memento__originator_memento_in_java.java

public final class Editor {

    private final List<String> text;
    private int caretPosition;

    public Editor() {
        this.text = new ArrayList<>();
        this.caretPosition = 0;
    }

    public void write(final String sentence) {
        text.add(sentence);
        caretPosition = calculateCaretPositionInEndOf(text);
    }

    public void edit(final int index, final String newSentence) {
        text.remove(index);
        text.add(index, newSentence);
        final List<String> subText = text.subList(0, index + 1);
        caretPosition = calculateCaretPositionInEndOf(subText);
    }

    public void delete(final int index) {
        final List<String> subText = new ArrayList<>(text.subList(0, index));
        text.remove(index);
        caretPosition = calculateCaretPositionInEndOf(subText);
    }

    public void render(final Screen screen) {
        final String allText = String.join("", text);
        screen.render(allText);
        screen.renderCaretAt(caretPosition);
    }

    public Memento backup() {
        return new Memento(text, caretPosition);
    }

    public void restore(final Memento memento) {
        text.clear();
        text.addAll(memento.text);
        caretPosition = memento.caretPosition;
    }

    private int calculateCaretPositionInEndOf(final List<String> lines) {
        return lines.stream().mapToInt(String::length).sum() + 1;
    }

    public static final class Memento {

        private final List<String> text;
        private final int caretPosition;

        public Memento(List<String> text, int caretPosition) {
            this.text = new ArrayList<>(text);
            this.caretPosition = caretPosition;
        }
    }
}