package watcher_test

import (
	"context"
	"log/slog"
	"strings"
	"testing"
	"time"

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

// answered is what a check saves for a nameserver that answered with
// these records.
func answered(records map[string][]string) *state.NameserverRecordState {
	return &state.NameserverRecordState{Records: records, Status: "ok"}
}

// failed is what a check saves for a nameserver that did not answer.
func failed() *state.NameserverRecordState {
	return &state.NameserverRecordState{
		Records: map[string][]string{},
		Status:  "error",
		Error:   "all queries timed out",
	}
}

// saved builds the hostname state a check saves.
func saved(
	byNameserver map[string]*state.NameserverRecordState,
) *state.HostnameState {
	return &state.HostnameState{RecordsByNameserver: byNameserver}
}

// alertCounts counts the hostname alerts sent, by kind.
type alertCounts struct {
	failures, recoveries, recordChanges, inconsistencies int
}

// countAlerts runs the hostname change detection from the state loaded
// at startup through each check in turn, and counts the alerts sent.
func countAlerts(
	t *testing.T,
	loaded *state.HostnameState,
	checks []*state.HostnameState,
) alertCounts {
	t.Helper()

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

	prev := loaded

	for _, current := range checks {
		w.DetectHostnameChanges(t.Context(), host, prev, current)
		prev = current
	}

	var got alertCounts

	for _, n := range notifier.getNotifications() {
		kind, _, _ := strings.Cut(n.Title, ":")

		switch kind {
		case "NS Failure":
			got.failures++
		case "NS Recovery":
			got.recoveries++
		case "Record Change":
			got.recordChanges++
		case "Inconsistency":
			got.inconsistencies++
		}
	}

	return got
}

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

	records := map[string][]string{"A": {ip1}}

	bothAnswer := saved(map[string]*state.NameserverRecordState{
		nsA: answered(records), nsB: answered(records),
	})
	bFails := saved(map[string]*state.NameserverRecordState{
		nsA: answered(records), nsB: failed(),
	})
	onlyA := saved(map[string]*state.NameserverRecordState{
		nsA: answered(records),
	})
	bAnswersNoRecords := saved(map[string]*state.NameserverRecordState{
		nsA: answered(records), nsB: answered(map[string][]string{}),
	})
	bAnswersDifferently := saved(map[string]*state.NameserverRecordState{
		nsA: answered(records), nsB: answered(map[string][]string{"A": {ip2}}),
	})

	// Each case starts from the state loaded at startup and runs the
	// checks in order.
	tests := []struct {
		name   string
		loaded *state.HostnameState
		checks []*state.HostnameState
		want   alertCounts
	}{
		{
			"failure lasting several checks alerts once",
			bothAnswer, []*state.HostnameState{bFails, bFails, bFails},
			alertCounts{failures: 1},
		},
		{
			"recovery alerts once",
			bFails, []*state.HostnameState{bothAnswer, bothAnswer},
			alertCounts{recoveries: 1},
		},
		{
			"failing again after recovering alerts again",
			bothAnswer, []*state.HostnameState{bFails, bothAnswer, bFails},
			alertCounts{failures: 2, recoveries: 1},
		},
		{
			"nameserver failing when first seen does not alert",
			onlyA, []*state.HostnameState{bFails, bFails},
			alertCounts{},
		},
		{
			"answer with no records is a record change, not a failure",
			bothAnswer, []*state.HostnameState{bAnswersNoRecords},
			alertCounts{recordChanges: 1, inconsistencies: 1},
		},
		{
			"recovered nameserver that answers differently disagrees",
			bFails, []*state.HostnameState{bAnswersDifferently},
			alertCounts{recoveries: 1, inconsistencies: 1},
		},
	}

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

			got := countAlerts(t, tt.loaded, tt.checks)
			if got != tt.want {
				t.Errorf("sent %+v, want %+v", got, tt.want)
			}
		})
	}
}

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

	records := map[string][]string{"A": {ip1}}

	notifier := &mockNotifier{}
	w := watcher.NewForTest(nil, nil, nil, nil, nil, notifier)

	w.DetectHostnameChanges(
		t.Context(), host,
		saved(map[string]*state.NameserverRecordState{nsA: answered(records)}),
		saved(map[string]*state.NameserverRecordState{nsA: failed()}),
	)

	notifications := notifier.getNotifications()
	if len(notifications) != 1 {
		t.Fatalf("sent %v, want one NS Failure", notifications)
	}

	msg := notifications[0].Message
	if !strings.Contains(msg, nsA) ||
		!strings.Contains(msg, failed().Error) {
		t.Errorf("message %q does not name %s and the reason", msg, nsA)
	}
}

// TestNameserverThatNeverAnswers asks a nameserver address where
// nothing answers, 192.0.2.1, and checks what the watcher saves for it.
// The deadline outlasts the resolver's first two-second try, as in the
// resolver's timeout test.
func TestNameserverThatNeverAnswers(t *testing.T) {
	t.Parallel()

	ctx, cancel := context.WithTimeout(t.Context(), 3*time.Second)
	t.Cleanup(cancel)

	res := resolver.NewFromLogger(slog.Default())

	resp, err := res.QueryNameserverIP(ctx, nsA, "192.0.2.1", host)
	if err != nil {
		t.Fatal(err)
	}

	hs := watcher.BuildHostnameState(
		map[string]*resolver.NameserverResponse{nsA: resp}, time.Now(),
	)

	got := hs.RecordsByNameserver[nsA]
	if got.Status != "error" || got.Error == "" {
		t.Errorf(
			"saved status %q, error %q; want status error with a reason",
			got.Status, got.Error,
		)
	}
}