// Copyright 2004 Adam Megacz, see the COPYING file for licensing [GPL]
package org.xwt.translators;

import java.util.*;
import java.net.*;
import java.io.*;
import org.xwt.js.*;
import org.xwt.util.*;

/* 
 * While entities are limited to a subset of Unicode characters ,
 * numeric character references can specify any character. Numeric
 * character references may be given in decimal or hexadecimal, though
 * browser support is stronger for decimal references. Decimal
 * references are of the form &#number; while hexadecimal references
 * take the case-insensitive form &#xnumber;. Examples of numeric
 * character references include © or © for the copyright
 * symbol, Α or Α for the Greek capital letter alpha, and
 * ا or ا for the Arabic letter ALEF.
 *
 * http://www.htmlhelp.com/reference/html40/entities/special.html
 * http://www.htmlhelp.com/reference/html40/entities/symbols.html
 * http://www.htmlhelp.com/reference/html40/entities/latin1.html
 */

/**
 *   This class parses an InputStream containing HTML and returns it
 *   as an XWT DOM tree. Each HTML Element is returned as a struct,
 *   with the following members:
 *
 *   Since HTML may have multiple top level elements (unlike XML),
 *   this class will search all top level elements for one with a tag
 *   name 'html'. If such a node is found, only it is returned. If no
 *   top-level element has the tag name 'html', such a node is
 *   fabricated, and all top level elements become the children of
 *   that node, which is then returned.
 */
public class HTML {

    private final static String[] noEndTag =
        new String[] { "area", "base", "basefont", "br", "col", "frame", "hr", "img",
                       "input", "isindex", "link", "meta", "param" };

    /** we keep a char[] around for use by removeRedundantWhitespace() */
    private static char[] cbuf = null;

    /** we keep a StringBuffer around for use by removeRedundantWhitespace() */
    private static StringBuffer sbuf = null;

    /** true iff we have encountered an LI more recently than the last OL/UL */
    private static boolean withinLI = false;

    public static synchronized JS parseReader(Reader r) throws IOException, JSExn {
        CharStream cs = new CharStream(r);
        JS h = new JS();

        withinLI = false;
        h.put("$name", "html");

        try {
            while (true) parseBody(cs, h, null);
        } catch (EOFException e) {
            // continue until we get an EOFException
        }
        
        /* FIXME
        Object[] ids = h.keys();
        for(int i=0; i<ids.length; i++) {
            Object el = h.get((String)ids[i]);
            if (el instanceof JS && "html".equals(((JS)el).get("$name")))
                return (JS)el;
        }
        */        
        return h;
    }

    /**
     *  Parses a single element and stores it in <tt>h</tt>. The
     *  CharStream should be positioned immediately <i>after</i> the
     *  open bracket.
     *
     *  If a close tag not matching this open tag is found, the
     *  tagname on the close tag will be returned in order to
     *  facilitate correcting broken HTML. Otherwise, this returns
     *  null.
     */
    private static String parseElement(CharStream cs, JS h) throws IOException, JSExn {
        // scan element name
        while(Character.isSpace(cs.peek())) cs.get();
        String elementName = parseElementName(cs);

        boolean saveWithinLI = withinLI;
        if (elementName.equals("li")) {
            if (withinLI) {
                cs.unread(new char[] { '<', 'l', 'i', ' ' });
                return "li";
            } else {
                withinLI = true;
            }
        } else if (elementName.equals("ol") || elementName.equals("ul")) {
            withinLI = false;
        }

        h.put("$name", elementName);
        if (elementName.equals("!--")) {
            h.put("0", parseComment(cs));
            h.put("$numchildren", new Integer(0));
            return null;
        }

        // scan attributes
        while (cs.peek() != '>') {
            String name = parseAttributeName(cs);
            if (name.equals("")) break;
            String value = expandEntities(parseAttributeValue(cs));
            h.put(name, value);
        } 

        // eat the close-angle bracket
        cs.get();

        // bodyless tags return here
        for(int i=0; i<noEndTag.length; i++)
            if (noEndTag[i].equals(elementName))
                return null;

        // scan body
        String ret = parseBody(cs, h, elementName);
        withinLI = saveWithinLI;
        return ret;
    }

    /**
     *  Parses the body of an element. The CharStream should be
     *  positioned at the character immediately after the right
     *  bracket closing the start-tag
     */
    private static String parseBody(CharStream cs, JS h, String elementName) throws IOException, JSExn {
        String cdata = "";
        int length = h.get("$numchildren") == null ? 0 : Integer.parseInt(h.get("$numchildren").toString());
        while(true) {
            String closetag = null;

            try {
                char c = cs.get();
                if (c != '<') { cdata += c; continue; }
                String expanded = removeRedundantWhitespace(expandEntities(cdata));
                if (expanded.length() > 0) {
                    h.put(String.valueOf(length), expanded);
                    h.put("$numchildren", new Integer(++length));
                }
                cdata = "";

            } catch (EOFException e) {
                String expanded = removeRedundantWhitespace(expandEntities(cdata));
                if (expanded.length() > 0) {
                    h.put(String.valueOf(length), expanded);
                    h.put("$numchildren", new Integer(++length));
                }
                throw e;
            }
                
            try {
                // scan subelement
                if (cs.peek() != '/') {
                    JS kid = new JS();
                    closetag = parseElement(cs, kid);
                    h.put(String.valueOf(length), kid); 
                    h.put("$numchildren", new Integer(++length));
                    
                // scan close-tag
                } else {
                    cs.get(); // drop the slash
                    closetag = parseElementName(cs);
                    while(cs.get() != '>');
                }
            } catch (EOFException e) {
                throw e;

            }
            
            if (closetag != null)
                return closetag.equals(elementName) ? null : closetag;
        }
    }

    /** Parses an element name and returns it. The CharStream should
     *  be positioned at the first character of the name.
     */
    private static String parseElementName(CharStream cs) throws IOException, JSExn {
        String ret = "";
        while (cs.peek() != '>' && !Character.isSpace(cs.peek())) ret += cs.get();
        return ret.toLowerCase();
    }

    /** Parses an attribute name and returns it. The CharStream should
     *  be positioned at the first character of the name, possibly
     *  with intervening whitespace.
     */
    private static String parseAttributeName(CharStream cs) throws IOException, JSExn {
        while(Character.isSpace(cs.peek())) cs.get();
        String ret = "";
        while(!Character.isSpace(cs.peek()) && cs.peek() != '=' && cs.peek() != '>') ret += cs.get();
        return ret.toLowerCase();
    }

    /** Parses an attribute value and returns it. The CharStream
     *  should be positioned at the equals sign, possibly with
     *  intervening whitespace.
     */
    private static String parseAttributeValue(CharStream cs) throws IOException, JSExn {

        // eat whitespace and equals sign
        while(Character.isSpace(cs.peek())) cs.get();
        if (cs.peek() != '=') return "";
        cs.get();
        while(Character.isSpace(cs.peek())) cs.get();

        boolean doublequoted = false;
        boolean singlequoted = false;
        String ret = "";

        if (cs.peek() == '\"') { doublequoted = true; cs.get(); }
        else if (cs.peek() == '\'') { singlequoted = true; cs.get(); }

        while(true) {
            char c = cs.peek();
            if (!doublequoted && !singlequoted && (Character.isSpace(c) || c == '>')) break;
            if (singlequoted && c == '\'') { cs.get(); break; }
            if (doublequoted && c == '\"') { cs.get(); break; }
            ret += cs.get();
        }
        return ret;
    }

    /** Parses a comment and returns its body. The CharStream should
     *  be positioned immediately after the <!--
     */
    private static String parseComment(CharStream cs) throws IOException, JSExn {
        int dashes = 0;
        String ret = "";
        while(true) {
            char c = cs.get();
            if (c == '>' && dashes == 2) return ret.substring(0, ret.length() - 2);
            if (c == '-') dashes++;
            else dashes = 0;
            ret += c;
        }
    }

    /** Expands all SGML entities in string <tt>s</tt> */
    public static String expandEntities(String s) throws IOException, JSExn {
        if (s.indexOf('&') == -1) return s;
        StringBuffer sb = new StringBuffer();
        int i=0;
        int nextamp = 0;
        while(nextamp != -1) {
            nextamp = s.indexOf('&', i);
            sb.append(nextamp == -1 ? s.substring(i) : s.substring(i, nextamp));
            if (nextamp == -1) break;
            if (s.regionMatches(nextamp, "&", 0, 5)) {
                sb.append("&");
                i = nextamp + 5;
            } else if (s.regionMatches(nextamp, ">", 0, 4)) {
                sb.append(">");
                i = nextamp + 4;
            } else if (s.regionMatches(nextamp, "<", 0, 4)) {
                sb.append("<");
                i = nextamp + 4;
            } else if (s.regionMatches(nextamp, """, 0, 6)) {
                sb.append("\"");
                i = nextamp + 6;
            } else if (s.regionMatches(nextamp, " ", 0, 6)) {
                // FEATURE: perhaps we should distinguish this somehow
                sb.append(" ");
                i = nextamp + 6;
            } else {
                sb.append("&");
                i = nextamp + 1;
            }
        }
        return sb.toString();
    }

    /** removes all redundant whitespace */
    private static String removeRedundantWhitespace(String s) throws JSExn {

        if (s.indexOf(' ') == -1 && s.indexOf('\n') == -1 && s.indexOf('\t') == -1 && s.indexOf('\r') == -1) return s;

        int len = s.length();
        if (cbuf == null || cbuf.length < len) {
            cbuf = new char[len * 2];
            sbuf = new StringBuffer(len * 2);
        }
        sbuf.setLength(0);
        s.getChars(0, len, cbuf, 0);

        int last = 0;
        boolean lastWasWhitespace = false;
        for(int i=0; i<len; i++) {
            boolean lastlast = lastWasWhitespace;
            switch(cbuf[i]) {
            case '\n': case '\r': case '\t':
                cbuf[i] = ' ';
            case ' ':
                lastWasWhitespace = true;
                break;
            default:
                lastWasWhitespace = false;
                break;
            }
            if (lastWasWhitespace && lastlast) {
                if (last != i) sbuf.append(cbuf, last, i - last);
                last = i+1;
            }
        }
            
        if (last != len) sbuf.append(cbuf, last, len - last);
        return sbuf.toString().trim();
    }

    // CharStream /////////////////////////////////////////////////////////////////////

    private static class CharStream extends PushbackReader {
        public CharStream(Reader r) { super(r, 1024); }

        public char peek() throws IOException {
            char c = get();
            unread(c);
            return c;
        }

        public char get() throws IOException {
            int i = read();
            if (i == -1) throw new EOFException();
            return (char)i;
        }
    }

}