/**
 * 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 "PipeParser.java".  Description:
 * "An implementation of Parser that supports traditionally encoded (i.e"
 *
 * The Initial Developer of the Original Code is University Health Network. Copyright (C)
 * 2001.  All Rights Reserved.
 *
 * Contributor(s): Kenneth Beaton.
 *
 * 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.parser;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.StringTokenizer;

import ca.uhn.hl7v2.validation.ValidationContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import ca.uhn.hl7v2.DefaultHapiContext;
import ca.uhn.hl7v2.ErrorCode;
import ca.uhn.hl7v2.HL7Exception;
import ca.uhn.hl7v2.HapiContext;
import ca.uhn.hl7v2.Version;
import ca.uhn.hl7v2.model.AbstractSuperMessage;
import ca.uhn.hl7v2.model.DoNotCacheStructure;
import ca.uhn.hl7v2.model.Group;
import ca.uhn.hl7v2.model.Message;
import ca.uhn.hl7v2.model.Primitive;
import ca.uhn.hl7v2.model.Segment;
import ca.uhn.hl7v2.model.Structure;
import ca.uhn.hl7v2.model.SuperStructure;
import ca.uhn.hl7v2.model.Type;
import ca.uhn.hl7v2.model.Varies;
import ca.uhn.hl7v2.util.ReflectionUtil;
import ca.uhn.hl7v2.util.Terser;
import ca.uhn.hl7v2.validation.impl.NoValidation;
import ca.uhn.hl7v2.validation.impl.ValidationContextFactory;

/**
 * An implementation of Parser that supports traditionally encoded (ie delimited
 * with characters like |, ^, and ~) HL7 messages. Unexpected segments and
 * fields are parsed into generic elements that are added to the message.
 * 
 * @see ParserConfiguration for configuration options which may affect parser encoding and decoding behaviour
 * @author Bryan Tripp (bryan_tripp@sourceforge.net)
 */
public class PipeParser extends Parser {

        private static final Logger log = LoggerFactory.getLogger(PipeParser.class);

        /**
         * The HL7 ER7 segment delimiter (see section 2.8 of spec)
         */
        final static String SEGMENT_DELIMITER = "\r";

        private final HashMap<Class<? extends Message>, HashMap<String, StructureDefinition>> myStructureDefinitions = new HashMap<Class<? extends Message>, HashMap<String, StructureDefinition>>();

        /**
         * System property key. If value is "true", legacy mode will default to true
         * 
         * @see #isLegacyMode()
         * @deprecated This will be removed in HAPI 3.0
         */
        public static final String DEFAULT_LEGACY_MODE_PROPERTY = "ca.uhn.hl7v2.parser.PipeParser.default_legacy_mode";

        private Boolean myLegacyMode = null;

        public PipeParser() {
                super();
        }

        /**
         * @param context
         *            the context containing all configuration items to be used
         */
        public PipeParser(HapiContext context) {
                super(context);
        }

        /**
         * Creates a new PipeParser
         * 
         * @param theFactory
         *            custom factory to use for model class lookup
         */
        public PipeParser(ModelClassFactory theFactory) {
                super(theFactory);
        }

    @Override
    public void setValidationContext(ValidationContext context) {
        super.setValidationContext(context);
    }

    /**
         * Returns a String representing the encoding of the given message, if the
         * encoding is recognized. For example if the given message appears to be
         * encoded using HL7 2.x XML rules then "XML" would be returned. If the
         * encoding is not recognized then null is returned. That this method
         * returns a specific encoding does not guarantee that the message is
         * correctly encoded (e.g. well formed XML) - just that it is not encoded
         * using any other encoding than the one returned.
         */
        public String getEncoding(String message) {
                return EncodingDetector.isEr7Encoded(message) ? getDefaultEncoding() : null;
        }

        /**
         * @return the preferred encoding of this Parser
         */
        public String getDefaultEncoding() {
                return "VB";
        }

        /**
         * @deprecated this method should not be public
         * @param message HL7 message
         * @return message structure
         * @throws HL7Exception
         */
        public String getMessageStructure(String message) throws HL7Exception {
                return getStructure(message).messageStructure;
        }

        /**
         * @return the message structure from MSH-9-3
         */
        private MessageStructure getStructure(String message) throws HL7Exception {
                EncodingCharacters ec = getEncodingChars(message);
                String messageStructure;
                boolean explicityDefined = true;
                String wholeFieldNine;
                try {
                        String[] fields = split(message.substring(0, Math.max(message.indexOf(SEGMENT_DELIMITER), message.length())), String.valueOf(ec.getFieldSeparator()));
                        wholeFieldNine = fields[8];

                        // message structure is component 3 but we'll accept a composite of
                        // 1 and 2 if there is no component 3 ...
                        // if component 1 is ACK, then the structure is ACK regardless of
                        // component 2
                        String[] comps = split(wholeFieldNine, String.valueOf(ec.getComponentSeparator()));
                        if (comps.length >= 3) {
                                messageStructure = comps[2];
                        } else if (comps.length > 0 && comps[0] != null && comps[0].equals("ACK")) {
                                messageStructure = "ACK";
                        } else if (comps.length == 2) {
                                explicityDefined = false;
                                messageStructure = comps[0] + "_" + comps[1];
                        }
                        /*
                         * else if (comps.length == 1 && comps[0] != null &&
                         * comps[0].equals("ACK")) { messageStructure = "ACK"; //it's common
                         * for people to only populate component 1 in an ACK msg }
                         */
                        else {
                                StringBuilder buf = new StringBuilder("Can't determine message structure from MSH-9: ");
                                buf.append(wholeFieldNine);
                                if (comps.length < 3) {
                                        buf.append(" HINT: there are only ");
                                        buf.append(comps.length);
                                        buf.append(" of 3 components present");
                                }
                                throw new HL7Exception(buf.toString(), ErrorCode.UNSUPPORTED_MESSAGE_TYPE);
                        }
                } catch (IndexOutOfBoundsException e) {
                        throw new HL7Exception("Can't find message structure (MSH-9-3): " + e.getMessage(), ErrorCode.UNSUPPORTED_MESSAGE_TYPE);
                }

                return new MessageStructure(messageStructure, explicityDefined);
        }

        /**
         * Returns object that contains the field separator and encoding characters
         * for this message.
         * 
         * @throws HL7Exception
         */
        private static EncodingCharacters getEncodingChars(String message) throws HL7Exception {
                if (message.length() < 8) {
                        throw new HL7Exception("Invalid message content: \"" + message + "\"");
                }
                return new EncodingCharacters(message.charAt(3), message.substring(4, 8));
        }

        /**
         * Parses a message string and returns the corresponding Message object.
         * Unexpected segments added at the end of their group.
         * 
         * @throws HL7Exception
         *             if the message is not correctly formatted.
         * @throws EncodingNotSupportedException
         *             if the message encoded is not supported by this parser.
         */
        protected Message doParse(String message, String version) throws HL7Exception {

                // try to instantiate a message object of the right class
                MessageStructure structure = getStructure(message);
                Message m = instantiateMessage(structure.messageStructure, version, structure.explicitlyDefined);
                // Note: this will change in future to reuse the Parser's/HapiContext's
                // ValidationContext.
                m.setValidationContext(getValidationContext());
                
                m.setParser(this);
                
                parse(m, message);

                return m;
        }

        /**
         * {@inheritDoc}
         */
        protected Message doParseForSpecificPackage(String message, String version, String packageName) throws HL7Exception {

                // try to instantiate a message object of the right class
                MessageStructure structure = getStructure(message);
                Message m = instantiateMessageInASpecificPackage(structure.messageStructure, version, structure.explicitlyDefined, packageName);

                parse(m, message);

                return m;
        }

        /**
         * Generates (or returns the cached value of) the message
         */
        private IStructureDefinition getStructureDefinition(Message theMessage) throws HL7Exception {

                Class<? extends Message> clazz = theMessage.getClass();
                HashMap<String, StructureDefinition> definitions = myStructureDefinitions.get(clazz);

                StructureDefinition retVal;
                if (definitions != null) {
                        retVal = definitions.get(theMessage.getName());
                        if (retVal != null) {
                                return retVal;
                        }
                }

                if (theMessage instanceof SuperStructure) {
                        Set<String> appliesTo = ((SuperStructure) theMessage).getStructuresWhichChildAppliesTo("MSH");
                        if (!appliesTo.contains(theMessage.getName())) {
                                throw new HL7Exception("Superstructure " + theMessage.getClass().getSimpleName() + " does not apply to message " + theMessage.getName() + ", can not parse.");
                        }
                }
                
                if (clazz.isAnnotationPresent(DoNotCacheStructure.class)) {
                        Holder<StructureDefinition> previousLeaf = new Holder<StructureDefinition>();
                        retVal = createStructureDefinition(theMessage, previousLeaf, theMessage.getName());
                } else {
                        Message message = ReflectionUtil.instantiateMessage(clazz, getFactory());
                        Holder<StructureDefinition> previousLeaf = new Holder<StructureDefinition>();
                        retVal = createStructureDefinition(message, previousLeaf, theMessage.getName());

                        if (!myStructureDefinitions.containsKey(clazz)) {
                                myStructureDefinitions.put(clazz, new HashMap<String, StructureDefinition>());
                        }
                        myStructureDefinitions.get(clazz).put(theMessage.getName(), retVal);
                }

                return retVal;
        }

        private StructureDefinition createStructureDefinition(Structure theStructure, Holder<StructureDefinition> thePreviousLeaf, String theStructureName) throws HL7Exception {

                StructureDefinition retVal = new StructureDefinition();
                retVal.setName(theStructure.getName());

                if (theStructure instanceof Group) {
                        retVal.setSegment(false);
                        Group group = (Group) theStructure;
                        int index = 0;
                        List<String> childNames = Arrays.asList(group.getNames());
                        
                        /*
                         * For SuperStructures, which can hold more than one type of structure,
                         * we only actually bring in the child names that are actually a part
                         * of the structure we are trying to parse
                         */
                        if (theStructure instanceof SuperStructure) {
                                String struct = theStructureName;
                                Map<String, String> evtMap = new DefaultModelClassFactory().getEventMapForVersion(Version.versionOf(theStructure.getMessage().getVersion()));
                                if (evtMap.containsKey(struct)) {
                                        struct = evtMap.get(struct);
                                }
                                childNames = ((SuperStructure) theStructure).getChildNamesForStructure(struct);
                        }
                        
                        for (String nextName : childNames) {
                                Structure nextChild = group.get(nextName);
                                StructureDefinition structureDefinition = createStructureDefinition(nextChild, thePreviousLeaf, theStructureName);
                                structureDefinition.setNameAsItAppearsInParent(nextName);
                                structureDefinition.setRepeating(group.isRepeating(nextName));
                                structureDefinition.setRequired(group.isRequired(nextName));
                                structureDefinition.setChoiceElement(group.isChoiceElement(nextName));
                                structureDefinition.setPosition(index++);
                                structureDefinition.setParent(retVal);
                                retVal.addChild(structureDefinition);
                        }
                } else {
                        if (thePreviousLeaf.getObject() != null) {
                                thePreviousLeaf.getObject().setNextLeaf(retVal);
                        }
                        thePreviousLeaf.setObject(retVal);
                        retVal.setSegment(true);
                }

                return retVal;
        }

        /**
         * Parses a segment string and populates the given Segment object.
         * Unexpected fields are added as Varies' at the end of the segment.
     *
         * @param destination segment to parse the segment string into
     * @param segment encoded segment
     * @param encodingChars encoding characters to be used
         * @throws HL7Exception
         *             if the given string does not contain the given segment or if
         *             the string is not encoded properly
         */
        public void parse(Segment destination, String segment, EncodingCharacters encodingChars) throws HL7Exception {
                parse(destination, segment, encodingChars, 0);
        }

        /**
         * Parses a segment string and populates the given Segment object.
         * Unexpected fields are added as Varies' at the end of the segment.
         *
     * @param destination segment to parse the segment string into
     * @param segment encoded segment
     * @param encodingChars encoding characters to be used
         * @param theRepetition the repetition number of this segment within its group
         * @throws HL7Exception
         *             if the given string does not contain the given segment or if
         *             the string is not encoded properly
         */
        public void parse(Segment destination, String segment, EncodingCharacters encodingChars, int theRepetition) throws HL7Exception {
                int fieldOffset = 0;
                if (isDelimDefSegment(destination.getName())) {
                        fieldOffset = 1;
                        // set field 1 to fourth character of string
                        Terser.set(destination, 1, 0, 1, 1, String.valueOf(encodingChars.getFieldSeparator()));
                }

                String[] fields = split(segment, String.valueOf(encodingChars.getFieldSeparator()));
                // destination.setName(fields[0]);
                for (int i = 1; i < fields.length; i++) {
                        String[] reps = split(fields[i], String.valueOf(encodingChars.getRepetitionSeparator()));

                        // MSH-2 will get split incorrectly so we have to fudge it ...
                        boolean isMSH2 = isDelimDefSegment(destination.getName()) && i + fieldOffset == 2;
                        if (isMSH2) {
                                reps = new String[1];
                                reps[0] = fields[i];
                        }

                        for (int j = 0; j < reps.length; j++) {
                                try {
                                        log.trace("Parsing field {} repetition {}", i + fieldOffset, j);
                                        Type field = destination.getField(i + fieldOffset, j);
                                        if (isMSH2) {
                                                Terser.getPrimitive(field, 1, 1).setValue(reps[j]);
                                        } else {
                                                parse(field, reps[j], encodingChars);
                                        }
                                } catch (HL7Exception e) {
                                        // set the field location and throw again ...
                                        e.setFieldPosition(i);
                                        if (theRepetition > 1) {
                                                e.setSegmentRepetition(theRepetition);
                                        }
                                        e.setSegmentName(destination.getName());
                                        throw e;
                                }
                        }
                }

                // set data type of OBX-5
                if (destination.getClass().getName().contains("OBX")) {
                        Varies.fixOBX5(destination, getFactory(), getHapiContext().getParserConfiguration());
                }

        }

        /**
         * @return true if the segment is MSH, FHS, or BHS. These need special
         *         treatment because they define delimiters.
         * @param theSegmentName
         *            segment name
         */
        private static boolean isDelimDefSegment(String theSegmentName) {
                boolean is = false;
                if (theSegmentName.equals("MSH") || theSegmentName.equals("FHS") || theSegmentName.equals("BHS")) {
                        is = true;
                }
                return is;
        }

        /**
         * Fills a field with values from an unparsed string representing the field.
         * 
         * @param destinationField
         *            the field Type
         * @param data
         *            the field string (including all components and subcomponents;
         *            not including field delimiters)
         * @param encodingCharacters
         *            the encoding characters used in the message
         */
        @Override
        public void parse(Type destinationField, String data, EncodingCharacters encodingCharacters) throws HL7Exception {
                String[] components = split(data, String.valueOf(encodingCharacters.getComponentSeparator()));
                for (int i = 0; i < components.length; i++) {
                        String[] subcomponents = split(components[i], String.valueOf(encodingCharacters.getSubcomponentSeparator()));
                        for (int j = 0; j < subcomponents.length; j++) {
                                String val = subcomponents[j];
                                if (val != null) {
                                        val = getParserConfiguration().getEscaping().unescape(val, encodingCharacters);
                                }
                                Terser.getPrimitive(destinationField, i + 1, j + 1).setValue(val);
                        }
                }
        }

        /**
         * Splits the given composite string into an array of components using the
         * given delimiter.
     *
     * @param composite encoded composite string
     * @param delim delimiter to split upon
     * @return split string
         */
        public static String[] split(String composite, String delim) {
                ArrayList<String> components = new ArrayList<String>();

                // defend against evil nulls
                if (composite == null)
                        composite = "";
                if (delim == null)
                        delim = "";

                StringTokenizer tok = new StringTokenizer(composite, delim, true);
                boolean previousTokenWasDelim = true;
                while (tok.hasMoreTokens()) {
                        String thisTok = tok.nextToken();
                        if (thisTok.equals(delim)) {
                                if (previousTokenWasDelim)
                                        components.add(null);
                                previousTokenWasDelim = true;
                        } else {
                                components.add(thisTok);
                                previousTokenWasDelim = false;
                        }
                }

                String[] ret = new String[components.size()];
                for (int i = 0; i < components.size(); i++) {
                        ret[i] = components.get(i);
                }

                return ret;
        }

        /**
         * {@inheritDoc }
         */
        @Override
        public String doEncode(Segment structure, EncodingCharacters encodingCharacters) throws HL7Exception {
                return encode(structure, encodingCharacters, getParserConfiguration(), null);
        }

        /**
         * {@inheritDoc }
         */
        @Override
        public String doEncode(Type type, EncodingCharacters encodingCharacters) throws HL7Exception {
                return encode(type, encodingCharacters, getParserConfiguration(), null);
        }

        /**
         * Encodes the given Type, using the given encoding characters. It is
         * assumed that the Type represents a complete field rather than a
         * component.
     *
     * @param source type to be encoded
     * @param encodingChars encoding characters to be used
     * @return encoded type
         */
        public static String encode(Type source, EncodingCharacters encodingChars) {
                return encode(source, encodingChars, source.getMessage().getParser().getParserConfiguration(), null);
        }

        private static String encode(Type source, EncodingCharacters encodingChars, ParserConfiguration parserConfig, String currentTerserPath) {
                if (source instanceof Varies) {
                        Varies varies = (Varies) source;
                        if (varies.getData() != null) {
                                source = varies.getData();
                        }
                }

                StringBuilder field = new StringBuilder();
                for (int i = 1; i <= Terser.numComponents(source); i++) {
                        StringBuilder comp = new StringBuilder();
                        for (int j = 1; j <= Terser.numSubComponents(source, i); j++) {
                                Primitive p = Terser.getPrimitive(source, i, j);
                                comp.append(encodePrimitive(p, parserConfig.getEscaping(), encodingChars));
                                comp.append(encodingChars.getSubcomponentSeparator());
                        }
                        field.append(stripExtraDelimiters(comp.toString(), encodingChars.getSubcomponentSeparator()));
                        field.append(encodingChars.getComponentSeparator());
                }

                int forceUpToFieldNum = 0;
                if (parserConfig != null && currentTerserPath != null) {
                        for (String nextPath : parserConfig.getForcedEncode()) {
                                if (nextPath.startsWith(currentTerserPath + "-") && nextPath.length() > currentTerserPath.length()) {
                                        int endOfFieldDef = nextPath.indexOf('-', currentTerserPath.length());
                                        if (endOfFieldDef == -1) {
                                                forceUpToFieldNum = 0;
                                                break;
                                        }
                                        String fieldNumString = nextPath.substring(endOfFieldDef + 1, nextPath.length());
                                        if (fieldNumString.length() > 0) {
                                                forceUpToFieldNum = Math.max(forceUpToFieldNum, Integer.parseInt(fieldNumString));
                                        }
                                }
                        }
                }

                char componentSeparator = encodingChars.getComponentSeparator();
                String retVal = stripExtraDelimiters(field.toString(), componentSeparator);

                while (forceUpToFieldNum > 0 && (countInstancesOf(retVal, componentSeparator) + 1) < forceUpToFieldNum) {
                        retVal = retVal + componentSeparator;
                }

                return retVal;
        }

        private static String encodePrimitive(Primitive p, Escaping escaping, EncodingCharacters encodingChars) {
                String val = (p).getValue();
                if (val == null) {
                        val = "";
                } else {
                        val = escaping.escape(val, encodingChars);
                }
                return val;
        }

        /**
         * Removes unecessary delimiters from the end of a field or segment. This
         * seems to be more convenient than checking to see if they are needed while
         * we are building the encoded string.
         */
        private static String stripExtraDelimiters(String in, char delim) {
                char[] chars = in.toCharArray();

                // search from back end for first occurance of non-delimiter ...
                int c = chars.length - 1;
                boolean found = false;
                while (c >= 0 && !found) {
                        if (chars[c--] != delim)
                                found = true;
                }

                String ret = "";
                if (found)
                        ret = String.valueOf(chars, 0, c + 2);
                return ret;
        }

        /**
         * Formats a Message object into an HL7 message string using the given
         * encoding.
         * 
         * @throws HL7Exception
         *             if the data fields in the message do not permit encoding
         *             (e.g. required fields are null)
         * @throws EncodingNotSupportedException
         *             if the requested encoding is not supported by this parser.
         */
        protected String doEncode(Message source, String encoding) throws HL7Exception {
                if (!this.supportsEncoding(encoding))
                        throw new EncodingNotSupportedException("This parser does not support the " + encoding + " encoding");

                return encode(source);
        }

        /**
         * Formats a Message object into an HL7 message string using this parser's
         * default encoding ("VB").
         * 
         * @throws HL7Exception
         *             if the data fields in the message do not permit encoding
         *             (e.g. required fields are null)
         */
        protected String doEncode(Message source) throws HL7Exception {
                // get encoding characters ...
                Segment msh = (Segment) source.get("MSH");
                String fieldSepString = Terser.get(msh, 1, 0, 1, 1);

                if (fieldSepString == null)
                        throw new HL7Exception("Can't encode message: MSH-1 (field separator) is missing");

                char fieldSep = '|';
                if (fieldSepString.length() > 0)
                        fieldSep = fieldSepString.charAt(0);

                String encCharString = Terser.get(msh, 2, 0, 1, 1);

                if (encCharString == null)
                        throw new HL7Exception("Can't encode message: MSH-2 (encoding characters) is missing");

                if (encCharString.length() != 4)
                        throw new HL7Exception("Encoding characters (MSH-2) value '" + encCharString + "' invalid -- must be 4 characters", ErrorCode.DATA_TYPE_ERROR);
                EncodingCharacters en = new EncodingCharacters(fieldSep, encCharString);

                // pass down to group encoding method which will operate recursively on
                // children ...
                return encode(source, en, getParserConfiguration(), "");
        }

        /**
         * Returns given group serialized as a pipe-encoded string - this method is
         * called by encode(Message source, String encoding).
     *
     * @param source group to be encoded
     * @param encodingChars encoding characters to be used
     * @throws HL7Exception if an error occurred while encoding
     * @return encoded group
         */
        public static String encode(Group source, EncodingCharacters encodingChars) throws HL7Exception {
                return encode(source, encodingChars, source.getMessage().getParser().getParserConfiguration(), "");
        }

        /**
         * Returns given group serialized as a pipe-encoded string - this method is
         * called by encode(Message source, String encoding).
         */
        private static String encode(Group source, EncodingCharacters encodingChars, ParserConfiguration parserConfiguration, String currentTerserPath) throws HL7Exception {
                StringBuilder result = new StringBuilder();

                String[] names = source.getNames();

                String firstMandatorySegmentName = null;
                boolean haveEncounteredMandatorySegment = false;
                boolean haveEncounteredContent = false;
                boolean haveHadMandatorySegment = false;
                boolean haveHadSegmentBeforeMandatorySegment = false;

                for (String nextName : names) {

                        source.get(nextName, 0);
                        Structure[] reps = source.getAll(nextName);
                        boolean nextNameIsRequired = source.isRequired(nextName);

                        boolean havePreviouslyEncounteredMandatorySegment = haveEncounteredMandatorySegment;
                        haveEncounteredMandatorySegment |= nextNameIsRequired;
                        if (nextNameIsRequired && !haveHadMandatorySegment) {
                                if (!source.isGroup(nextName)) {
                                        firstMandatorySegmentName = nextName;
                                }
                        }

                        String nextTerserPath = currentTerserPath.length() > 0 ? currentTerserPath + "/" + nextName : nextName;

                        // Add all reps of the next segment/group
                        for (Structure rep : reps) {

                                if (rep instanceof Group) {

                                        String encodedGroup = encode((Group) rep, encodingChars, parserConfiguration, nextTerserPath);
                                        result.append(encodedGroup);

                                        if (encodedGroup.length() > 0) {
                                                if (!haveHadMandatorySegment && !haveEncounteredMandatorySegment) {
                                                        haveHadSegmentBeforeMandatorySegment = true;
                                                }
                                                if (nextNameIsRequired && !haveHadMandatorySegment && !havePreviouslyEncounteredMandatorySegment) {
                                                        haveHadMandatorySegment = true;
                                                }
                                                haveEncounteredContent = true;
                                        }

                                } else {

                                        // Check if we are configured to force the encoding of this
                                        // segment
                                        boolean encodeEmptySegments = parserConfiguration.determineForcedEncodeIncludesTerserPath(nextTerserPath);
                                        String segString = encode((Segment) rep, encodingChars, parserConfiguration, nextTerserPath);
                                        if (segString.length() >= 4 || encodeEmptySegments) {
                                                result.append(segString);

                                                if (segString.length() == 3) {
                                                        result.append(encodingChars.getFieldSeparator());
                                                }

                                                result.append(SEGMENT_DELIMITER);

                                                haveEncounteredContent = true;

                                                if (nextNameIsRequired) {
                                                        haveHadMandatorySegment = true;
                                                }

                                                if (!haveHadMandatorySegment && !haveEncounteredMandatorySegment) {
                                                        haveHadSegmentBeforeMandatorySegment = true;
                                                }

                                        }

                                }

                        }

                }

                if (firstMandatorySegmentName != null && !haveHadMandatorySegment && !haveHadSegmentBeforeMandatorySegment && haveEncounteredContent && parserConfiguration.isEncodeEmptyMandatorySegments()) {
                        return firstMandatorySegmentName.substring(0, 3) + encodingChars.getFieldSeparator() + SEGMENT_DELIMITER + result;
                } else {
                        return result.toString();
                }
        }

        /**
         * Convenience factory method which returns an instance that has a new
         * {@link DefaultHapiContext} initialized with a {@link NoValidation
         * NoValidation validation context}.
     *
     * @return PipeParser with disabled validation
         */
        public static PipeParser getInstanceWithNoValidation() {
                HapiContext context = new DefaultHapiContext();
                context.setValidationContext(ValidationContextFactory.noValidation());
                return new PipeParser(context);
        }

    /**
     * Returns given segment serialized as a pipe-encoded string.
     *
     * @param source segment to be encoded
     * @param encodingChars encoding characters to be used
     * @return encoded group
     */
        public static String encode(Segment source, EncodingCharacters encodingChars) {
                return encode(source, encodingChars, source.getMessage().getParser().getParserConfiguration(), null);
        }

        private static String encode(Segment source, EncodingCharacters encodingChars, ParserConfiguration parserConfig, String currentTerserPath) {
                StringBuilder result = new StringBuilder();
                result.append(source.getName());
                result.append(encodingChars.getFieldSeparator());

                // start at field 2 for MSH segment because field 1 is the field
                // delimiter
                int startAt = 1;
                if (isDelimDefSegment(source.getName()))
                        startAt = 2;

                // loop through fields; for every field delimit any repetitions and add
                // field delimiter after ...
                int numFields = source.numFields();

                int forceUpToFieldNum = 0;
                if (parserConfig != null && currentTerserPath != null) {
                        forceUpToFieldNum = parserConfig.determineForcedFieldNumForTerserPath(currentTerserPath);
                }
                numFields = Math.max(numFields, forceUpToFieldNum);

                for (int i = startAt; i <= numFields; i++) {

                        String nextFieldTerserPath = currentTerserPath + "-" + i;
                        if (parserConfig != null && currentTerserPath != null) {
                                for (String nextPath : parserConfig.getForcedEncode()) {
                                        if (nextPath.startsWith(nextFieldTerserPath + "-")) {
                                                try {
                                                        source.getField(i, 0);
                                                } catch (HL7Exception e) {
                                                        log.error("Error while encoding segment: ", e);
                                                }
                                        }
                                }
                        }

                        try {
                                Type[] reps = source.getField(i);
                                for (int j = 0; j < reps.length; j++) {
                                        String fieldText = encode(reps[j], encodingChars, parserConfig, nextFieldTerserPath);
                                        // if this is MSH-2, then it shouldn't be escaped, so
                                        // unescape it again
                                        if (isDelimDefSegment(source.getName()) && i == 2)
                                                fieldText = parserConfig.getEscaping().unescape(fieldText, encodingChars);
                                        result.append(fieldText);
                                        if (j < reps.length - 1)
                                                result.append(encodingChars.getRepetitionSeparator());
                                }
                        } catch (HL7Exception e) {
                                log.error("Error while encoding segment: ", e);
                        }
                        result.append(encodingChars.getFieldSeparator());
                }

                // strip trailing delimiters ...
                char fieldSeparator = encodingChars.getFieldSeparator();
                String retVal = stripExtraDelimiters(result.toString(), fieldSeparator);

                int offset = isDelimDefSegment(source.getName()) ? 1 : 0;
                while (forceUpToFieldNum > 0 && (countInstancesOf(retVal, fieldSeparator) + offset) < forceUpToFieldNum) {
                        retVal = retVal + fieldSeparator;
                }

                return retVal;
        }

        private static int countInstancesOf(String theString, char theCharToSearchFor) {
                int retVal = 0;
                for (int i = 0; i < theString.length(); i++) {
                        if (theString.charAt(i) == theCharToSearchFor) {
                                retVal++;
                        }
                }
                return retVal;
        }

        /**
         * Removes leading whitespace from the given string. This method was created
         * to deal with frequent problems parsing messages that have been
         * hand-written in windows. The intuitive way to delimit segments is to hit
         * <ENTER> at the end of each segment, but this creates both a carriage
         * return and a line feed, so to the parser, the first character of the next
         * segment is the line feed.
     *
     * @param in input string
     * @return string with leading whitespaces removed
         */
        public static String stripLeadingWhitespace(String in) {
                StringBuilder out = new StringBuilder();
                char[] chars = in.toCharArray();
                int c = 0;
                while (c < chars.length) {
                        if (!Character.isWhitespace(chars[c]))
                                break;
                        c++;
                }
                for (int i = c; i < chars.length; i++) {
                        out.append(chars[i]);
                }
                return out.toString();
        }

        /**
         * <p>
         * Returns a minimal amount of data from a message string, including only
         * the data needed to send a response to the remote system. This includes
         * the following fields:
         * <ul>
         * <li>field separator</li>
         * <li>encoding characters</li>
         * <li>processing ID</li>
         * <li>message control ID</li>
         * </ul>
         * This method is intended for use when there is an error parsing a message,
         * (so the Message object is unavailable) but an error message must be sent
         * back to the remote system including some of the information in the
         * inbound message. This method parses only that required information,
         * hopefully avoiding the condition that caused the original error. The
         * other fields in the returned MSH segment are empty.
         * </p>
         */
        public Segment getCriticalResponseData(String message) throws HL7Exception {
                // try to get MSH segment
                int locStartMSH = message.indexOf("MSH");
                if (locStartMSH < 0)
                        throw new HL7Exception("Couldn't find MSH segment in message: " + message, ErrorCode.SEGMENT_SEQUENCE_ERROR);
                int locEndMSH = message.indexOf('\r', locStartMSH + 1);
                if (locEndMSH < 0)
                        locEndMSH = message.length();
                String mshString = message.substring(locStartMSH, locEndMSH);

                // find out what the field separator is
                char fieldSep = mshString.charAt(3);

                // get field array
                String[] fields = split(mshString, String.valueOf(fieldSep));

                try {
                        // parse required fields
                        String encChars = fields[1];
                        char compSep = encChars.charAt(0);
                        String messControlID = fields[9];
                        String[] procIDComps = split(fields[10], String.valueOf(compSep));

                        // fill MSH segment
                        String version = null;
                        try {
                                version = getVersion(message);
                        } catch (Exception e) { /* use the default */
                        }

                        if (version == null) {
                                Version availableVersion = Version.highestAvailableVersionOrDefault();
                                version = availableVersion.getVersion();
                        }

                        Segment msh = Parser.makeControlMSH(version, getFactory());
                        Terser.set(msh, 1, 0, 1, 1, String.valueOf(fieldSep));
                        Terser.set(msh, 2, 0, 1, 1, encChars);
                        Terser.set(msh, 10, 0, 1, 1, messControlID);
                        Terser.set(msh, 11, 0, 1, 1, procIDComps[0]);
                        Terser.set(msh, 12, 0, 1, 1, version);
                        return msh;

                } catch (Exception e) {
                        throw new HL7Exception("Can't parse critical fields from MSH segment (" + e.getClass().getName() + ": " + e.getMessage() + "): " + mshString, ErrorCode.REQUIRED_FIELD_MISSING, e);
                }

        }

        /**
         * For response messages, returns the value of MSA-2 (the message ID of the
         * message sent by the sending system). This value may be needed prior to
         * main message parsing, so that (particularly in a multi-threaded scenario)
         * the message can be routed to the thread that sent the request. We need
         * this information first so that any parse exceptions are thrown to the
         * correct thread. Returns null if MSA-2 can not be found (e.g. if the
         * message is not a response message).
         */
        public String getAckID(String message) {
                String ackID = null;
                int startMSA = message.indexOf("\rMSA");
                if (startMSA >= 0) {
                        int startFieldOne = startMSA + 5;
                        char fieldDelim = message.charAt(startFieldOne - 1);
                        int start = message.indexOf(fieldDelim, startFieldOne) + 1;
                        int end = message.indexOf(fieldDelim, start);
                        int segEnd = message.indexOf(String.valueOf(SEGMENT_DELIMITER), start);
                        if (segEnd > start && segEnd < end)
                                end = segEnd;

                        // if there is no field delim after MSH-2, need to go to end of
                        // message, but not including end seg delim if it exists
                        if (end < 0) {
                                if (message.charAt(message.length() - 1) == '\r') {
                                        end = message.length() - 1;
                                } else {
                                        end = message.length();
                                }
                        }
                        if (start > 0 && end > start) {
                                ackID = message.substring(start, end);
                        }
                }
                log.trace("ACK ID: {}", ackID);
                return ackID;
        }

        /**
         * Defaults to <code>false</code>
         * 
         * @see #isLegacyMode()
         * @deprecated This will be removed in HAPI 3.0
         */
        public void setLegacyMode(boolean legacyMode) {
                this.myLegacyMode = legacyMode;
        }

        /**
         * {@inheritDoc }
         */
        @Override
        public String encode(Message source) throws HL7Exception {
                if (myLegacyMode != null && myLegacyMode) {

                        @SuppressWarnings("deprecation")
                        OldPipeParser oldPipeParser = new OldPipeParser(getFactory());

                        return oldPipeParser.encode(source);
                }
                return super.encode(source);
        }

        /**
         * {@inheritDoc }
         */
        @Override
        public Message parse(String message) throws HL7Exception {
                if (myLegacyMode != null && myLegacyMode) {

                        @SuppressWarnings("deprecation")
                        OldPipeParser oldPipeParser = new OldPipeParser(getFactory());

                        return oldPipeParser.parse(message);
                }
                return super.parse(message);
        }

        /**
         * <p>
         * Returns <code>true</code> if legacy mode is on.
         * </p>
         * <p>
         * Prior to release 1.0, when an unexpected segment was encountered in a
         * message, HAPI would recurse to the deepest nesting in the last group it
         * encountered after the current position in the message, and deposit the
         * segment there. This could lead to unusual behaviour where all segments
         * afterward would not be in an expected spot within the message.
         * </p>
         * <p>
         * This should normally be set to false, but any code written before the
         * release of HAPI 1.0 which depended on this behaviour might need legacy
         * mode to be set to true.
         * </p>
         * <p>
         * Defaults to <code>false</code>. Note that this method only overrides
         * behaviour of the {@link #parse(java.lang.String)} and
         * {@link #encode(ca.uhn.hl7v2.model.Message) } methods
         * </p>
         * 
         * @deprecated This will be removed in HAPI 3.0
         */
        public boolean isLegacyMode() {
                if (myLegacyMode == null)
                        return (Boolean.parseBoolean(System.getProperty(DEFAULT_LEGACY_MODE_PROPERTY)));
                return this.myLegacyMode;
        }

        /**
         * Returns the version ID (MSH-12) from the given message, without fully
         * parsing the message. The version is needed prior to parsing in order to
         * determine the message class into which the text of the message should be
         * parsed.
         * 
         * @throws HL7Exception
         *             if the version field can not be found.
         */
        public String getVersion(String message) throws HL7Exception {
                int startMSH = message.indexOf("MSH");
                int endMSH = message.indexOf(PipeParser.SEGMENT_DELIMITER, startMSH);
                if (endMSH < 0)
                        endMSH = message.length();
                String msh = message.substring(startMSH, endMSH);
                String fieldSep;
                if (msh.length() > 3) {
                        fieldSep = String.valueOf(msh.charAt(3));
                } else {
                        throw new HL7Exception("Can't find field separator in MSH: " + msh, ErrorCode.UNSUPPORTED_VERSION_ID);
                }

                String[] fields = split(msh, fieldSep);

                String compSep;
                if (fields.length >= 2 && fields[1] != null && fields[1].length() == 4) {
                        compSep = String.valueOf(fields[1].charAt(0)); // get component
                                                                                                                        // separator as 1st
                                                                                                                        // encoding char
                } else {
                        throw new HL7Exception("Invalid or incomplete encoding characters - MSH-2 is " + fields[1], ErrorCode.REQUIRED_FIELD_MISSING);
                }

                String version;
                if (fields.length >= 12) {
                        String[] comp = split(fields[11], compSep);
                        if (comp.length >= 1) {
                                version = comp[0];
                        } else {
                                throw new HL7Exception("Can't find version ID - MSH.12 is " + fields[11], ErrorCode.REQUIRED_FIELD_MISSING);
                        }
                } else if (getParserConfiguration().isAllowUnknownVersions()) {
                        return Version.highestAvailableVersionOrDefault().getVersion();
                } else {
                        throw new HL7Exception("Can't find version ID - MSH has only " + fields.length + " fields.", ErrorCode.REQUIRED_FIELD_MISSING);
                }
                return version;
        }

        @Override
        public void parse(Message message, String string) throws HL7Exception {
                if (message instanceof AbstractSuperMessage && message.getName() == null) {
                        String structure = getStructure(string).messageStructure;
                        ((AbstractSuperMessage) message).setName(structure);
                }
                
                IStructureDefinition structureDef = getStructureDefinition(message);
                MessageIterator messageIter = new MessageIterator(message, structureDef, "MSH", true);

                String[] segments = split(string, SEGMENT_DELIMITER);

                if (segments.length == 0) {
                        throw new HL7Exception("Invalid message content: \"" + string + "\"");
                }

                if (segments[0] == null || segments[0].length() < 4) {
                        throw new HL7Exception("Invalid message content: \"" + string + "\"");
                }

                char delim = '|';
                String prevName = null;
                int repNum = 1;
                for (int i = 0; i < segments.length; i++) {

                        // get rid of any leading whitespace characters ...
                        if (segments[i] != null && segments[i].length() > 0 && Character.isWhitespace(segments[i].charAt(0)))
                                segments[i] = stripLeadingWhitespace(segments[i]);

                        // sometimes people put extra segment delimiters at end of msg ...
                        if (segments[i] != null && segments[i].length() >= 3) {

                                final String name;
                                if (i == 0) {
                                        if (segments[i].length() < 4) {
                                                throw new HL7Exception("Invalid message content: \"" + string + "\"");
                                        }
                                        name = segments[i].substring(0, 3);
                                        delim = segments[i].charAt(3);
                                } else {
                                        if (segments[i].indexOf(delim) >= 0) {
                                                name = segments[i].substring(0, segments[i].indexOf(delim));
                                        } else {
                                                name = segments[i];
                                        }
                                }

                                log.trace("Parsing segment {}", name);

                                if (name.equals(prevName)) {
                                        repNum++;
                                } else {
                                        repNum = 1;
                                        prevName = name;
                                }

                                messageIter.setDirection(name);

                                try {
                                        if (messageIter.hasNext()) {
                                                Segment next = (Segment) messageIter.next();
                                                parse(next, segments[i], getEncodingChars(string), repNum);
                                        }
                                } catch (Error e) {
                                        if (e.getCause() instanceof HL7Exception) {
                                                throw (HL7Exception)e.getCause();
                                        }
                                        throw e;
                                }
                        }
                }
                
                applySuperStructureName(message);
        }

        /**
         * A struct for holding a message class string and a boolean indicating
         * whether it was defined explicitly.
         */
        private static class MessageStructure {
                public String messageStructure;
                public boolean explicitlyDefined;

                public MessageStructure(String theMessageStructure, boolean isExplicitlyDefined) {
                        messageStructure = theMessageStructure;
                        explicitlyDefined = isExplicitlyDefined;
                }
        }

        private static class Holder<T> {
                private T myObject;

                public T getObject() {
                        return myObject;
                }

                public void setObject(T theObject) {
                        myObject = theObject;
                }
        }

}