package mesh

import (
	"fmt"
	"time"
)

func ValidateProductionEnvelopeRouteConfig(local PeerIdentity, envelope ProductionEnvelope, routes []SyntheticRoute, now time.Time) error {
	if len(routes) == 0 {
		return nil
	}
	route, ok := productionRouteByID(routes, envelope.RouteID)
	if !ok {
		return ErrRouteNotFound
	}
	if route.ClusterID != envelope.ClusterID || route.ClusterID != local.ClusterID {
		return ErrClusterMismatch
	}
	if route.SourceNodeID != envelope.SourceNodeID || route.DestinationNodeID != envelope.DestinationNodeID {
		return ErrInvalidRoutePath
	}
	if route.ExpiresAt.IsZero() || !route.ExpiresAt.After(now.UTC()) || envelope.ExpiresAt.After(route.ExpiresAt) {
		return ErrRouteExpired
	}
	if !contains(route.AllowedChannels, envelope.ChannelClass) {
		return ErrUnauthorizedChannel
	}
	path := routePath(route)
	if len(path) < 2 || path[0] != route.SourceNodeID || path[len(path)-1] != route.DestinationNodeID {
		return ErrInvalidRoutePath
	}
	if len(envelope.RoutePath) > 0 && !sameNodePath(envelope.RoutePath, path) {
		return ErrInvalidRoutePath
	}
	if len(path) > 2 && len(envelope.RoutePath) == 0 {
		return ErrInvalidRoutePath
	}
	currentIndex := indexOf(path, local.NodeID)
	if currentIndex < 0 || envelope.CurrentHopNodeID != local.NodeID {
		return ErrNodeMismatch
	}
	expectedNextHop := local.NodeID
	if local.NodeID != envelope.DestinationNodeID {
		if currentIndex >= len(path)-1 {
			return ErrInvalidRoutePath
		}
		expectedNextHop = path[currentIndex+1]
	}
	if envelope.NextHopNodeID != expectedNextHop {
		return ErrInvalidRoutePath
	}
	if route.MaxTTL > 0 && envelope.TTL > route.MaxTTL {
		return fmt.Errorf("%w: ttl exceeds configured route max_ttl", ErrForwardEnvelopeInvalid)
	}
	if route.MaxHops > 0 && envelope.HopCount > route.MaxHops {
		return fmt.Errorf("%w: hop_count exceeds configured route max_hops", ErrForwardEnvelopeInvalid)
	}
	return nil
}

func productionRouteByID(routes []SyntheticRoute, routeID string) (SyntheticRoute, bool) {
	for _, route := range routes {
		if route.RouteID == routeID {
			return route, true
		}
	}
	return SyntheticRoute{}, false
}

func sameNodePath(a []string, b []string) bool {
	if len(a) != len(b) {
		return false
	}
	for i := range a {
		if a[i] != b[i] {
			return false
		}
	}
	return true
}