package lottery

import (
	"testing"
)

func TestWeightedPicker_EmptyPool(t *testing.T) {
	p := NewWeightedPicker(42)
	if _, err := p.Pick(nil); err != ErrEmptyPool {
		t.Fatalf("expected ErrEmptyPool for nil pool, got %v", err)
	}
	if _, err := p.Pick([]Prize{{Weight: 0}, {Weight: 0}}); err != ErrEmptyPool {
		t.Fatalf("expected ErrEmptyPool when all weights are 0, got %v", err)
	}
}

func TestWeightedPicker_SkipsZeroWeight(t *testing.T) {
	p := NewWeightedPicker(1)
	pool := []Prize{
		{Id: 1, Weight: 0},   // 不参与
		{Id: 2, Weight: 100}, // 独占权重
		{Id: 3, Weight: 0},   // 不参与
	}
	for i := 0; i < 200; i++ {
		idx, err := p.Pick(pool)
		if err != nil {
			t.Fatalf("Pick err: %v", err)
		}
		if idx != 1 {
			t.Fatalf("expected idx 1 (only positive weight), got %d", idx)
		}
	}
}

func TestWeightedPicker_DistributionCloseToWeights(t *testing.T) {
	p := NewWeightedPicker(2026)
	pool := []Prize{
		{Id: 10, Weight: 10}, // 10/60 ≈ 16.67%
		{Id: 20, Weight: 20}, // 20/60 ≈ 33.33%
		{Id: 30, Weight: 30}, // 30/60 = 50%
	}
	const trials = 60000
	counts := make(map[int]int)
	for i := 0; i < trials; i++ {
		idx, err := p.Pick(pool)
		if err != nil {
			t.Fatalf("Pick err: %v", err)
		}
		counts[idx]++
	}
	// 允许 ±2% 偏差
	expect := []float64{10.0 / 60, 20.0 / 60, 30.0 / 60}
	for i, e := range expect {
		got := float64(counts[i]) / float64(trials)
		if got < e-0.02 || got > e+0.02 {
			t.Fatalf("prize %d: expected %.4f (±0.02), got %.4f", i, e, got)
		}
	}
}

func TestWeightedPicker_DeterministicWithFixedSeed(t *testing.T) {
	pool := []Prize{
		{Id: 1, Weight: 1},
		{Id: 2, Weight: 1},
		{Id: 3, Weight: 1},
	}
	a := NewWeightedPicker(7)
	b := NewWeightedPicker(7)
	for i := 0; i < 20; i++ {
		ai, _ := a.Pick(pool)
		bi, _ := b.Pick(pool)
		if ai != bi {
			t.Fatalf("iter %d: seed 7 diverged: a=%d b=%d", i, ai, bi)
		}
	}
}