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/*
* lemonad - Some functional sweetness for Java
* Copyright (C) 2019 Pacien TRAN-GIRARD
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
package org.pacien.lemonad.validation;
import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.function.Function;
import java.util.function.Predicate;
import lombok.NonNull;
import lombok.val;
import static java.util.stream.Collectors.toUnmodifiableList;
import static org.pacien.lemonad.validation.Validation.invalid;
import static org.pacien.lemonad.validation.Validation.valid;
/**
* A function which applies validation rules on a subject and reports possible errors.
*
* @param <S> the subject type
* @param <E> the error type
* @author pacien
*/
@FunctionalInterface public interface Validator<S, E> {
/**
* @param subject the subject to validate, which can potentially be null.
* @return the non-null result of the validation of the supplied subject.
*/
Validation<S, E> validate(S subject);
/**
* @param predicate the validation predicate testing the validity of a subject.
* @param negativeError an error to return if the subject does not pass the test.
* @return a {@link Validator} based on the supplied predicate and error.
*/
static <S, E> Validator<S, E> ensuringPredicate(@NonNull Predicate<? super S> predicate, @NonNull E negativeError) {
return subject -> predicate.test(subject) ? valid(subject) : invalid(subject, negativeError);
}
/**
* @param validators the {@link Validator}s to combine, to be evaluated in order of listing.
* @return a {@link Validator} based on the supplied ones.
*/
@SafeVarargs static <S, E> Validator<S, E> validatingAll(@NonNull Validator<? super S, ? extends E>... validators) {
val validatorList = Arrays.stream(validators).map(Objects::requireNonNull).collect(toUnmodifiableList());
return subject -> new ValidationContainer<>(
subject,
validatorList.stream()
.flatMap(validator -> validator.validate(subject).getErrors().stream())
.collect(toUnmodifiableList()));
}
/**
* @param getter the field getter mapping the validation subject.
* @param validator the {@link Validator} validating the field.
* @return a {@link Validator} validating the parent object.
*/
static <S, F, E> Validator<S, E> validatingField(@NonNull Function<? super S, ? extends F> getter,
@NonNull Validator<? super F, ? extends E> validator) {
//noinspection unchecked
return subject -> new ValidationContainer<>(subject, (List<E>) validator.validate(getter.apply(subject)).getErrors());
}
}
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