/*******************************************************************************
 *  Copyright (c) 2005, 2016 IBM Corporation and others.
 *
 *  This program and the accompanying materials
 *  are made available under the terms of the Eclipse Public License 2.0
 *  which accompanies this distribution, and is available at
 *  https://www.eclipse.org/legal/epl-2.0/
 *
 *  SPDX-License-Identifier: EPL-2.0
 *
 *  Contributors:
 *     IBM Corporation - initial API and implementation
 *     Bjorn Freeman-Benson - initial API and implementation
 *******************************************************************************/
package org.eclipse.cdt.examples.ant.tasks;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.Vector;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.DirectoryScanner;
import org.apache.tools.ant.Task;
import org.apache.tools.ant.types.FileSet;
import org.apache.tools.ant.util.FileUtils;

/**
 * Java preprocessor for code examples. Used to export source code for
 * example plug-ins with parts of code missing/inserted etc., for
 * various exercises.
 * <p>
 * The preprocessor looks for #ifdef statements in java comments, and is
 * run with a set of symbols. For example:
 * <pre>
 * //#ifdef ex1
 * ... code to insert when 'ex1' symbol is on
 * //#else
 * ... code to insert when not 'ex1'
 * //#endif
 * </pre>
 * </p>
 */
public class PreProcessor extends Task {

	private Vector<FileSet> fFileSets = new Vector<>();
	private File fDestDir = null;
	private Set<String> fSymbols = new HashSet<>();
	private FileUtils fUtils = FileUtils.getFileUtils();

	// possible states
	private static final int STATE_OUTSIDE_CONDITION = 0;
	private static final int STATE_TRUE_CONDITION = 1;
	private static final int STATE_FALSE_CONDITION = 2;
	private static final int STATE_POST_TRUE_CONDITION = 3;

	// matchers
	private Matcher IF_DEF_MATCHER = Pattern.compile("#ifdef\\s+\\w+").matcher("");
	private Matcher ELSE_IF_MATCHER = Pattern.compile("#elseif\\s+\\w+").matcher("");
	private Matcher ELSE_MATCHER = Pattern.compile("#else$|#else\\W+").matcher("");
	private Matcher END_MATCHER = Pattern.compile("#endif").matcher("");

	/**
	 * Constructs a new preprocessor task
	 */
	public PreProcessor() {
	}

	/**
	 * Adds a set of files to process.
	 *
	 * @param set a set of files to process
	 */
	public void addFileset(FileSet set) {
		fFileSets.addElement(set);
	}

	/**
	 * Sets the destination directory for processed files.
	 *
	 * @param destDir destination directory for processed files
	 */
	public void setDestdir(File destDir) {
		fDestDir = destDir;
	}

	/**
	 * Sets the symbols that are "on" for the preprocessing.
	 *
	 * @param symbols symbols that are "on" for the preprocessing
	 */
	public void setSymbols(String symbols) {
		String[] strings = symbols.split(",");
		for (int i = 0; i < strings.length; i++) {
			String string = strings[i].trim();
			if (string.length() > 0) {
				fSymbols.add(string);
			}
		}
	}

	@Override
	public void execute() throws BuildException {
		if (fSymbols.size() == 0) {
			throw new BuildException("No symbols specified for preprocessor");
		}
		if (fFileSets.isEmpty()) {
			throw new BuildException("No filesets specified for processing");
		}
		if (!fDestDir.exists()) {
			throw new BuildException("destdir does not exist: " + fDestDir.getAbsolutePath());
		}
		StringBuilder buf = new StringBuilder("Symbols: ");
		String[] symbols = fSymbols.toArray(new String[fSymbols.size()]);
		for (int i = 0; i < symbols.length; i++) {
			String symbol = symbols[i];
			buf.append(symbol);
			if (i < (symbols.length - 1)) {
				buf.append(", ");
			}
		}
		log(buf.toString());

		Iterator<FileSet> fileSets = fFileSets.iterator();
		while (fileSets.hasNext()) {
			FileSet fileSet = fileSets.next();
			DirectoryScanner scanner = fileSet.getDirectoryScanner(getProject());
			String[] includedFiles = scanner.getIncludedFiles();
			File baseDir = fileSet.getDir(getProject());
			for (int i = 0; i < includedFiles.length; i++) {
				String fileName = includedFiles[i];
				processFile(baseDir, fileName, fDestDir);
			}
		}

	}

	/**
	 * Process the file
	 * @param baseDir base directory source file is relative to
	 * @param fileName source file name
	 * @param destDir root destination directory
	 */
	private void processFile(File baseDir, String fileName, File destDir) throws BuildException {
		File destFile = new File(destDir, fileName);
		File srcFile = new File(baseDir, fileName);
		File dir = destFile.getParentFile();
		if (!dir.exists()) {
			dir.mkdirs();
		}
		String contents = null;
		if (fileName.endsWith(".java")) {
			contents = preProcessFile(srcFile);
		} else if (fileName.equals("plugin.xml")) {
			contents = preProcessFile(srcFile);
		}
		if (contents == null) {
			// no change, just copy file
			try {
				fUtils.copyFile(srcFile, destFile);
			} catch (IOException e) {
				throw new BuildException(e);
			}
		} else {
			// write new file
			FileWriter writer;
			try {
				writer = new FileWriter(destFile);
				writer.write(contents);
				writer.close();
			} catch (IOException e) {
				throw new BuildException(e);
			}

		}
	}

	/**
	 * Preprocesses a file
	 *
	 * @param srcFile the file to process
	 * @return
	 */
	public String preProcessFile(File srcFile) {
		try (BufferedReader reader = new BufferedReader(new FileReader(srcFile))) {
			StringBuilder buffer = new StringBuilder();
			String line = reader.readLine();
			String activeSymbol = null;
			int state = STATE_OUTSIDE_CONDITION;
			boolean changed = false;
			while (line != null) {
				boolean ifdef = IF_DEF_MATCHER.reset(line).find();
				boolean elseif = ELSE_IF_MATCHER.reset(line).find();
				boolean elze = ELSE_MATCHER.reset(line).find();
				boolean endif = END_MATCHER.reset(line).find();
				boolean commandLine = ifdef || elseif || elze || endif;
				boolean written = false;
				switch (state) {
				case STATE_OUTSIDE_CONDITION:
					if (ifdef) {
						String condition = line.substring(IF_DEF_MATCHER.start(), IF_DEF_MATCHER.end());
						String[] strings = condition.split("\\s+");
						activeSymbol = strings[1].trim();
						if (fSymbols.contains(activeSymbol)) {
							state = STATE_TRUE_CONDITION;
						} else {
							state = STATE_FALSE_CONDITION;
						}
					} else if (elseif) {
						throw new BuildException("#elseif encountered without corresponding #ifdef");
					} else if (elze) {
						throw new BuildException(
								"#else encountered without corresponding #ifdef (" + srcFile.getPath() + ")");
					} else if (endif) {
						throw new BuildException("#endif encountered without corresponding #ifdef");
					}
					break;
				case STATE_TRUE_CONDITION:
					if (elze || elseif) {
						state = STATE_POST_TRUE_CONDITION;
						break;
					} else if (endif) {
						state = STATE_OUTSIDE_CONDITION;
						break;
					} else if (ifdef) {
						throw new BuildException("illegal nested #ifdef");
					}
				case STATE_FALSE_CONDITION:
					if (elseif) {
						String condition = line.substring(ELSE_IF_MATCHER.start(), ELSE_IF_MATCHER.end());
						String[] strings = condition.split("\\s+");
						activeSymbol = strings[1].trim();
						if (fSymbols.contains(activeSymbol)) {
							state = STATE_TRUE_CONDITION;
						} else {
							state = STATE_FALSE_CONDITION;
						}
					} else if (elze) {
						state = STATE_TRUE_CONDITION;
						break;
					} else if (endif) {
						state = STATE_OUTSIDE_CONDITION;
						break;
					} else if (ifdef) {
						throw new BuildException("illegal nested #ifdef");
					}
				case STATE_POST_TRUE_CONDITION:
					if (endif) {
						state = STATE_OUTSIDE_CONDITION;
						break;
					} else if (ifdef) {
						throw new BuildException("illegal nested #ifdef");
					}
				}
				if (!commandLine) {
					if (state == STATE_OUTSIDE_CONDITION || state == STATE_TRUE_CONDITION) {
						if (state == STATE_TRUE_CONDITION) {
							line = line.replaceFirst("^(\t*)//#", "$1");
						}
						buffer.append(line);
						buffer.append("\n");
						written = true;
					}
				}
				changed = changed || !written;
				line = reader.readLine();
			}
			if (!changed) {
				return null;
			}
			return buffer.toString();
		} catch (IOException e) {
			throw new BuildException(e);
		}
	}

	public static void main(String[] args) {
		PreProcessor processor = new PreProcessor();
		processor.setSymbols("ex2");
		String string = processor.preProcessFile(new File(
				"c:\\eclipse3.1\\dev\\example.debug.core\\src\\example\\debug\\core\\launcher\\PDALaunchDelegate.java"));
		//String string = processor.preProcessFile(new File("c:\\eclipse3.1\\dev\\example.debug.core\\plugin.xml"), null);
		System.out.println(string);
	}
}