package jalview.ext.ensembl;

import jalview.io.FileParse;

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.List;

import javax.ws.rs.HttpMethod;

/**
 * Base class for Ensembl REST service clients
 * 
 * @author gmcarstairs
 */
abstract class EnsemblRestClient extends EnsemblSequenceFetcher
{
  protected final static String ENSEMBL_REST = "http://rest.ensembl.org";

  protected static final String SEQUENCE_ID_URL = ENSEMBL_REST
          + "/sequence/id";

  // @see https://github.com/Ensembl/ensembl-rest/wiki/Output-formats
  private static final String PING_URL = "http://rest.ensembl.org/info/ping.json";

  private final static long RETEST_INTERVAL = 10000L; // 10 seconds

  private static boolean ensemblRestAvailable = false;

  private static long lastCheck = -1;

  protected volatile boolean inProgress = false;

  @Override
  public boolean queryInProgress()
  {
    return inProgress;
  }

  @Override
  public StringBuffer getRawRecords()
  {
    return null;
  }

  /**
   * Returns the URL for the client http request
   * 
   * @param ids
   * @return
   * @throws MalformedURLException
   */
  protected abstract URL getUrl(List<String> ids)
          throws MalformedURLException;

  /**
   * Returns true if client uses GET method, false if it uses POST
   * 
   * @return
   */
  protected abstract boolean useGetRequest();

  /**
   * Return the desired value for the Content-Type request header
   * 
   * @return
   * @see https://github.com/Ensembl/ensembl-rest/wiki/HTTP-Headers
   */
  protected abstract String getRequestMimeType();

  /**
   * Return the desired value for the Accept request header
   * 
   * @return
   * @see https://github.com/Ensembl/ensembl-rest/wiki/HTTP-Headers
   */
  protected abstract String getResponseMimeType();

  /**
   * Tries to connect to Ensembl's REST 'ping' endpoint, and returns true if
   * successful, else false
   * 
   * @return
   */
  private boolean checkEnsembl()
  {
    try
    {
      URL ping = new URL(PING_URL);
      HttpURLConnection conn = (HttpURLConnection) ping.openConnection();
      int rc = conn.getResponseCode();
      conn.disconnect();
      if (rc >= 200 && rc < 300)
      {
        return true;
      }
    } catch (Throwable t)
    {
      System.err.println("Error connecting to " + PING_URL + ": "
              + t.getMessage());
    }
    return false;
  }

  /**
   * returns a reader to a Fasta response from the Ensembl sequence endpoint
   * 
   * @param ids
   * @return
   * @throws IOException
   */
  protected FileParse getSequenceReader(List<String> ids)
          throws IOException
  {
    URL url = getUrl(ids);
  
    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
  
    /*
     * POST method allows multiple queries in one request; it is supported for
     * sequence queries, but not for overlap
     */
    connection.setRequestMethod(useGetRequest() ? HttpMethod.GET
            : HttpMethod.POST);
    connection.setRequestProperty("Content-Type", getRequestMimeType());
    connection.setRequestProperty("Accept", getResponseMimeType());

    connection.setUseCaches(false);
    connection.setDoInput(true);
    connection.setDoOutput(true);

    if (!useGetRequest())
    {
      writePostBody(connection, ids);
    }
  
    InputStream response = connection.getInputStream();
    int responseCode = connection.getResponseCode();
  
    if (responseCode != 200)
    {
      throw new RuntimeException(
              "Response code was not 200. Detected response was "
                      + responseCode);
    }
  
    BufferedReader reader = null;
    reader = new BufferedReader(new InputStreamReader(response, "UTF-8"));
    FileParse fp = new FileParse(reader, url.toString(), "HTTP_POST");
    return fp;
  }

  /**
   * Rechecks if Ensembl is responding, unless the last check was successful and
   * the retest interval has not yet elapsed. Returns true if Ensembl is up,
   * else false.
   * 
   * @return
   */
  protected boolean isEnsemblAvailable()
  {
    long now = System.currentTimeMillis();
    boolean retest = now - lastCheck > RETEST_INTERVAL;
    if (ensemblRestAvailable && !retest)
    {
      return true;
    }
    ensemblRestAvailable = checkEnsembl();
    lastCheck = now;
    return ensemblRestAvailable;
  }

  /**
   * Constructs, writes and flushes the POST body of the request, containing the
   * query ids in JSON format
   * 
   * @param connection
   * @param ids
   * @throws IOException
   */
  protected void writePostBody(HttpURLConnection connection,
          List<String> ids) throws IOException
  {
    boolean first;
    StringBuilder postBody = new StringBuilder(64);
    postBody.append("{\"ids\":[");
    first = true;
    for (String id : ids)
    {
      if (!first)
      {
        postBody.append(",");
      }
      first = false;
      postBody.append("\"");
      postBody.append(id.trim());
      postBody.append("\"");
    }
    postBody.append("]}");
    byte[] thepostbody = postBody.toString().getBytes();
    connection.setRequestProperty("Content-Length",
            Integer.toString(thepostbody.length));
    DataOutputStream wr = new DataOutputStream(connection.getOutputStream());
    wr.write(thepostbody);
    wr.flush();
    wr.close();
  }

}