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/*
 * Copyright 2016-2022 the original author or authors.
 *
 * All rights reserved. This program and the accompanying materials are
 * made available under the terms of the Eclipse Public License v2.0 which
 * accompanies this distribution and is available at
 *
 * http://www.eclipse.org/legal/epl-v20.html
 */

package org.junitpioneer.jupiter.cartesian;

import static java.util.Arrays.stream;
import static java.util.stream.Collectors.toSet;

import java.lang.reflect.Parameter;
import java.util.EnumSet;
import java.util.Set;
import java.util.stream.Stream;

import org.junit.jupiter.api.extension.ExtensionContext;
import org.junit.platform.commons.PreconditionViolationException;
import org.junit.platform.commons.support.AnnotationSupport;

/**
 * This is basically an enhanced copy of Jupiter's {@code EnumArgumentsProvider},
 * except it does NOT support {@code @ParameterizedTest} and implements
 * {@link CartesianParameterArgumentsProvider} for use with {@code @CartesianTest}.
 */
class CartesianEnumArgumentsProvider> implements CartesianParameterArgumentsProvider {

	@Override
	public Stream provideArguments(ExtensionContext context, Parameter parameter) {
		CartesianTest.Enum enumSource = AnnotationSupport
				.findAnnotation(parameter, CartesianTest.Enum.class)
				.orElseThrow(() -> new PreconditionViolationException(
					"Parameter has to be annotated with " + CartesianTest.Enum.class.getName()));

		Class parameterType = parameter.getType();
		Set constants = getEnumConstants(enumSource, parameterType);
		CartesianTest.Enum.Mode mode = enumSource.mode();
		String[] declaredConstantNames = enumSource.names();
		if (declaredConstantNames.length > 0) {
			Set uniqueNames = stream(declaredConstantNames).collect(toSet());
			if (uniqueNames.size() != declaredConstantNames.length)
				throw new PreconditionViolationException("Duplicate enum constant name(s) found in " + enumSource);

			mode.validate(enumSource, constants, uniqueNames);
			constants.removeIf(constant -> !mode.select(constant, uniqueNames));
		}
		return constants.stream();
	}

	private Set getEnumConstants(CartesianTest.Enum enumSource, Class parameterType) {
		Class enumClass = determineEnumClass(enumSource, parameterType);
		return EnumSet.allOf(enumClass);
	}

	@SuppressWarnings({ "unchecked", "rawtypes" })
	private Class determineEnumClass(CartesianTest.Enum enumSource, Class parameterType) {
		Class enumClass = enumSource.value();
		if (enumClass.equals(NullEnum.class)) {
			if (!Enum.class.isAssignableFrom(parameterType))
				throw new PreconditionViolationException(
					String.format("Parameter of type %s must reference an Enum type", parameterType));
			enumClass = parameterType;
		}
		return enumClass;
	}

	enum NullEnum {
	}

}