package web

import (
	"os"
	"path/filepath"
	"testing"
	"time"
)

func TestWatchLogDebouncesChanges(t *testing.T) {
	logPath := filepath.Join(t.TempDir(), "trace.jsonl")
	if err := os.WriteFile(logPath, []byte("initial\n"), 0o644); err != nil {
		t.Fatal(err)
	}

	done := make(chan struct{})
	stopped := make(chan struct{})
	rebuilt := make(chan struct{}, 2)
	go func() {
		defer close(stopped)
		watchLogUntil(newFileLog(logPath), 60*time.Millisecond, 5*time.Millisecond, done, func() {
			rebuilt <- struct{}{}
		})
	}()
	time.Sleep(20 * time.Millisecond)

	if err := os.WriteFile(logPath, []byte("first change\n"), 0o644); err != nil {
		t.Fatal(err)
	}
	time.Sleep(30 * time.Millisecond)
	if err := os.WriteFile(logPath, []byte("second change\n"), 0o644); err != nil {
		t.Fatal(err)
	}

	select {
	case <-rebuilt:
		t.Fatal("rebuilt before the debounce interval elapsed")
	case <-time.After(40 * time.Millisecond):
	}
	select {
	case <-rebuilt:
	case <-time.After(200 * time.Millisecond):
		t.Fatal("did not rebuild after changes settled")
	}
	select {
	case <-rebuilt:
		t.Fatal("multiple changes produced more than one rebuild")
	case <-time.After(40 * time.Millisecond):
	}

	close(done)
	select {
	case <-stopped:
	case <-time.After(time.Second):
		t.Fatal("watcher did not stop")
	}
}