package org.junit.rules;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.junit.runner.Description;
import org.junit.runners.model.Statement;

/**
 * The RuleChain rule allows ordering of TestRules. You create a
 * {@code RuleChain} with {@link #outerRule(TestRule)} and subsequent calls of
 * {@link #around(TestRule)}:
 *
 * <pre>
 * public static class UseRuleChain {
 * 	@Rule
 * 	public RuleChain chain= RuleChain
 * 	                       .outerRule(new LoggingRule("outer rule")
 * 	                       .around(new LoggingRule("middle rule")
 * 	                       .around(new LoggingRule("inner rule");
 *
 * 	@Test
 * 	public void example() {
 * 		assertTrue(true);
 *     }
 * }
 * </pre>
 *
 * writes the log
 *
 * <pre>
 * starting outer rule
 * starting middle rule
 * starting inner rule
 * finished inner rule
 * finished middle rule
 * finished outer rule
 * </pre>
 *
 * @since 4.10
 */
public class RuleChain implements TestRule {
    private static final RuleChain EMPTY_CHAIN = new RuleChain(
            Collections.<TestRule>emptyList());

    private List<TestRule> rulesStartingWithInnerMost;

    /**
     * Returns a {@code RuleChain} without a {@link TestRule}. This method may
     * be the starting point of a {@code RuleChain}.
     *
     * @return a {@code RuleChain} without a {@link TestRule}.
     */
    public static RuleChain emptyRuleChain() {
        return EMPTY_CHAIN;
    }

    /**
     * Returns a {@code RuleChain} with a single {@link TestRule}. This method
     * is the usual starting point of a {@code RuleChain}.
     *
     * @param outerRule the outer rule of the {@code RuleChain}.
     * @return a {@code RuleChain} with a single {@link TestRule}.
     */
    public static RuleChain outerRule(TestRule outerRule) {
        return emptyRuleChain().around(outerRule);
    }

    private RuleChain(List<TestRule> rules) {
        this.rulesStartingWithInnerMost = rules;
    }

    /**
     * Create a new {@code RuleChain}, which encloses the {@code nextRule} with
     * the rules of the current {@code RuleChain}.
     *
     * @param enclosedRule the rule to enclose.
     * @return a new {@code RuleChain}.
     */
    public RuleChain around(TestRule enclosedRule) {
        List<TestRule> rulesOfNewChain = new ArrayList<TestRule>();
        rulesOfNewChain.add(enclosedRule);
        rulesOfNewChain.addAll(rulesStartingWithInnerMost);
        return new RuleChain(rulesOfNewChain);
    }

    /**
     * {@inheritDoc}
     */
    public Statement apply(Statement base, Description description) {
        for (TestRule each : rulesStartingWithInnerMost) {
            base = each.apply(base, description);
        }
        return base;
    }
}