// Copyright Istio Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package xds

import (
	"math"

	endpoint "github.com/envoyproxy/go-control-plane/envoy/config/endpoint/v3"
	"google.golang.org/protobuf/proto"
	wrappers "google.golang.org/protobuf/types/known/wrapperspb"

	"istio.io/istio/pilot/pkg/model"
	"istio.io/istio/pilot/pkg/networking/util"
	labelutil "istio.io/istio/pilot/pkg/serviceregistry/util/label"
	"istio.io/istio/pkg/cluster"
	"istio.io/istio/pkg/config/labels"
	"istio.io/istio/pkg/network"
)

// EndpointsByNetworkFilter is a network filter function to support Split Horizon EDS - filter the endpoints based on the network
// of the connected sidecar. The filter will filter out all endpoints which are not present within the
// sidecar network and add a gateway endpoint to remote networks that have endpoints
// (if gateway exists and its IP is an IP and not a dns name).
// Information for the mesh networks is provided as a MeshNetwork config map.
func (b *EndpointBuilder) EndpointsByNetworkFilter(endpoints []*LocalityEndpoints) []*LocalityEndpoints {
	if !b.push.NetworkManager().IsMultiNetworkEnabled() {
		// Multi-network is not configured (this is the case by default). Just access all endpoints directly.
		return endpoints
	}

	// A new array of endpoints to be returned that will have both local and
	// remote gateways (if any)
	filtered := make([]*LocalityEndpoints, 0)

	// Scale all weights by the lcm of gateways per network and gateways per cluster.
	// This will allow us to more easily spread traffic to the endpoint across multiple
	// network gateways, increasing reliability of the endpoint.
	scaleFactor := b.push.NetworkManager().GetLBWeightScaleFactor()

	// Go through all cluster endpoints and add those with the same network as the sidecar
	// to the result. Also count the number of endpoints per each remote network while
	// iterating so that it can be used as the weight for the gateway endpoint
	for _, ep := range endpoints {
		lbEndpoints := &LocalityEndpoints{
			llbEndpoints: endpoint.LocalityLbEndpoints{
				Locality: ep.llbEndpoints.Locality,
				Priority: ep.llbEndpoints.Priority,
				// Endpoints and weight will be reset below.
			},
		}

		// Create a map to keep track of the gateways used and their aggregate weights.
		gatewayWeights := make(map[model.NetworkGateway]uint32)

		// Process all of the endpoints.
		for i, lbEp := range ep.llbEndpoints.LbEndpoints {
			istioEndpoint := ep.istioEndpoints[i]

			// If the proxy can't view the network for this endpoint, exclude it entirely.
			if !b.proxyView.IsVisible(istioEndpoint) {
				continue
			}

			// Copy the endpoint in order to expand the load balancing weight.
			// When multiplying, be careful to avoid overflow - clipping the
			// result at the maximum value for uint32.
			weight := b.scaleEndpointLBWeight(lbEp, scaleFactor)
			if lbEp.GetLoadBalancingWeight().GetValue() != weight {
				lbEp = proto.Clone(lbEp).(*endpoint.LbEndpoint)
				lbEp.LoadBalancingWeight = &wrappers.UInt32Value{
					Value: weight,
				}
			}

			epNetwork := istioEndpoint.Network
			epCluster := istioEndpoint.Locality.ClusterID
			gateways := b.selectNetworkGateways(epNetwork, epCluster)

			// Check if the endpoint is directly reachable. It's considered directly reachable if
			// the endpoint is either on the local network or on a remote network that can be reached
			// directly from the local network.
			if b.proxy.InNetwork(epNetwork) || len(gateways) == 0 {
				// The endpoint is directly reachable - just add it.
				lbEndpoints.append(ep.istioEndpoints[i], lbEp)
				continue
			}

			// Cross-network traffic relies on mTLS to be enabled for SNI routing
			// TODO BTS may allow us to work around this
			if b.mtlsChecker.isMtlsDisabled(lbEp) {
				continue
			}

			// Apply the weight for this endpoint to the network gateways.
			splitWeightAmongGateways(weight, gateways, gatewayWeights)
		}

		// Sort the gateways into an ordered list so that the generated endpoints are deterministic.
		gateways := make([]model.NetworkGateway, 0, len(gatewayWeights))
		for gw := range gatewayWeights {
			gateways = append(gateways, gw)
		}
		gateways = model.SortGateways(gateways)

		// Create endpoints for the gateways.
		for _, gw := range gateways {
			epWeight := gatewayWeights[gw]
			if epWeight == 0 {
				log.Warnf("gateway weight must be greater than 0, scaleFactor is %d", scaleFactor)
				epWeight = 1
			}
			epAddr := util.BuildAddress(gw.Addr, gw.Port)

			// Generate a fake IstioEndpoint to carry network and cluster information.
			gwIstioEp := &model.IstioEndpoint{
				Network: gw.Network,
				Locality: model.Locality{
					ClusterID: gw.Cluster,
				},
				Labels: labelutil.AugmentLabels(nil, gw.Cluster, "", "", gw.Network),
			}

			// Generate the EDS endpoint for this gateway.
			gwEp := &endpoint.LbEndpoint{
				HostIdentifier: &endpoint.LbEndpoint_Endpoint{
					Endpoint: &endpoint.Endpoint{
						Address: epAddr,
					},
				},
				LoadBalancingWeight: &wrappers.UInt32Value{
					Value: epWeight,
				},
			}
			// TODO: figure out a way to extract locality data from the gateway public endpoints in meshNetworks
			gwEp.Metadata = util.BuildLbEndpointMetadata(gw.Network, model.IstioMutualTLSModeLabel,
				"", "", b.clusterID, labels.Instance{})
			// Currently gateway endpoint does not support tunnel.
			lbEndpoints.append(gwIstioEp, gwEp)
		}

		// Endpoint members could be stripped or aggregated by network. Adjust weight value here.
		lbEndpoints.refreshWeight()
		filtered = append(filtered, lbEndpoints)
	}

	return filtered
}

// selectNetworkGateways chooses the gateways that best match the network and cluster. If there is
// no match for the network+cluster, then all gateways matching the network are returned. Preferring
// gateways that match against cluster has the following advantages:
//
//  1. Potentially reducing extra latency incurred when the gateway and endpoint reside in different
//     clusters.
//
//  2. Enables Kubernetes MCS use cases, where endpoints for a service might be exported in one
//     cluster but not another within the same network. By targeting the gateway for the cluster
//     where the exported endpoints reside, we ensure that we only send traffic to exported endpoints.
func (b *EndpointBuilder) selectNetworkGateways(nw network.ID, c cluster.ID) []model.NetworkGateway {
	// Get the gateways for this network+cluster combination.
	gws := b.push.NetworkManager().GatewaysForNetworkAndCluster(nw, c)
	if len(gws) == 0 {
		// No match for network+cluster, just match the network.
		gws = b.push.NetworkManager().GatewaysForNetwork(nw)
	}
	return gws
}

func (b *EndpointBuilder) scaleEndpointLBWeight(ep *endpoint.LbEndpoint, scaleFactor uint32) uint32 {
	if ep.GetLoadBalancingWeight() == nil || ep.GetLoadBalancingWeight().Value == 0 {
		return scaleFactor
	}
	weight := uint32(math.MaxUint32)
	if ep.GetLoadBalancingWeight().Value < math.MaxUint32/scaleFactor {
		weight = ep.GetLoadBalancingWeight().Value * scaleFactor
	}
	return weight
}

// Apply the weight for this endpoint to the network gateways.
func splitWeightAmongGateways(weight uint32, gateways []model.NetworkGateway, gatewayWeights map[model.NetworkGateway]uint32) {
	// Spread the weight across the gateways.
	weightPerGateway := weight / uint32(len(gateways))
	for _, gateway := range gateways {
		gatewayWeights[gateway] += weightPerGateway
	}
}

// EndpointsWithMTLSFilter removes all endpoints that do not handle mTLS. This is determined by looking at
// auto-mTLS, DestinationRule, and PeerAuthentication to determine if we would send mTLS to these endpoints.
// Note there is no guarantee these destinations *actually* handle mTLS; just that we are configured to send mTLS to them.
func (b *EndpointBuilder) EndpointsWithMTLSFilter(endpoints []*LocalityEndpoints) []*LocalityEndpoints {
	// A new array of endpoints to be returned that will have both local and
	// remote gateways (if any)
	filtered := make([]*LocalityEndpoints, 0)

	// Go through all cluster endpoints and add those with mTLS enabled
	for _, ep := range endpoints {
		lbEndpoints := &LocalityEndpoints{
			llbEndpoints: endpoint.LocalityLbEndpoints{
				Locality: ep.llbEndpoints.Locality,
				Priority: ep.llbEndpoints.Priority,
				// Endpoints and will be reset below.
			},
		}

		for i, lbEp := range ep.llbEndpoints.LbEndpoints {
			if b.mtlsChecker.isMtlsDisabled(lbEp) {
				// no mTLS, skip it
				continue
			}
			lbEndpoints.append(ep.istioEndpoints[i], lbEp)
		}

		lbEndpoints.refreshWeight()
		filtered = append(filtered, lbEndpoints)
	}

	return filtered
}
