package eu.dnetlib.download.plugin;

import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

import com.google.common.collect.Iterables;
import com.google.gson.Gson;
import eu.dnetlib.data.download.rmi.AbstractDownloadPlugin;
import eu.dnetlib.data.download.rmi.DownloadItem;
import eu.dnetlib.data.download.rmi.DownloadPlugin;
import eu.dnetlib.data.download.rmi.DownloadPluginException;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;

public class DSpacePDFLinkPlugins extends AbstractDownloadPlugin implements DownloadPlugin {

    /**
     * The Constant log.
     */
    private static final Log log = LogFactory.getLog(DSpacePDFLinkPlugins.class);

    private final static int maxNumberJump = 10;

    private final static int maxNumberConnectRetries = 5;

    /**
     * Milliseconds used to backoff in case of connection errors.
     */
    private final static int BACKOFF_FACTOR = 100;

    private String getHTTPRedirectedURL(final String mainURL) throws Exception {
        URL startURL = new URL(mainURL);
        HttpURLConnection conn = (HttpURLConnection) startURL.openConnection();

        conn.setConnectTimeout(AbstractDownloadPlugin.DEFAULT_TIMEOUT);

        conn.setInstanceFollowRedirects(true);  // you still need to handle redirect manually.
        HttpURLConnection.setFollowRedirects(true);
        String location = mainURL;

        int numJump = 1;

        int responseCode = conn.getResponseCode();

        while ((responseCode >= 300) && (responseCode < 400) && (numJump++ < maxNumberJump)) {
            location = conn.getHeaderFields().get("Location").get(0);
            conn.disconnect();
            startURL = new URL(location);
            conn = (HttpURLConnection) startURL.openConnection();
            conn.setConnectTimeout(AbstractDownloadPlugin.DEFAULT_TIMEOUT);
            conn.setInstanceFollowRedirects(true);  // you still need to handle redirect manually.
            HttpURLConnection.setFollowRedirects(true);
            responseCode = conn.getResponseCode();
        }
        conn.disconnect();
        if (!((responseCode >= 200) && (responseCode < 300)))
            return null;
        return location;
    }

    /**
     * Extract url.
     *
     * @param url the url
     * @return the string
     */
    @Override
    public String extractURL(final String url) throws DownloadPluginException {
        try {
            final String location = getHTTPRedirectedURL(url);

            if (location == null) {
                return null;
            }

            Document doc = null;
            int retries = 0;
            boolean success = false;

            while(retries < maxNumberConnectRetries) {
                try {
                    doc = Jsoup.connect(location).timeout(AbstractDownloadPlugin.DEFAULT_TIMEOUT).get();
                    success = true;
                    break;
                } catch (IOException e) {
                    final int millis = BACKOFF_FACTOR * (retries + 1);
                    log.debug(String.format("backoff for %s ms before retrying on %s", millis, location));
                    Thread.sleep(millis);
                }
                retries++;
            }

            if (!success) {
                throw new DownloadPluginException("reached max number of connect retries for URL: " + location);
            }

            final Elements links = doc.select("meta[content][name=citation_pdf_url]");

            for (Element link : links) {
                String linkValue = link.attr("content");
                if (regularExpression != null) {
                    for (String regex : regularExpression) {
                        if (linkValue.matches(regex)) {
                            return linkValue;
                        }
                    }
                } else {
                    //if(linkValue.matches("^http.*pdf$")){
                        return linkValue;
                    //}
                }

            }
            return null;
        } catch (Throwable e) {
	        throw new DownloadPluginException("Error on extract URL", e);
        }
    }

    @Override
    public Iterable<DownloadItem> retrieveUrls(final Iterable<DownloadItem> urls) {
        return Iterables.transform(urls, input -> retrieveUrl(input));
    }

    /*
     * (non-Javadoc)
     *
     * @see eu.dnetlib.data.download.rmi.DownloadPlugin#getPluginName()
     */
    @Override
    public String getPluginName() {
        return "DSpacePDFLinkPlugins";
    }

    /*
     * (non-Javadoc)
     *
     * @see eu.dnetlib.data.download.rmi.DownloadPlugin#retrieveUrl(eu.dnetlib.data.download.rmi.DownloadItem)
     */
    @Override
    public DownloadItem retrieveUrl(final DownloadItem input) {
        if (checkOpenAccess(input) == null) return null;
        String url = input.getOriginalUrl();

        if ((url == null) || (url.trim().length() == 0)) return input;
        @SuppressWarnings("unchecked")
        List<String> urls = new Gson().fromJson(url, ArrayList.class);
        if ((urls == null) || (urls.size() == 0)) return input;
        if (checkUrlsNotNull(input, urls))
            return input;
        input.setOriginalUrl(null);
        input.setUrl(null);
        return input;
    }

    @Override
    public void setBasePath(final String basePath) {
        // TODO Auto-generated method stub

    }

}