package graph

import (
	"sync/atomic"
	"testing"
	"testing/synctest"
	"time"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

func TestDebouncer_Coalesces(t *testing.T) {
	synctest.Test(t, func(t *testing.T) {
		d := NewDebouncer(50 * time.Millisecond)
		var calls atomic.Int32

		// Fire 10 rapid calls for the same key — only the last should execute.
		for range 10 {
			d.Debounce("key1", func() {
				calls.Add(1)
			})
		}

		// Advance fake clock past the debounce delay and let goroutines settle.
		time.Sleep(50 * time.Millisecond)
		synctest.Wait()

		assert.Equal(t, int32(1), calls.Load(), "rapid calls should coalesce into a single execution")
	})
}

func TestDebouncer_DifferentKeys(t *testing.T) {
	synctest.Test(t, func(t *testing.T) {
		d := NewDebouncer(50 * time.Millisecond)
		var calls atomic.Int32

		d.Debounce("key-a", func() { calls.Add(1) })
		d.Debounce("key-b", func() { calls.Add(1) })
		d.Debounce("key-c", func() { calls.Add(1) })

		time.Sleep(50 * time.Millisecond)
		synctest.Wait()

		assert.Equal(t, int32(3), calls.Load(), "different keys should fire independently")
	})
}

func TestDebouncer_TimerReset(t *testing.T) {
	synctest.Test(t, func(t *testing.T) {
		d := NewDebouncer(100 * time.Millisecond)
		var value atomic.Int32

		// First call sets value to 1.
		d.Debounce("key", func() { value.Store(1) })

		// Advance 60ms (less than the 100ms delay) — first timer hasn't fired.
		time.Sleep(60 * time.Millisecond)

		// Replace with value 2 — resets the timer to fire at 60+100 = 160ms.
		d.Debounce("key", func() { value.Store(2) })

		// Advance another 100ms (total 160ms) to fire the reset timer.
		time.Sleep(100 * time.Millisecond)
		synctest.Wait()

		require.Equal(t, int32(2), value.Load(), "later call should replace the earlier one")
	})
}