package service

import (
	"context"
	"fmt"
	"sync"
	"testing"
	"time"

	"github.com/google/uuid"
	"github.com/igodwin/notifier/internal/domain"
)

// TestConcurrentSendGetListNoRace hammers Send, GetNotification, and
// ListNotifications concurrently while worker goroutines process notifications
// pulled from the queue in the background. It is meant to be run with
// `go test -race`: if the service ever stored or returned a raw pointer that a
// worker also mutates (the bug this test guards against), the race detector
// flags a data race here.
func TestConcurrentSendGetListNoRace(t *testing.T) {
	svc := createTestService(t)

	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
	defer cancel()

	if err := svc.Start(ctx); err != nil {
		t.Fatalf("Failed to start service: %v", err)
	}
	defer func() { _ = svc.Stop() }()

	const numSenders = 8
	const sendsPerSender = 25

	var idsMu sync.Mutex
	var ids []string

	var sendersWg sync.WaitGroup
	for s := 0; s < numSenders; s++ {
		sendersWg.Add(1)
		go func(sender int) {
			defer sendersWg.Done()
			for i := 0; i < sendsPerSender; i++ {
				notification := &domain.Notification{
					ID:         uuid.New().String(),
					Type:       domain.TypeStdout,
					Status:     domain.StatusPending,
					Subject:    fmt.Sprintf("race-test-%d-%d", sender, i),
					Body:       "race test body",
					Recipients: []string{"race@example.com"},
					CC:         []string{"cc@example.com"},
					Metadata:   map[string]interface{}{"sender": sender},
					CreatedAt:  time.Now(),
					MaxRetries: 1,
				}

				if _, err := svc.Send(ctx, notification); err != nil {
					t.Errorf("Send failed: %v", err)
					continue
				}

				idsMu.Lock()
				ids = append(ids, notification.ID)
				idsMu.Unlock()
			}
		}(s)
	}

	// Readers race against the senders and against the worker pool mutating
	// notifications as they're processed.
	stopReaders := make(chan struct{})
	var readersWg sync.WaitGroup
	for r := 0; r < 4; r++ {
		readersWg.Add(1)
		go func() {
			defer readersWg.Done()
			for {
				select {
				case <-stopReaders:
					return
				default:
				}

				idsMu.Lock()
				n := len(ids)
				var id string
				if n > 0 {
					id = ids[n-1]
				}
				idsMu.Unlock()

				if id != "" {
					if notif, err := svc.GetNotification(ctx, id); err == nil {
						// Touch the returned notification's reference fields;
						// if it were aliased with the stored/queued copy a
						// concurrent worker mutation would trip the race
						// detector right here.
						_ = notif.Status
						_ = append([]string(nil), notif.Recipients...)
					}
				}

				list, err := svc.ListNotifications(ctx, &domain.NotificationFilter{})
				if err != nil {
					t.Errorf("ListNotifications failed: %v", err)
					continue
				}
				for _, notif := range list {
					_ = notif.Status
					_ = append([]string(nil), notif.Recipients...)
				}
			}
		}()
	}

	sendersWg.Wait()
	close(stopReaders)
	readersWg.Wait()

	// Give the worker pool a moment to drain the queue, then sanity check the
	// service is still consistent.
	deadline := time.Now().Add(5 * time.Second)
	for time.Now().Before(deadline) {
		stats, err := svc.GetStats(ctx)
		if err != nil {
			t.Fatalf("GetStats failed: %v", err)
		}
		if stats.TotalSent == numSenders*sendsPerSender {
			return
		}
		time.Sleep(20 * time.Millisecond)
	}

	stats, err := svc.GetStats(ctx)
	if err != nil {
		t.Fatalf("GetStats failed: %v", err)
	}
	t.Logf("final stats: sent=%d failed=%d queued=%d pending=%d", stats.TotalSent, stats.TotalFailed, stats.TotalQueued, stats.TotalPending)
	if stats.TotalSent != numSenders*sendsPerSender {
		t.Errorf("expected all %d notifications to reach Sent, got %d", numSenders*sendsPerSender, stats.TotalSent)
	}
}