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package com.esotericsoftware.yamlbeans.document;

import static com.esotericsoftware.yamlbeans.parser.EventType.*;

import java.io.Reader;
import java.io.StringReader;

import com.esotericsoftware.yamlbeans.Version;
import com.esotericsoftware.yamlbeans.YamlException;
import com.esotericsoftware.yamlbeans.parser.AliasEvent;
import com.esotericsoftware.yamlbeans.parser.Event;
import com.esotericsoftware.yamlbeans.parser.MappingStartEvent;
import com.esotericsoftware.yamlbeans.parser.Parser;
import com.esotericsoftware.yamlbeans.parser.Parser.ParserException;
import com.esotericsoftware.yamlbeans.parser.ScalarEvent;
import com.esotericsoftware.yamlbeans.parser.SequenceStartEvent;
import com.esotericsoftware.yamlbeans.tokenizer.Tokenizer.TokenizerException;

public class YamlDocumentReader {

	Parser parser;
	
	public YamlDocumentReader(String yaml) {
		this(new StringReader(yaml));
	}

	public YamlDocumentReader(String yaml, Version version) {
		this(new StringReader(yaml), version);
	}

	public YamlDocumentReader(Reader reader) {
		this(reader, null);
	}

	public YamlDocumentReader(Reader reader, Version version) {
		if(version==null)
			version = Version.DEFAULT_VERSION;
		parser = new Parser(reader, version);
	}

	public YamlDocument read() throws YamlException {
		try {
			while (true) {
				Event event = parser.peekNextEvent();
				if (event == null) 
					return null;
				switch (event.type) {
				case STREAM_START:
					parser.getNextEvent(); // consume it
					break;
				case STREAM_END:
					parser.getNextEvent(); // consume it
					return null;
				case DOCUMENT_START:
					parser.getNextEvent(); // consume it
					return readDocument();
				default:
					throw new IllegalStateException();	
				}
			}
		} catch (ParserException ex) {
			throw new YamlException("Error parsing YAML.", ex);
		} catch (TokenizerException ex) {
			throw new YamlException("Error tokenizing YAML.", ex);
		}
		
	}

	private YamlDocument readDocument() {
		Event event = parser.peekNextEvent();
		switch (event.type) {
			case MAPPING_START:
				return readMapping();
			case SEQUENCE_START:
				return readSequence();
			default:
				throw new IllegalStateException();
		}
	}

	private YamlMapping readMapping() {
		Event event = parser.getNextEvent();
		if(event.type!=MAPPING_START)
			throw new IllegalStateException();
		YamlMapping element = new YamlMapping();
		MappingStartEvent mapping = (MappingStartEvent)event;
		element.setTag(mapping.tag);
		element.setAnchor(mapping.anchor);
		readMappingElements(element);
		return element;
	}

	private void readMappingElements(YamlMapping mapping) {
		while(true) {
			Event event = parser.peekNextEvent();
			if(event.type == MAPPING_END) {
				parser.getNextEvent(); // consume it
				return;
			} else {
				YamlEntry entry = readEntry();
				mapping.addEntry(entry);
			}
		}		
	}

	private YamlEntry readEntry() {
		YamlScalar scalar = readScalar();
		YamlElement value = readValue();
		return new YamlEntry(scalar, value);
	}

	private YamlElement readValue() {
		Event event = parser.peekNextEvent();
		switch(event.type) {
			case SCALAR:
				return readScalar();
			case ALIAS:
				return readAlias();
			case MAPPING_START:
				return readMapping();
			case SEQUENCE_START:
				return readSequence();
			default:
				throw new IllegalStateException();
		}
	}

	private YamlAlias readAlias() {
		Event event = parser.getNextEvent();
		if(event.type!=ALIAS)
			throw new IllegalStateException();
		YamlAlias element = new YamlAlias();
		AliasEvent alias = (AliasEvent)event;
		element.setAnchor(alias.anchor);
		return element;
	}

	private YamlSequence readSequence() {
		Event event = parser.getNextEvent();
		if(event.type!=SEQUENCE_START)
			throw new IllegalStateException();
		YamlSequence element = new YamlSequence();
		SequenceStartEvent sequence = (SequenceStartEvent)event;
		element.setTag(sequence.tag);
		element.setAnchor(sequence.anchor);
		readSequenceElements(element);
		return element;
	}

	private void readSequenceElements(YamlSequence sequence) {
		while(true) {
			Event event = parser.peekNextEvent();
			if(event.type==SEQUENCE_END) {
				parser.getNextEvent(); // consume it
				return;
			} else {
				YamlElement element = readValue();
				sequence.addElement(element);
			}
		}
	}

	private YamlScalar readScalar() {
		Event event = parser.getNextEvent();
		if(event.type!= SCALAR)
			throw new IllegalStateException();
		ScalarEvent scalar = (ScalarEvent)event;
		YamlScalar element = new YamlScalar();
		element.setTag(scalar.tag);
		element.setAnchor(scalar.anchor);
		element.setValue(scalar.value);
		return element;
	}
	
}