package overlay

import (
	"errors"
	"strings"
	"testing"
)

const cidr = "10.42.0.0/16"

func at(name, site, address, endpoint string, hub bool) Node {
	return Node{Name: name, Key: "key-" + name, Site: site, Address: address,
		Endpoint: endpoint, Hub: hub}
}

func peersOf(t *testing.T, g Graph, node string) map[string]Peer {
	t.Helper()
	out := map[string]Peer{}
	for _, p := range g[node] {
		out[p.Name] = p
	}
	return out
}

func TestEveryNodeReachesTheHub(t *testing.T) {
	// The property that makes this a network at all. Without it a node has no route to anything
	// it does not share a site with.
	g, err := Compute([]Node{
		at("anchor", "datacentre", "10.42.0.1", "198.51.100.1:51820", true),
		at("laptop", "", "10.42.0.2", "", false),
		at("home", "house", "10.42.0.3", "", false),
	}, cidr)
	if err != nil {
		t.Fatal(err)
	}
	for _, node := range []string{"laptop", "home"} {
		hub, ok := peersOf(t, g, node)["anchor"]
		if !ok {
			t.Fatalf("%s has no route to the hub", node)
		}
		if hub.Allowed != cidr {
			t.Errorf("%s routes %s through the hub; it must be the whole overlay or the hub is "+
				"not a route of last resort", node, hub.Allowed)
		}
	}
}

func TestNodesAtOneSitePeerDirectly(t *testing.T) {
	// Machines that share a site have a path that does not need the hub, and using it keeps their
	// traffic off a link that may be on another continent.
	g, err := Compute([]Node{
		at("anchor", "datacentre", "10.42.0.1", "198.51.100.1:51820", true),
		at("desk", "house", "10.42.0.2", "192.0.2.2:51820", false),
		at("server", "house", "10.42.0.3", "192.0.2.3:51820", false),
	}, cidr)
	if err != nil {
		t.Fatal(err)
	}

	direct, ok := peersOf(t, g, "desk")["server"]
	if !ok {
		t.Fatal("two machines at one site do not peer directly")
	}
	if direct.Allowed != "10.42.0.3/32" {
		t.Errorf("the direct peer allows %s; a single address is what makes it win on "+
			"specificity over the hub's whole-overlay route", direct.Allowed)
	}
}

func TestARoamingNodeGetsExactlyOnePath(t *testing.T) {
	// Hub-only, and not as a simplification. WireGuard has no failover: a more specific route to
	// a dead endpoint blackholes rather than falling back, so two paths would mean one of them
	// silently swallowing traffic.
	g, err := Compute([]Node{
		at("anchor", "datacentre", "10.42.0.1", "198.51.100.1:51820", true),
		at("laptop", "", "10.42.0.2", "", false),
		at("other", "", "10.42.0.3", "", false),
	}, cidr)
	if err != nil {
		t.Fatal(err)
	}
	if got := len(g["laptop"]); got != 1 {
		t.Fatalf("a roaming node has %d peers; it gets exactly one path", got)
	}
	if g["laptop"][0].Name != "anchor" {
		t.Errorf("a roaming node's single path is %s, not the hub", g["laptop"][0].Name)
	}
}

func TestTwoRoamingNodesDoNotPeerWithEachOther(t *testing.T) {
	// An empty site is not a site. Nodes that roam have no shared location, and treating "" as
	// one would have every roaming machine try to dial every other, none of which can be dialled.
	g, err := Compute([]Node{
		at("anchor", "datacentre", "10.42.0.1", "198.51.100.1:51820", true),
		at("laptop", "", "10.42.0.2", "", false),
		at("phone", "", "10.42.0.3", "", false),
	}, cidr)
	if err != nil {
		t.Fatal(err)
	}
	if _, ok := peersOf(t, g, "laptop")["phone"]; ok {
		t.Error("two nodes with no site peered as though they shared one")
	}
}

func TestOnlyTheSideThatCannotBeDialledKeepsThePathOpen(t *testing.T) {
	// Keepalive matters exactly once: on the node behind NAT. Without it the peer's first packet
	// arrives at a mapping that has already expired. On the reachable side it is pointless
	// traffic for ever.
	g, err := Compute([]Node{
		at("anchor", "datacentre", "10.42.0.1", "198.51.100.1:51820", true),
		at("laptop", "", "10.42.0.2", "", false),
	}, cidr)
	if err != nil {
		t.Fatal(err)
	}
	if !peersOf(t, g, "laptop")["anchor"].Keepalive {
		t.Error("a node that cannot be dialled does not keep its path open")
	}
	if peersOf(t, g, "anchor")["laptop"].Keepalive {
		t.Error("a reachable node sends keepalives it does not need")
	}

	// And between two direct peers at one site, where whether to keep the path open depends on
	// which end you are. Checked here because the hub's own peer list happens not to set the
	// field at all, so asserting only against the hub tests an absence rather than the rule.
	same, err := Compute([]Node{
		at("anchor", "datacentre", "10.42.0.1", "198.51.100.1:51820", true),
		at("desk", "house", "10.42.0.2", "192.0.2.2:51820", false),
		at("server", "house", "10.42.0.3", "", false),
	}, cidr)
	if err != nil {
		t.Fatal(err)
	}
	if !peersOf(t, same, "server")["desk"].Keepalive {
		t.Error("the peer that cannot be dialled does not keep the path open")
	}
	if peersOf(t, same, "desk")["server"].Keepalive {
		t.Error("the peer that can be dialled sends keepalives it does not need")
	}
}

func TestTheHubKnowsEveryoneItRoutesFor(t *testing.T) {
	// The replies have to get back. A hub that does not hold a peer cannot answer it.
	g, err := Compute([]Node{
		at("anchor", "datacentre", "10.42.0.1", "198.51.100.1:51820", true),
		at("laptop", "", "10.42.0.2", "", false),
		at("home", "house", "10.42.0.3", "", false),
	}, cidr)
	if err != nil {
		t.Fatal(err)
	}
	hub := peersOf(t, g, "anchor")
	for _, want := range []string{"laptop", "home"} {
		if _, ok := hub[want]; !ok {
			t.Errorf("the hub does not hold %s, so replies to it have nowhere to go", want)
		}
	}
}

func TestAMeshWithNoHubIsRefused(t *testing.T) {
	// Not an empty graph. A mesh with no hub has no path between sites, and answering "no peers"
	// would look like a working network in which nothing can reach anything — which is how the
	// old arrangement failed, silently, when nobody knew the address convention.
	_, err := Compute([]Node{
		at("a", "", "10.42.0.1", "", false),
		at("b", "", "10.42.0.2", "", false),
	}, cidr)
	if !errors.Is(err, ErrNoHub) {
		t.Fatalf("a mesh with no hub gave %v", err)
	}
}

func TestAnUnreachableHubIsRefused(t *testing.T) {
	// The hub is the one node that must be dialable from wherever the others are. Left
	// unchecked, every node would be given a peer it can never reach and the mesh would look
	// configured and be silent.
	_, err := Compute([]Node{
		at("anchor", "datacentre", "10.42.0.1", "", true),
		at("laptop", "", "10.42.0.2", "", false),
	}, cidr)
	if err == nil {
		t.Fatal("a hub with no endpoint was accepted")
	}
	if !strings.Contains(err.Error(), "must be reachable") {
		t.Errorf("the refusal does not say why: %v", err)
	}
}

func TestANodeWithNoPlaceYetIsSkippedRatherThanFatal(t *testing.T) {
	// A node that has enrolled and not yet been given an address is an ordinary in-between state.
	// Failing the whole graph over it would mean no node gets a network because one is half done.
	g, err := Compute([]Node{
		at("anchor", "datacentre", "10.42.0.1", "198.51.100.1:51820", true),
		at("laptop", "", "10.42.0.2", "", false),
		{Name: "newcomer", Key: "", Address: ""},
	}, cidr)
	if err != nil {
		t.Fatal(err)
	}
	if _, ok := g["newcomer"]; ok {
		t.Error("a node with no key or address was given a peer list")
	}
	if _, ok := peersOf(t, g, "laptop")["newcomer"]; ok {
		t.Error("a node with no key was put in somebody's peer list")
	}
}

func TestNobodyPeersWithThemselves(t *testing.T) {
	g, err := Compute([]Node{
		at("anchor", "house", "10.42.0.1", "198.51.100.1:51820", true),
		at("desk", "house", "10.42.0.2", "192.0.2.2:51820", false),
	}, cidr)
	if err != nil {
		t.Fatal(err)
	}
	for node, peers := range g {
		for _, p := range peers {
			if p.Name == node {
				t.Errorf("%s peers with itself", node)
			}
		}
	}
}

func TestAHubAtYourOwnSiteAppearsOnceNotTwice(t *testing.T) {
	// WireGuard takes one entry per public key. A hub that shares a site with a spoke was being
	// emitted twice — once as a direct peer and once as the route of last resort — producing a
	// configuration the interface refuses, from a mesh that thought it had succeeded.
	//
	// Found in the lab on the first two machines that shared a site with their hub, which is the
	// ordinary case for a small mesh and was in none of the tests above.
	g, err := Compute([]Node{
		at("anchor", "lab", "10.42.0.1", "192.0.2.10:51820", true),
		at("laptop", "lab", "10.42.0.2", "", false),
	}, cidr)
	if err != nil {
		t.Fatal(err)
	}

	seen := map[string]int{}
	for _, p := range g["laptop"] {
		seen[p.Key]++
	}
	for key, count := range seen {
		if count > 1 {
			t.Errorf("the key %s appears %d times; WireGuard takes one entry per key", key, count)
		}
	}

	if len(g["laptop"]) != 1 {
		t.Fatalf("laptop has %d peers; the hub at its own site is one peer, not two", len(g["laptop"]))
	}
	// And that single entry has to carry everything, or the node keeps a direct path to the hub
	// and loses its route to everywhere else.
	if got := g["laptop"][0].Allowed; got != cidr {
		t.Errorf("the single entry allows %s; it is both the direct path and the route of last "+
			"resort, so it carries the whole overlay", got)
	}
}

func TestTwoUnreachableNodesAtOneSiteDoNotPeerDirectly(t *testing.T) {
	// Nobody would open the path, and the direct route is more specific than the hub's — so it
	// wins and blackholes. Both nodes would reach the hub perfectly and be unable to reach each
	// other, which is the worst arrangement available: it looks configured and is not.
	//
	// This is the design's own warning arriving in its implementation, and the lab found it with
	// two machines at one site behind no reachable address — the ordinary shape of a house.
	g, err := Compute([]Node{
		at("anchor", "datacentre", "10.42.0.1", "198.51.100.1:51820", true),
		at("desk", "house", "10.42.0.2", "", false),
		at("server", "house", "10.42.0.3", "", false),
	}, cidr)
	if err != nil {
		t.Fatal(err)
	}

	if _, ok := peersOf(t, g, "desk")["server"]; ok {
		t.Error("two nodes that neither can be dialled were peered directly; neither could open " +
			"the path and the route is more specific than the hub's, so it blackholes")
	}
	// And they must still be able to reach each other — through the hub.
	if hub := peersOf(t, g, "desk")["anchor"]; hub.Allowed != cidr {
		t.Errorf("desk's route to everything else allows %s", hub.Allowed)
	}
}

func TestOneReachableNodeIsEnoughToPeerDirectly(t *testing.T) {
	// The other side of it: if either end can be dialled, the path can be opened, and using it
	// keeps their traffic off a hub that may be on another continent.
	g, err := Compute([]Node{
		at("anchor", "datacentre", "10.42.0.1", "198.51.100.1:51820", true),
		at("desk", "house", "10.42.0.2", "192.0.2.2:51820", false),
		at("server", "house", "10.42.0.3", "", false),
	}, cidr)
	if err != nil {
		t.Fatal(err)
	}
	if _, ok := peersOf(t, g, "server")["desk"]; !ok {
		t.Error("a node did not peer with a reachable neighbour at its own site")
	}
	if _, ok := peersOf(t, g, "desk")["server"]; !ok {
		t.Error("the reachable node did not hold its unreachable neighbour, so replies have " +
			"nowhere to go")
	}
}