from django.conf import settings
from django.db.models import Count
from django.shortcuts import get_object_or_404
from django_pglocks import advisory_lock
from rest_framework import status
from rest_framework.decorators import action
from rest_framework.exceptions import PermissionDenied
from rest_framework.response import Response

from extras.api.views import CustomFieldModelViewSet
from ipam import filters
from ipam.models import Aggregate, IPAddress, Prefix, RIR, Role, Service, VLAN, VLANGroup, VRF
from utilities.api import FieldChoicesViewSet, ModelViewSet
from utilities.constants import ADVISORY_LOCK_KEYS
from utilities.utils import get_subquery
from . import serializers


#
# Field choices
#

class IPAMFieldChoicesViewSet(FieldChoicesViewSet):
    fields = (
        (serializers.AggregateSerializer, ['family']),
        (serializers.PrefixSerializer, ['family', 'status']),
        (serializers.IPAddressSerializer, ['family', 'status', 'role']),
        (serializers.VLANSerializer, ['status']),
        (serializers.ServiceSerializer, ['protocol']),
    )


#
# VRFs
#

class VRFViewSet(CustomFieldModelViewSet):
    queryset = VRF.objects.prefetch_related('tenant').prefetch_related('tags').annotate(
        ipaddress_count=get_subquery(IPAddress, 'vrf'),
        prefix_count=get_subquery(Prefix, 'vrf')
    )
    serializer_class = serializers.VRFSerializer
    filterset_class = filters.VRFFilterSet


#
# RIRs
#

class RIRViewSet(ModelViewSet):
    queryset = RIR.objects.annotate(
        aggregate_count=Count('aggregates')
    )
    serializer_class = serializers.RIRSerializer
    filterset_class = filters.RIRFilterSet


#
# Aggregates
#

class AggregateViewSet(CustomFieldModelViewSet):
    queryset = Aggregate.objects.prefetch_related('rir').prefetch_related('tags')
    serializer_class = serializers.AggregateSerializer
    filterset_class = filters.AggregateFilterSet


#
# Roles
#

class RoleViewSet(ModelViewSet):
    queryset = Role.objects.annotate(
        prefix_count=get_subquery(Prefix, 'role'),
        vlan_count=get_subquery(VLAN, 'role')
    )
    serializer_class = serializers.RoleSerializer
    filterset_class = filters.RoleFilterSet


#
# Prefixes
#

class PrefixViewSet(CustomFieldModelViewSet):
    queryset = Prefix.objects.prefetch_related('site', 'vrf__tenant', 'tenant', 'vlan', 'role', 'tags')
    serializer_class = serializers.PrefixSerializer
    filterset_class = filters.PrefixFilterSet

    @action(detail=True, url_path='available-prefixes', methods=['get', 'post'])
    @advisory_lock(ADVISORY_LOCK_KEYS['available-prefixes'])
    def available_prefixes(self, request, pk=None):
        """
        A convenience method for returning available child prefixes within a parent.

        The advisory lock decorator uses a PostgreSQL advisory lock to prevent this API from being
        invoked in parallel, which results in a race condition where multiple insertions can occur.
        """
        prefix = get_object_or_404(Prefix, pk=pk)
        available_prefixes = prefix.get_available_prefixes()

        if request.method == 'POST':

            # Permissions check
            if not request.user.has_perm('ipam.add_prefix'):
                raise PermissionDenied()

            # Normalize to a list of objects
            requested_prefixes = request.data if isinstance(request.data, list) else [request.data]

            # Allocate prefixes to the requested objects based on availability within the parent
            for i, requested_prefix in enumerate(requested_prefixes):

                # Validate requested prefix size
                prefix_length = requested_prefix.get('prefix_length')
                if prefix_length is None:
                    return Response(
                        {
                            "detail": "Item {}: prefix_length field missing".format(i)
                        },
                        status=status.HTTP_400_BAD_REQUEST
                    )
                try:
                    prefix_length = int(prefix_length)
                except ValueError:
                    return Response(
                        {
                            "detail": "Item {}: Invalid prefix length ({})".format(i, prefix_length),
                        },
                        status=status.HTTP_400_BAD_REQUEST
                    )
                if prefix.family == 4 and prefix_length > 32:
                    return Response(
                        {
                            "detail": "Item {}: Invalid prefix length ({}) for IPv4".format(i, prefix_length),
                        },
                        status=status.HTTP_400_BAD_REQUEST
                    )
                elif prefix.family == 6 and prefix_length > 128:
                    return Response(
                        {
                            "detail": "Item {}: Invalid prefix length ({}) for IPv6".format(i, prefix_length),
                        },
                        status=status.HTTP_400_BAD_REQUEST
                    )

                # Find the first available prefix equal to or larger than the requested size
                for available_prefix in available_prefixes.iter_cidrs():
                    if requested_prefix['prefix_length'] >= available_prefix.prefixlen:
                        allocated_prefix = '{}/{}'.format(available_prefix.network, requested_prefix['prefix_length'])
                        requested_prefix['prefix'] = allocated_prefix
                        requested_prefix['vrf'] = prefix.vrf.pk if prefix.vrf else None
                        break
                else:
                    return Response(
                        {
                            "detail": "Insufficient space is available to accommodate the requested prefix size(s)"
                        },
                        status=status.HTTP_204_NO_CONTENT
                    )

                # Remove the allocated prefix from the list of available prefixes
                available_prefixes.remove(allocated_prefix)

            # Initialize the serializer with a list or a single object depending on what was requested
            context = {'request': request}
            if isinstance(request.data, list):
                serializer = serializers.PrefixSerializer(data=requested_prefixes, many=True, context=context)
            else:
                serializer = serializers.PrefixSerializer(data=requested_prefixes[0], context=context)

            # Create the new Prefix(es)
            if serializer.is_valid():
                serializer.save()
                return Response(serializer.data, status=status.HTTP_201_CREATED)

            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

        else:

            serializer = serializers.AvailablePrefixSerializer(available_prefixes.iter_cidrs(), many=True, context={
                'request': request,
                'vrf': prefix.vrf,
            })

            return Response(serializer.data)

    @action(detail=True, url_path='available-ips', methods=['get', 'post'])
    @advisory_lock(ADVISORY_LOCK_KEYS['available-ips'])
    def available_ips(self, request, pk=None):
        """
        A convenience method for returning available IP addresses within a prefix. By default, the number of IPs
        returned will be equivalent to PAGINATE_COUNT. An arbitrary limit (up to MAX_PAGE_SIZE, if set) may be passed,
        however results will not be paginated.

        The advisory lock decorator uses a PostgreSQL advisory lock to prevent this API from being
        invoked in parallel, which results in a race condition where multiple insertions can occur.
        """
        prefix = get_object_or_404(Prefix, pk=pk)

        # Create the next available IP within the prefix
        if request.method == 'POST':

            # Permissions check
            if not request.user.has_perm('ipam.add_ipaddress'):
                raise PermissionDenied()

            # Normalize to a list of objects
            requested_ips = request.data if isinstance(request.data, list) else [request.data]

            # Determine if the requested number of IPs is available
            available_ips = prefix.get_available_ips()
            if available_ips.size < len(requested_ips):
                return Response(
                    {
                        "detail": "An insufficient number of IP addresses are available within the prefix {} ({} "
                                  "requested, {} available)".format(prefix, len(requested_ips), len(available_ips))
                    },
                    status=status.HTTP_204_NO_CONTENT
                )

            # Assign addresses from the list of available IPs and copy VRF assignment from the parent prefix
            available_ips = iter(available_ips)
            prefix_length = prefix.prefix.prefixlen
            for requested_ip in requested_ips:
                requested_ip['address'] = '{}/{}'.format(next(available_ips), prefix_length)
                requested_ip['vrf'] = prefix.vrf.pk if prefix.vrf else None

            # Initialize the serializer with a list or a single object depending on what was requested
            context = {'request': request}
            if isinstance(request.data, list):
                serializer = serializers.IPAddressSerializer(data=requested_ips, many=True, context=context)
            else:
                serializer = serializers.IPAddressSerializer(data=requested_ips[0], context=context)

            # Create the new IP address(es)
            if serializer.is_valid():
                serializer.save()
                return Response(serializer.data, status=status.HTTP_201_CREATED)

            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

        # Determine the maximum number of IPs to return
        else:
            try:
                limit = int(request.query_params.get('limit', settings.PAGINATE_COUNT))
            except ValueError:
                limit = settings.PAGINATE_COUNT
            if settings.MAX_PAGE_SIZE:
                limit = min(limit, settings.MAX_PAGE_SIZE)

            # Calculate available IPs within the prefix
            ip_list = []
            for index, ip in enumerate(prefix.get_available_ips(), start=1):
                ip_list.append(ip)
                if index == limit:
                    break
            serializer = serializers.AvailableIPSerializer(ip_list, many=True, context={
                'request': request,
                'prefix': prefix.prefix,
                'vrf': prefix.vrf,
            })

            return Response(serializer.data)


#
# IP addresses
#

class IPAddressViewSet(CustomFieldModelViewSet):
    queryset = IPAddress.objects.prefetch_related(
        'vrf__tenant', 'tenant', 'nat_inside', 'interface__device__device_type', 'interface__virtual_machine',
        'nat_outside', 'tags',
    )
    serializer_class = serializers.IPAddressSerializer
    filterset_class = filters.IPAddressFilterSet


#
# VLAN groups
#

class VLANGroupViewSet(ModelViewSet):
    queryset = VLANGroup.objects.prefetch_related('site').annotate(
        vlan_count=Count('vlans')
    )
    serializer_class = serializers.VLANGroupSerializer
    filterset_class = filters.VLANGroupFilterSet


#
# VLANs
#

class VLANViewSet(CustomFieldModelViewSet):
    queryset = VLAN.objects.prefetch_related(
        'site', 'group', 'tenant', 'role', 'tags'
    ).annotate(
        prefix_count=get_subquery(Prefix, 'role')
    )
    serializer_class = serializers.VLANSerializer
    filterset_class = filters.VLANFilterSet


#
# Services
#

class ServiceViewSet(ModelViewSet):
    queryset = Service.objects.prefetch_related('device').prefetch_related('tags')
    serializer_class = serializers.ServiceSerializer
    filterset_class = filters.ServiceFilterSet