/*
    * This file is part of ***  M y C o R e  ***
    * See http://www.mycore.de/ for details.
    *
    * MyCoRe is free software: you can redistribute it and/or modify
    * it under the terms of the GNU General Public License as published by
    * the Free Software Foundation, either version 3 of the License, or
    * (at your option) any later version.
    *
   * MyCoRe is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with MyCoRe.  If not, see <http://www.gnu.org/licenses/>.
   */
  
  package org.mycore.datamodel.metadata;
  
  import static org.mycore.common.MCRConstants.XLINK_NAMESPACE;
  
  import java.util.Objects;
  
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.Logger;
  import org.apache.xml.utils.XMLChar;
  import org.jdom2.Element;
  import org.mycore.common.MCRException;
  import org.mycore.common.MCRUtils;
  
  import com.google.gson.JsonObject;
  
  /**
   * This class implements all method for generic handling with the MCRMetaLink part of a metadata object.
   * The MCRMetaLink class present two types. At once a reference to an URL.
   * At second a bidirectional link between two URL's. Optional you can append the reference with the label attribute.
   * See to W3C XLink Standard for more informations.
   * <p>
   * &lt;tag class="MCRMetaLink"&gt; <br>
   * &lt;subtag xlink:type="locator" xlink:href=" <em>URL</em>" xlink:label="..." xlink:title="..."/&gt; <br>
   * &lt;subtag xlink:type="arc" xlink:from=" <em>URL</em>" xlink:to="URL"/&gt; <br>
   * &lt;/tag&gt; <br>
   * 
   * @author Jens Kupferschmidt
   */
  public class MCRMetaLink extends MCRMetaDefault {
      // MetaLink data
      protected String href;
  
      protected String label;
  
      protected String title;
  
      protected String linktype;
  
      protected String role;
  
      protected String from;
  
      protected String to;
  
      private static final Logger LOGGER = LogManager.getLogger();
  
      /**
       * initializes with empty values.
       */
      public MCRMetaLink() {
          super();
      }
  
      /**
       * This is the constructor. <br>
       * The language element was set. If the value of <em>default_lang</em> is null, empty or false <b>en </b> was set.
       * The subtag element was set to the value of <em>subtag</em>.
       * If the value of <em>subtag</em> is null or empty an exception was throwed.
       * @param subtag
       *            the name of the subtag
       * @param inherted
       *            a value &gt;= 0
       * @exception MCRException
       *                if the set_datapart or subtag value is null or empty
       */
      public MCRMetaLink(String subtag, int inherted) throws MCRException {
          super(subtag, null, null, inherted);
      }
  
      /**
       * This method set a reference with xlink:href, xlink:label and xlink:title.
       * 
       * @param href
       *            the reference
       * @param label
       *            the new label string
       * @param title
       *            the new title string
       * @exception MCRException
       *                if the href value is null or empty
       */
     public void setReference(String href, String label, String title) throws MCRException {
         linktype = "locator";
 
         this.href = MCRUtils.filterTrimmedNotEmpty(href)
             .orElseThrow(() -> new MCRException("The href value is null or empty."));
         setXLinkLabel(label);
         this.title = title;
     }
 
     /**
      * This method set a bidirectional link with xlink:from, xlink:to and xlink:title.
      * 
      * @param from
      *            the source
      * @param to
      *            the target
      * @param title
      *            the new title string
      * @exception MCRException
      *                if the from or to element is null or empty
      */
     public void setBiLink(String from, String to, String title) throws MCRException {
         this.from = MCRUtils.filterTrimmedNotEmpty(from)
             .orElseThrow(() -> new MCRException("The from value is null or empty."));
         this.to = MCRUtils.filterTrimmedNotEmpty(to)
             .orElseThrow(() -> new MCRException("The to value is null or empty."));
         linktype = "arc";
         this.title = title;
     }
 
     /**
      * This method get the xlink:type element.
      * 
      * @return the xlink:type
      */
     public final String getXLinkType() {
         return linktype;
     }
 
     /**
      * This method get the xlink:href element as string.
      * 
      * @return the xlink:href element as string
      */
     public final String getXLinkHref() {
         return href;
     }
 
     /**
      * This method get the xlink:label element.
      * 
      * @return the xlink:label
      */
     public final String getXLinkLabel() {
         return label;
     }
 
     /**
      * This method set the xlink:label
      * 
      * @param label
      *            the xlink:label
      */
     public final void setXLinkLabel(String label) {
         if (label != null && !XMLChar.isValidNCName(label)) {
             throw new MCRException("xlink:label is not a valid NCName: " + label);
         }
         this.label = label;
     }
 
     /**
      * This method get the xlink:title element.
      * 
      * @return the xlink:title
      */
     public final String getXLinkTitle() {
         return title;
     }
 
     /**
      * This method set the xlink:title
      * 
      * @param title
      *            the xlink:title
      */
     public final void setXLinkTitle(String title) {
         this.title = title;
     }
 
     /**
      * This method get the xlink:from element as string.
      * 
      * @return the xlink:from element as string
      */
     public final String getXLinkFrom() {
         return from;
     }
 
     /**
      * This method get the xlink:to element as string.
      * 
      * @return the xlink:to element as string
      */
     public final String getXLinkTo() {
         return to;
     }
 
     /**
      * This method sets the xlink:role.
      * 
      */
     public void setXLinkRole(String role) {
         this.role = role;
     }
 
     /**
      * This method get the xlink:role element as string.
      * 
      */
     public String getXLinkRole() {
         return role;
     }
 
     /**
      * The method compare this instance of MCRMetaLink with a input object of the class type MCRMetaLink.
      * The both instances are equal, if: <br>
      * <ul>
      * <li>for the type 'arc' the 'from' and 'to' element is equal</li>
      * <li>for the type 'locator' the 'href' element is equal</li>
      * </ul>
      * <br>
      * 
      * @param input
      *            the MCRMetaLink input
      * @return true if it is compare, else return false
      */
     public final boolean compare(MCRMetaLink input) {
         if (linktype.equals("locator")) {
             if (linktype.equals(input.getXLinkType()) && href.equals(input.getXLinkHref())) {
                 return true;
             }
         }
 
         if (linktype.equals("arc")) {
             return linktype.equals(input.getXLinkType()) && from.equals(input.getXLinkFrom())
                 && to.equals(input.getXLinkTo());
         }
 
         return false;
     }
 
     @Override
     public int hashCode() {
         return Objects.hash(super.hashCode(), from, href, label, linktype, role, title, to);
     }
 
     @Override
     public boolean equals(Object obj) {
         if (!super.equals(obj)) {
             return false;
         }
         MCRMetaLink other = (MCRMetaLink) obj;
         if (!Objects.equals(from, other.from)) {
             return false;
         } else if (!Objects.equals(href, other.href)) {
             return false;
         } else if (!Objects.equals(label, other.label)) {
             return false;
         } else if (!Objects.equals(linktype, other.linktype)) {
             return false;
         } else if (!Objects.equals(role, other.role)) {
             return false;
         } else if (!Objects.equals(title, other.title)) {
             return false;
         } else {
             return Objects.equals(to, other.to);
         }
     }
 
     /**
      * This method read the XML input stream part from a DOM part for the metadata of the document.
      * 
      * @param element
      *            a relevant DOM element for the metadata
      * @exception MCRException
      *                if the xlink:type is not locator or arc or if href or from and to are null or empty
      */
     @Override
     public void setFromDOM(Element element) throws MCRException {
         super.setFromDOM(element);
 
         String temp = element.getAttributeValue("type", XLINK_NAMESPACE);
 
         if (temp != null && (temp.equals("locator") || temp.equals("arc"))) {
             linktype = temp;
         } else {
             throw new MCRException("The xlink:type is not locator or arc.");
         }
 
         if (linktype.equals("locator")) {
             String temp1 = element.getAttributeValue("href", XLINK_NAMESPACE);
             String temp2 = element.getAttributeValue("label", XLINK_NAMESPACE);
             String temp3 = element.getAttributeValue("title", XLINK_NAMESPACE);
             setReference(temp1, temp2, temp3);
         } else {
             String temp1 = element.getAttributeValue("from", XLINK_NAMESPACE);
             String temp2 = element.getAttributeValue("to", XLINK_NAMESPACE);
             String temp3 = element.getAttributeValue("title", XLINK_NAMESPACE);
             setBiLink(temp1, temp2, temp3);
         }
 
         setXLinkRole(element.getAttributeValue("role", XLINK_NAMESPACE));
     }
 
     /**
      * This method create a XML stream for all data in this class,
      * defined by the MyCoRe XML MCRMetaLink definition for the given subtag.
      * 
      * @exception MCRException
      *                if the content of this class is not valid
      * @return a JDOM Element with the XML MCRMetaLink part
      */
     @Override
     public Element createXML() throws MCRException {
         Element elm = super.createXML();
         elm.setAttribute("type", linktype, XLINK_NAMESPACE);
 
         if (title != null) {
             elm.setAttribute("title", title, XLINK_NAMESPACE);
         }
 
         if (label != null) {
             elm.setAttribute("label", label, XLINK_NAMESPACE);
         }
 
         if (role != null) {
             elm.setAttribute("role", role, XLINK_NAMESPACE);
         }
 
         if (linktype.equals("locator")) {
             elm.setAttribute("href", href, XLINK_NAMESPACE);
         } else {
             elm.setAttribute("from", from, XLINK_NAMESPACE);
             elm.setAttribute("to", to, XLINK_NAMESPACE);
         }
 
         return elm;
     }
 
     /**
      * Creates the JSON representation. Extends the {@link MCRMetaDefault#createJSON()} method
      * with the following data.
      * 
      * For linktype equals 'locator':
      * <pre>
      *   {
      *     label: "MyCoRe Derivate Image",
      *     title: "MyCoRe Derivate Image",
      *     role: "image_reference",
      *     href: "mycore_derivate_00000001/image.tif"
      *   }
      * </pre>
      * 
      * For all other linktypes (arc):
      * <pre>
      *   {
      *     label: "Link between Issue and Person",
      *     title: "Link between Issue and Person",
      *     role: "link",
      *     from: "mycore_issue_00000001",
      *     to: "mycore_person_00000001"
      *   }
      * </pre>
      */
     @Override
     public JsonObject createJSON() {
         JsonObject obj = super.createJSON();
         if (title != null) {
             obj.addProperty("title", title);
         }
         if (label != null) {
             obj.addProperty("label", label);
         }
         if (role != null) {
             obj.addProperty("role", role);
         }
         if (linktype.equals("locator")) {
             obj.addProperty("href", href);
         } else {
             obj.addProperty("from", from);
             obj.addProperty("to", to);
         }
         return obj;
     }
 
     /**
      * Validates this MCRMetaLink. This method throws an exception if:
      * <ul>
      * <li>the subtag is not null or empty</li>
      * <li>the xlink:type not "locator" or "arc"</li>
      * <li>the from or to are not valid</li>
      * </ul>
      * 
      * @throws MCRException the MCRMetaLink is invalid
      */
     public void validate() throws MCRException {
         super.validate();
         if (label != null && label.length() > 0) {
             if (!XMLChar.isValidNCName(label)) {
                 throw new MCRException(getSubTag() + ": label is no valid NCName:" + label);
             }
         }
         if (linktype == null) {
             throw new MCRException(getSubTag() + ": linktype is null");
         }
         if (!linktype.equals("locator") && !linktype.equals("arc")) {
             throw new MCRException(getSubTag() + ": linktype is unsupported: " + linktype);
         }
         if (linktype.equals("arc")) {
             if (from == null || from.length() == 0) {
                 throw new MCRException(getSubTag() + ": from is null or empty");
             } else if (!XMLChar.isValidNCName(from)) {
                 throw new MCRException(getSubTag() + ": from is no valid NCName:" + from);
             }
 
             if (to == null || to.length() == 0) {
                 throw new MCRException(getSubTag() + ": to is null or empty");
             } else if (!XMLChar.isValidNCName(to)) {
                 throw new MCRException(getSubTag() + ": to is no valid NCName:" + to);
             }
         }
         if (linktype.equals("locator")) {
             if (href == null || href.length() == 0) {
                 throw new MCRException(getSubTag() + ": href is null or empty");
             }
         }
     }
 
     /**
      * clone of this instance
      * 
      * you will get a (deep) clone of this element
      * 
      * @see java.lang.Object#clone()
      */
     @Override
     public MCRMetaLink clone() {
         MCRMetaLink clone = (MCRMetaLink) super.clone();
 
         clone.href = this.href;
         clone.label = this.label;
         clone.title = this.title;
         clone.linktype = this.linktype;
         clone.role = this.role;
         clone.from = this.from;
         clone.to = this.to;
 
         return clone;
     }
 
     /**
      * This method put debug data to the logger (for the debug mode).
      */
     @Override
     public final void debug() {
         if (LOGGER.isDebugEnabled()) {
             super.debugDefault();
             LOGGER.debug("Link Type          = {}", linktype);
             LOGGER.debug("Label              = {}", label);
             LOGGER.debug("Title              = {}", title);
             LOGGER.debug("HREF               = {}", href);
             LOGGER.debug("Role               = {}", role);
             LOGGER.debug("From               = {}", from);
             LOGGER.debug("To                 = {}", to);
             LOGGER.debug("");
         }
     }
 }