SimpleCommand

class SimpleCommand(
    private val action: () -> Unit,
    private val isEnabledPredicate: () -> Boolean = { true },
    private val isVisiblePredicate: () -> Boolean = { true }
) : Command {
    private val boundComponents = LinkedHashSet<Component>(1)

    private val listener = object : Property.ValueChangeListener, Container.ItemSetChangeListener, Button.ClickListener {
        override fun valueChange(event: Property.ValueChangeEvent?) = refresh()

        override fun containerItemSetChange(event: Container.ItemSetChangeEvent?) = refresh()

        override fun buttonClick(event: Button.ClickEvent?) = execute()
    }

    override fun execute() = when {
        isEnabled -> action()
        else -> throw IllegalStateException("Command is disabled")
    }

    override val isEnabled: Boolean
        get() = isEnabledPredicate()

    override val isVisible: Boolean
        get() = isVisiblePredicate()

    private fun bindComponent(component: Component) {
        if (boundComponents.add(component)) {
            refreshComponent(component)
        }
    }

    private fun unbindComponent(component: Component) {
        if (boundComponents.remove(component)) {
            component.isEnabled = true
            component.isVisible = true
        }
    }

    private fun refreshComponent(component: Component) {
        component.isEnabled = isEnabled
        component.isVisible = isVisible
    }

    private fun refresh() {
        for (component in boundComponents) {
            refreshComponent(component)
        }
    }

    override fun bindNotifier(notifier: Property.ValueChangeNotifier) = notifier.addValueChangeListener(listener)

    override fun unbindNotifier(notifier: Property.ValueChangeNotifier) = notifier.removeValueChangeListener(listener)

    override fun bindNotifier(notifier: Container.ItemSetChangeNotifier) = notifier.addItemSetChangeListener(listener)

    override fun unbindNotifier(notifier: Container.ItemSetChangeNotifier) = notifier.removeItemSetChangeListener(listener)

    override fun bindButton(button: Button) {
        button.addClickListener(listener)
        bindComponent(button)
    }

    override fun unbindButton(button: Button) {
        button.removeClickListener(listener)
        unbindComponent(button)
    }
}