package ds

import "testing"

func TestStackBasic(t *testing.T) {
	var s Stack[int]
	if !s.Empty() {
		t.Fatal("新建栈应为空")
	}
	if _, ok := s.Pop(); ok {
		t.Fatal("空栈 Pop 应返回 false")
	}
	if _, ok := s.Peek(); ok {
		t.Fatal("空栈 Peek 应返回 false")
	}

	s.Push(1)
	s.Push(2)
	s.Push(3)
	if s.Len() != 3 {
		t.Fatalf("Len = %d, want 3", s.Len())
	}

	// LIFO 顺序
	for _, want := range []int{3, 2, 1} {
		got, ok := s.Pop()
		if !ok {
			t.Fatalf("Pop 失败,期望 %d", want)
		}
		if got != want {
			t.Fatalf("Pop = %d, want %d", got, want)
		}
	}
	if !s.Empty() {
		t.Fatal("全部弹出后应为空")
	}
}

func TestStackStringType(t *testing.T) {
	var s Stack[string]
	s.Push("a")
	s.Push("b")
	top, ok := s.Peek()
	if !ok || top != "b" {
		t.Fatalf("Peek = %q,%v, want \"b\",true", top, ok)
	}
	v, _ := s.Pop()
	if v != "b" {
		t.Fatalf("Pop = %q, want \"b\"", v)
	}
}

func TestStackLeakFunctional(t *testing.T) {
	// 功能性验证:大量 push/pop 交替后仍正确,间接验证无状态泄漏。
	var s Stack[int]
	s.Push(1)
	s.Push(2)
	v, _ := s.Pop()
	if v != 2 {
		t.Fatalf("Pop = %d, want 2", v)
	}
	s.Push(3)
	v, _ = s.Pop()
	if v != 3 {
		t.Fatalf("Pop = %d, want 3", v)
	}
	v, _ = s.Pop()
	if v != 1 {
		t.Fatalf("Pop = %d, want 1", v)
	}
	if !s.Empty() {
		t.Fatal("应为空")
	}
}