package retry

import (
	"testing"
	"time"
)

func TestExponentialBackoff(t *testing.T) {
	t.Run("doubles each attempt", func(t *testing.T) {
		b := ExponentialBackoff(100*time.Millisecond, 10*time.Second, false)

		want := []time.Duration{
			100 * time.Millisecond,  // attempt 0: base
			200 * time.Millisecond,  // attempt 1: base*2
			400 * time.Millisecond,  // attempt 2: base*4
			800 * time.Millisecond,  // attempt 3: base*8
			1600 * time.Millisecond, // attempt 4: base*16
		}

		for i, expected := range want {
			got := b.Delay(i)
			if got != expected {
				t.Errorf("attempt %d: expected %v, got %v", i, expected, got)
			}
		}
	})

	t.Run("caps at max", func(t *testing.T) {
		b := ExponentialBackoff(100*time.Millisecond, 500*time.Millisecond, false)

		// attempt 0: 100ms, 1: 200ms, 2: 400ms, 3: 500ms (capped), 4: 500ms
		for _, attempt := range []int{3, 4, 10} {
			got := b.Delay(attempt)
			if got != 500*time.Millisecond {
				t.Errorf("attempt %d: expected cap at 500ms, got %v", attempt, got)
			}
		}
	})

	t.Run("with jitter adds randomness", func(t *testing.T) {
		base := 100 * time.Millisecond
		b := ExponentialBackoff(base, 10*time.Second, true)

		// Run multiple times; with jitter, delay >= base for attempt 0.
		// Also verify not all values are identical (randomness).
		seen := make(map[time.Duration]bool)
		for range 20 {
			d := b.Delay(0)
			if d < base {
				t.Fatalf("delay %v is less than base %v", d, base)
			}
			// With jitter: delay = base + rand in [0, base/2), so max is base*1.5
			maxExpected := base + base/2
			if d > maxExpected {
				t.Fatalf("delay %v exceeds expected max %v", d, maxExpected)
			}
			seen[d] = true
		}
		if len(seen) < 2 {
			t.Errorf("expected jitter to produce varying delays, got %d unique values", len(seen))
		}
	})
}

func TestConstantBackoff(t *testing.T) {
	t.Run("always returns same value", func(t *testing.T) {
		d := 250 * time.Millisecond
		b := ConstantBackoff(d)

		for _, attempt := range []int{0, 1, 2, 5, 100} {
			got := b.Delay(attempt)
			if got != d {
				t.Errorf("attempt %d: expected %v, got %v", attempt, d, got)
			}
		}
	})
}