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package io.github.cwdesautels.monad;

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

/**
 * Right biased either monad.
 */
public interface Either {

    // Constructors

    static  Either left(L left) {
        return ImmutableLeft.builder()
                .left(left)
                .build();
    }

    static  Either right(R right) {
        return ImmutableRight.builder()
                .get(right)
                .build();
    }

    // Behaviour

    L getLeft();

    R get();

    boolean isLeft();

    boolean isRight();

    // Templates

    default R orElse(R other) {
        if (isRight()) {
            return get();
        } else {
            return other;
        }
    }

    default R orElseGet(Supplier other) {
        Objects.requireNonNull(other);

        if (isRight()) {
            return get();
        } else {
            return other.get();
        }
    }

    default R orElseMap(Function function) {
        Objects.requireNonNull(function);

        if (isRight()) {
            return get();
        } else {
            return function.apply(getLeft());
        }
    }

    default  R orElseThrow(Supplier supplier) throws X {
        Objects.requireNonNull(supplier);

        if (isLeft()) {
            throw supplier.get();
        } else {
            return get();
        }
    }

    default Either swap() {
        if (isRight()) {
            return left(get());
        } else {
            return right(getLeft());
        }
    }

    default  Either map(Function function) {
        Objects.requireNonNull(function);

        if (isRight()) {
            return right(function.apply(get()));
        } else {
            return left(getLeft());
        }
    }

    default  Either flatMap(Function> function) {
        Objects.requireNonNull(function);

        if (isRight()) {
            return Objects.requireNonNull(function.apply(get()));
        } else {
            return left(getLeft());
        }
    }

    default  Either mapLeft(Function function) {
        Objects.requireNonNull(function);

        if (isLeft()) {
            return left(function.apply(getLeft()));
        } else {
            return right(get());
        }
    }

    default  Either flatMapLeft(Function> function) {
        Objects.requireNonNull(function);

        if (isLeft()) {
            return Objects.requireNonNull(function.apply(getLeft()));
        } else {
            return right(get());
        }
    }

    default  T fold(Function leftMapper, Function rightMapper) {
        Objects.requireNonNull(leftMapper);
        Objects.requireNonNull(rightMapper);

        if (isRight()) {
            return rightMapper.apply(get());
        } else {
            return leftMapper.apply(getLeft());
        }
    }

    default Either ifRight(Consumer consumer) {
        Objects.requireNonNull(consumer);

        if (isRight()) {
            consumer.accept(get());
        }

        return this;
    }

    default Either ifLeft(Consumer consumer) {
        Objects.requireNonNull(consumer);

        if (isLeft()) {
            consumer.accept(getLeft());
        }

        return this;
    }

    default Optional toOptional() {
        if (isRight()) {
            return Optional.ofNullable(get());
        } else {
            return Optional.empty();
        }
    }
}