// (C) 2007 by Michael Peter Christen; mc@yacy.net, Frankfurt a. M., Germany

// first published 03.07.2007 on http://yacy.net

//

// This is a part of YaCy, a peer-to-peer based web search engine

//

// $LastChangedDate: 2011-03-09 10:29:05 +0100 (Mi, 09. Mär 2011) $

// $LastChangedRevision: 7572 $

// $LastChangedBy: orbiter $

//

// LICENSE

//

// This program is free software; you can redistribute it and/or modify

// it under the terms of the GNU General Public License as published by

// the Free Software Foundation; either version 2 of the License, or

// (at your option) any later version.

//

// This program is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

//

// You should have received a copy of the GNU General Public License

// along with this program; if not, write to the Free Software

// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

    // this class defines a license-generation for URLs

    // it is used in case of snippet- and preview-Image-fetching to grant also non-authorized users the usage of a image-fetcher servlet

    private static final int maxQueue = 500;

    private static final long minCheck = 5000;

   

    private final Random random;

    private final ConcurrentHashMap<String, DigestURI> permissions;

    private final ConcurrentLinkedQueue<String> aging;

    private long lastCheck;

    private final int keylen;

   

    public URLLicense(final int keylen) {

        this.permissions = new ConcurrentHashMap<String, DigestURI>();

        this.aging = new ConcurrentLinkedQueue<String>();

        this.lastCheck = System.currentTimeMillis();

        this.random = new Random(System.currentTimeMillis());

        this.keylen = keylen;

    }

   

    public String aquireLicense(final DigestURI url) {

        // generate license key

        StringBuilder stringBuilder = new StringBuilder(keylen * 2);

        if (url == null) return stringBuilder.toString();

        while (stringBuilder.length() < keylen) stringBuilder.append(Integer.toHexString(random.nextInt()));

        String license = stringBuilder.substring(0, keylen);

        // store reference to url with license key

        permissions.put(license, url);

        aging.add(license);

        if (System.currentTimeMillis() - this.lastCheck > minCheck) {

            // check aging

            this.lastCheck = System.currentTimeMillis();

            String s;

            while (aging.size() > maxQueue) {

                s = aging.poll();

                if (s != null) permissions.remove(s);

            }

        }

        // return the license key

        return license;

    }

   

    public DigestURI releaseLicense(final String license) {

        DigestURI url = null;

        url = permissions.remove(license);

        return url;

    }

   

}