package org.wso2.caching.digest;

import java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;

import org.apache.axiom.om.OMAttribute;
import org.apache.axiom.om.OMElement;
import org.apache.axiom.om.OMNode;
import org.apache.axiom.om.OMProcessingInstruction;
import org.apache.axiom.om.OMText;
import org.apache.axis2.context.MessageContext;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.wso2.caching.CachingException;

/**
 * This is the extended implementation of
 * <a href="http://www.ietf.org/rfc/rfc2803.txt">DOMHASH algorithm</a> over a HTTP request
 * and Payload (XML Node) for retrieving a unique key for the request
 *
 * @see org.wso2.caching.digest.DigestGenerator
 */
public class REQUESTHASHGenerator extends DOMHASHGenerator {
	
	 /** String representing the MD5 digest algorithm */
    public static final String MD5_DIGEST_ALGORITHM = "MD5";
    
    private static final Log log = LogFactory.getLog(REQUESTHASHGenerator.class);

    /**
     * This is the implementation of the getDigest method and will implement the Extended DOMHASH
     * algorithm based HTTP request identifications. This will consider To address of the request,
     * HTTP headers and XML Payload in generating the digets. So, in effect
     * this will uniquely identify the HTTP request with the same To address, Headers and Payload.
     * 
     * @param msgContext - MessageContext on which the XML node identifier will be generated
     * @return Object representing the DOMHASH value of the normalized XML node
     * @throws CachingException if there is an error in generating the digest key
     *
     * @see org.wso2.caching.digest.DigestGenerator
     *          #getDigest(org.apache.axis2.context.MessageContext) 
     */
    public String getDigest(MessageContext msgContext) throws CachingException {
		OMNode body = msgContext.getEnvelope().getBody();
		String toAddress = null;
		if (msgContext.getTo() != null) {
			toAddress = msgContext.getTo().getAddress();			
		}
		Map<String, String> headers = (Map) msgContext.getProperty(org.apache.axis2.context.MessageContext.TRANSPORT_HEADERS);
	    if (body != null) {
	    	byte[] digest = null;
	    	if (toAddress != null) {
	    		digest = getDigest(body, toAddress, headers, MD5_DIGEST_ALGORITHM);
	    	} else {
	    		digest = getDigest(body, MD5_DIGEST_ALGORITHM);
	    	}
	        return digest != null ? getStringRepresentation(digest) : null;
	    } else {
	    	return null;
	    }
	}
	
	/**
     * This is an overloaded method for the digest generation for OMNode and request
     *
     * @param node              - OMNode to be subjected to the key generation
     * @param toAddress         - Request To address to be subjected to the key generation
     * @param headers           - Header parameters to be subjected to the key generation
     * @param digestAlgorithm   - digest algorithm as a String
     * @return byte[] representing the calculated digest over the provided node
     * @throws CachingException if there is an error in generating the digest
     */
	public byte[] getDigest(OMNode node, String toAddress, Map<String, String> headers, 
			String digestAlgorithm) throws CachingException {

        if (node.getType() == OMNode.ELEMENT_NODE) {
            return getDigest((OMElement) node, toAddress, headers, digestAlgorithm);
        } else if (node.getType() == OMNode.TEXT_NODE) {
            return getDigest((OMText) node, digestAlgorithm);
        } else if (node.getType() == OMNode.PI_NODE) {
            return getDigest((OMProcessingInstruction) node, digestAlgorithm);
        } else {
            return new byte[0];
        }
    }
	
	/**
     * This is an overloaded method for the digest generation for OMElement and request
     *
     * @param element           - OMElement to be subjected to the key generation
     * @param toAddress         - Request To address to be subjected to the key generation
     * @param headers           - Header parameters to be subjected to the key generation
     * @param digestAlgorithm   - digest algorithm as a String
     * @return byte[] representing the calculated digest over the provided element
     * @throws CachingException if there is an io error or the specified algorithm is incorrect
     */	
	public byte[] getDigest(OMElement element, String toAddress, Map<String, String> headers, 
			String digestAlgorithm) throws CachingException {
        
        byte[] digest = new byte[0];

        try {
            
            MessageDigest md = MessageDigest.getInstance(digestAlgorithm);
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            DataOutputStream dos = new DataOutputStream(baos);
            dos.writeInt(1);
            dos.write(getExpandedName(element).getBytes("UnicodeBigUnmarked"));
            dos.write((byte) 0);
            dos.write((byte) 0);
            
            dos.write(toAddress.getBytes("UnicodeBigUnmarked"));
            
            /*String acceptHeader = headers.get("accept");
            acceptHeader = (acceptHeader == null) ? headers.get("Accept") : acceptHeader;
            
            if (acceptHeader != null) {
            	dos.write(acceptHeader.getBytes("UnicodeBigUnmarked"));
            }
            
            String contentTypeHeader = headers.get("content-type");
            contentTypeHeader = (contentTypeHeader == null) ? headers.get("Content-Type") : contentTypeHeader;
            
            if (contentTypeHeader != null) {
            	dos.write(contentTypeHeader.getBytes("UnicodeBigUnmarked"));
            }*/
            
            Iterator itr = headers.keySet().iterator();
            while (itr.hasNext()) {
            	String key = (String) itr.next();
            	String value = headers.get(key);
            	dos.write(getDigest(key, value, digestAlgorithm));
            }
            
            Collection attrs = getAttributesWithoutNS(element);
            dos.writeInt(attrs.size());
                        
            
            itr = attrs.iterator();
            while (itr.hasNext())
                dos.write(getDigest((OMAttribute) itr.next(), digestAlgorithm));
            OMNode node = element.getFirstOMChild();
            
            // adjoining Texts are merged,
            // there is  no 0-length Text, and
            // comment nodes are removed.
            int length = 0;
            itr = element.getChildElements();
            while (itr.hasNext()) {
                length++;
                itr.next();
            }
            dos.writeInt(length);
            
            while (node != null) {
                dos.write(getDigest(node, toAddress, headers, digestAlgorithm));
                node = node.getNextOMSibling();
            }
            dos.close();
            md.update(baos.toByteArray());
            
            digest = md.digest();
            
        } catch (NoSuchAlgorithmException e) {
            handleException("Can not locate the algorithm " +
                "provided for the digest generation : " + digestAlgorithm, e);
        } catch (IOException e) {
            handleException("Error in calculating the " +
                "digest value for the OMElement : " + element, e);
        }
        
        return digest;
    }
	
	/**
     * This is an overloaded method for the digest generation for HTTP header property
     *
     * @param key         - Key of the header property subjected to the key generation
     * @param value         - Value of the header property subjected to the key generation
     * @param digestAlgorithm   - digest algorithm as a String
     * @return byte[] representing the calculated digest over the provided attribute
     * @throws CachingException if the specified algorithm is incorrect or the encoding
     *                          is not supported by the processor
     */
    public byte[] getDigest(String key,String value, String digestAlgorithm) throws CachingException {

        byte[] digest = new byte[0];
        
        if (!key.equalsIgnoreCase("Date") && !key.equalsIgnoreCase("User-Agent")) {
	        try {
	
	                MessageDigest md = MessageDigest.getInstance(digestAlgorithm);
	                md.update((byte) 0);
	                md.update((byte) 0);
	                md.update((byte) 0);
	                md.update((byte) 2);
	                md.update(key.getBytes("UnicodeBigUnmarked"));
	
	                if (value != null) {
	                	md.update((byte) 0);
	                	md.update((byte) 0);
	                	md.update(value.getBytes("UnicodeBigUnmarked"));
	                }
	
	                digest = md.digest();
	
	            } catch (NoSuchAlgorithmException e) {
	                handleException("Can not locate the algorithm " +
	                    "provided for the digest generation : " + digestAlgorithm, e);
	            } catch (UnsupportedEncodingException e) {
	                handleException("Error in generating the digest " +
	                    "using the provided encoding : UnicodeBigUnmarked", e);
	            }
        }
               
        return digest;
    }
	
	private void handleException(String message, Throwable cause) throws CachingException {
        log.debug(message, cause);
        throw new CachingException(message, cause);
    }

}