package io;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.logging.Logger;
import java.util.zip.GZIPInputStream;
import mining.Stream;
import org.apache.commons.io.Charsets;
import org.apache.commons.lang.StringUtils;
import org.json.JSONException;
import org.json.JSONObject;
import org.json.JSONTokener;
import provider.ExceptionListener;
import provider.ResultListener;

/**
 * Provides access to Twitter stream data. Data is processed in a separate
 * thread and consumers are notified via callbacks.
 *
 * @author Peter Wu
 */
public class StreamImpl implements Stream {

    private final static String STREAM_URL
            = "https://stream.twitter.com/1.1/statuses/filter.json";

    private final Set<String> keywords = new HashSet<>();
    /**
     * The target that is interested in received tweets.
     */
    private final ResultListener resultListener;
    /**
     * The target that is interesting in receiving changes.
     */
    private final ExceptionListener exceptionListener;

    /**
     * Holds an instance that represents an active worker that contains a thread
     * to watch for new tweets.
     */
    private WorkerContainer workerContainer;

    public StreamImpl(ResultListener resultListener, ExceptionListener el) {
        this.resultListener = resultListener;
        this.exceptionListener = el;
    }

    @Override
    public void watchKeyword(String keyword) {
        keywords.add(keyword);
    }

    @Override
    public void unwatchKeyword(String keyword) {
        keywords.remove(keyword);
    }

    @Override
    public void commit() throws IOException {
        String keywordsStr = StringUtils.join(keywords, ",");
        /* do not reconnect if a connection already exists for the keywords */
        if (workerContainer != null
                && workerContainer.getWorker().getKeywords().equals(keywordsStr)) {
            return;
        }
        /* connect (or reconnect) after setting new keywords */
        disconnect();
        Worker worker = new Worker(keywordsStr);
        workerContainer = new WorkerContainer(worker);
        workerContainer.start();
    }

    @Override
    public boolean isValid() {
        return workerContainer != null && workerContainer.isValid();
    }

    @Override
    public void close() {
        disconnect();
    }

    /**
     * Stops the worker if any.
     */
    private void disconnect() {
        // wait for the worker thread to stop
        while (workerContainer != null) {
            workerContainer.finish();
            workerContainer = null;
        }
    }

    private class WorkerContainer {

        private final Worker worker;
        private final Thread thread;

        /**
         * Holds a thread for the worker.
         *
         * @param worker Worker that should be processed in a separate thread.
         */
        public WorkerContainer(Worker worker) {
            this.worker = worker;
            thread = new Thread(worker);
        }

        public void start() {
            thread.start();
        }

        public void finish() {
            worker.stopWorker();
            while (thread.isAlive()) {
                try {
                    thread.join();
                } catch (InterruptedException ex) {
                    Logger.getLogger(getClass().getName())
                            .warning("Interrupted while waiting for stream finish");
                }
            }
        }

        public Worker getWorker() {
            return worker;
        }

        public boolean isValid() {
            return thread.isAlive();
        }
    }

    private class Worker implements Runnable {

        private final String keywords;
        private final HttpURLConnection connection;
        private AtomicBoolean running;

        Worker(String keywords) throws IOException {
            this.keywords = keywords;
            this.connection = connect(keywords);
            this.running = new AtomicBoolean(true);
        }

        /**
         * @return The search keywords associated with this worker.
         */
        public String getKeywords() {
            return keywords;
        }

        private HttpURLConnection connect(String keywords) throws IOException {
            String postData = "follow=" + URLEncoder.encode(keywords, "UTF-8");
            HttpURLConnection conn;
            conn = (HttpURLConnection) new URL(STREAM_URL).openConnection();
            conn.setRequestMethod("POST");
            // set request headers
            conn.addRequestProperty("Content-Type",
                    "application/x-www-form-urlencoded; charset=UTF-8");
            conn.addRequestProperty("Accept-Encoding", "gzip");
            // connect and send request
            conn.setDoOutput(true);
            conn.getOutputStream().write(postData.getBytes(Charsets.UTF_8));
            int respCode = conn.getResponseCode();
            if (respCode != 200) {
                getLogger().severe("Response code " + respCode);
                conn.disconnect();
                throw new IOException("Unexpected stream response " + respCode);
            }
            return conn;
        }

        /**
         * Wraps an inputstream as gzip if possible.
         *
         * @param is The raw input stream.
         * @return An inputstream that outputs decoded data.
         * @throws IOException
         */
        private InputStream wrapGzip(InputStream is) throws IOException {
            if ("gzip".equals(connection.getContentEncoding())) {
                return new GZIPInputStream(is);
            }
            return is;
        }

        @Override
        public void run() {
            InputStream is = null;
            try {
                is = connection.getInputStream();
                parseMainLoop(wrapGzip(is));
            } catch (IOException ex) {
                if (is != null) {
                    try {
                        is.close();
                    } catch (IOException ioex) {
                        /* probably already closed? */
                    }
                }
                connection.disconnect();
                exceptionListener.exceptionGenerated(ex);
            }
        }

        public void stopWorker() {
            /* inform the worker to stop as soon as possible */
            running.set(false);
        }

        private void parseMainLoop(InputStream is) throws IOException {
            InputStreamReader isr = new InputStreamReader(is, Charsets.UTF_8);
            BufferedReader reader = new BufferedReader(isr);
            JSONTokener jsonTokener = new JSONTokener(reader);
            while (running.get()) {
                try {
                    Object obj = jsonTokener.nextValue();
                    if (obj instanceof JSONObject) {
                        processReceivedObject((JSONObject) obj);
                    } else {
                        getLogger().severe("Got unexpected object: " + obj);
                        throw new IOException("Got unexpected type from stream");
                    }
                } catch (JSONException ex) {
                    throw new IOException(ex);
                }
            }
        }

        private void processReceivedObject(JSONObject obj) {
        }

        private Logger getLogger() {
            return Logger.getLogger(getClass().getName());
        }
    }
}