package runtimex

import (
	"errors"
	"io"
	"testing"
)

func TestChanStackPushPop(t *testing.T) {
	stack := NewChanStack(2)
	if err := stack.Push("a"); err != nil {
		t.Fatalf("Push failed: %v", err)
	}
	if err := stack.Push("b"); err != nil {
		t.Fatalf("Push failed: %v", err)
	}
	if stack.Len() != 2 {
		t.Fatalf("expected len=2, got %d", stack.Len())
	}
	if stack.Free() != 0 {
		t.Fatalf("expected free=0, got %d", stack.Free())
	}

	first, err := stack.Pop()
	if err != nil {
		t.Fatalf("Pop failed: %v", err)
	}
	if first.(string) != "a" {
		t.Fatalf("unexpected first value: %v", first)
	}
	second, err := stack.Pop()
	if err != nil {
		t.Fatalf("Pop failed: %v", err)
	}
	if second.(string) != "b" {
		t.Fatalf("unexpected second value: %v", second)
	}
}

func TestChanStackTryPushFull(t *testing.T) {
	stack := NewChanStack(1)
	if err := stack.TryPush("a"); err != nil {
		t.Fatalf("TryPush should succeed on empty stack: %v", err)
	}
	if err := stack.TryPush("b"); !errors.Is(err, ErrStackFull) {
		t.Fatalf("TryPush should return ErrStackFull, got %v", err)
	}
}

func TestChanStackCloseBehavior(t *testing.T) {
	stack := NewChanStack(1)
	if err := stack.Close(); err != nil {
		t.Fatalf("Close should succeed first time: %v", err)
	}
	if err := stack.Close(); !errors.Is(err, ErrStackClosed) {
		t.Fatalf("Close should return ErrStackClosed on second call, got %v", err)
	}
	if err := stack.Push("x"); !errors.Is(err, io.EOF) {
		t.Fatalf("Push after close should return io.EOF, got %v", err)
	}
	if _, err := stack.Pop(); !errors.Is(err, io.EOF) {
		t.Fatalf("Pop after close should return io.EOF, got %v", err)
	}
}