/*
    The contents of this file are subject to the Mozilla Public License Version 1.1
    (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.mozilla.org/MPL/
    Software distributed under the License is distributed on an "AS IS" basis,
    WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the
    specific language governing rights and limitations under the License.
   
    The Original Code is "MllpDecoderState.java".  Description:
   "State machine that handles reading MLLP frames"
  
   The Initial Developer of the Original Code is University Health Network. Copyright (C)
   2013.  All Rights Reserved.
  
   Contributor(s): ______________________________________.
  
   Alternatively, the contents of this file may be used under the terms of the
   GNU General Public License (the "GPL"), in which case the provisions of the GPL are
   applicable instead of those above.  If you wish to allow use of your version of this
   file only under the terms of the GPL and not to allow others to use your version
   of this file under the MPL, indicate your decision by deleting  the provisions above
   and replace  them with the notice and other provisions required by the GPL License.
   If you do not delete the provisions above, a recipient may use your version of
   this file under either the MPL or the GPL.
   */
  
  package ca.uhn.hl7v2.llp;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.net.SocketException;
  import java.net.SocketTimeoutException;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import static ca.uhn.hl7v2.llp.MllpConstants.END_BYTE1;
  import static ca.uhn.hl7v2.llp.MllpConstants.END_BYTE2;
  import static ca.uhn.hl7v2.llp.MllpConstants.START_BYTE;
  
  /**
   * MllpDecoderState implements a small state machine that handles reading bytes at the various
   * positions in the MLLP input stream, thereby promoting the state if the MLLP marker bytes
   * are encountered.
   *
   * @author Christian Ohr
   */
  enum MllpDecoderState {
  
      START(START_BYTE, true) {
          @Override
          protected MllpDecoderState proceed() {
              return BODY;
          }
  
          @Override
          protected void handleEndOfStream() throws IOException {
              LOG.info("End of input stream reached.");
              throw new SocketException("End of input stream reached before message starts");
          }
  
      },
      BODY(END_BYTE1, false) {
          @Override
          protected MllpDecoderState proceed() {
              return PREPARE_END;
          }
  
          @Override
          protected void handleEndOfStream() throws LLPException {
              throw new LLPException("MLLP protocol violation - Stream ends in the message body");
          }
  
      },
      PREPARE_END(END_BYTE2, true) {
          @Override
          protected MllpDecoderState proceed() {
              return END;
          }
  
          @Override
          protected void handleEndOfStream() throws LLPException {
              throw new LLPException("MLLP protocol violation - Stream ends before LLP end byte");
          }
      },
      END(0, false) {
          @Override
          protected MllpDecoderState proceed() {
              return END;
          }
  
          @Override
          protected void handleEndOfStream() {
          }
  
          @Override
          MllpDecoderState read(InputStream in, OutputStream out) throws LLPException {
              throw new LLPException("Internal error - reading after end of message");
         }
     };
 
     private final int nextStateByte; // byte required for state transition
     private final boolean mustChangeState; // next byte must be nextStateByte
 
     private static final Logger LOG = LoggerFactory.getLogger(MllpDecoderState.class);
 
 
     MllpDecoderState(int nextStateByte, boolean mustChangeState) {
         this.nextStateByte = nextStateByte;
         this.mustChangeState = mustChangeState;
     }
 
     /**
      * Reads data from the input stream, records the actual payload and promtes the
      * state if applicable.
      *
      * @param in  input
      * @param out recorded data
      * @return next decoder state
      * @throws SocketTimeoutException If the socket times out
      * @throws IOException
      * @throws LLPException
      */
     MllpDecoderState read(InputStream in, OutputStream out) throws SocketTimeoutException, IOException, LLPException {
         int c;
         try {
             if ((c = in.read()) == -1) {
                 handleEndOfStream();
             } else {
                 LowerLayerProtocol.logCharacterReceived(c);
             }
             if (c == nextStateByte) {
             	return proceed();
             }
             if (mustChangeState) {
                 throw new LLPException("MLLP protocol violation - Expected byte '" + nextStateByte +
                         "' in state " + this + " but was '" + c + "'");
             }
             out.write(c);
         } catch (SocketException e) {
             LOG.info("SocketException on read() attempt.  Socket appears to have been closed: " + e.getMessage());
             throw e;
         }
         return this;
     }
 
     /**
      * Proceed to the next state
      *
      * @return next decoder state
      */
     protected abstract MllpDecoderState proceed();
 
     /**
      * Handle occurences of unexpected ends of streams
      *
      * @throws IOException
      * @throws LLPException
      */
     protected abstract void handleEndOfStream() throws IOException, LLPException;
 
 }