//Author: ^-^Veerle^-^
import org.xml.sax.Attributes;
import org.xml.sax.XMLReader;
import org.xml.sax.SAXException; //Thrown when a syntax error occurs
import org.xml.sax.InputSource;
import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.helpers.XMLReaderFactory;
import java.io.FileReader;
import java.io.IOException;
import java.util.Hashtable; //Allows conversions to be in any order they want, since rates are found via their associated currency
import java.util.Vector; //Stores the original order of the currencies so at the end they can be sorted into that order

public class calcReadXML extends DefaultHandler
{
	//Allows the tags to quickly be updated for all the checks
	private final String strRootTag = "conversions";
	private final String strSourceTag = "convertFrom";
	private final String strDesTag = "convertTo";
	//By using Hashtables, the conversions need not be in order in the xml document
	private Hashtable[] conversions = new Hashtable[2];
	private Vector vecCurrencies;
	private String strCurrentTag = "START", strCurrentCurrency = "";
	private boolean secondChance = false;
	
	private String[] strCurrencies;
	private float[] conversionsFrom, conversionsTo;
	
	public void calcReadXML ()
	{			
	}
	
	public String[] getCurrencies ()
	{
		return strCurrencies;
	}
	
	public float[] getConversionsFrom ()
	{
		return conversionsFrom;
	}
	
	public float[] getConversionsTo ()
	{
		return conversionsTo;
	}
	
	public boolean getSecondChance ()
	{
		return secondChance;
	}
	
	public void parseConversionFile (String strFile) throws Exception
	{
		
		XMLReader xr = XMLReaderFactory.createXMLReader();
		xr.setContentHandler(this);
		
		try
		{			
			xr.parse(new InputSource(new FileReader(strFile)));		
		}
		catch (IOException ex) //If the file could not be found
		{
			
			try //Try to create the default document
			{
				calcWriteXML.create(strFile);
			}
			catch (Exception ex2)
			{
				throw new Exception("Could not locate nor create file: " + strFile + ", please check File permissions as the xml file must be created in the same folder as this application");
			}
			
			try //Should never give an error, but just in case
			{
				
				xr.parse(new InputSource(new FileReader(strFile)));
				secondChance = true; //By default, when the error message is shown the combo boxes are disabled, this gives the combo boxes a second chance
				
			}
			catch (SAXException ex2)
			{
				throw new Exception("If you see this, then I've messed up");
			}
			//Tell the user a default xml document was created
			throw new Exception("Could not locate: " + strFile + " and so a default file has been created with conversions that were true on the 15th of December 2005");
			
		}
		catch (SAXException ex) //Any syntax errors occured
		{
			throw new Exception(ex.getMessage());
		}
		
		
	}
	
	public void startDocument () //Save time and memory by only creating these if the document was found
	{
		
		conversions[0] = new Hashtable(); //ConvertFrom
		conversions[1] = new Hashtable(); //convertTo
		vecCurrencies = new Vector(); //Keeps the order of the currencies
		
	}		
	
	//Called everytime a start tag is found, e.g. <convertFrom>
	public void startElement (String nameSpaceURI, String strTag, String qName, Attributes attr) throws SAXException
	{
		
		if (strCurrentTag.equalsIgnoreCase("START")) //First structure tag in the xml document
		{
			
			if (strTag.equalsIgnoreCase(strRootTag)) //Being the first tag, it must equal the root tag
			{
				strCurrentTag = strRootTag;
			}
			else //Display friendly message so that some people can actually fix the error
			{
				throw new SAXException("The first structure tag in the xml document must be <" + strRootTag + ">, but <" + strTag + "> was found");
			}
			
		}
		else if (strCurrentTag.equalsIgnoreCase("END")) //No tags should appear after the end root tag
		{
			throw new SAXException("The last structure tag in the xml document must be <\\" + strRootTag + ">, but <" + strTag + "> was found");
		}		
		else if (strTag.equalsIgnoreCase(strRootTag)) //The start tag should not be found anywhere else in the document
		{
			throw new SAXException("<" + strRootTag + "> must only appear at the start of the xml document and no where else");
		}
		else if (!strCurrentTag.equalsIgnoreCase(strRootTag)) //When a tag is closed it is set to the root, if this hasn't happened then a tag hasn't be closed
		{
			throw new SAXException("Missing end tag or ilegal nesting, was expecting <\\" + strCurrentTag + ">, but <" + strTag + "> was found");
		}
		else
		{
		
			int whichWay = 0; //Direction flag to know if doing a convertFrom or a convertTo
			strCurrentTag = strTag;
		
			if (strCurrentTag.equalsIgnoreCase(strDesTag)) //Since "whichWay" is already 0, don't need to change it for strSourceTag
			{				
				whichWay = 1;				
			}
			else if (!strCurrentTag.equalsIgnoreCase(strSourceTag)) //If not any of the valid tags
			{
				throw new SAXException("Unknown start xml tag <" + strCurrentTag + ">");
			}
			
			testAttributeSyntax(attr);
			
			strCurrentCurrency = attr.getValue(0);
			
			if (conversions[whichWay].containsKey(strCurrentCurrency)) //If currency already exists in that hash table
			{
				throw new SAXException("Duplicate <" + strCurrentTag + " currency=\"" + attr.getValue(0) + "\"> were found");
			}
			else if (strTag.equalsIgnoreCase(strSourceTag))
			{
				vecCurrencies.addElement(strCurrentCurrency);
			}
			
			
		}
			
	}
	
	private void testAttributeSyntax (Attributes attr) throws SAXException
	{
		//Must have the attribute currency="" but nothing else
		if (!(attr.getLength() == 1 && attr.getLocalName(0).equalsIgnoreCase("currency")))
		{
			throw new SAXException("Every convert xml tag must have a \"currency\" attribute");
		}
		
	}
	
	//Called everytime data is found between a tag pair, e.g. <convertFrom>...</convertFrom>
	public void characters (char[] value, int start, int length) throws SAXException
	{
		//The char array stores every single character in the xml document
		//start says where to start reading, and length says how many characters to read
		//valueToString gets this and turns it into a string
		String strData = valueToString(value, start, length);
		
		int whichWay = 0;
		
		if (strCurrentTag.equalsIgnoreCase(strDesTag))
		{
			whichWay = 1;
		}
		else if (!strCurrentTag.equalsIgnoreCase(strSourceTag))
		{
			throw new SAXException("Unspecified data \"" + strData + "\" was found. Only conversion rates between convert tags is allowed");
		}
		
		try //Error thrown if can not convert into a float
		{
			conversions[whichWay].put(strCurrentCurrency, new Float(Float.parseFloat(strData)));
		}
		catch (NumberFormatException ex)
		{
			throw new SAXException("Error converting conversion rate found at: <" + strCurrentTag + " currency=\"" + strCurrentCurrency + "\">" + strData + "<\\" + strCurrentTag + ">");
		}
		
	}
	
	//Converts the char array for the data into a string
	private String valueToString (char[] value, int start, int length)
	{
		
		String strBuffer = "";
		
		for (int i = start, counter = 0; counter < length; i++, counter++)
		{
			strBuffer = strBuffer + value[i];
		}
		
		return strBuffer;
		
	}
	
	//Called everytime an end tag is found, e.g. </convertFrom>
	public void endElement (String nameSpaceURI, String strTag, String qName) throws SAXException
	{
		//Tags appear before or after the <conversions></conversions> tags
		if (strCurrentTag.equalsIgnoreCase("START") || strCurrentTag.equalsIgnoreCase("END"))
		{
			throw new SAXException("Tags must not appear before or after the <" + strRootTag + "><\\" + strRootTag + "> tags, but <\\" + strTag + "> was found");
		}
		else if (!strCurrentTag.equalsIgnoreCase(strTag)) //Must close the current open tag
		{
			throw new SAXException("Missing start tag, or ilegal nesting, was expecting <" + strCurrentTag + ">, but <\\" + strTag + "> was found");
		}
		else if (strTag.equalsIgnoreCase(strSourceTag) || strTag.equalsIgnoreCase(strDesTag)) //Closes the tag by setting current tag back to root
		{
			strCurrentTag = strRootTag;
		}
		else if (strTag.equalsIgnoreCase(strRootTag)) //Nothing else can appear after this
		{
			strCurrentTag = "END";
		}
		else
		{
			throw new SAXException("Unknown end xml tag <\\" + strTag + ">");
		}
		
	}	

	public void endDocument () throws SAXException
	{
		
		if (!strCurrentTag.equalsIgnoreCase("END")) //If end of document without </conversions>
		{
			throw new SAXException("The last structure tag in the xml document must be <\\" + strRootTag + "> but this was not found");
		}
		else if (conversions[0].size() != conversions[1].size() || conversions[0].size() != vecCurrencies.size()) //Unequal amount of conversions
		{
			throw new SAXException("The amount of conversions to and from are not equal. There are " + conversions[0].size() + " from, and " + conversions[1].size() + " to");
		}
		
		int amountofConverts = conversions[0].size();
		Float fromRate = 0.0f;
		Float toRate = 0.0f;
		
		strCurrencies = new String[amountofConverts]; //Store all of the currencies to be used
		conversionsFrom = new float[amountofConverts]; //Store the conversions from * to pound
		conversionsTo = new float[amountofConverts]; //Store the conversions from pound to *	
		
		for (int i = 0; i < amountofConverts; i++) //Populate the conversion arrays in the same order as the currencies appear
		{
			
			strCurrencies[i] = (String)vecCurrencies.elementAt(i); //Everything must now be put in the same order
			fromRate = (Float)conversions[0].get(strCurrencies[i]); //Tries to find the value associated with the supplied key
			toRate = (Float)conversions[1].get(strCurrencies[i]); //Returns null if the key was not reconised
						
			if (fromRate == null) //Could not the value for the conversion (possible spelling mistake or obmission from xml file)
			{ //Try to give the end user a helpful message and possible solution
				throw new SAXException("<" + strDesTag + " currency=\"" + strCurrencies[i] + "\"><\\" + strDesTag + "> was found\n\nbut could not find <" + strSourceTag + " currency=\"" + strCurrencies[i] + "\"><\\" + strSourceTag + ">");
			}
			else if (toRate == null)
			{
				throw new SAXException("<" + strSourceTag + " currency=\"" + strCurrencies[i] + "\"><\\" + strSourceTag + "> was found\n\nbut could not find <" + strDesTag + " currency=\"" + strCurrencies[i] + "\"><\\" + strDesTag + ">");
			}
			
			conversionsFrom[i] = fromRate; //Store the conversions in the right order
			conversionsTo[i] = toRate;
			
		}
		
		conversions[0] = null; //Making these null means the garbage collector can remove them
		conversions[1] = null;
		vecCurrencies = null;
	
	}
	
}