from __future__ import unicode_literals
import datetime
import random
import string

from .exceptions import MessageAttributesInvalid


def generate_receipt_handle():
    # http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/ImportantIdentifiers.html#ImportantIdentifiers-receipt-handles
    length = 185
    return ''.join(random.choice(string.ascii_lowercase) for x in range(length))


def unix_time(dt=None):
    dt = dt or datetime.datetime.utcnow()
    epoch = datetime.datetime.utcfromtimestamp(0)
    delta = dt - epoch
    return (delta.days * 86400) + (delta.seconds + (delta.microseconds / 1e6))


def unix_time_millis(dt=None):
    return unix_time(dt) * 1000.0


def parse_message_attributes(querystring, base='', value_namespace='Value.'):
    message_attributes = {}
    index = 1
    while True:
        # Loop through looking for message attributes
        name_key = base + 'MessageAttribute.{0}.Name'.format(index)
        name = querystring.get(name_key)
        if not name:
            # Found all attributes
            break

        data_type_key = base + 'MessageAttribute.{0}.{1}DataType'.format(index, value_namespace)
        data_type = querystring.get(data_type_key)
        if not data_type:
            raise MessageAttributesInvalid("The message attribute '{0}' must contain non-empty message attribute value.".format(name[0]))

        data_type_parts = data_type[0].split('.')
        if len(data_type_parts) > 2 or data_type_parts[0] not in ['String', 'Binary', 'Number']:
            raise MessageAttributesInvalid("The message attribute '{0}' has an invalid message attribute type, the set of supported type prefixes is Binary, Number, and String.".format(name[0]))

        type_prefix = 'String'
        if data_type_parts[0] == 'Binary':
            type_prefix = 'Binary'

        value_key = base + 'MessageAttribute.{0}.{1}{2}Value'.format(index, value_namespace, type_prefix)
        value = querystring.get(value_key)
        if not value:
            raise MessageAttributesInvalid("The message attribute '{0}' must contain non-empty message attribute value for message attribute type '{1}'.".format(name[0], data_type[0]))

        message_attributes[name[0]] = {'data_type': data_type[0], type_prefix.lower() + '_value': value[0]}

        index += 1

    return message_attributes