/**

  * Copyright (c) 2008-2012, http://www.snakeyaml.org

  *

  * 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 org.yaml.snakeyaml.parser;

 import java.util.HashMap;

 import java.util.List;

 import java.util.Map;

 import org.yaml.snakeyaml.DumperOptions.Version;

 import org.yaml.snakeyaml.error.Mark;

 import org.yaml.snakeyaml.error.YAMLException;

 import org.yaml.snakeyaml.events.AliasEvent;

 import org.yaml.snakeyaml.events.DocumentEndEvent;

 import org.yaml.snakeyaml.events.DocumentStartEvent;

 import org.yaml.snakeyaml.events.Event;

 import org.yaml.snakeyaml.events.ImplicitTuple;

 import org.yaml.snakeyaml.events.MappingEndEvent;

 import org.yaml.snakeyaml.events.MappingStartEvent;

 import org.yaml.snakeyaml.events.ScalarEvent;

 import org.yaml.snakeyaml.events.SequenceEndEvent;

 import org.yaml.snakeyaml.events.SequenceStartEvent;

 import org.yaml.snakeyaml.events.StreamEndEvent;

 import org.yaml.snakeyaml.events.StreamStartEvent;

 import org.yaml.snakeyaml.nodes.Tag;

 import org.yaml.snakeyaml.reader.StreamReader;

 import org.yaml.snakeyaml.scanner.Scanner;

 import org.yaml.snakeyaml.scanner.ScannerImpl;

 import org.yaml.snakeyaml.tokens.AliasToken;

 import org.yaml.snakeyaml.tokens.AnchorToken;

 import org.yaml.snakeyaml.tokens.BlockEntryToken;

 import org.yaml.snakeyaml.tokens.DirectiveToken;

 import org.yaml.snakeyaml.tokens.ScalarToken;

 import org.yaml.snakeyaml.tokens.StreamEndToken;

 import org.yaml.snakeyaml.tokens.StreamStartToken;

 import org.yaml.snakeyaml.tokens.TagToken;

 import org.yaml.snakeyaml.tokens.TagTuple;

 import org.yaml.snakeyaml.tokens.Token;

 import org.yaml.snakeyaml.util.ArrayStack;

 /**

  * <pre>

  * # The following YAML grammar is LL(1) and is parsed by a recursive descent

  * parser.

  * stream            ::= STREAM-START implicit_document? explicit_document* STREAM-END

  * implicit_document ::= block_node DOCUMENT-END*

  * explicit_document ::= DIRECTIVE* DOCUMENT-START block_node? DOCUMENT-END*

  * block_node_or_indentless_sequence ::=

  *                       ALIAS

  *                       | properties (block_content | indentless_block_sequence)?

  *                       | block_content

  *                       | indentless_block_sequence

  * block_node        ::= ALIAS

  *                       | properties block_content?

  *                       | block_content

  * flow_node         ::= ALIAS

  *                       | properties flow_content?

  *                       | flow_content

  * properties        ::= TAG ANCHOR? | ANCHOR TAG?

  * block_content     ::= block_collection | flow_collection | SCALAR

  * flow_content      ::= flow_collection | SCALAR

  * block_collection  ::= block_sequence | block_mapping

  * flow_collection   ::= flow_sequence | flow_mapping

  * block_sequence    ::= BLOCK-SEQUENCE-START (BLOCK-ENTRY block_node?)* BLOCK-END

  * indentless_sequence   ::= (BLOCK-ENTRY block_node?)+

  * block_mapping     ::= BLOCK-MAPPING_START

  *                       ((KEY block_node_or_indentless_sequence?)?

  *                       (VALUE block_node_or_indentless_sequence?)?)*

  *                       BLOCK-END

  * flow_sequence     ::= FLOW-SEQUENCE-START

  *                       (flow_sequence_entry FLOW-ENTRY)*

  *                       flow_sequence_entry?

  *                       FLOW-SEQUENCE-END

  * flow_sequence_entry   ::= flow_node | KEY flow_node? (VALUE flow_node?)?

  * flow_mapping      ::= FLOW-MAPPING-START

  *                       (flow_mapping_entry FLOW-ENTRY)*

  *                       flow_mapping_entry?

  *                       FLOW-MAPPING-END

  * flow_mapping_entry    ::= flow_node | KEY flow_node? (VALUE flow_node?)?

  * FIRST sets:

  * stream: { STREAM-START }

  * explicit_document: { DIRECTIVE DOCUMENT-START }

  * implicit_document: FIRST(block_node)

  * block_node: { ALIAS TAG ANCHOR SCALAR BLOCK-SEQUENCE-START BLOCK-MAPPING-START FLOW-SEQUENCE-START FLOW-MAPPING-START }

  * flow_node: { ALIAS ANCHOR TAG SCALAR FLOW-SEQUENCE-START FLOW-MAPPING-START }

  * block_content: { BLOCK-SEQUENCE-START BLOCK-MAPPING-START FLOW-SEQUENCE-START FLOW-MAPPING-START SCALAR }

  * flow_content: { FLOW-SEQUENCE-START FLOW-MAPPING-START SCALAR }

  * block_collection: { BLOCK-SEQUENCE-START BLOCK-MAPPING-START }

  * flow_collection: { FLOW-SEQUENCE-START FLOW-MAPPING-START }

  * block_sequence: { BLOCK-SEQUENCE-START }

  * block_mapping: { BLOCK-MAPPING-START }

  * block_node_or_indentless_sequence: { ALIAS ANCHOR TAG SCALAR BLOCK-SEQUENCE-START BLOCK-MAPPING-START FLOW-SEQUENCE-START FLOW-MAPPING-START BLOCK-ENTRY }

  * indentless_sequence: { ENTRY }

  * flow_collection: { FLOW-SEQUENCE-START FLOW-MAPPING-START }

  * flow_sequence: { FLOW-SEQUENCE-START }

  * flow_mapping: { FLOW-MAPPING-START }

  * flow_sequence_entry: { ALIAS ANCHOR TAG SCALAR FLOW-SEQUENCE-START FLOW-MAPPING-START KEY }

  * flow_mapping_entry: { ALIAS ANCHOR TAG SCALAR FLOW-SEQUENCE-START FLOW-MAPPING-START KEY }

  * </pre>

  * 

  * Since writing a recursive-descendant parser is a straightforward task, we do

  * not give many comments here.

  */

 public final class ParserImpl implements Parser {

     private static final Map<String, String> DEFAULT_TAGS = new HashMap<String, String>();

     static {

         DEFAULT_TAGS.put("!", "!");

         DEFAULT_TAGS.put("!!", Tag.PREFIX);

     }

     private final Scanner scanner;

     private Event currentEvent;

     private final ArrayStack<Production> states;

     private final ArrayStack<Mark> marks;

     private Production state;

     private VersionTagsTuple directives;

     public ParserImpl(StreamReader reader) {

         this.scanner = new ScannerImpl(reader);

         currentEvent = null;

         directives = new VersionTagsTuple(null, new HashMap<String, String>(DEFAULT_TAGS));

         states = new ArrayStack<Production>(100);

         marks = new ArrayStack<Mark>(10);

         state = new ParseStreamStart();

     }

     /**

      * Check the type of the next event.

      */

     public boolean checkEvent(Event.ID choices) {

         peekEvent();

         if (currentEvent != null) {

             if (currentEvent.is(choices)) {

                 return true;

             }

         }

         return false;

     }

     /**

      * Get the next event.

      */

     public Event peekEvent() {

         if (currentEvent == null) {

             if (state != null) {

                 currentEvent = state.produce();

             }

         }

         return currentEvent;

     }

     /**

      * Get the next event and proceed further.

      */

     public Event getEvent() {

         peekEvent();

         Event value = currentEvent;

         currentEvent = null;

         return value;

     }

     /**

      * <pre>

      * stream    ::= STREAM-START implicit_document? explicit_document* STREAM-END

      * implicit_document ::= block_node DOCUMENT-END*

      * explicit_document ::= DIRECTIVE* DOCUMENT-START block_node? DOCUMENT-END*

      * </pre>

      */

     private class ParseStreamStart implements Production {

         public Event produce() {

             // Parse the stream start.

             StreamStartToken token = (StreamStartToken) scanner.getToken();

             Event event = new StreamStartEvent(token.getStartMark(), token.getEndMark());

             // Prepare the next state.

             state = new ParseImplicitDocumentStart();

             return event;

         }

     }

     private class ParseImplicitDocumentStart implements Production {

         public Event produce() {

             // Parse an implicit document.

             if (!scanner.checkToken(Token.ID.Directive, Token.ID.DocumentStart, Token.ID.StreamEnd)) {

                 directives = new VersionTagsTuple(null, DEFAULT_TAGS);

                 Token token = scanner.peekToken();

                 Mark startMark = token.getStartMark();

                 Mark endMark = startMark;

                 Event event = new DocumentStartEvent(startMark, endMark, false, null, null);

                 // Prepare the next state.

                 states.push(new ParseDocumentEnd());

                 state = new ParseBlockNode();

                 return event;

             } else {

                 Production p = new ParseDocumentStart();

                 return p.produce();

             }

         }

     }

     private class ParseDocumentStart implements Production {

         public Event produce() {

             // Parse any extra document end indicators.

             while (scanner.checkToken(Token.ID.DocumentEnd)) {

                 scanner.getToken();

             }

             // Parse an explicit document.

             Event event;

             if (!scanner.checkToken(Token.ID.StreamEnd)) {

                 Token token = scanner.peekToken();

                 Mark startMark = token.getStartMark();

                 VersionTagsTuple tuple = processDirectives();

                 if (!scanner.checkToken(Token.ID.DocumentStart)) {

                     throw new ParserException(null, null, "expected '<document start>', but found "

                             + scanner.peekToken().getTokenId(), scanner.peekToken().getStartMark());

                 }

                 token = scanner.getToken();

                 Mark endMark = token.getEndMark();

                 event = new DocumentStartEvent(startMark, endMark, true, tuple.getVersion(),

                         tuple.getTags());

                 states.push(new ParseDocumentEnd());

                 state = new ParseDocumentContent();

             } else {

                 // Parse the end of the stream.

                 StreamEndToken token = (StreamEndToken) scanner.getToken();

                 event = new StreamEndEvent(token.getStartMark(), token.getEndMark());

                 if (!states.isEmpty()) {

                     throw new YAMLException("Unexpected end of stream. States left: " + states);

                 }

                 if (!marks.isEmpty()) {

                     throw new YAMLException("Unexpected end of stream. Marks left: " + marks);

                 }

                 state = null;

             }

             return event;

         }

     }

     private class ParseDocumentEnd implements Production {

         public Event produce() {

             // Parse the document end.

             Token token = scanner.peekToken();

             Mark startMark = token.getStartMark();

             Mark endMark = startMark;

             boolean explicit = false;

             if (scanner.checkToken(Token.ID.DocumentEnd)) {

                 token = scanner.getToken();

                 endMark = token.getEndMark();

                 explicit = true;

             }

             Event event = new DocumentEndEvent(startMark, endMark, explicit);

             // Prepare the next state.

             state = new ParseDocumentStart();

             return event;

         }

     }

     private class ParseDocumentContent implements Production {

         public Event produce() {

             Event event;

             if (scanner.checkToken(Token.ID.Directive, Token.ID.DocumentStart,

                     Token.ID.DocumentEnd, Token.ID.StreamEnd)) {

                 event = processEmptyScalar(scanner.peekToken().getStartMark());

                 state = states.pop();

                 return event;

             } else {

                 Production p = new ParseBlockNode();

                 return p.produce();

             }

         }

     }

     @SuppressWarnings("unchecked")

     private VersionTagsTuple processDirectives() {

         Version yamlVersion = null;

         HashMap<String, String> tagHandles = new HashMap<String, String>();

         while (scanner.checkToken(Token.ID.Directive)) {

             @SuppressWarnings("rawtypes")

             DirectiveToken token = (DirectiveToken) scanner.getToken();

             if (token.getName().equals("YAML")) {

                 if (yamlVersion != null) {

                     throw new ParserException(null, null, "found duplicate YAML directive",

                             token.getStartMark());

                 }

                 List<Integer> value = (List<Integer>) token.getValue();

                 Integer major = value.get(0);

                 if (major != 1) {

                     throw new ParserException(null, null,

                             "found incompatible YAML document (version 1.* is required)",

                             token.getStartMark());

                 }

                 Integer minor = value.get(1);

                 switch (minor) {

                 case 0:

                     yamlVersion = Version.V1_0;

                     break;

                 default:

                     yamlVersion = Version.V1_1;

                     break;

                 }

             } else if (token.getName().equals("TAG")) {

                 List<String> value = (List<String>) token.getValue();

                 String handle = value.get(0);

                 String prefix = value.get(1);

                 if (tagHandles.containsKey(handle)) {

                     throw new ParserException(null, null, "duplicate tag handle " + handle,

                             token.getStartMark());

                 }

                 tagHandles.put(handle, prefix);

             }

         }

         if (yamlVersion != null || !tagHandles.isEmpty()) {

             // directives in the document found - drop the previous

             for (String key : DEFAULT_TAGS.keySet()) {

                 // do not overwrite re-defined tags

                 if (!tagHandles.containsKey(key)) {

                     tagHandles.put(key, DEFAULT_TAGS.get(key));

                 }

             }

             directives = new VersionTagsTuple(yamlVersion, tagHandles);

         }

         return directives;

     }

     /**

      * <pre>

      *  block_node_or_indentless_sequence ::= ALIAS

      *                | properties (block_content | indentless_block_sequence)?

      *                | block_content

      *                | indentless_block_sequence

      *  block_node    ::= ALIAS

      *                    | properties block_content?

      *                    | block_content

      *  flow_node     ::= ALIAS

      *                    | properties flow_content?

      *                    | flow_content

      *  properties    ::= TAG ANCHOR? | ANCHOR TAG?

      *  block_content     ::= block_collection | flow_collection | SCALAR

      *  flow_content      ::= flow_collection | SCALAR

      *  block_collection  ::= block_sequence | block_mapping

      *  flow_collection   ::= flow_sequence | flow_mapping

      * </pre>

      */

     private class ParseBlockNode implements Production {

         public Event produce() {

             return parseNode(true, false);

         }

     }

     private Event parseFlowNode() {

         return parseNode(false, false);

     }

     private Event parseBlockNodeOrIndentlessSequence() {

         return parseNode(true, true);

     }

     private Event parseNode(boolean block, boolean indentlessSequence) {

         Event event;

         Mark startMark = null;

         Mark endMark = null;

         Mark tagMark = null;

         if (scanner.checkToken(Token.ID.Alias)) {

             AliasToken token = (AliasToken) scanner.getToken();

             event = new AliasEvent(token.getValue(), token.getStartMark(), token.getEndMark());

             state = states.pop();

         } else {

             String anchor = null;

             TagTuple tagTokenTag = null;

             if (scanner.checkToken(Token.ID.Anchor)) {

                 AnchorToken token = (AnchorToken) scanner.getToken();

                 startMark = token.getStartMark();

                 endMark = token.getEndMark();

                 anchor = token.getValue();

                 if (scanner.checkToken(Token.ID.Tag)) {

                     TagToken tagToken = (TagToken) scanner.getToken();

                     tagMark = tagToken.getStartMark();

                     endMark = tagToken.getEndMark();

                     tagTokenTag = tagToken.getValue();

                 }

             } else if (scanner.checkToken(Token.ID.Tag)) {

                 TagToken tagToken = (TagToken) scanner.getToken();

                 startMark = tagToken.getStartMark();

                 tagMark = startMark;

                 endMark = tagToken.getEndMark();

                 tagTokenTag = tagToken.getValue();

                 if (scanner.checkToken(Token.ID.Anchor)) {

                     AnchorToken token = (AnchorToken) scanner.getToken();

                     endMark = token.getEndMark();

                     anchor = token.getValue();

                 }

             }

             String tag = null;

             if (tagTokenTag != null) {

                 String handle = tagTokenTag.getHandle();

                 String suffix = tagTokenTag.getSuffix();

                 if (handle != null) {

                     if (!directives.getTags().containsKey(handle)) {

                         throw new ParserException("while parsing a node", startMark,

                                 "found undefined tag handle " + handle, tagMark);

                     }

                     tag = directives.getTags().get(handle) + suffix;

                 } else {

                     tag = suffix;

                 }

             }

             if (startMark == null) {

                 startMark = scanner.peekToken().getStartMark();

                 endMark = startMark;

             }

             event = null;

             boolean implicit = (tag == null || tag.equals("!"));

             if (indentlessSequence && scanner.checkToken(Token.ID.BlockEntry)) {

                 endMark = scanner.peekToken().getEndMark();

                 event = new SequenceStartEvent(anchor, tag, implicit, startMark, endMark,

                         Boolean.FALSE);

                 state = new ParseIndentlessSequenceEntry();

             } else {

                 if (scanner.checkToken(Token.ID.Scalar)) {

                     ScalarToken token = (ScalarToken) scanner.getToken();

                     endMark = token.getEndMark();

                     ImplicitTuple implicitValues;

                     if ((token.getPlain() && tag == null) || "!".equals(tag)) {

                         implicitValues = new ImplicitTuple(true, false);

                     } else if (tag == null) {

                         implicitValues = new ImplicitTuple(false, true);

                     } else {

                         implicitValues = new ImplicitTuple(false, false);

                     }

                     event = new ScalarEvent(anchor, tag, implicitValues, token.getValue(),

                             startMark, endMark, token.getStyle());

                     state = states.pop();

                 } else if (scanner.checkToken(Token.ID.FlowSequenceStart)) {

                     endMark = scanner.peekToken().getEndMark();

                     event = new SequenceStartEvent(anchor, tag, implicit, startMark, endMark,

                             Boolean.TRUE);

                     state = new ParseFlowSequenceFirstEntry();

                 } else if (scanner.checkToken(Token.ID.FlowMappingStart)) {

                     endMark = scanner.peekToken().getEndMark();

                     event = new MappingStartEvent(anchor, tag, implicit, startMark, endMark,

                             Boolean.TRUE);

                     state = new ParseFlowMappingFirstKey();

                 } else if (block && scanner.checkToken(Token.ID.BlockSequenceStart)) {

                     endMark = scanner.peekToken().getStartMark();

                     event = new SequenceStartEvent(anchor, tag, implicit, startMark, endMark,

                             Boolean.FALSE);

                     state = new ParseBlockSequenceFirstEntry();

                 } else if (block && scanner.checkToken(Token.ID.BlockMappingStart)) {

                     endMark = scanner.peekToken().getStartMark();

                     event = new MappingStartEvent(anchor, tag, implicit, startMark, endMark,

                             Boolean.FALSE);

                     state = new ParseBlockMappingFirstKey();

                 } else if (anchor != null || tag != null) {

                     // Empty scalars are allowed even if a tag or an anchor is

                     // specified.

                     event = new ScalarEvent(anchor, tag, new ImplicitTuple(implicit, false), "",

                             startMark, endMark, (char) 0);

                     state = states.pop();

                 } else {

                     String node;

                     if (block) {

                         node = "block";

                     } else {

                         node = "flow";

                     }

                     Token token = scanner.peekToken();

                     throw new ParserException("while parsing a " + node + " node", startMark,

                             "expected the node content, but found " + token.getTokenId(),

                             token.getStartMark());

                 }

             }

         }

         return event;

     }

     // block_sequence ::= BLOCK-SEQUENCE-START (BLOCK-ENTRY block_node?)*

     // BLOCK-END

     private class ParseBlockSequenceFirstEntry implements Production {

         public Event produce() {

             Token token = scanner.getToken();

             marks.push(token.getStartMark());

             return new ParseBlockSequenceEntry().produce();

         }

     }

     private class ParseBlockSequenceEntry implements Production {

         public Event produce() {

             if (scanner.checkToken(Token.ID.BlockEntry)) {

                 BlockEntryToken token = (BlockEntryToken) scanner.getToken();

                 if (!scanner.checkToken(Token.ID.BlockEntry, Token.ID.BlockEnd)) {

                     states.push(new ParseBlockSequenceEntry());

                     return new ParseBlockNode().produce();

                 } else {

                     state = new ParseBlockSequenceEntry();

                     return processEmptyScalar(token.getEndMark());

                 }

             }

             if (!scanner.checkToken(Token.ID.BlockEnd)) {

                 Token token = scanner.peekToken();

                 throw new ParserException("while parsing a block collection", marks.pop(),

                         "expected <block end>, but found " + token.getTokenId(),

                         token.getStartMark());

             }

             Token token = scanner.getToken();

             Event event = new SequenceEndEvent(token.getStartMark(), token.getEndMark());

             state = states.pop();

             marks.pop();

             return event;

         }

     }

     // indentless_sequence ::= (BLOCK-ENTRY block_node?)+

     private class ParseIndentlessSequenceEntry implements Production {

         public Event produce() {

             if (scanner.checkToken(Token.ID.BlockEntry)) {

                 Token token = scanner.getToken();

                 if (!scanner.checkToken(Token.ID.BlockEntry, Token.ID.Key, Token.ID.Value,

                         Token.ID.BlockEnd)) {

                     states.push(new ParseIndentlessSequenceEntry());

                     return new ParseBlockNode().produce();

                 } else {

                     state = new ParseIndentlessSequenceEntry();

                     return processEmptyScalar(token.getEndMark());

                 }

             }

             Token token = scanner.peekToken();

             Event event = new SequenceEndEvent(token.getStartMark(), token.getEndMark());

             state = states.pop();

             return event;

         }

     }

     private class ParseBlockMappingFirstKey implements Production {

         public Event produce() {

             Token token = scanner.getToken();

             marks.push(token.getStartMark());

             return new ParseBlockMappingKey().produce();

         }

     }

     private class ParseBlockMappingKey implements Production {

         public Event produce() {

             if (scanner.checkToken(Token.ID.Key)) {

                 Token token = scanner.getToken();

                 if (!scanner.checkToken(Token.ID.Key, Token.ID.Value, Token.ID.BlockEnd)) {

                     states.push(new ParseBlockMappingValue());

                     return parseBlockNodeOrIndentlessSequence();

                 } else {

                     state = new ParseBlockMappingValue();

                     return processEmptyScalar(token.getEndMark());

                 }

             }

             if (!scanner.checkToken(Token.ID.BlockEnd)) {

                 Token token = scanner.peekToken();

                 throw new ParserException("while parsing a block mapping", marks.pop(),

                         "expected <block end>, but found " + token.getTokenId(),

                         token.getStartMark());

             }

             Token token = scanner.getToken();

             Event event = new MappingEndEvent(token.getStartMark(), token.getEndMark());

             state = states.pop();

             marks.pop();

             return event;

         }

     }

     private class ParseBlockMappingValue implements Production {

         public Event produce() {

             if (scanner.checkToken(Token.ID.Value)) {

                 Token token = scanner.getToken();

                 if (!scanner.checkToken(Token.ID.Key, Token.ID.Value, Token.ID.BlockEnd)) {

                     states.push(new ParseBlockMappingKey());

                     return parseBlockNodeOrIndentlessSequence();

                 } else {

                     state = new ParseBlockMappingKey();

                     return processEmptyScalar(token.getEndMark());

                 }

             }

             state = new ParseBlockMappingKey();

             Token token = scanner.peekToken();

             return processEmptyScalar(token.getStartMark());

         }

     }

     /**

      * <pre>

      * flow_sequence     ::= FLOW-SEQUENCE-START

      *                       (flow_sequence_entry FLOW-ENTRY)*

      *                       flow_sequence_entry?

      *                       FLOW-SEQUENCE-END

      * flow_sequence_entry   ::= flow_node | KEY flow_node? (VALUE flow_node?)?

      * Note that while production rules for both flow_sequence_entry and

      * flow_mapping_entry are equal, their interpretations are different.

      * For `flow_sequence_entry`, the part `KEY flow_node? (VALUE flow_node?)?`

      * generate an inline mapping (set syntax).

      * </pre>

      */

     private class ParseFlowSequenceFirstEntry implements Production {

         public Event produce() {

             Token token = scanner.getToken();

             marks.push(token.getStartMark());

             return new ParseFlowSequenceEntry(true).produce();

         }

     }

     private class ParseFlowSequenceEntry implements Production {

         private boolean first = false;

         public ParseFlowSequenceEntry(boolean first) {

             this.first = first;

         }

         public Event produce() {

             if (!scanner.checkToken(Token.ID.FlowSequenceEnd)) {

                 if (!first) {

                     if (scanner.checkToken(Token.ID.FlowEntry)) {

                         scanner.getToken();

                     } else {

                         Token token = scanner.peekToken();

                         throw new ParserException("while parsing a flow sequence", marks.pop(),

                                 "expected ',' or ']', but got " + token.getTokenId(),

                                 token.getStartMark());

                     }

                 }

                 if (scanner.checkToken(Token.ID.Key)) {

                     Token token = scanner.peekToken();

                     Event event = new MappingStartEvent(null, null, true, token.getStartMark(),

                             token.getEndMark(), Boolean.TRUE);

                     state = new ParseFlowSequenceEntryMappingKey();

                     return event;

                 } else if (!scanner.checkToken(Token.ID.FlowSequenceEnd)) {

                     states.push(new ParseFlowSequenceEntry(false));

                     return parseFlowNode();

                 }

             }

             Token token = scanner.getToken();

             Event event = new SequenceEndEvent(token.getStartMark(), token.getEndMark());

             state = states.pop();

             marks.pop();

             return event;

         }

     }

     private class ParseFlowSequenceEntryMappingKey implements Production {

         public Event produce() {

             Token token = scanner.getToken();

             if (!scanner.checkToken(Token.ID.Value, Token.ID.FlowEntry, Token.ID.FlowSequenceEnd)) {

                 states.push(new ParseFlowSequenceEntryMappingValue());

                 return parseFlowNode();

             } else {

                 state = new ParseFlowSequenceEntryMappingValue();

                 return processEmptyScalar(token.getEndMark());

             }

         }

     }

     private class ParseFlowSequenceEntryMappingValue implements Production {

         public Event produce() {

             if (scanner.checkToken(Token.ID.Value)) {

                 Token token = scanner.getToken();

                 if (!scanner.checkToken(Token.ID.FlowEntry, Token.ID.FlowSequenceEnd)) {

                     states.push(new ParseFlowSequenceEntryMappingEnd());

                     return parseFlowNode();

                 } else {

                     state = new ParseFlowSequenceEntryMappingEnd();

                     return processEmptyScalar(token.getEndMark());

                 }

             } else {

                 state = new ParseFlowSequenceEntryMappingEnd();

                 Token token = scanner.peekToken();

                 return processEmptyScalar(token.getStartMark());

             }

         }

     }

     private class ParseFlowSequenceEntryMappingEnd implements Production {

         public Event produce() {

             state = new ParseFlowSequenceEntry(false);

             Token token = scanner.peekToken();

             return new MappingEndEvent(token.getStartMark(), token.getEndMark());

         }

     }

     /**

      * <pre>

      *   flow_mapping  ::= FLOW-MAPPING-START

      *          (flow_mapping_entry FLOW-ENTRY)*

      *          flow_mapping_entry?

      *          FLOW-MAPPING-END

      *   flow_mapping_entry    ::= flow_node | KEY flow_node? (VALUE flow_node?)?

      * </pre>

      */

     private class ParseFlowMappingFirstKey implements Production {

         public Event produce() {

             Token token = scanner.getToken();

             marks.push(token.getStartMark());

             return new ParseFlowMappingKey(true).produce();

         }

     }

     private class ParseFlowMappingKey implements Production {

         private boolean first = false;

         public ParseFlowMappingKey(boolean first) {

             this.first = first;

         }

         public Event produce() {

             if (!scanner.checkToken(Token.ID.FlowMappingEnd)) {

                 if (!first) {

                     if (scanner.checkToken(Token.ID.FlowEntry)) {

                         scanner.getToken();

                     } else {

                         Token token = scanner.peekToken();

                         throw new ParserException("while parsing a flow mapping", marks.pop(),

                                 "expected ',' or '}', but got " + token.getTokenId(),

                                 token.getStartMark());

                     }

                 }

                 if (scanner.checkToken(Token.ID.Key)) {

                     Token token = scanner.getToken();

                     if (!scanner.checkToken(Token.ID.Value, Token.ID.FlowEntry,

                             Token.ID.FlowMappingEnd)) {

                         states.push(new ParseFlowMappingValue());

                         return parseFlowNode();

                     } else {

                         state = new ParseFlowMappingValue();

                         return processEmptyScalar(token.getEndMark());

                     }

                 } else if (!scanner.checkToken(Token.ID.FlowMappingEnd)) {

                     states.push(new ParseFlowMappingEmptyValue());

                     return parseFlowNode();

                 }

             }

             Token token = scanner.getToken();

             Event event = new MappingEndEvent(token.getStartMark(), token.getEndMark());

             state = states.pop();

             marks.pop();

             return event;

         }

     }

     private class ParseFlowMappingValue implements Production {

         public Event produce() {

             if (scanner.checkToken(Token.ID.Value)) {

                 Token token = scanner.getToken();

                 if (!scanner.checkToken(Token.ID.FlowEntry, Token.ID.FlowMappingEnd)) {

                     states.push(new ParseFlowMappingKey(false));

                     return parseFlowNode();

                 } else {

                     state = new ParseFlowMappingKey(false);

                     return processEmptyScalar(token.getEndMark());

                 }

             } else {

                 state = new ParseFlowMappingKey(false);

                 Token token = scanner.peekToken();

                 return processEmptyScalar(token.getStartMark());

             }

         }

     }

     private class ParseFlowMappingEmptyValue implements Production {

         public Event produce() {

             state = new ParseFlowMappingKey(false);

             return processEmptyScalar(scanner.peekToken().getStartMark());

         }

     }

     /**

      * <pre>

      * block_mapping     ::= BLOCK-MAPPING_START

      *           ((KEY block_node_or_indentless_sequence?)?

      *           (VALUE block_node_or_indentless_sequence?)?)*

      *           BLOCK-END

      * </pre>

      */

     private Event processEmptyScalar(Mark mark) {

         return new ScalarEvent(null, null, new ImplicitTuple(true, false), "", mark, mark, (char) 0);

     }

 }