditional request failed')
            condition_op = get_filter_expression(
                condition_expression,
                expression_attribute_names,
                expression_attribute_values)
            if not condition_op.expr(current):
                raise ValueError('The conditional request failed')

        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):
        if self.has_range_key and not range_key:
            raise ValueError(
                "Table has a range key, but no range key was passed into get_item")
        try:
            if range_key:
                return self.items[hash_key][range_key]

            if hash_key in self.items:
                return self.items[hash_key]

            raise KeyError
        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['IndexName'], i) for i in all_indexes)
            if index_name not in indexes_by_name:
                raise ValueError('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[
                    'KeySchema'] if key['KeyType'] == 'HASH'][0]
            except IndexError:
                raise ValueError('Missing Hash Key. KeySchema: %s' %
                                 index['KeySchema'])

            try:
                index_range_key = [key for key in index[
                    'KeySchema'] 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:
                results.sort(key=lambda item: item.attrs[index_range_key['AttributeName']].value
                             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()))

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

        if projection_expression:
            expressions = [x.strip() for x in projection_expression.split(',')]
            results = copy.deepcopy(results)
            for result in results:
                for attr in list(result.attrs):
                    if attr not in expressions:
                        result.attrs.pop(attr)

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

        all_indexes = self.all_indexes()
        indexes_by_name = dict((i['IndexName'], i) for i in all_indexes)
        idx = indexes_by_name[index_name]
        idx_col_set = set([i['AttributeName'] for i in idx['KeySchema']])

        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
        all_indexes = self.all_indexes()
        indexes_by_name = dict((i['IndexName'], i) for i in all_indexes)

        if index_name:
            if index_name not in indexes_by_name:
                raise InvalidIndexNameError('The table does not have the specified index: %s' % index_name)
            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 filter_expression is not None:
                passes_all_conditions &= filter_expression.expr(item)

            if passes_all_conditions:
                results.append(item)

        if projection_expression:
            expressions = [x.strip() for x in projection_expression.split(',')]
            results = copy.deepcopy(results)
            for result in results:
                for attr in list(result.attrs):
                    if attr not in expressions:
                        result.attrs.pop(attr)

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

    def _trim_results(self, results, limit, exclusive_start_key, scaned_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
        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 scaned_index:
                all_indexes = self.all_indexes()
                indexes_by_name = dict((i['IndexName'], i) for i in all_indexes)
                idx = indexes_by_name[scaned_index]
                idx_col_list = [i['AttributeName'] for i in idx['KeySchema']]
                for col in idx_col_list:
                    last_evaluated_key[col] = results[-1].attrs[col]

        return results, last_evaluated_key

    def lookup(self, *args, **kwargs):
        if not self.schema:
            self.describe()
        for x, arg in enumerate(args):
            kwargs[self.schema[x].name] = arg
        ret = self.get_item(**kwargs)
        if not ret.keys():
            return None
        return ret


class DynamoDBBackend(BaseBackend):

    def __init__(self, region_name=None):
        self.region_name = region_name
        self.tables = OrderedDict()

    def reset(self):
        region_name = self.region_name

        self.__dict__ = {}
        self.__init__(region_name)

    def create_table(self, name, **params):
        if name in self.tables:
            return None
        table = Table(name, **params)
        self.tables[name] = table
        return table

    def delete_table(self, name):
        return self.tables.pop(name, None)

    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):
        required_table = None
        for table in self.tables:
            if self.tables[table].table_arn == table_arn:
                required_table = self.tables[table]
        return required_table.tags

    def update_table_throughput(self, name, throughput):
        table = self.tables[name]
        table.throughput = throughput
        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 ValueError('Table already has stream enabled')
        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['IndexName'], 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' %
                                     gsi_to_update['IndexName'])
                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']] = gsi_to_create

        # 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.tables.get(table_name)
        if not table:
            return None
        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):
            raise ValueError(
                "Table has a range key, but no range key was passed into get_item")
        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_table(self, table_name):
        return self.tables.get(table_name)

    def get_item(self, table_name, keys):
        table = self.get_table(table_name)
        if not table:
            raise ValueError("No table found")
        hash_key, range_key = self.get_keys_value(table, keys)
        return table.get_item(hash_key, range_key)

    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.tables.get(table_name)
        if not table:
            return None, None

        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.tables.get(table_name)
        if not table:
            return None, None, None

        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)

        projection_expression = ','.join([expr_names.get(attr, attr) for attr in projection_expression.replace(' ', '').split(',')])

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

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

        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)

        if not expected:
            expected = {}

        if not get_expected(expected).expr(item):
            raise ValueError('The conditional request failed')
        condition_op = get_filter_expression(
            condition_expression,
            expression_attribute_names,
            expression_attribute_values)
        if not condition_op.expr(item):
            raise ValueError('The conditional request failed')

        # Update does not fail on new items, so create one
        if item is None:
            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 update_expression:
            item.update(update_expression, expression_attribute_names,
                        expression_attribute_values)
        else:
            item.update_with_attribute_updates(attribute_updates)
        return item

    def delete_item(self, table_name, keys):
        table = self.get_table(table_name)
        if not table:
            return None
        hash_key, range_key = self.get_keys_value(table, keys)
        return table.delete_item(hash_key, range_key)

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

        return table.ttl


available_regions = boto3.session.Session().get_available_regions("dynamodb")
dynamodb_backends = {region: DynamoDBBackend(region_name=region) for region in available_regions}
