/*
 * =========================================================================================
 * Copyright  2013-2014 the kamon project <http://kamon.io/>
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the
 * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific language governing permissions
 * and limitations under the License.
 * =========================================================================================
 */

package kamon.util;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Default implementation of PathFilter.  Uses glob based includes and excludes to determine whether to export.
 *
 * @author John E. Bailey
 * @author <a href="mailto:david.lloyd@redhat.com">David M. Lloyd</a>
 */
public final class GlobPathFilter implements PathFilter  {
    private static final Pattern GLOB_PATTERN = Pattern.compile("(\\*\\*?)|(\\?)|(\\\\.)|(/+)|([^*?]+)");

    private final String glob;
    private final Pattern pattern;

    /**
     * Construct a new instance.
     *
     * @param glob the path glob to match
     */
    public GlobPathFilter(final String glob) {
        pattern = getGlobPattern(glob);
        this.glob = glob;
    }

    /**
     * Determine whether a path should be accepted.
     *
     * @param path the path to check
     * @return true if the path should be accepted, false if not
     */
    public boolean accept(final String path) {
        return pattern.matcher(path).matches();
    }

    /**
     * Get a regular expression pattern which accept any path names which match the given glob.  The glob patterns
     * function similarly to {@code ant} file patterns.  Valid metacharacters in the glob pattern include:
     * <ul>
     * <li><code>"\"</code> - escape the next character (treat it literally, even if it is itself a recognized metacharacter)</li>
     * <li><code>"?"</code> - match any non-slash character</li>
     * <li><code>"*"</code> - match zero or more non-slash characters</li>
     * <li><code>"**"</code> - match zero or more characters, including slashes</li>
     * <li><code>"/"</code> - match one or more slash characters.  Consecutive {@code /} characters are collapsed down into one.</li>
     * </ul>
     * In addition, any glob pattern matches all subdirectories thereof.  A glob pattern ending in {@code /} is equivalent
     * to a glob pattern ending in <code>/**</code> in that the named directory is not itself included in the glob.
     * <p/>
     * <b>See also:</b> <a href="http://ant.apache.org/manual/dirtasks.html#patterns">"Patterns" in the Ant Manual</a>
     *
     * @param glob the glob to match
     *
     * @return the pattern
     */
    private static Pattern getGlobPattern(final String glob) {
        StringBuilder patternBuilder = new StringBuilder();
        final Matcher m = GLOB_PATTERN.matcher(glob);
        boolean lastWasSlash = false;
        while (m.find()) {
            lastWasSlash = false;
            String grp;
            if ((grp = m.group(1)) != null) {
                // match a * or **
                if (grp.length() == 2) {
                    // it's a *workers are able to process multiple metrics*
                    patternBuilder.append(".*");
                } else {
                    // it's a *
                    patternBuilder.append("[^/]*");
                }
            } else if ((grp = m.group(2)) != null) {
                // match a '?' glob pattern; any non-slash character
                patternBuilder.append("[^/]");
            } else if ((grp = m.group(3)) != null) {
                // backslash-escaped value
                patternBuilder.append(Pattern.quote(m.group().substring(1)));
            } else if ((grp = m.group(4)) != null) {
                // match any number of / chars
                patternBuilder.append("/+");
                lastWasSlash = true;
            } else {
                // some other string
                patternBuilder.append(Pattern.quote(m.group()));
            }
        }
        if (lastWasSlash) {
            // ends in /, append **
            patternBuilder.append(".*");
        }
        return Pattern.compile(patternBuilder.toString());
    }
}