package geniusweb.profilesserver;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.net.URISyntaxException;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.LinkedList;
import java.util.List;
import java.util.logging.Level;

import geniusweb.issuevalue.Domain;
import geniusweb.profile.Profile;
import tudelft.utilities.files.FileInfo;
import tudelft.utilities.files.FileWatcher;
import tudelft.utilities.immutablelist.Tuple;
import tudelft.utilities.listener.Listenable;
import tudelft.utilities.listener.Listener;
import tudelft.utilities.logging.Reporter;

/**
 * As {@link DefaultProfilesFactory}, but auto synchronizes the contents of the
 * factory according to changes in the filesystem. Domain and profile contents
 * should match their directoryname/filename. A directory can only contain files
 * for the domain with the same name as the directoryname.
 * 
 * This factory tries to use the value in the environment variable
 * "PROFILES_ROOT" as base dir for the available profiles. If it does not exist,
 * it assumes "repo" in the current working directory. It is assumed ot contain
 * a directory for each domain, with the name of the directory matching the
 * {@link Domain#getName()}. We recomend to set an absolute path to
 * PROFILES_ROOT to avoid problems if something changes the working directory.
 * <p>
 * Thread safe. It is heavily synchronized to ensure thread safety. It does not
 * manipulate the filesystem to avoid collisions between trackers and updaters.
 * <p>
 * Tech note: This is not a singleton because we need to override functions for
 * testing purposes.
 */
public class AutoUpdatingProfilesFactory extends DefaultProfilesFactory {

	private static final String PROFILES_ROOTDIR = "PROFILES_ROOTDIR";
	private static final String DOMAINSREPO = "domainsrepo";
	private static final String JSON = ".json";
	private final Listenable<Tuple<FileInfo, FileInfo>> watcher;
	private Path rootdir;
	private final Reporter log;

	public AutoUpdatingProfilesFactory(Reporter logger) {
		this.log = logger;
		this.rootdir = getRootDir();

		watcher = getFileWatcher(rootdir.toFile());
		watcher.addListener(new Listener<Tuple<FileInfo, FileInfo>>() {
			@Override
			public void notifyChange(Tuple<FileInfo, FileInfo> info) {
				update(info);
			}
		});
		// manually trigger the first event.
		update(new Tuple<FileInfo, FileInfo>(null,
				new FileInfo(rootdir.toFile(), 2)));
	}

	@Override
	public synchronized void putProfile(Profile profile) throws IOException {
		if (!available.containsKey(profile.getDomain())) {
			throw new IOException("profile's domain does not exist");
		}
		String domainname = profile.getDomain().getName();
		String profilename = profile.getName();
		if (!profilename.matches("[a-zA-Z0-9-]+"))
			throw new IOException("illegal profile name " + profilename
					+ ", only letters, numbers and - allowed");
		File file = Paths
				.get(rootdir.toString(), domainname, profilename + JSON)
				.toFile();
		if (file.exists()) {
			String msg = fileCheck(file, false, true);
			if (msg != null)
				throw new IOException(msg);
		}

		// CHECK utf-8 compatibility? Do we need that anyway?
		try (Writer out = new FileWriter(file, false)) {
			out.write(Jackson.instance().writeValueAsString(profile));
		}
		// trigger the update immediately, avoid wait for FileChecker.
		super.add(profile);

	}

	/**
	 * Called when some file that may be relevant has changed. Synchronized to
	 * avoid weird states if filesystem changes rapidly.
	 */
	private synchronized void update(Tuple<FileInfo, FileInfo> info) {
		log.log(Level.INFO, "change: " + info);
		File oldfile = info.get1() == null ? null : info.get1().getFile();
		File newfile = info.get2() == null ? null : info.get2().getFile();

		File file = oldfile != null ? oldfile : newfile;
		Path relpath = file.toPath().relativize(rootdir);
		// workaround: root gives "" with depth 1 instead of 0.
		int depth = relpath.toString().isEmpty() ? 0 : relpath.getNameCount();

		switch (depth) {
		case 0:
			// root changed! Update ALL directories we saw and see.
			reset();
			break;
		case 1: // change of directory name?
			if (newfile != null) {
				if (newfile.isDirectory()) {
					updateDomainDirectory(newfile);
				} else {
					log.log(Level.INFO, "expected directory but found file: "
							+ newfile.getAbsolutePath());
				}
			} else {
				// new file is null. Removed
				remove(getDomain(oldfile.getName()));
			}
			break;
		case 2: // A file changed, added or removed inside profile directory
			if (newfile != null) {
				// file was added.
				if (newfile.isDirectory()) {
					log.log(Level.INFO,
							"expected file but found directory: " + file);
				}
				updateDomainDirectory(newfile.getParentFile());
			} else {
				// Some file was removed. Check entire directory again
				updateDomainDirectory(oldfile.getParentFile());
			}
			break;
		default:
			log.log(Level.WARNING, "Ignoring unexpected event at " + info);
		}

	}

	/**
	 * Remove all domains and reload them all from scratch
	 */
	private void reset() {
		// first remove all old stuff. Copy domains as we're going to modify.
		for (Domain domain : new LinkedList<>(available.keySet())) {
			remove(domain);
		}
		if (!basicFileCheck(rootdir.toFile(), true))
			return;
		for (File dir : rootdir.toFile().listFiles()) {
			if (!dir.isDirectory())
				continue;
			updateDomainDirectory(dir);
		}
	}

	/**
	 * A domain directory was added or updated (not deleted). Scan the contents
	 * and compare/update the repo.
	 * 
	 * @param dir the directory that could contain domain specific files -
	 *            domain description and profiles.
	 */
	private void updateDomainDirectory(File dir) {
		if (!basicFileCheck(dir, true)) {
			remove(getDomain(dir.getName()));
			return;
		}
		// if we get here, dir is indeed a directory and we can read contents.
		File domainfile = domainFile(dir.getName());
		Domain newdomain = deserializeDomain(domainfile);
		Domain olddomain = getDomain(dir.getName());
		if (olddomain != null && !olddomain.equals(newdomain)) {
			remove(olddomain); // also removes old profiles.
		}

		if (newdomain == null) {
			return;
		}
		add(newdomain);
		updateProfiles(newdomain);
	}

	/**
	 * Update all profiles in given directory
	 * 
	 * @param dir
	 */
	private void updateProfiles(Domain domain) {
		final Path domaindir = rootdir.resolve(domain.getName());
		final File domainfile = domainFile(domain.getName());
		final List<Profile> newprofiles = new LinkedList<>();
		for (File file : domaindir.toFile().listFiles()) {
			if (file.equals(domainfile))
				continue;
			Profile newprofile = deserializeProfile(file);
			if (newprofile == null)
				continue;
			if (!newprofile.getDomain().equals(domain)) {
				log.log(Level.WARNING,
						"Profile " + file + " contains incorrect domain "
								+ newprofile.getDomain());
				continue;
			}
			if (!newprofile.getName()
					.equals(withoutExtension(file.getName()))) {
				log.log(Level.WARNING, "Profile " + file
						+ " contains incorrect name " + newprofile.getName());
				continue;
			}
			newprofiles.add(newprofile);
		}
		// remove profiles not on the filesystem anymore/have errors
		for (Profile profile : getProfiles(domain.getName())) {
			if (!newprofiles.contains(profile)) {
				remove(profile);
			}
		}
		// (re)add currently existing profiles.
		for (Profile profile : newprofiles) {
			add(profile);
		}
	}

	/**
	 * Reads profile and also checks that this profile is in the correct
	 * directory (the domain should match the registered domain for this
	 * directory). The domain for this directory MUST have been registered.
	 * 
	 * @param profilefiile the profile file to read. Should contain a
	 *                     {@link Profile}.
	 * @return profile, or null if failed to read. If failed, we log the
	 *         details.
	 */

	private Profile deserializeProfile(File profilefile) {
		if (!basicFileCheck(profilefile, false))
			return null;
		Profile profile = null;
		try {
			profile = Jackson.instance().readValue(profilefile, Profile.class);
		} catch (IOException e) {
			log.log(Level.WARNING, "File " + profilefile
					+ " does not appear to contain a profile", e);
			return null;
		}
		Domain expectedDomain = getDomain(
				profilefile.getParentFile().getName());
		if (!profile.getDomain().equals(expectedDomain)) {
			log.log(Level.WARNING, "Profile has incorrect domain: expected "
					+ expectedDomain + " but found " + profile.getDomain());
			return null;

		}
		return profile;
	}

	/**
	 * Try to deserialize a domain file in given directory.
	 * 
	 * @param dir the directory where we expect a domain file
	 * @return deserialized domain file, or null if deserialization fails (eg no
	 *         such file, or wrong contents, domain has name not matching the
	 *         actual file). If fails, a warning is logged with details.
	 * 
	 * 
	 */
	private Domain deserializeDomain(File domainfile) {
		if (!basicFileCheck(domainfile, false))
			return null;
		Domain domain = null;
		String expectedName = withoutExtension(domainfile.getName());
		try {
			domain = Jackson.instance().readValue(domainfile, Domain.class);
		} catch (IOException e) {
			log.log(Level.WARNING, "File " + domainfile
					+ " does not appear to contain a Domain", e);
			return null;
		}
		if (!expectedName.equals(domain.getName())) {
			log.log(Level.WARNING,
					"domain file " + domainfile + " contains name:'"
							+ domain.getName()
							+ "' which does not match the required name "
							+ expectedName);
			return null;
		}
		return domain;

	}

	/**
	 * Silent check and report basic problems with a file. Silent in the sense
	 * that errors are logged but cause no exception.
	 * 
	 * @param file              the file to check
	 * @param shouldbeDirectory true if the file should be a directory
	 * @return false iff basic checks on the file fails.
	 * 
	 */
	private boolean basicFileCheck(File file, boolean shouldbeDirectory) {
		String msg = fileCheck(file, shouldbeDirectory, false);
		if (msg != null) {
			log.log(Level.WARNING, msg);
			return false;
		}
		return true;
	}

	/**
	 * 
	 * @param file              the file to check
	 * @param shouldbeDirectory true if expected a directory
	 * @param shouldbeWritable  true if expected to be writable
	 * @return null if file is there, is file/directory, allows reading and
	 *         allows writing (if specified).
	 */
	private String fileCheck(File file, boolean shouldbeDirectory,
			boolean shouldbeWritable) {
		if (!file.exists()) {
			return file + " is missing";
		}
		if (!file.canRead()) {
			return "directory " + file + "does not allow reading ";
		}
		if (shouldbeDirectory) {
			if (!file.isDirectory()) {
				return file + " is not a directory";
			}
		} else {
			if (!file.isFile()) {
				return file + " is not a file";
			}
		}
		if (shouldbeWritable && !file.canWrite()) {
			return file + "is read-only";
		}
		return null;

	}

	private String withoutExtension(String name) {
		if (!name.contains("."))
			return name;
		return name.substring(0, name.indexOf("."));
	}

	/**
	 * @param directory a directory that might contain a domain file.
	 * @return the file that contains the domain description in the given
	 *         directory.
	 * 
	 */
	private File domainFile(String domainname) {
		return Paths.get(rootdir.toString(), domainname, domainname + JSON)
				.toFile();
	}

	/**
	 * Factory method that gives a watcher for file changes. See
	 * {@link FileWatcher}.
	 * 
	 * @param file
	 * @return a class that watches for file changes below the given file.
	 */
	protected Listenable<Tuple<FileInfo, FileInfo>> getFileWatcher(File file) {
		return new FileWatcher(file, 3000, 2);
	}

	/**
	 * Search from location of this class upwards till we find a directory
	 * called "domainsrepo".
	 * 
	 * @return the root dir of the repo. This is the 'database' where all known
	 *         profiles are stored.
	 * @throws URISyntaxException
	 */
	protected Path getRootDir() {
		// If you run this normal from tomcat we are somewhere inside
		// projectroot/WEB_INF/classes/....
		// Search back upwards to projectroot.
		Path dir;
		String path = System.getenv(PROFILES_ROOTDIR);
		if (path != null) {
			dir = Paths.get(path);
			if (!dir.toFile().exists())
				throw new RuntimeException("Hard set path PROFILES_ROOTDIR='"
						+ PROFILES_ROOTDIR + "' does not exist ");
			return dir;
		}
		try {
			dir = Paths.get(getClass().getProtectionDomain().getCodeSource()
					.getLocation().toURI()).getParent();
		} catch (URISyntaxException e) {
			throw new RuntimeException("Problem with path URI", e);
		}
		System.out.println("searching from " + dir);
		while (dir.getNameCount() > 1) {
			Path repo = dir.resolve(DOMAINSREPO);
			if (repo.toFile().exists())
				return repo;
			System.out.println("Directory did not contain repo:" + dir);
			dir = dir.getParent();
		}
		throw new RuntimeException("Path to " + DOMAINSREPO + " was not found");
	}

}