package wdclient

import (
	"testing"
	"time"
)

func TestJitterBounds(t *testing.T) {
	cases := []time.Duration{
		1 * time.Millisecond,
		100 * time.Millisecond,
		1 * time.Second,
		5 * time.Second,
	}

	for _, d := range cases {
		for i := 0; i < 100; i++ {
			j := jitter(d)
			if j < d/2 {
				t.Errorf("jitter(%v) = %v, below lower bound %v", d, j, d/2)
			}
			if j >= d {
				t.Errorf("jitter(%v) = %v, at or above upper bound %v", d, j, d)
			}
		}
	}
}

func TestJitterZeroAndNegative(t *testing.T) {
	if j := jitter(0); j != 0 {
		t.Errorf("jitter(0) = %v, want 0", j)
	}
	if j := jitter(-1 * time.Second); j != 0 {
		t.Errorf("jitter(-1s) = %v, want 0", j)
	}
}

func TestJitterTinyDuration(t *testing.T) {
	// When d < 2, half == 0 and rand.Int63n(0) panics.
	// We should return d unmodified in that case.
	j := jitter(1 * time.Nanosecond)
	if j != 1*time.Nanosecond {
		t.Errorf("jitter(1ns) = %v, want 1ns", j)
	}
}

func TestJitterDistribution(t *testing.T) {
	const iterations = 10000
	const base = 100 * time.Millisecond
	var sum time.Duration

	for i := 0; i < iterations; i++ {
		j := jitter(base)
		sum += j
	}

	avg := sum / iterations
	// Equal jitter average should be around 75% of base (midpoint of [50%, 100%))
	expected := base * 3 / 4
	tolerance := base / 10 // ±10%

	if avg < expected-tolerance || avg > expected+tolerance {
		t.Errorf("average jitter %v deviated from expected %v", avg, expected)
	}
}