/*
 * Copyright (c) 2011-2017 Contributors to the Eclipse Foundation
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
 * which is available at https://www.apache.org/licenses/LICENSE-2.0.
 *
 * SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
 */

package io.vertx.core.impl.launcher.commands;

import io.vertx.core.Handler;
import io.vertx.core.logging.Logger;
import io.vertx.core.logging.LoggerFactory;

import java.io.File;
import java.nio.file.WatchService;
import java.util.*;
import java.util.stream.Collectors;

A file alteration monitor based on a home made file system scan and watching files matching a set of includes patterns. These patterns are Ant patterns (can use **, * or ?). This class takes 2 Handler as parameter and orchestrate the redeployment method when a matching file is modified (created, updated or deleted). Users have the possibility to execute a shell command during the redeployment. On a file change, the undeploy Handler is called, followed by the execution of the user command. Then the deploy Handler is invoked. 

The watcher watches all files from the current directory and sub-directories.
Author:
Clement Escoffier /**
 * A file alteration monitor based on a home made file system scan and watching files matching a set of includes
 * patterns. These patterns are Ant patterns (can use {@literal **, * or ?}). This class takes 2 {@link Handler} as
 * parameter and orchestrate the redeployment method when a matching file is modified (created, updated or deleted).
 * Users have the possibility to execute a shell command during the redeployment. On a file change, the {@code undeploy}
 * {@link Handler} is called, followed by the execution of the user command. Then the {@code deploy} {@link Handler}
 * is invoked.
 * <p/>
 * The watcher watches all files from the current directory and sub-directories.
 *
 * @author Clement Escoffier <clement@apache.org>
 */
public class Watcher implements Runnable {

  private final static Logger LOGGER = LoggerFactory.getLogger(Watcher.class);

  private final long gracePeriod;
  private final Map<File, Map<File, FileInfo>> fileMap = new LinkedHashMap<>();
  private final Set<File> filesToWatch = new HashSet<>();
  private final long scanPeriod;
  private final List<File> roots;
  private final File cwd;

  
This field is always access from the scan thread. No need to be volatile.
/**
   * This field is always access from the scan thread. No need to be volatile.
   */
  private long lastChange = -1;

  private final List<String> includes;
  private final Handler<Handler<Void>> deploy;
  private final Handler<Handler<Void>> undeploy;
  private final String cmd;

  private volatile boolean closed;

  
Creates a new Watcher. 
Params:
root –              the root directory
includes –  the list of include patterns, should not be null or empty
deploy –            the function called when deployment is required
undeploy –          the function called when un-deployment is required
onRedeployCommand – an optional command executed after the un-deployment and before the deployment
gracePeriod –       the amount of time in milliseconds to wait between two redeploy even
                         if there are changes
scanPeriod –        the time in millisecond between 2 file system scans/**
   * Creates a new {@link Watcher}.
   *
   * @param root              the root directory
   * @param includes          the list of include patterns, should not be {@code null} or empty
   * @param deploy            the function called when deployment is required
   * @param undeploy          the function called when un-deployment is required
   * @param onRedeployCommand an optional command executed after the un-deployment and before the deployment
   * @param gracePeriod       the amount of time in milliseconds to wait between two redeploy even
   *                          if there are changes
   * @param scanPeriod        the time in millisecond between 2 file system scans
   */
  public Watcher(File root, List<String> includes, Handler<Handler<Void>> deploy, Handler<Handler<Void>> undeploy,
                 String onRedeployCommand, long gracePeriod, long scanPeriod) {
    this.gracePeriod = gracePeriod;
    this.includes = sanitizeIncludePatterns(includes);
    this.roots = extractRoots(root, this.includes);
    this.cwd = root;
    LOGGER.info("Watched paths: " + this.roots);
    this.deploy = deploy;
    this.undeploy = undeploy;
    this.cmd = onRedeployCommand;
    this.scanPeriod = scanPeriod;
    addFilesToWatchedList(roots);
  }

  static List<File> extractRoots(File root, List<String> includes) {
    return includes.stream().map(s -> {
      if (s.startsWith("*")) {
        return root.getAbsolutePath();
      }
      if (s.contains("*")) {
        s = s.substring(0, s.indexOf("*"));
      }
      File file = new File(s);
      if (file.isAbsolute()) {
        return file.getAbsolutePath();
      } else {
        return new File(root, s).getAbsolutePath();
      }
    }).collect(Collectors.toSet()).stream().map(File::new).collect(Collectors.toList());
  }

  private List<String> sanitizeIncludePatterns(List<String> includes) {
    return includes.stream().map(p -> {
      if (ExecUtils.isWindows()) {
        return p.replace('/', File.separatorChar);
      }
      return p.replace('\\', File.separatorChar);
    }).collect(Collectors.toList());
  }

  private void addFilesToWatchedList(List<File> roots) {
    roots.forEach(this::addFileToWatchedList);
  }

  private void addFileToWatchedList(File file) {
    filesToWatch.add(file);
    Map<File, FileInfo> map = new HashMap<>();
    if (file.isDirectory()) {
      // We're watching a directory contents and its children for changes
      File[] children = file.listFiles();
      if (children != null) {
        for (File child : children) {
          map.put(child, new FileInfo(child.lastModified(), child.length()));
          if (child.isDirectory()) {
            addFileToWatchedList(child);
          }
        }
      }
    } else {
      // Not a directory - we're watching a specific file - e.g. a jar
      map.put(file, new FileInfo(file.lastModified(), file.length()));
    }
    fileMap.put(file, map);
  }

  
Checks whether or not a change has occurred in one of the watched file that match one of the given include pattern . Are detected: new files, modified file and deleted files. File modification is detected using File.lastModified(), so the behavior depends on the file system precision. 
Returns:
true if a change occurred requiring the redeployment./**
   * Checks whether or not a change has occurred in one of the watched file that match one of the given include pattern
   * . Are detected: new files, modified file and deleted files. File modification is detected using
   * {@link File#lastModified()}, so the behavior depends on the file system precision.
   *
   * @return {@code true} if a change occurred requiring the redeployment.
   */
  private boolean changesHaveOccurred() {
    boolean changed = false;
    for (File toWatch : new HashSet<>(filesToWatch)) {

      // The new files in the directory
      Map<File, File> newFiles = new LinkedHashMap<>();
      if (toWatch.isDirectory()) {
        File[] files = toWatch.exists() ? toWatch.listFiles() : new File[]{};

        if (files == null) {
          // something really bad happened to the file system.
          throw new IllegalStateException("Cannot scan the file system to detect file changes");
        }

        for (File file : files) {
          newFiles.put(file, file);
        }
      } else {
        newFiles.put(toWatch, toWatch);
      }

      // Lookup the old list for that file/directory
      Map<File, FileInfo> currentFileMap = fileMap.get(toWatch);
      for (Map.Entry<File, FileInfo> currentEntry : new HashMap<>(currentFileMap).entrySet()) {
        File currFile = currentEntry.getKey();
        FileInfo currInfo = currentEntry.getValue();
        File newFile = newFiles.get(currFile);
        if (newFile == null) {
          // File has been deleted
          currentFileMap.remove(currFile);
          if (currentFileMap.isEmpty()) {
            fileMap.remove(toWatch);
            filesToWatch.remove(toWatch);
          }
          LOGGER.trace("File: " + currFile + " has been deleted");
          if (match(currFile)) {
            changed = true;
          }
        } else if (newFile.lastModified() != currInfo.lastModified || newFile.length() != currInfo.length) {
          // File has been modified
          currentFileMap.put(newFile, new FileInfo(newFile.lastModified(), newFile.length()));
          LOGGER.trace("File: " + currFile + " has been modified");
          if (match(currFile)) {
            changed = true;
          }
        }
      }

      // Now process any added files
      for (File newFile : newFiles.keySet()) {
        if (!currentFileMap.containsKey(newFile)) {
          // Add new file
          currentFileMap.put(newFile, new FileInfo(newFile.lastModified(), newFile.length()));
          if (newFile.isDirectory()) {
            addFileToWatchedList(newFile);
          }
          LOGGER.trace("File was added: " + newFile);
          if (match(newFile)) {
            changed = true;
          }
        }
      }
    }

    long now = System.currentTimeMillis();
    if (changed) {
      lastChange = now;
    }

    if (lastChange != -1 && now - lastChange >= gracePeriod) {
      lastChange = -1;
      return true;
    }

    return false;
  }


  
Checks whether the given file matches one of the includes patterns. 
Params:
file – the file
Returns:
true if the file matches at least one pattern, false otherwise./**
   * Checks whether the given file matches one of the {@link #includes} patterns.
   *
   * @param file the file
   * @return {@code true} if the file matches at least one pattern, {@code false} otherwise.
   */
  protected boolean match(File file) {
    // Compute relative path.
    String rel = null;
    String relFromCwd = null;
    for (File root : roots) {
      if (file.getAbsolutePath().startsWith(root.getAbsolutePath())) {
        if (file.getAbsolutePath().equals(root.getAbsolutePath())) {
          rel = file.getAbsolutePath();
        } else {
          rel = file.getAbsolutePath().substring(root.getAbsolutePath().length() + 1);
        }
      }
    }
    if (rel == null) {
      LOGGER.warn("A change in " + file.getAbsolutePath() + " has been detected, but the file does not belong to a " +
          "watched roots: " + roots);
      return false;
    }

    if (file.getAbsolutePath().startsWith(cwd.getAbsolutePath())) {
      relFromCwd = file.getAbsolutePath().substring(cwd.getAbsolutePath().length() + 1);
    }

    for (String include : includes) {
      // Windows files are not case sensitive
      // 3 checks: two for the relative file (root and cwd), and one taking the absolute path, for pattern using
      // absolute path
      if ((relFromCwd != null && FileSelector.matchPath(include, relFromCwd, !ExecUtils.isWindows()))
          || FileSelector.matchPath(include, file.getAbsolutePath(), !ExecUtils.isWindows())) {
        return true;
      }
    }
    return false;
  }

  
Starts watching. The watch processing is made in another thread started in this method.
Returns:
the current watcher./**
   * Starts watching. The watch processing is made in another thread started in this method.
   *
   * @return the current watcher.
   */
  public Watcher watch() {
    new Thread(this).start();
    LOGGER.info("Starting the vert.x application in redeploy mode");
    deploy.handle(null);

    return this;
  }

  
Stops watching. This method stops the underlying WatchService. /**
   * Stops watching. This method stops the underlying {@link WatchService}.
   */
  public void close() {
    LOGGER.info("Stopping redeployment");
    // closing the redeployment thread. If waiting, it will shutdown at the next iteration.
    closed = true;
    // Un-deploy application on close.
    undeploy.handle(null);
  }

  
The watching thread runnable method.
/**
   * The watching thread runnable method.
   */
  @Override
  public void run() {
    try {
      while (!closed) {
        if (changesHaveOccurred()) {
          trigger();
        }
        // Wait for the next scan.
        Thread.sleep(scanPeriod);
      }
    } catch (Throwable e) {
      LOGGER.error("An error have been encountered while watching resources - leaving the redeploy mode", e);
      close();
    }
  }

  
Redeployment process.
/**
   * Redeployment process.
   */
  private void trigger() {
    long begin = System.currentTimeMillis();
    LOGGER.info("Redeploying!");
    // 1)
    undeploy.handle(v1 -> {
      // 2)
      executeUserCommand(v2 -> {
        // 3)
        deploy.handle(v3 -> {
          long end = System.currentTimeMillis();
          LOGGER.info("Redeployment done in " + (end - begin) + " ms.");
        });
      });
    });
  }

  private void executeUserCommand(Handler<Void> onCompletion) {
    if (cmd != null) {
      try {
        List<String> command = new ArrayList<>();
        if (ExecUtils.isWindows()) {
          ExecUtils.addArgument(command, "cmd");
          ExecUtils.addArgument(command, "/c");
        } else {
          ExecUtils.addArgument(command, "sh");
          ExecUtils.addArgument(command, "-c");
        }
        // Do not add quote to the given command:
        command.add(cmd);

        final Process process = new ProcessBuilder(command)
            .redirectError(ProcessBuilder.Redirect.INHERIT)
            .redirectOutput(ProcessBuilder.Redirect.INHERIT)
            .start();

        int status = process.waitFor();
        LOGGER.info("User command terminated with status " + status);
      } catch (Throwable e) {
        LOGGER.error("Error while executing the on-redeploy command : '" + cmd + "'", e);
      }
    }
    onCompletion.handle(null);
  }

  private static final class FileInfo {
    long lastModified;
    long length;

    private FileInfo(long lastModified, long length) {
      this.lastModified = lastModified;
      this.length = length;
    }
  }
}