package api

import (
	"reflect"
	"unsafe"
)

// ChanIsClosed 判断channel是否关闭
func ChanIsClosed(ch any) bool {
	if reflect.TypeOf(ch).Kind() != reflect.Chan {
		panic("only channels!")
	}
	cptr := *(*uintptr)(unsafe.Pointer(
		unsafe.Pointer(uintptr(unsafe.Pointer(&ch)) + unsafe.Sizeof(uint(0))),
	))
	// this function will return true if chan.closed > 0
	// see hchan on https://github.com/golang/go/blob/master/src/runtime/chan.go
	// type hchan struct {
	// qcount   uint           // total data in the queue
	// dataqsiz uint           // size of the circular queue
	// buf      unsafe.Pointer // points to an array of dataqsiz elements
	// elemsize uint16
	// closed   uint32
	// **
	cptr += unsafe.Sizeof(uint(0)) * 2
	cptr += unsafe.Sizeof(unsafe.Pointer(uintptr(0)))
	cptr += unsafe.Sizeof(uint16(0))
	return *(*uint32)(unsafe.Pointer(cptr)) > 0
}