org.eclipse.mylyn.commons.core/src/org/eclipse/mylyn/internal/commons/core/Html2TextReader.java

/*******************************************************************************
 * Copyright (c) 2000, 2012 IBM Corporation and others.
 * 
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * https://www.eclipse.org/legal/epl-2.0
 * 
 * SPDX-License-Identifier: EPL-2.0
 *
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.mylyn.internal.commons.core;

import java.io.IOException;
import java.io.PushbackReader;
import java.io.Reader;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Locale;
import java.util.Map;
import java.util.Set;

/**
 * Reads the text contents from a reader of HTML contents and translates the tags or cut them out.
 * <p>
 * Moved into this package from <code>org.eclipse.jface.internal.text.revisions</code>.
 * </p>
 * <p>
 * Based on {@link org.eclipse.jface.internal.text.html.HTML2TextReader}.
 * </p>
 */
@SuppressWarnings({ "rawtypes", "unchecked" })
public class Html2TextReader extends SubstitutionTextReader {

	private static final String EMPTY_STRING = ""; //$NON-NLS-1$

	private static final Map fgEntityLookup;

	private static final Set fgTags;

	static {

		fgTags = new HashSet();
		fgTags.add("b"); //$NON-NLS-1$
		fgTags.add("br"); //$NON-NLS-1$
		fgTags.add("br/"); //$NON-NLS-1$
		fgTags.add("div"); //$NON-NLS-1$
		fgTags.add("h1"); //$NON-NLS-1$
		fgTags.add("h2"); //$NON-NLS-1$
		fgTags.add("h3"); //$NON-NLS-1$
		fgTags.add("h4"); //$NON-NLS-1$
		fgTags.add("h5"); //$NON-NLS-1$
		fgTags.add("p"); //$NON-NLS-1$
		fgTags.add("dl"); //$NON-NLS-1$
		fgTags.add("dt"); //$NON-NLS-1$
		fgTags.add("dd"); //$NON-NLS-1$
		fgTags.add("li"); //$NON-NLS-1$
		fgTags.add("ul"); //$NON-NLS-1$
		fgTags.add("pre"); //$NON-NLS-1$
		fgTags.add("head"); //$NON-NLS-1$

		fgEntityLookup = new HashMap(7);
		fgEntityLookup.put("lt", "<"); //$NON-NLS-1$ //$NON-NLS-2$
		fgEntityLookup.put("gt", ">"); //$NON-NLS-1$ //$NON-NLS-2$
		fgEntityLookup.put("nbsp", " "); //$NON-NLS-1$ //$NON-NLS-2$
		fgEntityLookup.put("amp", "&"); //$NON-NLS-1$ //$NON-NLS-2$
		fgEntityLookup.put("circ", "^"); //$NON-NLS-1$ //$NON-NLS-2$
		fgEntityLookup.put("tilde", "~"); //$NON-NLS-1$ //$NON-NLS-2$
		fgEntityLookup.put("quot", "\""); //$NON-NLS-1$ //$NON-NLS-2$
	}

	private boolean fInParagraph = false;

	private boolean fIsPreformattedText = false;

	private boolean fIgnore = false;

	/**
	 * Transforms the HTML text from the reader to formatted text.
	 * 
	 * @param reader
	 *            the reader
	 * @param presentation
	 *            If not <code>null</code>, formattings will be applied to the presentation.
	 */
	public Html2TextReader(Reader reader) {
		super(new PushbackReader(reader));
	}

	protected void startBold() {
	}

	protected void startPreformattedText() {
		fIsPreformattedText = true;
		//setSkipWhitespace(false);
	}

	protected void stopPreformattedText() {
		fIsPreformattedText = false;
		//setSkipWhitespace(true);
	}

	protected void stopBold() {
	}

	/*
	 * @see org.eclipse.jdt.internal.ui.text.SubstitutionTextReader#computeSubstitution(int)
	 */
	@Override
	protected String computeSubstitution(int c) throws IOException {

		if (c == '<') {
			return processHTMLTag();
		} else if (fIgnore) {
			return EMPTY_STRING;
		} else if (c == '&') {
			return processEntity();
		} else if (fIsPreformattedText) {
			return processPreformattedText(c);
		} else if (c == '\n') {
			return EMPTY_STRING;
		}

		return null;
	}

	private String html2Text(String html) {

		if (html == null || html.length() == 0) {
			return EMPTY_STRING;
		}

		html = html.toLowerCase(Locale.ENGLISH);

		String tag = html;
		if ('/' == tag.charAt(0)) {
			tag = tag.substring(1);
		}

		if (!fgTags.contains(tag)) {
			return EMPTY_STRING;
		}

		if ("pre".equals(html)) { //$NON-NLS-1$
			startPreformattedText();
			return EMPTY_STRING;
		}

		if ("/pre".equals(html)) { //$NON-NLS-1$
			stopPreformattedText();
			return EMPTY_STRING;
		}

		if (fIsPreformattedText) {
			return EMPTY_STRING;
		}

		if ("b".equals(html)) { //$NON-NLS-1$
			startBold();
			return EMPTY_STRING;
		}

		if ((html.length() > 1 && html.charAt(0) == 'h' && Character.isDigit(html.charAt(1))) || "dt".equals(html)) { //$NON-NLS-1$
			startBold();
			return EMPTY_STRING;
		}

		if ("dl".equals(html)) { //$NON-NLS-1$
			return LINE_DELIM;
		}

		if ("dd".equals(html)) { //$NON-NLS-1$
			return "\t"; //$NON-NLS-1$
		}

		if ("li".equals(html)) { //$NON-NLS-1$
			return LINE_DELIM + "  - "; //$NON-NLS-1$
		}

		if ("/b".equals(html)) { //$NON-NLS-1$
			stopBold();
			return EMPTY_STRING;
		}

		if ("p".equals(html)) { //$NON-NLS-1$
			fInParagraph = true;
			return LINE_DELIM;
		}

		if ("br".equals(html) || "br/".equals(html) || "div".equals(html)) { //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
			return LINE_DELIM;
		}

		if ("/p".equals(html)) { //$NON-NLS-1$
			boolean inParagraph = fInParagraph;
			fInParagraph = false;
			return inParagraph ? EMPTY_STRING : LINE_DELIM;
		}

		if ((html.startsWith("/h") && html.length() > 2 && Character.isDigit(html.charAt(2))) || "/dt".equals(html)) { //$NON-NLS-1$ //$NON-NLS-2$
			stopBold();
			return LINE_DELIM;
		}

		if ("/dd".equals(html)) { //$NON-NLS-1$
			return LINE_DELIM;
		}

		if ("head".equals(html)) { //$NON-NLS-1$
			fIgnore = true;
			return EMPTY_STRING;
		}

		if ("/head".equals(html)) { //$NON-NLS-1$
			fIgnore = false;
			return EMPTY_STRING;
		}

		return EMPTY_STRING;
	}

	/*
	 * A '<' has been read. Process a html tag
	 */
	private String processHTMLTag() throws IOException {

		StringBuilder buf = new StringBuilder();
		int ch;
		do {

			ch = nextChar();

			while (ch != -1 && ch != '>') {
				buf.append(Character.toLowerCase((char) ch));
				ch = nextChar();
				if (ch == '"') {
					buf.append(Character.toLowerCase((char) ch));
					ch = nextChar();
					while (ch != -1 && ch != '"') {
						buf.append(Character.toLowerCase((char) ch));
						ch = nextChar();
					}
				}
				if (ch == '<') {
					unread(ch);
					return '<' + buf.toString();
				}
			}

			if (ch == -1) {
				return null;
			}

			int tagLen = buf.length();
			// needs special treatment for comments
			if ((tagLen >= 3 && "!--".equals(buf.substring(0, 3))) //$NON-NLS-1$
					&& !(tagLen >= 5 && "--".equals(buf.substring(tagLen - 2)))) { //$NON-NLS-1$
				// unfinished comment
				buf.append(ch);
			} else {
				break;
			}
		} while (true);

		return html2Text(buf.toString());
	}

	private String processPreformattedText(int c) {
		return null;
	}

	private void unread(int ch) throws IOException {
		((PushbackReader) getReader()).unread(ch);
	}

	protected String entity2Text(String symbol) {
		if (symbol.length() > 1 && symbol.charAt(0) == '#') {
			int ch;
			try {
				if (symbol.charAt(1) == 'x') {
					ch = Integer.parseInt(symbol.substring(2), 16);
				} else {
					ch = Integer.parseInt(symbol.substring(1), 10);
				}
				return EMPTY_STRING + (char) ch;
			} catch (NumberFormatException e) {
			}
		} else {
			String str = (String) fgEntityLookup.get(symbol);
			if (str != null) {
				return str;
			}
		}
		return "&" + symbol + ";"; // not found //$NON-NLS-1$ //$NON-NLS-2$
	}

	/*
	 * A '&' has been read. Process a entity
	 */
	private String processEntity() throws IOException {
		StringBuilder buf = new StringBuilder();
		int ch = nextChar();
		while (Character.isLetterOrDigit((char) ch) || ch == '#') {
			buf.append((char) ch);
			ch = nextChar();
		}

		if (ch == ';') {
			return entity2Text(buf.toString());
		}

		buf.insert(0, '&');
		if (ch != -1) {
			buf.append((char) ch);
		}
		return buf.toString();
	}
}