memento__caretaker_usage.kt

class UI(
    private val screen: Screen
) {

    private val editor = Editor()
    private val backups = mutableListOf<Memento>()

    fun write(text: String) {
        backups.add(0, editor.backup())
        editor.write(text)
        editor.render(screen)
    }

    fun edit(index: Int, text: String) {
        backups.add(0, editor.backup())
        editor.edit(index, text)
        editor.render(screen)
    }

    fun delete(index: Int) {
        backups.add(0, editor.backup())
        editor.delete(index)
        editor.render(screen)
    }

    fun undo() {
        val memento = backups.removeAt(0)
        editor.restore(memento)
        editor.render(screen)
    }
}

fun main() {
    val screen = StdoutScreen()
    val ui = UI(screen)

    with(ui) {
        write("Hello, there! ")
        write("How are you? ")
        write("I hope you feel good :)")
        edit(1, "Kotlin! ")
        delete(1)
        undo()
        undo()
        undo()
        undo()
        undo()
    }
}

/* which produces this:
Hello, there! |
Hello, there! How are you? |
Hello, there! How are you? I hope you feel good :)|
Hello, there! Kotlin! |I hope you feel good :)
Hello, there! |I hope you feel good :)
Hello, there! Kotlin! |I hope you feel good :)
Hello, there! How are you? I hope you feel good :)|
Hello, there! How are you? |
Hello, there! |
|
/*