import java.util.Map;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;
import java.io.BufferedWriter;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.IOException;

/**
A simple class to write XML to a stream. Does some pretty-printing.
*/
/*
TODO:

- more validation, eg of tags and attr names
- namespaces
- a ContentHandler adapter?
- drip-feeding text (needed to allow mixed content)
- proper handling of whitespace in mixed content (ie can't do it, only in element content, but how do we know where that is?)
- CDATA (as a separate method? a mode? a setting attached to tags? an intelligent decision based on content?)
- PIs
*/
public class XMLWriter {
	
	private static final String UTF8 = "UTF-8";
	
	private BufferedWriter out;
	private String publicID;
	private String systemID;
	private List<String> tagStack;
	
	public XMLWriter(BufferedWriter out, String charset, String publicID, String systemID) throws IOException {
		this.out = out;
		out.write("<?xml version=\"1.0\" encoding=\"");
		out.write(charset);
		out.write("\"?>");
		out.newLine();
		this.publicID = publicID;
		this.systemID = systemID;
		tagStack = new ArrayList<String>();
	}
	
	public XMLWriter(BufferedWriter out, String publicID, String systemID) throws IOException {
		this(out, UTF8, publicID, systemID);
	}
	
	public XMLWriter(BufferedWriter out) throws IOException {
		this(out, null, null);
	}
	
	public XMLWriter(OutputStream out, String charset, String publicID, String systemID) throws IOException {
		this(new BufferedWriter(new OutputStreamWriter(out, charset)), charset, publicID, systemID);
	}
	
	public XMLWriter(OutputStream out, String publicID, String systemID) throws IOException {
		this(out, UTF8, publicID, systemID);
	}
	
	public XMLWriter(OutputStream out) throws IOException {
		this(out, UTF8, null, null);
	}
	
	public void startElement(String tag, Map<String, String> attrs) throws IOException {
		writeTagOpen(tag, attrs);
		out.write(">");
		out.newLine();
		pushTag(tag);
	}
	
	public void startElement(String tag) throws IOException {
		startElement(tag, Collections.<String, String>emptyMap());
	}
	
	public void endElement() throws IOException {
		String tag = popTag();
		indent();
		out.write("</");
		out.write(tag);
		out.write(">");
		out.newLine();
	}
	
	public void element(String tag, Map<String, String> attrs, String text) throws IOException {
		writeTagOpen(tag, attrs);
		if (text.equals("")) {
			out.write("/>");
		}
		else {
			out.write(">");
			writeEscaped(text);
			out.write("</");
			out.write(tag);
			out.write(">");
		}
		out.newLine();
	}
	
	public void element(String tag, String text) throws IOException {
		element(tag, Collections.<String, String>emptyMap(), text);
	}
	
	public void comment(String text) throws IOException {
		if (text.contains("-->")) throw new IOException("bad comment text: " + text);
		indent();
		out.write("<!-- ");
		out.write(text);
		out.write(" -->");
		out.newLine();
	}
	
	private void writeTagOpen(String tag, Map<String, String> attrs) throws IOException {
		if ((publicID != null) || (systemID != null)) {
			out.write("<!DOCTYPE ");
			out.write(tag);
			if (publicID != null) {
				out.write(" PUBLIC \"");
				out.write(publicID);
				out.write("\"");
			}
			if (systemID != null) {
				out.write(" SYSTEM \"");
				out.write(systemID);
				out.write("\"");
			}
			out.write(">");
			out.newLine();
			publicID = null;
			systemID = null;
		}
		indent();
		out.write("<");
		out.write(tag);
		for (Map.Entry<String, String> attr: attrs.entrySet()) {
			out.write(" ");
			out.write(attr.getKey());
			out.write("=\"");
			writeEscaped(attr.getValue());
			out.write("\"");
		}
	}
	
	private void writeEscaped(String str) throws IOException {
		for (int i = 0; i < str.length(); ++i) {
			char ch = str.charAt(i);
			switch (ch) {
				case '&': {
					out.write("&amp;");
				} break;
				case '<': {
					out.write("&lt;");
				} break;
				case '>': {
					out.write("&gt;");
				} break;
				case '"': {
					out.write("&quot;");
				} break;
				default: {
					out.write(ch);
				}
			}
		}
	}
	
	private void pushTag(String tag) {
		tagStack.add(tag);
	}
	
	private String popTag() {
		return tagStack.remove(tagStack.size() - 1);
	}
	
	private void indent() throws IOException {
		for (int i = 0; i < tagStack.size(); ++i) out.write('\t');
	}
	
	public void newLine() throws IOException {
		indent();
		out.newLine();
	}
	
	public void close() throws IOException {
		if (!tagStack.isEmpty()) throw new IOException("some tags are unclosed: " + tagStack);
		out.flush();
	}
	
}