YamlParser

YamlParser.java

package fr.warlog.util;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.StringReader;
import java.util.ArrayList;
import java.util.Deque;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.Stack;


/**
 * Old school parsing:
 * lexer is (ID : - STRING SPACES >) 
 * grammar:
 * s-> arrayObject(0)
 * arrayObject(n)-> array(0) | object(0)
 * object(0)-> objectAttribute(n)+
 * ObjectAttribute(n)-> \n indent(n) id:val(n)
 * val(n)-> STRING valSuiv |  arrayObject(n+1)
 * valSuiv -> >\n indent(n) STRING valSuiv|epsilon
 * array(n)->arrayLine(n)+
 * arrayLine(n)-> \n indent(n) - val(n+1)
 * indent(n)->n* "__"
 */
@SuppressWarnings({"rawtypes","unchecked"})
public class YamlParser {
	private static final String INDENTATION = "INDENTATION";
	private static int nbSpaces = 1;
	private BufferedReader reader;
	private Queue<String> queue;
	private int lineNumber=0;
	private Deque<String> indentation;
	
	public YamlParser(BufferedReader reader) {
		super();
		this.reader = reader;
		this.queue = new LinkedList<String>();
		indentation=new LinkedList<String>();
	}
	
	public YamlParser(String s){
		this(new BufferedReader(new StringReader(s)));
	}
	
	private void log(String s){
		System.out.println(s);
	}

	/**
	 * splits token for (\s*)-?(id:)?string?
	 * @return
	 * @throws IOException
	 */
	private String getCurrent() {
		if(queue.isEmpty()){
			readOneLine();
		}
		return queue.peek();
	}

	private void readOneLine() {
		String line;
		try {
			line = reader.readLine();
			lineNumber++;
		} catch (IOException e) {
			return;
		}
		if (line == null) return;
		int spaces=0;
		while(line.charAt(spaces)==' ') spaces++;
		//TODO match spaces from a stack
//			if(spaces>0)
		queue.add(new String(new char[spaces]).replace("\0", " "));
		line=line.substring(spaces);
		if (line.startsWith("-")){
			queue.add("-");
			line=line.substring(1).trim();
		}
		
		String[] tokens=line.split(":",2);
		if(tokens.length==1){
			queue.add(line);
		}else{
			queue.add(tokens[0]);
			queue.add(":");
			if(tokens[1].length()>0)
				queue.add(tokens[1]);
		}
		queue.add("\n");
	}
	
	private String getNthToken(int n){
		if(queue.size()<=n)
			readOneLine();
		if(queue.size()>n)
			return ((List<String>)queue).get(n);
		return null;
	}
	
	private String getNext(){
		String current = getCurrent();
		queue.poll();
		return current;
	}
	private String getNext(String s) {
		String current = getCurrent();
		if(!current.equals(s)) throw new IllegalArgumentException("Syntax error, expected: "+s+" at line "+lineNumber);
		return getNext();
	}
	
	public Object parse() {
		return arrayObject(0);
		
	}
	
	private Object arrayObject(int i) {
		if("-".equals( getNthToken(1))){
			return array(i);
		}
		return object(i);
	}

	private static boolean isLevel(String spaces, int i){
		return spaces != null && spaces.matches("^\\s*$") && spaces.length()/nbSpaces == i;
	}
	
	private Object object(int i) {
		
		Map object= new LinkedHashMap();
		while(isLevel(getCurrent(),i)){
			objectAttribute(i,object);
		}
		return object;
	}
	
	private Object array(int i){
		List<Object> array = new ArrayList<>();
		while(isLevel(getCurrent(),i)){
			arrayLine(i,array);
		}
		return array;
	}

	private void arrayLine(int i, List<Object> array) {
		getNext();//INDENTATION
		getNext("-");
		array.add(value(i+1));
	}

	private void objectAttribute(int i, Map object) {
		getNext();//INDENTATION
		String key = getNext();
		getNext(":");
		Object value=value(i);
		object.put(key,value);
	}

	private Object value(int i) {
		String value = getCurrent();
		if(value.equals("\n")){
			getNext("\n");
			return arrayObject(i+1);
		}else{
			getNext();
			return valueSuiv(i,value);
		}
	}

	private Object valueSuiv(int i, String value) {
		while(getCurrent().equals(">")){
			getNext(">");
			getNext("\n");
			if(i!=0) getNext();//SPACES
			while (!getCurrent().equals('\n')){
				value+=getNext();
			}
		}
		getNext("\n");
		return value;
	}

	public static void main(String[] args) {
		//aa:\n bb:bb\n"
		Object parsed = new YamlParser("aa:aa\nbb:bb\nc:\n - 1\n - 2").parse();
		System.out.println(parsed);
	}

	

}