Add base implementation for torrent site filters.

diff --git a/src/main/java/net/pterodactylus/reactor/filters/TorrentSiteFilter.java b/src/main/java/net/pterodactylus/reactor/filters/TorrentSiteFilter.java
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index 0000000..968d671
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+++ b/src/main/java/net/pterodactylus/reactor/filters/TorrentSiteFilter.java
@@ -0,0 +1,163 @@
+/*
+ * Reactor - KickAssTorrentsFilter.java - Copyright © 2013 David Roden
+ *
+ * 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 3 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, see <http://www.gnu.org/licenses/>.
+ */
+
+package net.pterodactylus.reactor.filters;
+
+import static com.google.common.base.Preconditions.checkState;
+
+import java.io.UnsupportedEncodingException;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.net.URLEncoder;
+
+import net.pterodactylus.reactor.Filter;
+import net.pterodactylus.reactor.State;
+import net.pterodactylus.reactor.queries.HttpQuery;
+import net.pterodactylus.reactor.states.FailedState;
+import net.pterodactylus.reactor.states.HtmlState;
+import net.pterodactylus.reactor.states.TorrentState;
+import net.pterodactylus.reactor.states.TorrentState.TorrentFile;
+
+import org.jsoup.nodes.Document;
+import org.jsoup.nodes.Element;
+import org.jsoup.select.Elements;
+
+/**
+ * {@link Filter} implementation that parses a {@link TorrentState} from an
+ * {@link HtmlState} which was generated by a {@link HttpQuery} to
+ * {@code kickasstorrents.ph}.
+ *
+ * @author <a href="mailto:bombe@pterodactylus.net">David ‘Bombe’ Roden</a>
+ */
+public abstract class TorrentSiteFilter implements Filter {
+
+       /**
+        * {@inheritDoc}
+        */
+       @Override
+       public State filter(State state) {
+               if (!state.success()) {
+                       return FailedState.from(state);
+               }
+               checkState(state instanceof HtmlState, "state is not an HtmlState but a %s", state.getClass().getName());
+
+               /* get result table. */
+               Document document = ((HtmlState) state).document();
+
+               /* iterate over all rows. */
+               Elements dataRows = getDataRows(document);
+               TorrentState torrentState = new TorrentState();
+               for (Element dataRow : dataRows) {
+                       String name = extractName(dataRow);
+                       String size = extractSize(dataRow);
+                       String magnetUri = extractMagnetUri(dataRow);
+                       String downloadUri;
+                       int fileCount = extractFileCount(dataRow);
+                       int seedCount = extractSeedCount(dataRow);
+                       int leechCount = extractLeechCount(dataRow);
+                       try {
+                               downloadUri = new URI(((HtmlState) state).uri()).resolve(URLEncoder.encode(extractDownloadUri(dataRow), "UTF-8").replace("%2F", "/")).toString();
+                               TorrentFile torrentFile = new TorrentFile(name, size, magnetUri, downloadUri, fileCount, seedCount, leechCount);
+                               torrentState.addTorrentFile(torrentFile);
+                       } catch (URISyntaxException use1) {
+                               /* ignore; if uri was wrong, we wouldn’t be here. */
+                       } catch (UnsupportedEncodingException uee1) {
+                               /* ignore, all JVMs can do UTF-8. */
+                       }
+               }
+
+               return torrentState;
+       }
+
+       //
+       // ABSTRACT METHODS
+       //
+
+       /**
+        * Returns the data rows from the given document.
+        *
+        * @param document
+        *            The document to get the data rows from
+        * @return The data rows
+        */
+       protected abstract Elements getDataRows(Document document);
+
+       /**
+        * Extracts the name from the given row.
+        *
+        * @param dataRow
+        *            The row to extract the name from
+        * @return The extracted name
+        */
+       protected abstract String extractName(Element dataRow);
+
+       /**
+        * Extracts the size from the given row.
+        *
+        * @param dataRow
+        *            The row to extract the size from
+        * @return The extracted size
+        */
+       protected abstract String extractSize(Element dataRow);
+
+       /**
+        * Extracts the magnet URI from the given row.
+        *
+        * @param dataRow
+        *            The row to extract the magnet URI from
+        * @return The extracted magnet URI
+        */
+       protected abstract String extractMagnetUri(Element dataRow);
+
+       /**
+        * Extracts the download URI from the given row.
+        *
+        * @param dataRow
+        *            The row to extract the download URI from
+        * @return The extracted download URI
+        */
+       protected abstract String extractDownloadUri(Element dataRow);
+
+       /**
+        * Extracts the file count from the given row.
+        *
+        * @param dataRow
+        *            The row to extract the file count from
+        * @return The extracted file count, or {@code 0} if the file count can not
+        *         be extracted
+        */
+       protected abstract int extractFileCount(Element dataRow);
+
+       /**
+        * Extracts the seed count from the given row.
+        *
+        * @param dataRow
+        *            The row to extract the seed count from
+        * @return The extracted seed count
+        */
+       protected abstract int extractSeedCount(Element dataRow);
+
+       /**
+        * Extracts the leech count from the given row.
+        *
+        * @param dataRow
+        *            The row to extract the leech count from
+        * @return The extracted leech count
+        */
+       protected abstract int extractLeechCount(Element dataRow);
+
+}