package ysl.utils;

import java.util.*;
import java.util.function.Function;
import java.util.function.Supplier;

public class NullHelper {

    /**
     * Transforms the provided value if it is not null.
     *
     * @param value the value to transform
     * @param transform the transformation to apply
     * @param <T> the type of the provided value
     * @param <R> the return type of the transformation
     * @return the transformed value or null if the provided value was null
     */
    public static <T, R> R nullSafeGet(T value, Function<T, R> transform) {
        if (value == null) {
            return null;
        }
        return transform.apply(value);
    }

    /**
     * Transforms the provided value if it is not null or computes a default value.
     *
     * @param value the original value to transform
     * @param transform the transformation to apply if the provided value is not null
     * @param supplier the function to compute a default value if the provided one is null
     * @param <T> the type of the provided value
     * @param <R> the type of the returned value
     */
    public static <T, R> R nullSafeGetOr(T value, Function<T, R> transform, Supplier<R> supplier) {
        if (value == null) {
            return supplier.get();
        }
        return transform.apply(value);
    }

    /**
     * Returns the first non-null value from the provided arguments.
     *
     * @throws NullPointerException if there is no non-null value to return
     */
    @SafeVarargs
    public static <T> T or(T t, Supplier<? extends T>... suppliers) {
        if (t != null) {
            return t;
        }

        for (Supplier<? extends T> supplier : suppliers) {
            T t1 = supplier.get();
            if (t1 != null) {
                return t1;
            }
        }

        throw new NullPointerException();
    }
}