package org.junit.runner.manipulation;

import org.junit.runner.Description;
import org.junit.runner.Request;

/**
 * The canonical case of filtering is when you want to run a single test method in a class. Rather
 * than introduce runner API just for that one case, JUnit provides a general filtering mechanism.
 * If you want to filter the tests to be run, extend <code>Filter</code> and apply an instance of
 * your filter to the {@link org.junit.runner.Request} before running it (see
 * {@link org.junit.runner.JUnitCore#run(Request)}. Alternatively, apply a <code>Filter</code> to
 * a {@link org.junit.runner.Runner} before running tests (for example, in conjunction with
 * {@link org.junit.runner.RunWith}.
 *
 * @since 4.0
 */
public abstract class Filter {
    /**
     * A null <code>Filter</code> that passes all tests through.
     */
    public static final Filter ALL = new Filter() {
        @Override
        public boolean shouldRun(Description description) {
            return true;
        }

        @Override
        public String describe() {
            return "all tests";
        }

        @Override
        public void apply(Object child) throws NoTestsRemainException {
            // do nothing
        }

        @Override
        public Filter intersect(Filter second) {
            return second;
        }
    };

    /**
     * Returns a {@code Filter} that only runs the single method described by
     * {@code desiredDescription}
     */
    public static Filter matchMethodDescription(final Description desiredDescription) {
        return new Filter() {
            @Override
            public boolean shouldRun(Description description) {
                if (description.isTest()) {
                    return desiredDescription.equals(description);
                }

                // explicitly validate if any children want to run
                for (Description each : description.getChildren()) {
                    if (shouldRun(each)) {
                        return true;
                    }
                }
                return false;
            }

            @Override
            public String describe() {
                return String.format("Method %s", desiredDescription.getDisplayName());
            }
        };
    }


    /**
     * @param description the description of the test to be run
     * @return <code>true</code> if the test should be run
     */
    public abstract boolean shouldRun(Description description);

    /**
     * Returns a textual description of this Filter
     *
     * @return a textual description of this Filter
     */
    public abstract String describe();

    /**
     * Invoke with a {@link org.junit.runner.Runner} to cause all tests it intends to run
     * to first be checked with the filter. Only those that pass the filter will be run.
     *
     * @param child the runner to be filtered by the receiver
     * @throws NoTestsRemainException if the receiver removes all tests
     */
    public void apply(Object child) throws NoTestsRemainException {
        if (!(child instanceof Filterable)) {
            return;
        }
        Filterable filterable = (Filterable) child;
        filterable.filter(this);
    }

    /**
     * Returns a new Filter that accepts the intersection of the tests accepted
     * by this Filter and {@code second}
     */
    public Filter intersect(final Filter second) {
        if (second == this || second == ALL) {
            return this;
        }
        final Filter first = this;
        return new Filter() {
            @Override
            public boolean shouldRun(Description description) {
                return first.shouldRun(description)
                        && second.shouldRun(description);
            }

            @Override
            public String describe() {
                return first.describe() + " and " + second.describe();
            }
        };
    }
}