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package solid.optional;

import solid.functions.Action1;
import solid.functions.Func0;
import solid.functions.Func1;

/**
 * Optional is a wrapper around a value that can be empty (null).
 * It provides utility methods to handle different cases.
 */
public class Optional {

    private static final Optional EMPTY = new Optional<>(null);

    private final T value;

    private Optional(T value) {
        this.value = value;
    }

    /**
     * Returns an empty optional.
     */
    public static  Optional empty() {
        return (Optional) EMPTY;
    }

    /**
     * Returns an optional for a given value
     */
    public static  Optional of(T value) {
        return value == null ? (Optional) EMPTY : new Optional<>(value);
    }

    /**
     * Returns the optional value. Thrown {@link NullPointerException} if the value does not exist.
     */
    public T get() {
        if (value == null)
            throw new NullPointerException();
        return value;
    }

    /**
     * Returns true if the optional value does exist.
     */
    public boolean isPresent() {
        return value != null;
    }

    /**
     * Calls a given action if the optional value does exist.
     */
    public void ifPresent(Action1 action) {
        if (value != null)
            action.call(value);
    }

    /**
     * Returns the current value or default value if optional does not exist.
     */
    public T or(T default1) {
        return value != null ? value : default1;
    }

    /**
     * Returns value of uses a given factory if the value does not exist.
     */
    public T or(Func0 func1) {
        return value != null ? value : func1.call();
    }

    /**
     * Returns the value without null checking it.
     */
    public T orNull() {
        return value;
    }

    /**
     * Transforms the value if exists, returns empty Optional otherwise.
     */
    public  Optional map(Func1 func1) {
        return value == null ? Optional.empty() : Optional.of(func1.call(value));
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Optional optional = (Optional) o;

        return !(value != null ? !value.equals(optional.value) : optional.value != null);
    }

    @Override
    public int hashCode() {
        return value != null ? value.hashCode() : 0;
    }

    @Override
    public String toString() {
        return "Optional{" +
            "value=" + value +
            '}';
    }
}