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 this check does not alert",
			loaded: onlyA,
			checks: []map[string]map[string][]string{disagree},
			want:   [][][2]string{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, current := range tt.checks {
				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 = hostnameState(current)
			}
		})
	}
}

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

	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,
		},
	}

	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 {
				w.DetectHostnameChanges(t.Context(), host, prev, disagree)
				prev = hostnameState(disagree)
			}

			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)
			}
		})
	}
}