Ui.java

package sketch;

import java.awt.Rectangle;
import java.util.HashMap;

public class Ui {

//////////////////////////////////// STATE /////////////////////////////////////
    private static class State {

        State parent;
        HashMap<Object, State> children = new HashMap<Object, State>();
        Object value;
        int key;
    }

    private static State state = new State();

    private static State nextChildState(Object initialValue, Object key) {
        if (initialValue == null) {
            throw new IllegalArgumentException("Initial value must not be null.");
        }
        if (key == null) {
            key = ++state.key;
        }
        State child = state.children.get(key);
        if (child == null) {
            child = new State();
            child.parent = state;
            child.value = initialValue;
            state.children.put(key, child);
        } else {
            if (child.value.getClass() != initialValue.getClass()) {
                child.value = initialValue;
            }
        }
        return child;
    }

    public static <T> T nextState(T initialValue, Object key) {
        return (T) nextChildState(initialValue, key).value;
    }

    public static <T> T nextState(T initialValue) {
        return nextState(initialValue, null);
    }

    public static <T> T pushState(T initialValue, Object key) {
        return (T) (state = nextChildState(initialValue, key)).value;
    }

    public static <T> T pushState(T initialValue) {
        return pushState(initialValue, null);
    }

    public static void popState() {
        if (state.parent == null) {
            throw new IllegalStateException("Too many `popState()`.");
        }
        state = state.parent;
    }

    private static void resetState(State state) {
        state.key = 0;
        for (State child : state.children.values()) {
            resetState(child);
        }
    }

    static void resetState() {
        assert (state.parent == null); // This must be root state.
        resetState(state);
    }

/////////////////////////////////// LAYOUT /////////////////////////////////////
    private static class Layout {

        Layout previous;
        Layout next;
        Rectangle bounds;
        int spacing;
        int padding;
        int[] columnWidths;
        int rowHeight;
        int x;
        int y;
        int column;
        int row;
    }

    private static Layout layout = new Layout();

    public static void setBounds(Rectangle bounds) {
        layout.bounds = bounds;
    }

    public static void setPadding(int padding) {
        layout.padding = padding;
    }

    public static void setSpacing(int spacing) {
        layout.spacing = spacing;
    }

    public static void setColumnWidths(int[] columnWidths) {
        layout.columnWidths = columnWidths;
    }

    public static void setRowHeight(int rowHeight) {
        layout.rowHeight = rowHeight;
    }

    public static Rectangle nextLayout() {
        if (layout.column == 0 && layout.row == 0) {
            layout.x = layout.bounds.x + layout.padding;
            layout.y = layout.bounds.y + layout.padding;
        }
        int width = layout.columnWidths[layout.column];
        int height = layout.rowHeight;
        if (width == -1) {
            width = layout.bounds.width - layout.padding * 2;
        } else if (width < 0) {
            width = layout.bounds.width - layout.padding * 2 + width;
        }
        if (height == -1) {
            height = layout.bounds.height - layout.padding * 2;
        } else if (height < 0) {
            height = layout.bounds.height - layout.padding * 2 + height;
        }
        Rectangle next = new Rectangle(layout.x, layout.y, width, height);
        layout.x = layout.x + width + layout.spacing;
        layout.column++;
        if (layout.column >= layout.columnWidths.length) {
            layout.x = layout.bounds.x + layout.padding;
            layout.y = layout.y + height + layout.spacing;
            layout.column = 0;
            layout.row++;
        }
        return next;
    }

    public static Rectangle pushLayout() {
        Rectangle bounds = nextLayout();
        if (layout.next == null) {
            layout.next = new Layout();
            layout.next.previous = layout;
        }
        layout = layout.next;
        layout.bounds = bounds;
        layout.column = 0;
        layout.row = 0;
        return bounds;
    }

    public static void popLayout() {
        if (layout.previous == null) {
            throw new IllegalStateException("Too many `popLayout()`.");
        }
        layout = layout.previous;
    }

    static void resetLayout() {
        assert (layout.previous == null);
        layout.column = 0;
        layout.row = 0;
    }
}