//   Copyright 2012 Georg-August-Universität Göttingen, Germany
//
//   Licensed under the Apache License, Version 2.0 (the "License");
//   you may not use this file except in compliance with the License.
//   You may obtain a copy of the License at
//
//       http://www.apache.org/licenses/LICENSE-2.0
//
//   Unless required by applicable law or agreed to in writing, software
//   distributed under the License is distributed on an "AS IS" BASIS,
//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//   See the License for the specific language governing permissions and
//   limitations under the License.

package de.ugoe.cs.autoquest.genericeventmonitor;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.eclipse.jetty.servlet.DefaultServlet;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.JSONValue;
import org.json.simple.parser.ParseException;

import de.ugoe.cs.util.console.Console;

/**
 * <p>
 * the servlet deployed in the web server that receives all generic events. The messages are parsed,
 * validated, and forwarded to the provided message listener. If a message is not valid, it is
 * discarded. If an event in a message is not valid, it is discarded. Messages are only received via
 * the POST HTTP method.
 * </p>
 * 
 * @author Patrick Harms
 */
class GenericEventMonitorServlet extends DefaultServlet {

    /**  */
    private static final long serialVersionUID = 1L;
    
    /** must be true to do some detailed logging of what the server does */
    private static final boolean DO_TRACE = false;

    /**
     * the map of event target ids to the concrete target objects.
     */
    private Map<String, GenericEventTarget> eventTargets = new HashMap<>();

    /**
     * the message listener to forward received messages to.
     */
    private GenericEventMonitorMessageListener messageListener;

    /**
     * <p>
     * initializes the servlet with the message listener to which all events shall be forwarded
     * </p>
     *
     * @param messageListener the message listener that shall receive all events
     */
    GenericEventMonitorServlet(GenericEventMonitorMessageListener messageListener) {
        this.messageListener = messageListener;
    }

    /**
     * this implements handling of doPost. For this servlet this means that
     * the data from the post request will be parsed and validated.
     * 
     * (non-Javadoc)
     * @see org.mortbay.jetty.servlet.DefaultServlet#doPost(HttpServletRequest, HttpServletResponse)
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException
    {
        Object value = null;
        try {
            //InputStream requestInputStream = dumpStreamContent(request.getInputStream());
            InputStream requestInputStream = request.getInputStream();

            value = JSONValue.parseWithException
                (new InputStreamReader(requestInputStream, "UTF-8"));
            
            if (!(value instanceof JSONObject)) {
                Console.printerrln("incoming data is not of the expected type --> discarding it");
            }
            else {
                handleJSONObject((JSONObject) value);
            }
        }
        catch (ParseException e) {
            Console.printerrln
                ("could not parse incoming data --> discarding it (" + e.toString() + ")");
        }
        
        // this must be done to prevent firefox from notifying the "element not found" error
        response.setContentType("text/plain");
        response.getOutputStream().write(' ');
    }

    /**
     * <p>
     * processes a received JSON object and validates it. If the message is ok, it is forwarded
     * to the message listener
     * </p>
     *
     * @param object the JSON object that contains a client message
     */
    private void handleJSONObject(JSONObject object) {
        if (DO_TRACE) {
            dumpJSONObject(object, "");
        }
        
        JSONObject message = assertValue(object, "message", JSONObject.class);
        
        if (message == null) {
            Console.printerrln("incoming data is no valid message --> discarding it");
        }
        else {
            ClientInfos clientInfos = extractClientInfos(message);

            if (clientInfos == null) {
                Console.printerrln
                    ("incoming message does not contain valid client infos --> discarding it");
            }
            else {
                extractGenericEventTargets(message, clientInfos);
                GenericEvent[] events = extractGenericEvents(message, clientInfos);
                
                if (events == null) {
                    Console.printerrln
                        ("incoming message does not contain valid events --> discarding it");
                }
                else {
                    messageListener.handleEvents(clientInfos, events);
                    Console.println
                        ("handled message of " + clientInfos.getClientId() + " for app " + 
                         clientInfos.getAppId() + " (" + events.length + " events)");
                }
            }
        }
    }

    /**
     * <p>
     * tries to extract the client infos out of the received JSON object. If this is not fully
     * possible, an appropriate message is dumped and the whole message is discarded (the method
     * return null).
     * </p>
     *
     * @param message the message to parse the client infos from
     * 
     * @return the client infos, if the message is valid in this respect, or null if not
     */
    private ClientInfos extractClientInfos(JSONObject message) {
        ClientInfos clientInfos = null;
        
        JSONObject infos = assertValue(message, "clientInfos", JSONObject.class);
        
        if (infos != null) {
            String clientId = assertValue((JSONObject) infos, "clientId", String.class);
            String appId = assertValue((JSONObject) infos, "appId", String.class);
           
            if (clientId == null) {
                Console.printerrln("client infos do not contain a valid client id");
            }
            else if (appId == null) {
                Console.printerrln("client infos do not contain a valid application id");
            }
            else {
                clientInfos = new ClientInfos(clientId, appId);
            }
        }
        
        return clientInfos;
    }

    /**
     * <p>
     * tries to extract the events out of the received JSON object. If this is not fully
     * possible, an appropriate message is dumped and the errorprone event is discarded. If no
     * valid event is found, the whole message is discarded.
     * </p>
     *
     * @param object      the message to parse the events from
     * @param clientInfos the infos about the client that send the events
     *  
     * @return the valid events stored in the message, or null if there are none
     */
    private GenericEvent[] extractGenericEvents(JSONObject object, ClientInfos clientInfos) {
        List<GenericEvent> events = null;
        
        JSONArray eventArray = assertValue(object, "events", JSONArray.class);
        
        if (eventArray != null) {
            events = new ArrayList<GenericEvent>();
            
            for (int i = 0; i < eventArray.size(); i++) {
                Object eventObj = eventArray.get(i);
                if (!(eventObj instanceof JSONObject)) {
                    Console.printerrln("event number " + (i + 1) + " is not a valid event object");
                }
                else {
                    Long time = assertValue(((JSONObject) eventObj), "time", Long.class);
                    String eventType =
                        assertValue(((JSONObject) eventObj), "type", String.class);
                    String eventTargetId =
                        assertValue(((JSONObject) eventObj), "targetId", String.class);
                    
                    if (eventType == null) {
                        Console.printerrln("event number " + (i + 1) + " has no valid event type");
                    }
                    else if (eventTargetId == null) {
                        Console.printerrln(eventType + " event has no valid target id");
                    }
                    else if (time == null) {
                        Console.printerrln(eventType + " event has no valid timestamp");
                    }
                    else {
                        GenericEventTarget target = eventTargets.get(eventTargetId);
                        Map<String, String> parameters = getParameters
                            (((JSONObject) eventObj), "time", "type", "targetId");
                        
                        if (target != null) {
                            events.add(new GenericEvent(clientInfos, time, target, eventType,
                                                        parameters));
                        }
                        else {
                            Console.printerrln(eventType + " event has no known target");
                        }
                    }
                }
            }
            
        }
        
        if ((events != null) && (events.size() > 0)) {
            return events.toArray(new GenericEvent[events.size()]);
        }
        else {
            return null;
        }
    }

    /**
     * <p>
     * extracts the event target structure from the provided JSON object.
     * </p>
     *
     * @param object      the JSON object to extract the event target structure from
     * @param clientInfos infos about the client who send the data
     * 
     * @return the event target structure extracted from the JSON object of which the root nodes
     *         are provided
     */
    private GenericEventTarget[] extractGenericEventTargets(JSONObject  object,
                                                            ClientInfos clientInfos)
    {
        JSONObject[] jsonTargets = assertValue(object, "targetStructure", JSONObject[].class);
        
        if (jsonTargets != null) {
            GenericEventTarget[] result = new GenericEventTarget[jsonTargets.length];

            for (int i = 0; i < jsonTargets.length; i++) {
                result[i] = convert(jsonTargets[i], null);
            }

            return result;
        }
        else {
            return null;
        }
    }

    /**
     * <p>
     * converts a JSON object representing a target to the generic target. Calls
     * itself recursively to also convert the children of the element, if any.
     * </p>
     *
     * @param jsonTarget      the JSON object to be converted
     * @param parent          the parent target of the converted element, or null, if none
     *                        is present.
     *                        
     * @return as described.
     */
    private GenericEventTarget convert(JSONObject         jsonTarget,
                                       GenericEventTarget parent)
    {
        GenericEventTarget result = null;

        if (jsonTarget != null) {
            String targetId = assertValue(jsonTarget, "targetId", String.class);
            Map<String, String> parameters = getParameters(jsonTarget, "targetId", "children");

            result = new GenericEventTarget(targetId, parameters, parent);

            JSONArray childElements = assertValue(jsonTarget, "children", JSONArray.class);
            
            if (childElements != null) {
                Object jsonChild;

                for (int i = 0; i < childElements.size(); i++) {
                    jsonChild = childElements.get(i);
                    if (!(jsonChild instanceof JSONObject)) {
                        Console.printerrln("child " + (i + 1) + " of target " + targetId +
                                           " is no valid event target");
                    }
                    else {
                        result.addChild(convert((JSONObject) jsonChild, result));
                    }
                }
            }
            
        }
        
        if (result != null) {
            eventTargets.put(result.getId(), result);
        }
        
        return result;    
    }

    /**
     * <p>
     * converts a value in the provided object matching the provided key to the provided type. If
     * there is no value with the key or if the value can not be transformed to the provided type,
     * the method returns null. 
     * </p>
     *
     * @param object the object to read the value from
     * @param key    the key of the value
     * @param clazz  the type to which the value should be transformed
     * 
     * @return the value or null if either the value does not exist or if it can not be transformed
     *         to the expected type
     */
    @SuppressWarnings("unchecked")
    private <T> T assertValue(JSONObject object, String key, Class<T> clazz) {
        Object value = object.get(key);
        T result = null;
        
        if (clazz.isInstance(value)) {
            result = (T) value;
        }
        else if (value instanceof String) {
            if (URL.class.equals(clazz)) {
                try {
                    result = (T) new URL((String) value);
                }
                catch (MalformedURLException e) {
                    e.printStackTrace();
                    Console.printerrln("retrieved malformed URL for key '" + key + "': " + value +
                                       " (" + e.toString() + ")");
                }
            }
            else if ((int.class.equals(clazz)) || (Integer.class.equals(clazz))) {
                try {
                    result = (T) Integer.valueOf(Integer.parseInt((String) value));
                }
                catch (NumberFormatException e) {
                    Console.printerrln
                        ("retrieved malformed integer for key '" + key + "': " + value);
                }
            }
            else if ((long.class.equals(clazz)) || (Long.class.equals(clazz))) {
                try {
                    result = (T) Long.valueOf(Long.parseLong((String) value));
                }
                catch (NumberFormatException e) {
                    Console.printerrln
                        ("retrieved malformed long for key '" + key + "': " + value);
                }
            }
        }
        else if (value instanceof Long) {
            if ((int.class.equals(clazz)) || (Integer.class.equals(clazz))) {
                result = (T) (Integer) ((Long) value).intValue();
            }
        }
        else if (value instanceof JSONArray) {
            if ((int[].class.equals(clazz)) || (Integer[].class.equals(clazz))) {
                Integer[] resultArray = new Integer[((JSONArray) value).size()];
                boolean allCouldBeParsed = true;
                
                for (int i = 0; i < ((JSONArray) value).size(); i++) {
                    try {
                        if (((JSONArray) value).get(i) instanceof Long) {
                            resultArray[i] = (int) (long) (Long) ((JSONArray) value).get(i);
                        }
                        else if (((JSONArray) value).get(i) instanceof String) {
                            try {
                                resultArray[i] =
                                    (int) Long.parseLong((String) ((JSONArray) value).get(i));
                            }
                            catch (NumberFormatException e) {
                                Console.printerrln
                                    ("retrieved malformed integer array for key '" + key + "': " +
                                     value);
                        
                                allCouldBeParsed = false;
                                break;
                            }
                        }
                        else {
                            Console.printerrln
                                ("can not handle type of value in expected integer array '" + key +
                                 "': " + value);
                        }
                    }
                    catch (ClassCastException e) {
                        e.printStackTrace();
                        Console.printerrln("expected integer array for key '" + key +
                                           "' but it was something else: " + value);
                        
                        allCouldBeParsed = false;
                        break;
                    }
                }
                
                if (allCouldBeParsed) {
                    result = (T) resultArray;
                }
            }
            else if (JSONObject[].class.equals(clazz)) {
                JSONObject[] resultArray = new JSONObject[((JSONArray) value).size()];
                boolean allCouldBeParsed = true;
                
                for (int i = 0; i < ((JSONArray) value).size(); i++) {
                    try {
                        if (((JSONArray) value).get(i) instanceof JSONObject) {
                            resultArray[i] = (JSONObject) ((JSONArray) value).get(i);
                        }
                    }
                    catch (ClassCastException e) {
                        e.printStackTrace();
                        Console.printerrln("expected JSON Object array for key '" + key +
                                           "' but it was something else: " + value);
                        
                        allCouldBeParsed = false;
                        break;
                    }
                }
                
                if (allCouldBeParsed) {
                    result = (T) resultArray;
                }
            }
        }
        
        return result;
    }

    /**
     * <p>
     * determines other parameters provided in the JSON object. The parameters with the provided
     * keys to ignore are not put into the resulting map.
     * </p>
     *
     * @param object      the object, from which parameters shall be read
     * @param ignoredKeys the parameters not to be put into the resulting map
     * 
     * @return a map with the parameters contained in the provided JSON object
     */
    private Map<String, String> getParameters(JSONObject object, String ... ignoredKeys) {
        Map<String, String> result = new HashMap<>();
        
        NEXT_KEY:
        for (Object key : object.keySet()) {
            if (!(key instanceof String)) {
                continue NEXT_KEY;
            }
            
            for (String ignoredKey : ignoredKeys) {
                if (ignoredKey.equals(key)) {
                    continue NEXT_KEY;
                }
            }
            
            String value = assertValue(object, (String) key, String.class);
            
            result.put((String) key, value);
        }
        
        return result;
    }

    /**
     * <p>
     * convenience method for dumping the content of a stream and returning a new stream
     * containing the same data.
     * </p>
     *
     * @param inputStream the stream to be dumped and copied
     * @return the copy of the stream
     * 
     * @throws IOException if the stream can not be read 
     */
/*    private InputStream dumpStreamContent(ServletInputStream inputStream) throws IOException {
        List<Byte> bytes = new ArrayList<Byte>();
        int buf;
        
        while ((buf = inputStream.read()) >= 0) {
            bytes.add((byte) buf);
        }
        
        byte[] byteArray = new byte[bytes.size()];
        for (int i = 0; i < bytes.size(); i++) {
            byteArray[i] = bytes.get(i);
        }
        
        System.out.println(new String(byteArray, "UTF-8"));
        
        return new ByteArrayInputStream(byteArray);
    }*/

    /**
     * <p>
     * convenience method for dumping an object to std out. If the object is a JSON object, it is
     * deeply analyzed and its internal structure is dumped as well.
     * </p>
     *
     * @param object the object to dump
     * @param indent the indentation to be used.
     */
    private void dumpJSONObject(Object object, String indent) {
        if (object instanceof JSONArray) {
            boolean arrayContainsJSONObjects = false;
            for (Object arrayElem : (JSONArray) object) {
                if (arrayElem instanceof JSONObject) {
                    arrayContainsJSONObjects = true;
                    break;
                }                
            }
            
            if (arrayContainsJSONObjects) {
                System.out.println();
                System.out.print(indent);
                System.out.println('[');
                System.out.print(indent);
                System.out.print(' ');
            }
            else {
                System.out.print(' ');
                System.out.print('[');
            }
            
            int index = 0;
            for (Object arrayElem : (JSONArray) object) {
                if (index++ > 0) {
                    System.out.print(",");
                    if (arrayContainsJSONObjects) {
                        System.out.println();
                        System.out.print(indent);
                    }

                    System.out.print(' ');
                }

                dumpJSONObject(arrayElem, indent + "  ");
            }
            
            if (arrayContainsJSONObjects) {
                System.out.println();
                System.out.print(indent);
            }
            
            System.out.print(']');
        }
        else if (object instanceof JSONObject) {
            System.out.println(" {");
            
            @SuppressWarnings("unchecked")
            Set<Map.Entry<?,?>> entrySet = ((JSONObject) object).entrySet();
            
            int index = 0;
            for (Map.Entry<?,?> entry : entrySet) {
                if (index++ > 0) {
                    System.out.println(",");
                }
                System.out.print(indent);
                System.out.print("  \"");
                System.out.print(entry.getKey());
                System.out.print("\":");
                dumpJSONObject(entry.getValue(), indent + "  ");
            }
            
            System.out.println();
            System.out.print(indent);
            System.out.print('}');
        }
        else {
            System.out.print('"');
            System.out.print(object);
            System.out.print('"');
        }
    }

}