package uk.ac.vamsas.client.simpleclient;

import java.io.BufferedWriter;
import java.io.File;
import java.io.IOException;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.io.RandomAccessFile;
import java.io.Writer;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.log4j.Appender;
import org.apache.log4j.Logger;
import org.apache.log4j.FileAppender;

import uk.ac.vamsas.client.ClientHandle;
import uk.ac.vamsas.client.UserHandle;
/**
 * Does all the IO operations for a SimpleClient instance accessing 
 * a SimpleClient vamsas session.
 * 
 * Basically, it defines the various standard names for the files 
 * in the session directory (that maps to the sessionUrn), 
 * provides constructors for the file handlers and watchers of 
 * those file entities, and some higher level methods 
 * to check and change the state flags for the session.
 * 
 * TODO: move the stuff below to the SimpleClientFactory documentation.
 * much may not be valid now :
 * Vamsas client is intialised with a path to create live session directories. 
 * This path may contain a vamsas.properties file 
 * that sets additional parameters (otherwise client 
 * just uses the one on the classpath).
 * 
 * A vamsas session consists of :
 *  SessionDir - translates to urn of a live session.
 *  Contains: Vamsas Document (as a jar), Session client list file, 
 *  both of which may be locked, and additional 
 *  temporary versions of these files when write 
 *  operations are taking place.
 * 
 * Zip file entries
 *  - vamsasdocument.xml : core info
 *  one or more:
 *  - <applicationname>.version.sessionnumber.raw (string given in vamsasdocument.xml applicationData entry)
 *  
 * Lockfile
 *  - filename given in the vamsasdocument.xml. Should be checked for validity by any client and rewritten if necessary. 
 *    The lockfile can point to the jar itself.
 * Mode of operation.
 * Initially - documentHandler either:
 *  - creates a zip for a new session for the client
 *  - connect to an existing session zip 
 *   1. reads session urn file
 *   2. waits for lock
 *   3. examines session - decide whether to create new application data slice or connect to one stored in session.
 *   4. writes info into session file
 *   5. releases lock and generates local client events.
 *   6. Creates Watcher thread to generate events.
 * 
 * During the session
 *  - Update watcher checks for file change - 
 * 
 * Procedures for file based session message exchange
 *  - session document modification flag
 *    
 */

public class VamsasSession {
  /**
   * indicator file for informing other processes that 
   * they should finalise their vamsas datasets for 
   * storing into a vamsas archive.
   */
  public static final String CLOSEANDSAVE_FILE="stored.log";
  /**
   * session file storing the last_stored_stat data 
   */
  public static final String MODIFIEDDOC_FILE="modified";

  /**
   * called to clear update flag after a successful offline storage event
   */
  protected void clearUnsavedFlag() {
    SessionFlagFile laststored = new SessionFlagFile(new File(sessionDir, MODIFIEDDOC_FILE));
    if (!laststored.clearFlag())
      log.warn("Unsaved flag was not cleared for "+sessionDir);
  }
  /**
   * called to indicate session document has been modified.
   *
   */
  protected void setUnsavedFlag() {
    SessionFlagFile laststored = new SessionFlagFile(new File(sessionDir, MODIFIEDDOC_FILE));
    if (!laststored.setFlag())
      log.warn("Couldn't set the Unsaved flag for "+sessionDir);
  }
  /**
   * 
   * @return true if session document has been modified since last offline storage event 
   */
  protected boolean getUnsavedFlag() {
    SessionFlagFile laststored = new SessionFlagFile(new File(sessionDir, MODIFIEDDOC_FILE));
    return laststored.checkFlag();
  }
  /**
   * log file location
   */
  public static final String SESSION_LOG="Log.txt";
  private static Log log = LogFactory.getLog(VamsasSession.class);
  protected Logger slog = Logger.getLogger("uk.ac.vamsas.client.SessionLog");
  /**
   * setup the sessionLog using Log4j.
   * @throws IOException
   */
  private void initLog() throws IOException {
    // LATER: make dedicated appender format for session log.
    Appender app = slog.getAppender("SESSION_LOG");
   // slog.addAppender(new FileAppender(app.getLayout(), new File(sessionDir, SESSION_LOG).getAbsolutePath()));
    
    //Appender app = slog.getAppender("SESSION_LOG");
    if (app == null) log.info("No appender for SESSION_LOG");
  
    if (slog!= null && app != null)
      {
        if (app instanceof FileAppender)
          {
            File sessionLogFile =  new File(this.sessionDir, ((FileAppender)app).getFile());
            slog.addAppender(new FileAppender(app.getLayout(), sessionLogFile.getAbsolutePath()));
          }
        // slog.removeAppender("SESSION_LOG");
      }
  }
  
  /**
   * the sessionDir is given as the session location for new clients.
   */
  protected File sessionDir;
  /**
   * holds the list of attached clients
   */
  ClientsFile clist;
  public static final String CLIENT_LIST="Clients.obj";
  /**
   * holds the data
   */
  VamsasFile vamArchive; 
  public static final String VAMSAS_OBJ="VamDoc.jar";
  
  /**
   * sets up the vamsas session files and watchers in sessionDir
   * @param sessionDir1
   */
  protected VamsasSession(File sessionDir1) throws IOException {
    if (sessionDir1==null)
      throw new Error("Null directory for VamsasSession.");
    if (sessionDir1.exists()) {
      if (!sessionDir1.isDirectory() || !sessionDir1.canWrite() || !sessionDir1.canRead())
        throw new IOException("Cannot access '"+sessionDir1+"' as a read/writable Directory.");
      if (checkSessionFiles(sessionDir1)) {
        createSessionFiles();
      }
        // session files exist in the directory
        this.sessionDir = sessionDir1;
        initSessionObjects();
        slog.debug("Initialising additional VamsasSession instance");
        log.debug("Attached to VamsasSession in "+sessionDir1);
      //} 
    } else {
      // start from scratch
      if (!sessionDir1.mkdir())
        throw new IOException("Failed to make VamsasSession directory in "+sessionDir1);
      this.sessionDir = sessionDir1; 
      createSessionFiles();
      initSessionObjects();
      slog.debug("Session directory created.");
      log.debug("Initialised VamsasSession in "+sessionDir1);
    }
  }
  /**
   * tests presence of existing sessionfiles files in dir
   * @param dir
   * @return
   */
  private boolean checkSessionFiles(File dir) throws IOException {
    File c_file = new File(dir,CLIENT_LIST);
    File v_doc = new File(dir,VAMSAS_OBJ);
    if (c_file.exists() && v_doc.exists())
      return true;
    return false;
  }
  /**
   * create new empty files in dir
   *
   */
  private void createSessionFiles() throws IOException {
    if (sessionDir==null)
      throw new IOException("Invalid call to createSessionFiles() with null sessionDir");
    File c_file = new File(sessionDir,CLIENT_LIST);
    File v_doc = new File(sessionDir,VAMSAS_OBJ);
    if (c_file.createNewFile())
      log.debug("Created new ClientFile "+c_file); // don't care if this works or not
    if (v_doc.createNewFile())
      log.debug("Created new Vamsas Session Document File "+v_doc); 
  }
  /**
   * construct SessionFile objects and watchers for each
   */
  private void initSessionObjects() throws IOException {
    if (clist!=null || vamArchive!=null)
      throw new IOException("initSessionObjects called for initialised VamsasSession object.");
    clist = new ClientsFile(new File(sessionDir,CLIENT_LIST));
    vamArchive = new VamsasFile(new File(sessionDir,VAMSAS_OBJ));
    initLog();
  }
  /**
   * make a new watcher object for the clientFile
   * @return new ClientFile watcher instance
   */
  public FileWatcher getClientWatcher() {
    return new FileWatcher(clist.sessionFile);
  }
  FileWatcher session_doc_watcher=null;
  /**
   * make a new watcher object for the vamsas Document
   * @return new ClientFile watcher instance
   */
  public FileWatcher getDocWatcher() {
    if (session_doc_watcher==null)
      return session_doc_watcher = new FileWatcher(vamArchive.sessionFile);
    return new FileWatcher(vamArchive.sessionFile);
  }
  FileWatcher store_doc_file=null;
  /**
   * make a new watcher object for the messages file
   * (thread safe - keeps a reference to the first watcher)
   * @return new watcher instance
   */
  public FileWatcher getStoreWatcher() {
    if (store_doc_file==null)
      return store_doc_file = new FileWatcher(new File(CLOSEANDSAVE_FILE));
    return new FileWatcher(new File(CLOSEANDSAVE_FILE));

  }
  /**
   * write to the StoreWatcher file to indicate that a storeDocumentRequest has been made.
   * The local client's storeWatcher FileWatcher object is updated so the initial change is not registered.
   * @param client
   * @param user
   * @return
   */
  public void addStoreDocumentRequest(ClientHandle client, UserHandle user) throws IOException {
    SessionFile sfw = new SessionFile(new File(sessionDir, CLOSEANDSAVE_FILE));
    while (!sfw.lockFile())
      log.debug("Trying to get lock for "+CLOSEANDSAVE_FILE);
    RandomAccessFile sfwfile=sfw.fileLock.getRaFile();
    sfwfile.setLength(0); // wipe out any old info.
    // TODO: rationalise what gets written to this file (ie do we want other clients to read the id of the requestor?)
    sfwfile.writeUTF(client.getClientUrn()+":"+user.getFullName()+"@"+user.getOrganization());
    sfw.unlockFile();
    if (store_doc_file!=null)
      store_doc_file.setState();
    slog.info("FinalizeAppData request from "+user.getFullName()+" using "+client.getClientUrn()+"");
  }
  /**
   * create a new session with an existing vamsas Document - by copying it into the session.
   * @param archive
   */
  public void setVamsasDocument(File archive) throws IOException {
    log.debug("Transferring vamsas data from "+archive+" to session:"+vamArchive.sessionFile);
    SessionFile xtantdoc = new SessionFile(archive);
    vamArchive.updateFrom(null, xtantdoc);
    // LATER: decide if session archive provenance should be updated to reflect access.
    // TODO: soon! do a proper import objects from external file 
    log.debug("Transfer complete.");
  }
  /**
   * write session as a new vamsas Document (this will overwrite any existing file without warning)
   * TODO: test
   * TODO: verify that lock should be released for vamsas document.
   * @param destarchive
   */
  protected void writeVamsasDocument(File destarchive, Lock extlock) throws IOException {
    log.debug("Transferring vamsas data from "+vamArchive.sessionFile+" to session:"+destarchive);
    SessionFile newdoc = new SessionFile(destarchive);
    if (extlock==null && !vamArchive.lockFile())
      while (!vamArchive.lockFile())
        log.info("Trying to get lock for "+vamArchive.sessionFile);
    // TODO: LATER: decide if session archive provenance should be written in vamsasDocument file for this export.
    newdoc.updateFrom(extlock, vamArchive);
    // LATER: LATER: fix use of updateFrom for file systems where locks cannot be made (because they don't have a lockManager, ie NFS/Unix, etc).
    vamArchive.unLock();
    newdoc.unlockFile();
    log.debug("Transfer complete.");
  }
  
  /**
   * Creates a VamsasArchive Vobject for accessing and updating document
   * Note: this will lock the Vamsas Document for exclusive access to the client.
   * @return session vamsas document
   * @throws IOException if locks fail or vamsas document read fails.
   */
  protected VamsasArchive getVamsasDocument() throws IOException {
    // TODO: check we haven't already done this once
    if (!vamArchive.lockFile()) 
      throw new IOException("Failed to get lock for vamsas archive.");
    
    VamsasArchive va = new VamsasArchive(vamArchive.sessionFile, false, true, vamArchive);
    
    return va;
  }
  /**
   * create a uniquely named file in the session Directory
   * @see java.io.File.createTempFile
   * @param pref Prefix for name
   * @param suff Suffix for name
   * @return SessionFile object configured for the new file (of length zero)
   * @throws IOException
   */
  protected SessionFile getTempSessionFile(String pref, String suff) throws IOException {
    File tfile = File.createTempFile(pref,suff,sessionDir);
    SessionFile tempFile = new SessionFile(tfile);
    return tempFile;
  }
}