// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: MPL-2.0

package extensioncommon

import (
	"fmt"
	envoy_cluster_v3 "github.com/envoyproxy/go-control-plane/envoy/config/cluster/v3"
	envoy_listener_v3 "github.com/envoyproxy/go-control-plane/envoy/config/listener/v3"
	envoy_route_v3 "github.com/envoyproxy/go-control-plane/envoy/config/route/v3"
	envoy_tcp_proxy_v3 "github.com/envoyproxy/go-control-plane/envoy/extensions/filters/network/tcp_proxy/v3"
	envoy_resource_v3 "github.com/envoyproxy/go-control-plane/pkg/resource/v3"
	"github.com/hashicorp/go-multierror"
	"google.golang.org/protobuf/proto"
	"google.golang.org/protobuf/types/known/anypb"

	"github.com/hashicorp/consul/api"
	"github.com/hashicorp/consul/envoyextensions/xdscommon"
)

// BasicExtension is the interface that each user of BasicEnvoyExtender must implement. It
// is responsible for modifying the xDS structures based on only the state of
// the extension.
type BasicExtension interface {
	// CanApply determines if the extension can mutate resources for the given xdscommon.ExtensionConfiguration.
	CanApply(*RuntimeConfig) bool

	// PatchRoute patches a route to include the custom Envoy configuration
	// required to integrate with the built in extension template.
	PatchRoute(*RuntimeConfig, *envoy_route_v3.RouteConfiguration) (*envoy_route_v3.RouteConfiguration, bool, error)

	// PatchCluster patches a cluster to include the custom Envoy configuration
	// required to integrate with the built in extension template.
	PatchCluster(*RuntimeConfig, *envoy_cluster_v3.Cluster) (*envoy_cluster_v3.Cluster, bool, error)

	// PatchFilter patches an Envoy filter to include the custom Envoy
	// configuration required to integrate with the built in extension template.
	PatchFilter(cfg *RuntimeConfig, f *envoy_listener_v3.Filter, isInboundListener bool) (*envoy_listener_v3.Filter, bool, error)
}

var _ EnvoyExtender = (*BasicEnvoyExtender)(nil)

// BasicEnvoyExtender provides convenience functions for iterating and applying modifications
// to Envoy resources.
type BasicEnvoyExtender struct {
	Extension BasicExtension
}

func (b *BasicEnvoyExtender) Validate(_ *RuntimeConfig) error {
	return nil
}

func (b *BasicEnvoyExtender) Extend(resources *xdscommon.IndexedResources, config *RuntimeConfig) (*xdscommon.IndexedResources, error) {
	var resultErr error

	// We don't support patching the local proxy with an upstream's config except in special
	// cases supported by UpstreamEnvoyExtender.
	if config.IsSourcedFromUpstream {
		return nil, fmt.Errorf("%q extension applied as local config but is sourced from an upstream of the local service", config.EnvoyExtension.Name)
	}

	switch config.Kind {
	case api.ServiceKindTerminatingGateway, api.ServiceKindConnectProxy:
	default:
		return resources, nil
	}

	if !b.Extension.CanApply(config) {
		return resources, nil
	}

	for _, indexType := range []string{
		xdscommon.ListenerType,
		xdscommon.RouteType,
		xdscommon.ClusterType,
	} {
		for nameOrSNI, msg := range resources.Index[indexType] {
			switch resource := msg.(type) {
			case *envoy_cluster_v3.Cluster:
				newCluster, patched, err := b.Extension.PatchCluster(config, resource)
				if err != nil {
					resultErr = multierror.Append(resultErr, fmt.Errorf("error patching cluster: %w", err))
					continue
				}
				if patched {
					resources.Index[xdscommon.ClusterType][nameOrSNI] = newCluster
				}

			case *envoy_listener_v3.Listener:
				newListener, patched, err := b.patchListener(config, resource)
				if err != nil {
					resultErr = multierror.Append(resultErr, fmt.Errorf("error patching listener: %w", err))
					continue
				}
				if patched {
					resources.Index[xdscommon.ListenerType][nameOrSNI] = newListener
				}

			case *envoy_route_v3.RouteConfiguration:
				newRoute, patched, err := b.Extension.PatchRoute(config, resource)
				if err != nil {
					resultErr = multierror.Append(resultErr, fmt.Errorf("error patching route: %w", err))
					continue
				}
				if patched {
					resources.Index[xdscommon.RouteType][nameOrSNI] = newRoute
				}
			default:
				resultErr = multierror.Append(resultErr, fmt.Errorf("unsupported type was skipped: %T", resource))
			}
		}
	}

	return resources, resultErr
}

func (b *BasicEnvoyExtender) patchListener(config *RuntimeConfig, l *envoy_listener_v3.Listener) (proto.Message, bool, error) {
	switch config.Kind {
	case api.ServiceKindTerminatingGateway:
		return b.patchTerminatingGatewayListener(config, l)
	case api.ServiceKindConnectProxy:
		return b.patchConnectProxyListener(config, l)
	}
	return l, false, nil
}

func (b *BasicEnvoyExtender) patchTerminatingGatewayListener(config *RuntimeConfig, l *envoy_listener_v3.Listener) (proto.Message, bool, error) {
	var resultErr error
	patched := false

	for _, filterChain := range l.FilterChains {
		var filters []*envoy_listener_v3.Filter

		for _, filter := range filterChain.Filters {
			newFilter, ok, err := b.Extension.PatchFilter(config, filter, IsInboundPublicListener(l))

			if err != nil {
				resultErr = multierror.Append(resultErr, fmt.Errorf("error patching listener filter: %w", err))
				filters = append(filters, filter)
				continue
			}
			if ok {
				filters = append(filters, newFilter)
				patched = true
			} else {
				filters = append(filters, filter)
			}
		}
		filterChain.Filters = filters
	}

	return l, patched, resultErr
}

func (b *BasicEnvoyExtender) patchConnectProxyListener(config *RuntimeConfig, l *envoy_listener_v3.Listener) (proto.Message, bool, error) {
	var resultErr error
	patched := false

	if IsOutboundTProxyListener(l) {
		return b.patchTProxyListener(config, l)
	}

	for _, filterChain := range l.FilterChains {
		var filters []*envoy_listener_v3.Filter

		for _, filter := range filterChain.Filters {
			newFilter, ok, err := b.Extension.PatchFilter(config, filter, IsInboundPublicListener(l))
			if err != nil {
				resultErr = multierror.Append(resultErr, fmt.Errorf("error patching listener filter: %w", err))
				filters = append(filters, filter)
				continue
			}

			if ok {
				filters = append(filters, newFilter)
				patched = true
			} else {
				filters = append(filters, filter)
			}
		}
		filterChain.Filters = filters
	}

	return l, patched, resultErr
}

func (b *BasicEnvoyExtender) patchTProxyListener(config *RuntimeConfig, l *envoy_listener_v3.Listener) (proto.Message, bool, error) {
	var resultErr error
	patched := false

	vip := config.Upstreams[config.ServiceName].VIP

	for _, filterChain := range l.FilterChains {
		var filters []*envoy_listener_v3.Filter

		match := filterChainTProxyMatch(vip, filterChain)
		if !match {
			continue
		}

		for _, filter := range filterChain.Filters {
			newFilter, ok, err := b.Extension.PatchFilter(config, filter, IsInboundPublicListener(l))
			if err != nil {
				resultErr = multierror.Append(resultErr, fmt.Errorf("error patching listener filter: %w", err))
				filters = append(filters, filter)
				continue
			}

			if ok {
				filters = append(filters, newFilter)
				patched = true
			} else {
				filters = append(filters, filter)
			}
		}
		filterChain.Filters = filters
	}

	return l, patched, resultErr
}

func filterChainTProxyMatch(vip string, filterChain *envoy_listener_v3.FilterChain) bool {
	for _, prefixRange := range filterChain.FilterChainMatch.PrefixRanges {
		// Since we always set the address prefix as the full VIP (rather than a prefix), we can just check if they are
		// equal to find the matching filter chain.
		if vip == prefixRange.AddressPrefix {
			return true
		}
	}

	return false
}

func FilterClusterNames(filter *envoy_listener_v3.Filter) map[string]struct{} {
	clusterNames := make(map[string]struct{})
	if filter == nil {
		return clusterNames
	}

	if config := envoy_resource_v3.GetHTTPConnectionManager(filter); config != nil {
		// If it's using RDS, the cluster names will be in the route, rather than in the http filter's route config, so
		// we don't return any cluster names in this case. They can be gathered from the route.
		if config.GetRds() != nil {
			return clusterNames
		}

		cfg := config.GetRouteConfig()

		clusterNames = RouteClusterNames(cfg)
	}

	if config := GetTCPProxy(filter); config != nil {
		clusterNames[config.GetCluster()] = struct{}{}
	}

	return clusterNames
}

func RouteClusterNames(route *envoy_route_v3.RouteConfiguration) map[string]struct{} {
	if route == nil {
		return nil
	}

	clusterNames := make(map[string]struct{})

	for _, virtualHost := range route.VirtualHosts {
		for _, route := range virtualHost.Routes {
			r := route.GetRoute()
			if r == nil {
				continue
			}
			if c := r.GetCluster(); c != "" {
				clusterNames[r.GetCluster()] = struct{}{}
			}

			if wc := r.GetWeightedClusters(); wc != nil {
				for _, c := range wc.GetClusters() {
					if c.Name != "" {
						clusterNames[c.Name] = struct{}{}
					}
				}
			}
		}
	}
	return clusterNames
}

func GetTCPProxy(filter *envoy_listener_v3.Filter) *envoy_tcp_proxy_v3.TcpProxy {
	if typedConfig := filter.GetTypedConfig(); typedConfig != nil {
		config := &envoy_tcp_proxy_v3.TcpProxy{}
		if err := anypb.UnmarshalTo(typedConfig, config, proto.UnmarshalOptions{}); err == nil {
			return config
		}
	}

	return nil
}

func getSNI(chain *envoy_listener_v3.FilterChain) string {
	var sni string

	if chain == nil {
		return sni
	}

	if chain.FilterChainMatch == nil {
		return sni
	}

	if len(chain.FilterChainMatch.ServerNames) == 0 {
		return sni
	}

	return chain.FilterChainMatch.ServerNames[0]
}