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package org.reactfx.util;

import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Consumer;
import java.util.function.Function;

public interface Either {

    static  Either left(L l) {
        return new Left<>(l);
    }

    static  Either right(R r) {
        return new Right<>(r);
    }

    static  Either leftOrNull(Optional l) {
        return leftOrDefault(l, null);
    }

    static  Either rightOrNull(Optional r) {
        return rightOrDefault(r, null);
    }

    static  Either leftOrDefault(Optional l, R r) {
        return l.isPresent() ? left(l.get()) : right(r);
    }

    static  Either rightOrDefault(Optional r, L l) {
        return r.isPresent() ? right(r.get()) : left(l);
    }

    boolean isLeft();
    boolean isRight();
    L getLeft();
    R getRight();
    L toLeft(Function f);
    R toRight(Function f);
    Optional asLeft();
    Optional asRight();
    void ifLeft(Consumer f);
    void ifRight(Consumer f);
    void exec(
            Consumer ifLeft,
            Consumer ifRight);
     Either mapLeft(
            Function f);
     Either mapRight(
            Function f);
     Either map(
            Function f,
            Function g);
     Either flatMap(
            Function> f,
            Function> g);
     Either flatMapLeft(
            Function> f);
     Either flatMapRight(
            Function> f);
     T unify(
            Function f,
            Function g);
}


class Left implements Either {
    private final L value;

    public Left(L value) { this.value = value; }

    @Override
    public boolean isLeft() { return true; }

    @Override
    public boolean isRight() { return false; }

    @Override
    public L getLeft() { return value; }

    @Override
    public R getRight() { throw new NoSuchElementException(); }

    @Override
    public L toLeft(Function f) {
        return value;
    }

    @Override
    public R toRight(Function f) {
        return f.apply(value);
    }

    @Override
    public Optional asLeft() { return Optional.of(value); }

    @Override
    public Optional asRight() { return Optional.empty(); }

    @Override
    public void ifLeft(Consumer f) { f.accept(value); }

    @Override
    public void ifRight(Consumer f) { /* do nothing */ }

    @Override
    public void exec(
            Consumer ifLeft,
            Consumer ifRight) {
        ifLeft.accept(value);
    }

    @Override
    public  Either mapLeft(Function f) {
        return new Left<>(f.apply(value));
    }

    @Override
    public  Either mapRight(Function f) {
        return new Left<>(value);
    }

    @Override
    public  Either map(
            Function f,
            Function g) {
        return new Left<>(f.apply(value));
    }

    @Override
    public  Either flatMap(
            Function> f,
            Function> g) {
        return f.apply(value);
    }

    @Override
    public  Either flatMapLeft(
            Function> f) {
        return f.apply(value);
    }

    @Override
    public  Either flatMapRight(
            Function> f) {
        return new Left<>(value);
    }

    @Override
    public  T unify(
            Function f,
            Function g) {
        return f.apply(value);
    }

    @Override
    public final int hashCode() {
        return Objects.hash(value);
    }

    @Override
    public final boolean equals(Object other) {
        if(other instanceof Left) {
            Left that = (Left) other;
            return Objects.equals(this.value, that.value);
        } else {
            return false;
        }
    }

    @Override
    public String toString() {
        return "left(" + value + ")";
    }
}


class Right implements Either {
    private final R value;

    public Right(R value) { this.value = value; }

    @Override
    public boolean isLeft() { return false; }

    @Override
    public boolean isRight() { return true; }

    @Override
    public L getLeft() { throw new NoSuchElementException(); }

    @Override
    public R getRight() { return value; }

    @Override
    public L toLeft(Function f) {
        return f.apply(value);
    }

    @Override
    public R toRight(Function f) {
        return value;
    }

    @Override
    public Optional asLeft() { return Optional.empty(); }

    @Override
    public Optional asRight() { return Optional.of(value); }

    @Override
    public void ifLeft(Consumer f) { /* do nothing */ }

    @Override
    public void ifRight(Consumer f) { f.accept(value); }

    @Override
    public void exec(
            Consumer ifLeft,
            Consumer ifRight) {
        ifRight.accept(value);
    }

    @Override
    public  Either mapLeft(Function f) {
        return new Right<>(value);
    }

    @Override
    public  Either mapRight(Function f) {
        return new Right<>(f.apply(value));
    }

    @Override
    public  Either map(
            Function f,
            Function g) {
        return new Right<>(g.apply(value));
    }

    @Override
    public  Either flatMap(
            Function> f,
            Function> g) {
        return g.apply(value);
    }

    @Override
    public  Either flatMapLeft(
            Function> f) {
        return new Right<>(value);
    }

    @Override
    public  Either flatMapRight(
            Function> f) {
        return f.apply(value);
    }

    @Override
    public  T unify(
            Function f,
            Function g) {
        return g.apply(value);
    }

    @Override
    public final int hashCode() {
        return Objects.hash(value);
    }

    @Override
    public final boolean equals(Object other) {
        if(other instanceof Right) {
            Right that = (Right) other;
            return Objects.equals(this.value, that.value);
        } else {
            return false;
        }
    }

    @Override
    public String toString() {
        return "right(" + value + ")";
    }
}