/*
    * Copyright (C) 2020-2023 Dipl.-Inform. Kai Hofmann. All rights reserved!
    */
   package de.powerstat.validation.values;
   
   
   import java.io.IOException;
   import java.net.InetAddress;
   import java.net.UnknownHostException;
  import java.util.Objects;
  import java.util.regex.Pattern;
  
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.Logger;
  
  import de.powerstat.validation.generated.GeneratedTlds;
  import de.powerstat.validation.interfaces.IValueObject;
  
  
  /**
   * Hostname.
   *
   * Probably DSGVO relevant.
   *
   * TODO Verify TopLevelDomain
   * TODO ping ok?
   */
  public final class Hostname implements Comparable<Hostname>, IValueObject
   {
    /**
     * Logger.
     */
    private static final Logger LOGGER = LogManager.getLogger(Hostname.class);
  
    /* *
     * Cache for singletons.
     */
    // private static final Map<String, Hostname> CACHE = new WeakHashMap<>();
  
    /**
     * Hostname regexp.
     */
    private static final Pattern HOSTNAME_REGEXP = Pattern.compile("^[.0-9a-zA-Z-]+$"); //$NON-NLS-1$
  
    /**
     * Escaped dot.
     */
    private static final String ESC_DOT = "\\."; //$NON-NLS-1$
  
    /**
     * Hostname by dots regexp.
     */
    private static final Pattern HOSTNAME_BY_DOTS = Pattern.compile(Hostname.ESC_DOT);
  
    /**
     * Hostname.
     */
    private final String hostname;
  
    /**
     * Reverse hostname.
     */
    @SuppressWarnings("PMD.AvoidFieldNameMatchingMethodName")
    private final String reverseHostname;
  
  
    /**
     * Constructor.
     *
     * @param hostname Hostname
     * @throws NullPointerException if hostname is null
     * @throws IllegalArgumentException if hostname is not a hostname
     */
    private Hostname(final String hostname)
     {
      super();
      Objects.requireNonNull(hostname, "hostname"); //$NON-NLS-1$
      if ((hostname.length() < 2) || (hostname.length() > 253))
       {
        throw new IllegalArgumentException("To short or long for a hostname"); //$NON-NLS-1$
       }
      var tempHostname = ""; //$NON-NLS-1$
      try
       {
        tempHostname = IPV4Address.of(hostname).stringValue();
       }
      catch (final IllegalArgumentException ignored)
       {
        // LOGGER.debug("IllegalArgumentException", ignored);
       }
      try
       {
        if (tempHostname.isEmpty())
         {
          tempHostname = IPV6Address.of(hostname).stringValue();
         }
       }
      catch (final IllegalArgumentException ignored)
       {
       // LOGGER.debug("IllegalArgumentException", ignored);
      }
     if (tempHostname.isEmpty())
      {
       tempHostname = checkHostname(hostname);
       this.reverseHostname = reverseHostname(tempHostname);
      }
     else
      {
       this.reverseHostname = tempHostname;
      }
     this.hostname = tempHostname;
    }
 
 
   /**
    * Check hostname.
    *
    * @param hostname Hostname
    * @return Hostname
    */
   private static String checkHostname(final String hostname)
    {
     if (!Hostname.HOSTNAME_REGEXP.matcher(hostname).matches())
      {
       throw new IllegalArgumentException("Hostname contains illegal character"); //$NON-NLS-1$
      }
     final String[] parts = HOSTNAME_BY_DOTS.split(hostname, 0);
     // final String[] parts = hostname.split(Hostname.ESC_DOT);
     if (parts.length < 2)
      {
       throw new IllegalArgumentException("Hostname must be at a minimum consist of subdomain.topleveldomain"); //$NON-NLS-1$
      }
     for (final String part : parts)
      {
       if (part.isEmpty() || (part.length() > 63))
        {
         throw new IllegalArgumentException("Hostname part empty or to long"); //$NON-NLS-1$
        }
       if ((part.charAt(0) == '-') || (part.charAt(part.length() - 1) == '-'))
        {
         throw new IllegalArgumentException("Illegal character '-' at name start or end"); //$NON-NLS-1$
        }
      }
     if (!GeneratedTlds.contains(parts[parts.length - 1]))
      {
       throw new IllegalArgumentException("Unknown top level domain in hostname"); //$NON-NLS-1$
      }
     return hostname;
    }
 
 
   /**
    * Reverse hostname.
    *
    * @param hostname Hostname
    * @return Reversed hostname.
    */
   private static String reverseHostname(final String hostname)
    {
     final String[] parts = HOSTNAME_BY_DOTS.split(hostname, 0);
     // final String[] parts = hostname.split(Hostname.ESC_DOT);
     final var buffer = new StringBuilder(hostname.length());
     for (int i = parts.length - 1; i >= 0; --i)
      {
       if (buffer.length() != 0)
        {
         buffer.append('.');
        }
       buffer.append(parts[i]);
      }
     return buffer.toString();
    }
 
 
   /**
    * Hostname factory.
    *
    * @param hostname Hostname
    * @return Hostname object
    */
   public static Hostname of(final String hostname)
    {
     /*
     synchronized (Hostname.class)
      {
       Hostname obj = Hostname.CACHE.get(hostname);
       if (obj != null)
        {
         return obj;
        }
       obj = new Hostname(hostname);
       Hostname.CACHE.put(hostname, obj);
       return obj;
      }
     */
     return new Hostname(hostname);
    }
 
 
   /**
    * Returns the value of this Hostname as a string.
    *
    * @return The text value represented by this object after conversion to type string.
    */
   @Override
   public String stringValue()
    {
     return this.hostname;
    }
 
 
   /**
    * Get reverse hostname string.
    *
    * @return Reverse hostname string
    */
   public String getReverseHostname()
    {
     return this.reverseHostname;
    }
 
 
   /**
    * Exist hostname.
    *
    * @return true if hostname was found, false otherwise
    */
   public boolean exist()
    {
     try
      {
       /* final InetAddress address = */ InetAddress.getByName(this.hostname);
      }
     catch (final UnknownHostException ignored)
      {
       // LOGGER.debug("UnknownHostException", ignored);
       return false;
      }
     return true;
    }
 
 
   /**
    * Is hostname reachable.
    *
    * @param timeout Timeout in milliseconds.
    * @return true: Hostname is reachable; false otherwise
    */
   public boolean isReachable(final int timeout)
    {
     try
      {
       final var address = InetAddress.getByName(this.hostname);
       return address.isReachable(timeout);
      }
     catch (final IOException ignored)
      {
       // LOGGER.debug("IOException", ignored);
       return false;
      }
    }
 
 
   /**
    * Calculate hash code.
    *
    * @return Hash
    * @see java.lang.Object#hashCode()
    */
   @Override
   public int hashCode()
    {
     return this.hostname.hashCode();
    }
 
 
   /**
    * Is equal with another object.
    *
    * @param obj Object
    * @return true when equal, false otherwise
    * @see java.lang.Object#equals(java.lang.Object)
    */
   @Override
   public boolean equals(final Object obj)
    {
     if (this == obj)
      {
       return true;
      }
     if (!(obj instanceof Hostname))
      {
       return false;
      }
     final Hostname other = (Hostname)obj;
     return this.hostname.equals(other.hostname);
    }
 
 
   /**
    * Returns the string representation of this Hostname.
    *
    * The exact details of this representation are unspecified and subject to change, but the following may be regarded as typical:
    *
    * "Hostname[hostname=192.168.0.0]"
    *
    * @return String representation of this Hostname
    * @see java.lang.Object#toString()
    */
   @Override
   public String toString()
    {
     final var builder = new StringBuilder(19);
     builder.append("Hostname[hostname=").append(this.hostname).append(']'); //$NON-NLS-1$
     return builder.toString();
    }
 
 
   /**
    * Compare with another object.
    *
    * @param obj Object to compare with
    * @return 0: equal; 1: greater; -1: smaller
    * @see java.lang.Comparable#compareTo(java.lang.Object)
    */
   @Override
   public int compareTo(final Hostname obj)
    {
     Objects.requireNonNull(obj, "obj"); //$NON-NLS-1$
     return this.hostname.compareTo(obj.hostname);
    }
 
  }