/**********************************************************************
 Copyright (c) 2000, 2002 IBM Corp. and others.
 All rights reserved. This program and the accompanying materials
 are made available under the terms of the Common Public License v1.0
 which accompanies this distribution, and is available at
 http://www.eclipse.org/legal/cpl-v10.html

 Contributors:
 IBM Corporation - Initial implementation
 **********************************************************************/

package net.sourceforge.phpdt.internal.ui.text;

import java.io.IOException;
import java.io.Reader;

import net.sourceforge.phpdt.internal.corext.phpdoc.SingleCharReader;

/**
 * Reads the text contents from a reader and computes for each character a
 * potential substitution. The substitution may eat more characters than only
 * the one passed into the computation routine.
 */
public abstract class SubstitutionTextReader extends SingleCharReader {

	protected static final String LINE_DELIM = System.getProperty(
			"line.separator", "\n"); //$NON-NLS-1$ //$NON-NLS-2$

	private Reader fReader;

	private boolean fWasWhiteSpace;

	private int fCharAfterWhiteSpace;

	/**
	 * Tells whether white space characters are skipped.
	 */
	private boolean fSkipWhiteSpace = true;

	private boolean fReadFromBuffer;

	private StringBuffer fBuffer;

	private int fIndex;

	protected SubstitutionTextReader(Reader reader) {
		fReader = reader;
		fBuffer = new StringBuffer();
		fIndex = 0;
		fReadFromBuffer = false;
		fCharAfterWhiteSpace = -1;
		fWasWhiteSpace = true;
	}

	/**
	 * Implement to compute the substitution for the given character and if
	 * necessary subsequent characters. Use <code>nextChar</code> to read
	 * subsequent characters.
	 */
	protected abstract String computeSubstitution(int c) throws IOException;

	/**
	 * Returns the internal reader.
	 */
	protected Reader getReader() {
		return fReader;
	}

	/**
	 * Returns the next character.
	 */
	protected int nextChar() throws IOException {
		fReadFromBuffer = (fBuffer.length() > 0);
		if (fReadFromBuffer) {
			char ch = fBuffer.charAt(fIndex++);
			if (fIndex >= fBuffer.length()) {
				fBuffer.setLength(0);
				fIndex = 0;
			}
			return ch;
		} else {
			int ch = fCharAfterWhiteSpace;
			if (ch == -1) {
				ch = fReader.read();
			}
			if (fSkipWhiteSpace && Character.isWhitespace((char) ch)) {
				do {
					ch = fReader.read();
				} while (Character.isWhitespace((char) ch));
				if (ch != -1) {
					fCharAfterWhiteSpace = ch;
					return ' ';
				}
			} else {
				fCharAfterWhiteSpace = -1;
			}
			return ch;
		}
	}

	/**
	 * @see Reader#read()
	 */
	public int read() throws IOException {
		int c;
		do {

			c = nextChar();
			while (!fReadFromBuffer) {
				String s = computeSubstitution(c);
				if (s == null)
					break;
				if (s.length() > 0)
					fBuffer.insert(0, s);
				c = nextChar();
			}

		} while (fSkipWhiteSpace && fWasWhiteSpace && (c == ' '));
		fWasWhiteSpace = (c == ' ' || c == '\r' || c == '\n');
		return c;
	}

	/**
	 * @see Reader#ready()
	 */
	public boolean ready() throws IOException {
		return fReader.ready();
	}

	/**
	 * @see Reader#close()
	 */
	public void close() throws IOException {
		fReader.close();
	}

	/**
	 * @see Reader#reset()
	 */
	public void reset() throws IOException {
		fReader.reset();
		fWasWhiteSpace = true;
		fCharAfterWhiteSpace = -1;
		fBuffer.setLength(0);
		fIndex = 0;
	}

	protected final void setSkipWhitespace(boolean state) {
		fSkipWhiteSpace = state;
	}

	protected final boolean isSkippingWhitespace() {
		return fSkipWhiteSpace;
	}
}