package watcher_test

import (
	"slices"
	"testing"

	"sneak.berlin/go/dnswatcher/internal/state"
	"sneak.berlin/go/dnswatcher/internal/watcher"
)

const (
	host = "www.example.net"
	nsA  = "a.ns.example.net."
	nsB  = "b.ns.example.net."
	nsC  = "c.ns.example.net."
	ip1  = "192.0.2.1"
	ip2  = "192.0.2.2"
	ip3  = "192.0.2.3"
)

// hostnameState builds the state a check with these records leaves behind.
func hostnameState(
	records map[string]map[string][]string,
) *state.HostnameState {
	hs := &state.HostnameState{
		RecordsByNameserver: make(map[string]*state.NameserverRecordState),
	}

	for ns, recs := range records {
		hs.RecordsByNameserver[ns] = &state.NameserverRecordState{
			Records: recs,
			Status:  "ok",
		}
	}

	return hs
}

func TestNewlyDisagreeingPairs(t *testing.T) {
	t.Parallel()

	onlyA := map[string]map[string][]string{nsA: {"A": {ip1}}}
	agree := map[string]map[string][]string{nsA: {"A": {ip1}}, nsB: {"A": {ip1}}}
	disagree := map[string]map[string][]string{nsA: {"A": {ip1}}, nsB: {"A": {ip2}}}
	alert := [][2]string{{nsA, nsB}}

	// b already disagrees with a and c; then c changes, so a and c,
	// which agreed, now differ.
	bDiffers := map[string]map[string][]string{
		nsA: {"A": {ip1}}, nsB: {"A": {ip2}}, nsC: {"A": {ip1}},
	}
	cChanges := map[string]map[string][]string{
		nsA: {"A": {ip1}}, nsB: {"A": {ip2}}, nsC: {"A": {ip3}},
	}

	// Each case starts from the state loaded at startup and runs the
	// checks in order; want[i] is what check i alerts for.
	tests := []struct {
		name   string
		loaded map[string]map[string][]string
		checks []map[string]map[string][]string
		want   [][][2]string
	}{
		{
			name:   "disagreement persisting across checks alerts once",
			loaded: agree,
			checks: []map[string]map[string][]string{disagree, disagree, disagree},
			want:   [][][2]string{alert, nil, nil},
		},
		{
			name:   "disagreement starting on a later check alerts on it",
			loaded: agree,
			checks: []map[string]map[string][]string{agree, agree, disagree},
			want:   [][][2]string{nil, nil, alert},
		},
		{
			name:   "disagreement in the loaded state does not alert",
			loaded: disagree,
			checks: []map[string]map[string][]string{disagree, disagree},
			want:   [][][2]string{nil, nil},
		},
		{
			name:   "nameserver new on the first check and disagreeing alerts once",
			loaded: onlyA,
			checks: []map[string]map[string][]string{disagree, disagree},
			want:   [][][2]string{alert, nil},
		},
		{
			name:   "disagreement after agreeing again alerts again",
			loaded: agree,
			checks: []map[string]map[string][]string{disagree, agree, disagree},
			want:   [][][2]string{alert, nil, alert},
		},
		{
			name:   "new disagreement while another nameserver differs alerts",
			loaded: bDiffers,
			checks: []map[string]map[string][]string{cChanges, cChanges},
			want:   [][][2]string{{{nsA, nsC}}, nil},
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			prev := hostnameState(tt.loaded)

			for i, records := range tt.checks {
				current := hostnameState(records)

				got := watcher.NewlyDisagreeingPairs(prev, current)
				if !slices.Equal(got, tt.want[i]) {
					t.Errorf(
						"check %d: alerted for %v, want %v",
						i, got, tt.want[i],
					)
				}

				prev = current
			}
		})
	}
}

func TestInconsistencyAlert(t *testing.T) {
	t.Parallel()

	onlyA := map[string]map[string][]string{nsA: {"A": {ip1}}}
	agree := map[string]map[string][]string{nsA: {"A": {ip1}}, nsB: {"A": {ip1}}}
	disagree := map[string]map[string][]string{nsA: {"A": {ip1}}, nsB: {"A": {ip2}}}

	// Each case starts from the state loaded at startup and then sees
	// the nameservers disagree on three checks in a row.
	tests := []struct {
		name   string
		loaded map[string]map[string][]string
		want   int
	}{
		{
			name:   "disagreement lasting several checks alerts once",
			loaded: agree,
			want:   1,
		},
		{
			name:   "disagreement in the loaded state does not alert",
			loaded: disagree,
			want:   0,
		},
		{
			name:   "nameserver new on the first check and disagreeing alerts once",
			loaded: onlyA,
			want:   1,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			// The hostname change detection uses only the notifier.
			notifier := &mockNotifier{}
			w := watcher.NewForTest(nil, nil, nil, nil, nil, notifier)

			prev := hostnameState(tt.loaded)

			for range 3 {
				current := hostnameState(disagree)
				w.DetectHostnameChanges(t.Context(), host, prev, current)
				prev = current
			}

			got := 0

			for _, n := range notifier.getNotifications() {
				if n.Title == "Inconsistency: "+host {
					got++
				}
			}

			if got != tt.want {
				t.Errorf("sent %d inconsistency alerts, want %d", got, tt.want)
			}
		})
	}
}

// TestFirstCheckAfterRepeatedValuesLoaded saves a state file holding a
// hostname's CNAME once for every record type asked for, as checks did
// before each value was stored once, and two addresses each repeated,
// and loads it. A check that then finds each value once at each
// nameserver must notify nothing.
func TestFirstCheckAfterRepeatedValuesLoaded(t *testing.T) {
	t.Parallel()

	const (
		cnameType = "CNAME"
		cname     = "c.example.net."
	)

	cfg := defaultTestConfig(t)
	repeated := map[string][]string{
		"A":       {ip2, ip1, ip2, ip1},
		cnameType: {cname, cname, cname, cname, cname, cname, cname, cname},
	}
	once := map[string][]string{"A": {ip1, ip2}, cnameType: {cname}}

	saved := newTestDeps(t, cfg).state
	saved.SetHostnameState(host, hostnameState(map[string]map[string][]string{
		nsA: repeated, nsB: repeated,
	}))

	err := saved.Save()
	if err != nil {
		t.Fatalf("saving the state file: %v", err)
	}

	deps := newTestDeps(t, cfg)

	err = deps.state.Load()
	if err != nil {
		t.Fatalf("loading the state file: %v", err)
	}

	prev, ok := deps.state.GetHostnameState(host)
	if !ok {
		t.Fatal("the state file has no state for " + host)
	}

	current := hostnameState(map[string]map[string][]string{
		nsA: once, nsB: once,
	})

	// The hostname change detection uses only the notifier.
	w := watcher.NewForTest(nil, nil, nil, nil, nil, deps.notifier)
	w.DetectHostnameChanges(t.Context(), host, prev, current)

	if got := deps.notifier.getNotifications(); len(got) != 0 {
		t.Errorf("sent %v, want no notification", got)
	}
}