package org.junit.internal.runners.rules;

import org.junit.ClassRule;
import org.junit.Rule;
import org.junit.rules.MethodRule;
import org.junit.rules.TestRule;
import org.junit.runners.model.FrameworkMember;
import org.junit.runners.model.TestClass;

import java.lang.annotation.Annotation;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.List;

A RuleMemberValidator validates the rule fields/methods of a TestClass. All reasons for rejecting the TestClass are written to a list of errors. 
There are four slightly different validators. The CLASS_RULE_VALIDATOR validates fields with a ClassRule annotation and the RULE_VALIDATOR validates fields with a Rule annotation.
The CLASS_RULE_METHOD_VALIDATOR validates methods with a ClassRule annotation and the RULE_METHOD_VALIDATOR validates methods with a Rule annotation.
/**
 * A RuleMemberValidator validates the rule fields/methods of a
 * {@link org.junit.runners.model.TestClass}. All reasons for rejecting the
 * {@code TestClass} are written to a list of errors.
 *
 * <p>There are four slightly different validators. The {@link #CLASS_RULE_VALIDATOR}
 * validates fields with a {@link ClassRule} annotation and the
 * {@link #RULE_VALIDATOR} validates fields with a {@link Rule} annotation.</p>
 *
 * <p>The {@link #CLASS_RULE_METHOD_VALIDATOR}
 * validates methods with a {@link ClassRule} annotation and the
 * {@link #RULE_METHOD_VALIDATOR} validates methods with a {@link Rule} annotation.</p>
 */
public class RuleMemberValidator {
    
Validates fields with a ClassRule annotation. /**
     * Validates fields with a {@link ClassRule} annotation.
     */
    public static final RuleMemberValidator CLASS_RULE_VALIDATOR =
            classRuleValidatorBuilder()
            .withValidator(new DeclaringClassMustBePublic())
            .withValidator(new MemberMustBeStatic())
            .withValidator(new MemberMustBePublic())
            .withValidator(new FieldMustBeATestRule())
            .build();
    
Validates fields with a Rule annotation. /**
     * Validates fields with a {@link Rule} annotation.
     */
    public static final RuleMemberValidator RULE_VALIDATOR =
            testRuleValidatorBuilder()
            .withValidator(new MemberMustBeNonStaticOrAlsoClassRule())
            .withValidator(new MemberMustBePublic())
            .withValidator(new FieldMustBeARule())
            .build();
    
Validates methods with a ClassRule annotation. /**
     * Validates methods with a {@link ClassRule} annotation.
     */
    public static final RuleMemberValidator CLASS_RULE_METHOD_VALIDATOR =
            classRuleValidatorBuilder()
            .forMethods()
            .withValidator(new DeclaringClassMustBePublic())
            .withValidator(new MemberMustBeStatic())
            .withValidator(new MemberMustBePublic())
            .withValidator(new MethodMustBeATestRule())
            .build();

    
Validates methods with a Rule annotation. /**
     * Validates methods with a {@link Rule} annotation.
     */
    public static final RuleMemberValidator RULE_METHOD_VALIDATOR =
            testRuleValidatorBuilder()
            .forMethods()
            .withValidator(new MemberMustBeNonStaticOrAlsoClassRule())
            .withValidator(new MemberMustBePublic())
            .withValidator(new MethodMustBeARule())
            .build();

    private final Class<? extends Annotation> annotation;
    private final boolean methods;
    private final List<RuleValidator> validatorStrategies;

    RuleMemberValidator(Builder builder) {
        this.annotation = builder.annotation;
        this.methods = builder.methods;
        this.validatorStrategies = builder.validators;
    }

    
Validate the TestClass and adds reasons for rejecting the class to a list of errors. 
Params:
target – the TestClass to validate.
errors – the list of errors./**
     * Validate the {@link org.junit.runners.model.TestClass} and adds reasons
     * for rejecting the class to a list of errors.
     *
     * @param target the {@code TestClass} to validate.
     * @param errors the list of errors.
     */
    public void validate(TestClass target, List<Throwable> errors) {
        List<? extends FrameworkMember<?>> members = methods ? target.getAnnotatedMethods(annotation)
                : target.getAnnotatedFields(annotation);

        for (FrameworkMember<?> each : members) {
            validateMember(each, errors);
        }
    }

    private void validateMember(FrameworkMember<?> member, List<Throwable> errors) {
        for (RuleValidator strategy : validatorStrategies) {
            strategy.validate(member, annotation, errors);
        }
    }

    private static Builder classRuleValidatorBuilder() {
        return new Builder(ClassRule.class);
    }

    private static Builder testRuleValidatorBuilder() {
        return new Builder(Rule.class);
    }

    private static class Builder {
        private final Class<? extends Annotation> annotation;
        private boolean methods;
        private final List<RuleValidator> validators;

        private Builder(Class<? extends Annotation> annotation) {
            this.annotation = annotation;
            this.methods = false;
            this.validators = new ArrayList<RuleValidator>();
        }

        Builder forMethods() {
            methods = true;
            return this;
        }

        Builder withValidator(RuleValidator validator) {
            validators.add(validator);
            return this;
        }

        RuleMemberValidator build() {
            return new RuleMemberValidator(this);
        }
    }

    private static boolean isRuleType(FrameworkMember<?> member) {
        return isMethodRule(member) || isTestRule(member);
    }

    private static boolean isTestRule(FrameworkMember<?> member) {
        return TestRule.class.isAssignableFrom(member.getType());
    }

    private static boolean isMethodRule(FrameworkMember<?> member) {
        return MethodRule.class.isAssignableFrom(member.getType());
    }

    
Encapsulates a single piece of validation logic, used to determine if Rule and ClassRule annotations have been used correctly /**
     * Encapsulates a single piece of validation logic, used to determine if {@link org.junit.Rule} and
     * {@link org.junit.ClassRule} annotations have been used correctly
     */
    interface RuleValidator {
        
Examine the given member and add any violations of the strategy's validation logic to the given list of errors
Params:
member – The member (field or member) to examine
annotation – The type of rule annotation on the member
errors – The list of errors to add validation violations to/**
         * Examine the given member and add any violations of the strategy's validation logic to the given list of errors
         * @param member The member (field or member) to examine
         * @param annotation The type of rule annotation on the member
         * @param errors The list of errors to add validation violations to
         */
        void validate(FrameworkMember<?> member, Class<? extends Annotation> annotation, List<Throwable> errors);
    }

    
Requires the validated member to be non-static
/**
     * Requires the validated member to be non-static
     */
    private static final class MemberMustBeNonStaticOrAlsoClassRule implements RuleValidator {
        public void validate(FrameworkMember<?> member, Class<? extends Annotation> annotation, List<Throwable> errors) {
            boolean isMethodRuleMember = isMethodRule(member);
            boolean isClassRuleAnnotated = (member.getAnnotation(ClassRule.class) != null);

            // We disallow:
            //  - static MethodRule members
            //  - static @Rule annotated members
            //    - UNLESS they're also @ClassRule annotated
            // Note that MethodRule cannot be annotated with @ClassRule
            if (member.isStatic() && (isMethodRuleMember || !isClassRuleAnnotated)) {
                String message;
                if (isMethodRule(member)) {
                    message = "must not be static.";
                } else {
                    message = "must not be static or it must be annotated with @ClassRule.";
                }
                errors.add(new ValidationError(member, annotation, message));
            }
        }
    }

    
Requires the member to be static
/**
     * Requires the member to be static
     */
    private static final class MemberMustBeStatic implements RuleValidator {
        public void validate(FrameworkMember<?> member, Class<? extends Annotation> annotation, List<Throwable> errors) {
            if (!member.isStatic()) {
                errors.add(new ValidationError(member, annotation,
                        "must be static."));
            }
        }
    }

    
Requires the member's declaring class to be public
/**
     * Requires the member's declaring class to be public
     */
    private static final class DeclaringClassMustBePublic implements RuleValidator {
        public void validate(FrameworkMember<?> member, Class<? extends Annotation> annotation, List<Throwable> errors) {
            if (!isDeclaringClassPublic(member)) {
                errors.add(new ValidationError(member, annotation,
                        "must be declared in a public class."));
            }
        }

        private boolean isDeclaringClassPublic(FrameworkMember<?> member) {
            return Modifier.isPublic(member.getDeclaringClass().getModifiers());
        }
    }

    
Requires the member to be public
/**
     * Requires the member to be public
     */
    private static final class MemberMustBePublic implements RuleValidator {
        public void validate(FrameworkMember<?> member, Class<? extends Annotation> annotation, List<Throwable> errors) {
            if (!member.isPublic()) {
                errors.add(new ValidationError(member, annotation,
                        "must be public."));
            }
        }
    }

    
Requires the member is a field implementing MethodRule or TestRule /**
     * Requires the member is a field implementing {@link org.junit.rules.MethodRule} or {@link org.junit.rules.TestRule}
     */
    private static final class FieldMustBeARule implements RuleValidator {
        public void validate(FrameworkMember<?> member, Class<? extends Annotation> annotation, List<Throwable> errors) {
            if (!isRuleType(member)) {
                errors.add(new ValidationError(member, annotation,
                        "must implement MethodRule or TestRule."));
            }
        }
    }

    
Require the member to return an implementation of MethodRule or TestRule /**
     * Require the member to return an implementation of {@link org.junit.rules.MethodRule} or
     * {@link org.junit.rules.TestRule}
     */
    private static final class MethodMustBeARule implements RuleValidator {
        public void validate(FrameworkMember<?> member, Class<? extends Annotation> annotation, List<Throwable> errors) {
            if (!isRuleType(member)) {
                errors.add(new ValidationError(member, annotation,
                        "must return an implementation of MethodRule or TestRule."));
            }
        }
    }
    
    
Require the member to return an implementation of TestRule /**
     * Require the member to return an implementation of {@link org.junit.rules.TestRule}
     */
    private static final class MethodMustBeATestRule implements RuleValidator {
        public void validate(FrameworkMember<?> member,
                Class<? extends Annotation> annotation, List<Throwable> errors) {
            if (!isTestRule(member)) {
                errors.add(new ValidationError(member, annotation, 
                        "must return an implementation of TestRule."));
            }
        }
    }
    
    
Requires the member is a field implementing TestRule /**
     * Requires the member is a field implementing {@link org.junit.rules.TestRule}
     */
    private static final class FieldMustBeATestRule implements RuleValidator {

        public void validate(FrameworkMember<?> member,
                Class<? extends Annotation> annotation, List<Throwable> errors) {
            if (!isTestRule(member)) {
                errors.add(new ValidationError(member, annotation,
                        "must implement TestRule."));
            }
        }
    }
}