package main.java;
import java.util.AbstractMap;
import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;
import java.util.stream.StreamSupport;

public class ObjectColumnSelectorBuilder<T> {
    private final Class<T> _canon;
    private final List<AbstractMap.SimpleEntry<String, Function<T, Object>>> _items = new ArrayList<>();
    private final List<Function<T, Object>> _anonymous = new ArrayList<>();

    public ObjectColumnSelectorBuilder(Class<T> canon) {
        this._canon = canon;
    }

    public <TProperty> ObjectColumnSelectorBuilder<T> bind(String displayName, Function<T, TProperty> getter) {
        _items.add(new AbstractMap.SimpleEntry<>(displayName, getter::apply));
        return this;
    }

    public <TProperty> ObjectColumnSelectorBuilder<T> bindAnonymous(Function<T, TProperty> getter) {
        _anonymous.add(getter::apply);
        return this;
    }

    public Function<Object, Object[]> build() {
        return items -> {
            if (items instanceof Object[] && _canon.isAssignableFrom(((Object[]) items).getClass().getComponentType()) ||
                    items instanceof Iterable<?> &&
                            StreamSupport.stream(((Iterable<?>) items).spliterator(), false).
                                    allMatch(it->it==null||_canon.isInstance(it))) {
                if (!_items.isEmpty()) {
                    return _items.toArray(new AbstractMap.SimpleEntry[0]);
                } else {
                    return _anonymous.toArray(new Function[0]);
                }
            } else {
                return null;
            }
        };
    }
}