package telemetry_test

import (
	"bytes"
	"context"
	"encoding/json"
	"testing"
	"time"

	"github.com/rs/zerolog"

	"keycape/internal/server/telemetry"
)

func sampleEvent() telemetry.Event {
	return telemetry.Event{
		Timestamp:   time.Now().UTC(),
		ClientID:    "test-client",
		Endpoint:    "/oauth2/token",
		Feature:     "",
		Result:      "success",
		ErrorType:   "",
		Scopes:      []string{"openid", "profile"},
		GrantType:   "authorization_code",
		Environment: "test",
		TraceID:     "trace-abc-123",
		EventType:   telemetry.EventTokenIssued,
	}
}

// ---- NoopEmitter ----

func TestNoopEmitter_DoesNotPanic(t *testing.T) {
	e := telemetry.NoopEmitter{}
	e.Emit(context.Background(), sampleEvent())
}

func TestNoopEmitter_ImplementsInterface(t *testing.T) {
	var _ telemetry.Emitter = telemetry.NoopEmitter{}
}

// ---- LogEmitter ----

func TestLogEmitter_WritesJSON(t *testing.T) {
	var buf bytes.Buffer
	logger := zerolog.New(&buf)
	e := telemetry.NewLogEmitter(logger)

	ev := sampleEvent()
	e.Emit(context.Background(), ev)

	if buf.Len() == 0 {
		t.Fatal("expected output from LogEmitter, got nothing")
	}

	var out map[string]interface{}
	if err := json.Unmarshal(buf.Bytes(), &out); err != nil {
		t.Fatalf("LogEmitter output is not valid JSON: %v\noutput: %s", err, buf.String())
	}
}

func TestLogEmitter_ContainsEventFields(t *testing.T) {
	var buf bytes.Buffer
	logger := zerolog.New(&buf)
	e := telemetry.NewLogEmitter(logger)

	ev := sampleEvent()
	e.Emit(context.Background(), ev)

	var out map[string]interface{}
	_ = json.Unmarshal(buf.Bytes(), &out)

	requiredFields := []string{"client_id", "endpoint", "result", "environment", "trace_id", "event_type"}
	for _, f := range requiredFields {
		if _, ok := out[f]; !ok {
			t.Errorf("LogEmitter output missing field %q", f)
		}
	}
}

func TestLogEmitter_EventTypeValue(t *testing.T) {
	var buf bytes.Buffer
	logger := zerolog.New(&buf)
	e := telemetry.NewLogEmitter(logger)

	ev := sampleEvent()
	ev.EventType = telemetry.EventAuthFailure
	e.Emit(context.Background(), ev)

	var out map[string]interface{}
	_ = json.Unmarshal(buf.Bytes(), &out)

	if out["event_type"] != string(telemetry.EventAuthFailure) {
		t.Errorf("event_type: expected %q, got %v", telemetry.EventAuthFailure, out["event_type"])
	}
}

func TestLogEmitter_ImplementsInterface(t *testing.T) {
	var buf bytes.Buffer
	logger := zerolog.New(&buf)
	var _ telemetry.Emitter = telemetry.NewLogEmitter(logger)
}

// ---- MultiEmitter ----

type capturingEmitter struct {
	events []telemetry.Event
}

func (c *capturingEmitter) Emit(_ context.Context, ev telemetry.Event) {
	c.events = append(c.events, ev)
}

func TestMultiEmitter_FansOut(t *testing.T) {
	a := &capturingEmitter{}
	b := &capturingEmitter{}
	m := telemetry.NewMultiEmitter(a, b)

	ev := sampleEvent()
	m.Emit(context.Background(), ev)

	if len(a.events) != 1 {
		t.Errorf("emitter a: expected 1 event, got %d", len(a.events))
	}
	if len(b.events) != 1 {
		t.Errorf("emitter b: expected 1 event, got %d", len(b.events))
	}
}

func TestMultiEmitter_EmptyIsNoop(t *testing.T) {
	m := telemetry.NewMultiEmitter()
	m.Emit(context.Background(), sampleEvent()) // must not panic
}

func TestMultiEmitter_ImplementsInterface(t *testing.T) {
	var _ telemetry.Emitter = telemetry.NewMultiEmitter()
}

// ---- Context helpers ----

func TestWithEmitter_RoundTrip(t *testing.T) {
	orig := telemetry.NoopEmitter{}
	ctx := telemetry.WithEmitter(context.Background(), orig)
	got := telemetry.EmitterFromContext(ctx)
	if got == nil {
		t.Fatal("EmitterFromContext returned nil after WithEmitter")
	}
}

func TestEmitterFromContext_FallsBackToNoop(t *testing.T) {
	got := telemetry.EmitterFromContext(context.Background())
	if got == nil {
		t.Fatal("EmitterFromContext must never return nil — fallback to NoopEmitter expected")
	}
	// Verify the fallback doesn't panic
	got.Emit(context.Background(), sampleEvent())
}

// ---- EventType constants ----

func TestEventTypeConstants(t *testing.T) {
	cases := []struct {
		et   telemetry.EventType
		want string
	}{
		{telemetry.EventAuthStart, "auth_start"},
		{telemetry.EventAuthSuccess, "auth_success"},
		{telemetry.EventAuthFailure, "auth_failure"},
		{telemetry.EventTokenIssued, "token_issued"},
		{telemetry.EventUnsupportedFeature, "unsupported_feature"},
		{telemetry.EventInvalidRequest, "invalid_request"},
		{telemetry.EventMigration, "migration_event"},
	}
	for _, c := range cases {
		if string(c.et) != c.want {
			t.Errorf("EventType %q: expected %q", c.et, c.want)
		}
	}
}