package validate

import (
	"fmt"
	"strings"

	envoy_admin_v3 "github.com/envoyproxy/go-control-plane/envoy/admin/v3"
	envoy_cluster_v3 "github.com/envoyproxy/go-control-plane/envoy/config/cluster/v3"
	envoy_core_v3 "github.com/envoyproxy/go-control-plane/envoy/config/core/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_aggregate_cluster_v3 "github.com/envoyproxy/go-control-plane/envoy/extensions/clusters/aggregate/v3"
	envoy_resource_v3 "github.com/envoyproxy/go-control-plane/pkg/resource/v3"
	"github.com/hashicorp/consul/api"
	"google.golang.org/protobuf/proto"
	"google.golang.org/protobuf/types/known/anypb"

	"github.com/hashicorp/consul/envoyextensions/extensioncommon"
)

// Validate contains input information about which proxy resources to validate and output information about resources it
// has validated.
type Validate struct {
	// envoyID is an argument to the Validate plugin and identifies which listener to begin the validation with.
	envoyID string

	// vip is an argument to the Validate plugin and identifies which transparent proxy listener to begin the validation
	// with.
	vip string

	// snis is all of the upstream SNIs for this proxy. It is set via ExtensionConfiguration.
	snis map[string]struct{}

	// listener specifies if the service's listener has been seen.
	listener bool

	// usesRDS determines if the listener's outgoing filter uses RDS.
	usesRDS bool

	// listener specifies if the service's route has been seen.
	route bool

	// resources is a mapping from SNI to the expected resources
	// for that SNI. It is populated based on the cluster names on routes
	// (whether they are specified on listener filters or routes).
	resources map[string]*resource
}

type resource struct {
	// required determines if the resource is required for the given upstream.
	required bool
	// cluster specifies if the cluster has been seen.
	cluster bool
	// aggregateCluster determines if the resource is an aggregate cluster.
	aggregateCluster bool
	// aggregateClusterChildren is a list of SNIs to identify the child clusters of this aggregate cluster.
	aggregateClusterChildren []string
	// parentCluster is empty if this is a top level cluster, and has a value if this is a child of an aggregate
	// cluster.
	parentCluster string
	// loadAssignment specifies if the load assignment has been seen.
	loadAssignment bool
	// usesEDS specifies if the cluster has EDS configured.
	usesEDS bool
	// The number of endpoints for the cluster or load assignment.
	endpoints int
}

var _ extensioncommon.BasicExtension = (*Validate)(nil)

// EndpointValidator allows us to inject a different function for tests.
type EndpointValidator func(*resource, string, *envoy_admin_v3.Clusters)

// MakeValidate is a builtinextensiontemplate.PluginConstructor for a builtinextensiontemplate.EnvoyExtension.
func MakeValidate(ext extensioncommon.RuntimeConfig) (extensioncommon.BasicExtension, error) {
	var resultErr error
	var plugin Validate

	if name := ext.EnvoyExtension.Name; name != api.BuiltinValidateExtension {
		return nil, fmt.Errorf("expected extension name '%s' but got %q", api.BuiltinValidateExtension, name)
	}

	envoyID, _ := ext.EnvoyExtension.Arguments["envoyID"]
	mainEnvoyID, _ := envoyID.(string)
	vip := ""
	snis := map[string]struct{}{}
	upstream, ok := ext.Upstreams[ext.ServiceName]
	if ok {
		vip = upstream.VIP
		if upstream.SNI == nil || len(upstream.SNI) == 0 {
			return nil, fmt.Errorf("no SNIs were set, unable to validate Envoy clusters")
		}
		snis = upstream.SNI
	}
	if mainEnvoyID == "" && vip == "" {
		return nil, fmt.Errorf("envoyID or virtual IP is required")
	}
	plugin.vip = vip
	plugin.envoyID = mainEnvoyID
	plugin.snis = snis
	plugin.resources = make(map[string]*resource)

	return &plugin, resultErr
}

type Messages []Message

type Message struct {
	Success         bool
	Message         string
	PossibleActions []string
}

func (m Messages) Success() bool {
	for _, message := range m {
		if !message.Success {
			return false
		}
	}

	return true
}

func (m Messages) Errors() Messages {
	var errors Messages
	for _, message := range m {
		if !message.Success {
			errors = append(errors, message)
		}
	}

	return errors
}

// GetMessages returns the error based only on Validate's state.
func (v *Validate) GetMessages(validateEndpoints bool, endpointValidator EndpointValidator, clusters *envoy_admin_v3.Clusters) Messages {
	var messages Messages
	missingXDSActions := []string{
		"Check that your upstream service is registered with Consul",
		"Make sure your upstream exists by running the `consul[-k8s] troubleshoot upstreams` command",
		"If you are using transparent proxy for this upstream, ensure you have set up allow intentions to the upstream",
		"Check the logs of the Consul agent configuring the local proxy to ensure XDS resources were sent by Consul",
	}
	missingEndpointsActions := []string{
		"Check that your upstream service is healthy and running",
		"Check that your upstream service is registered with Consul",
		"Check that the upstream proxy is healthy and running",
		"If you are explicitly configuring upstreams, ensure the name of the upstream is correct",
	}

	var upstream string
	upstream = v.envoyID
	if v.envoyID == "" {
		upstream = v.vip
	}

	if !v.listener {
		messages = append(messages, Message{
			Message:         fmt.Sprintf("No listener for upstream %q", upstream),
			PossibleActions: missingXDSActions,
		})
	} else {
		messages = append(messages, Message{
			Message: fmt.Sprintf("Listener for upstream %q found", upstream),
			Success: true,
		})
	}

	if v.usesRDS && !v.route {
		messages = append(messages, Message{
			Message:         fmt.Sprintf("No route for upstream %q", upstream),
			PossibleActions: missingXDSActions,
		})
	} else if v.route {
		messages = append(messages, Message{
			Message: fmt.Sprintf("Route for upstream %q found", upstream),
			Success: true,
		})
	}

	numRequiredResources := 0
	// Resources will be marked as required in PatchFilter or PatchRoute because the listener or route will determine
	// which clusters/endpoints to validate.
	for sni, resource := range v.resources {
		if !resource.required {
			continue
		}
		numRequiredResources += 1

		_, ok := v.snis[sni]
		if !ok || !resource.cluster {
			messages = append(messages, Message{
				Message:         fmt.Sprintf("No cluster %q for upstream %q", sni, upstream),
				PossibleActions: missingXDSActions,
			})
			continue
		} else {
			messages = append(messages, Message{
				Message: fmt.Sprintf("Cluster %q for upstream %q found", sni, upstream),
				Success: true,
			})
		}

		// If the resource is a passthrough cluster, it will not have endpoints, so we need to skip the endpoint
		// validation.
		if strings.Contains(sni, "passthrough~") {
			messages = append(messages, Message{
				Message: fmt.Sprintf("Cluster %q is a passthrough cluster, skipping endpoint healthiness check", sni),
				Success: true,
			})
			continue
		}

		if validateEndpoints {
			// If resource is a top-level cluster (any cluster that is an aggregate cluster or not a child of an aggregate
			// cluster), it will have an empty parent. If resource is a child cluster, it will have a nonempty parent.
			if resource.parentCluster == "" && resource.aggregateCluster {
				// Aggregate cluster case: do endpoint verification by checking each child cluster. We need at least one
				// child cluster to have healthy endpoints.
				oneClusterHasEndpoints := false
				for _, childCluster := range resource.aggregateClusterChildren {
					endpointValidator(v.resources[childCluster], childCluster, clusters)
					if v.resources[childCluster].endpoints > 0 {
						oneClusterHasEndpoints = true
					}
				}
				if !oneClusterHasEndpoints {
					messages = append(messages, Message{
						Message:         fmt.Sprintf("No healthy endpoints for aggregate cluster %q for upstream %q", sni, upstream),
						PossibleActions: missingEndpointsActions,
					})
				} else {
					messages = append(messages, Message{
						Message: fmt.Sprintf("Healthy endpoints for aggregate cluster %q for upstream %q found", sni, upstream),
						Success: true,
					})
				}
			} else if resource.parentCluster == "" {
				// Top-level non-aggregate cluster case: check for load assignment and healthy endpoints.
				endpointValidator(resource, sni, clusters)
				if (resource.usesEDS && !resource.loadAssignment) || resource.endpoints == 0 {
					messages = append(messages, Message{
						Message:         fmt.Sprintf("No healthy endpoints for cluster %q for upstream %q", sni, upstream),
						PossibleActions: missingEndpointsActions,
					})
				} else {
					messages = append(messages, Message{
						Message: fmt.Sprintf("Healthy endpoints for cluster %q for upstream %q found", sni, upstream),
						Success: true,
					})
				}
			} else {
				// Child cluster case: skip, since it'll be verified by the parent aggregate cluster.
				continue
			}
		}

	}

	if numRequiredResources == 0 {
		messages = append(messages, Message{Message: fmt.Sprintf("No clusters found on route or listener")})
	}

	return messages
}

// DoEndpointValidation implements the EndpointVerifier function type.
func DoEndpointValidation(r *resource, sni string, clusters *envoy_admin_v3.Clusters) {
	clusterStatuses := clusters.GetClusterStatuses()
	if clusterStatuses == nil {
		return
	}
	status := &envoy_admin_v3.ClusterStatus{}
	r.loadAssignment = false
	for _, s := range clusterStatuses {
		if s.Name == sni {
			status = s
			r.loadAssignment = true
			break
		}
	}

	healthyEndpoints := 0
	hostStatuses := status.GetHostStatuses()

	if r.loadAssignment && hostStatuses != nil {
		for _, h := range hostStatuses {
			health := h.GetHealthStatus()
			if health != nil {
				if health.EdsHealthStatus == envoy_core_v3.HealthStatus_HEALTHY && health.FailedOutlierCheck == false {
					healthyEndpoints += 1
				}
			}
		}
	}
	r.endpoints = healthyEndpoints
}

// CanApply determines if the extension can apply to the given extension configuration.
func (p *Validate) CanApply(config *extensioncommon.RuntimeConfig) bool {
	return true
}

func (p *Validate) PatchRoute(config *extensioncommon.RuntimeConfig, route *envoy_route_v3.RouteConfiguration) (*envoy_route_v3.RouteConfiguration, bool, error) {
	// Route name on connect proxies will be the envoy ID. We are only validating routes for the specific upstream with
	// the envoyID configured.
	if route.Name != p.envoyID {
		return route, false, nil
	}
	p.route = true
	for sni := range extensioncommon.RouteClusterNames(route) {
		if _, ok := p.resources[sni]; ok {
			continue
		}
		p.resources[sni] = &resource{required: true}
	}
	return route, false, nil
}

func (p *Validate) PatchCluster(config *extensioncommon.RuntimeConfig, c *envoy_cluster_v3.Cluster) (*envoy_cluster_v3.Cluster, bool, error) {
	v, ok := p.resources[c.Name]
	if !ok {
		v = &resource{}
		p.resources[c.Name] = v
	}
	v.cluster = true

	// If it's an aggregate cluster, add the child clusters to p.resources if they are not already there.
	aggregateCluster, ok := isAggregateCluster(c)
	if ok {
		// Mark this as an aggregate cluster, so we know we do not need to validate its endpoints directly.
		v.aggregateCluster = true
		for _, clusterName := range aggregateCluster.Clusters {
			r, ok := p.resources[clusterName]
			if !ok {
				r = &resource{}
				p.resources[clusterName] = r
			}
			if v.aggregateClusterChildren == nil {
				v.aggregateClusterChildren = []string{}
			}
			// On the parent cluster, add the children.
			v.aggregateClusterChildren = append(v.aggregateClusterChildren, clusterName)
			// On the child cluster, set the parent.
			r.parentCluster = c.Name
			// The child clusters of an aggregate cluster will be required if the parent cluster is.
			r.required = v.required
		}
		return c, false, nil
	}

	if c.EdsClusterConfig != nil {
		v.usesEDS = true
	} else {
		la := c.LoadAssignment
		if la == nil {
			return c, false, nil
		}
		v.endpoints = len(la.Endpoints) + len(la.NamedEndpoints)
	}
	return c, false, nil
}

func (p *Validate) PatchFilter(config *extensioncommon.RuntimeConfig, filter *envoy_listener_v3.Filter, _ bool) (*envoy_listener_v3.Filter, bool, error) {
	// If a single filter exists for a listener we say it exists.
	p.listener = true

	if httpConfig := envoy_resource_v3.GetHTTPConnectionManager(filter); httpConfig != nil {
		// If the http filter uses RDS, then the clusters we need to validate exist in the route, and there's nothing
		// else we need to do with the filter.
		if httpConfig.GetRds() != nil {
			p.usesRDS = true

			// Edit the runtime configuration to add an envoy ID based on the route name in the filter. This is because
			// routes are matched by envoyID and in the transparent proxy case, we only have the VIP set in the
			// RuntimeConfig.
			p.envoyID = httpConfig.GetRds().RouteConfigName
			emptyServiceKey := api.CompoundServiceName{}
			upstream, ok := config.Upstreams[emptyServiceKey]
			if ok {
				upstream.EnvoyID = p.envoyID
			}
			return filter, true, nil
		}
	}

	// FilterClusterNames handles the filter being an http or tcp filter.
	for sni := range extensioncommon.FilterClusterNames(filter) {
		// Mark any clusters we see as required resources.
		if r, ok := p.resources[sni]; ok {
			r.required = true
		} else {
			p.resources[sni] = &resource{required: true}
		}
	}

	return filter, true, nil
}

func isAggregateCluster(c *envoy_cluster_v3.Cluster) (*envoy_aggregate_cluster_v3.ClusterConfig, bool) {
	aggregateCluster := &envoy_aggregate_cluster_v3.ClusterConfig{}
	cdt, ok := c.ClusterDiscoveryType.(*envoy_cluster_v3.Cluster_ClusterType)
	if ok {
		cct := cdt.ClusterType.TypedConfig
		if cct != nil {
			err := anypb.UnmarshalTo(cct, aggregateCluster, proto.UnmarshalOptions{})
			if err == nil {
				return aggregateCluster, true
			}
		}
	}
	return nil, false
}