///////////////////////////////////////////////////////////////////////////////////////////////
   // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
   // Copyright (C) 2001-2026 the original author or authors.
   //
   // This library is free software; you can redistribute it and/or
   // modify it under the terms of the GNU Lesser General Public
   // License as published by the Free Software Foundation; either
   // version 2.1 of the License, or (at your option) any later version.
   //
  // This library 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
  // Lesser General Public License for more details.
  //
  // You should have received a copy of the GNU Lesser General Public
  // License along with this library; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  ///////////////////////////////////////////////////////////////////////////////////////////////
  
  package com.puppycrawl.tools.checkstyle.checks.javadoc;
  
  import java.util.Set;
  
  import javax.annotation.Nullable;
  
  import com.puppycrawl.tools.checkstyle.StatelessCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailNode;
  import com.puppycrawl.tools.checkstyle.api.JavadocCommentsTokenTypes;
  import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
  import com.puppycrawl.tools.checkstyle.utils.JavadocUtil;
  
  /**
   * <div>
   * Checks the Javadoc paragraph.
   * </div>
   *
   * <p>
   * Checks that:
   * </p>
   * <ul>
   * <li>There is one blank line between each of two paragraphs.</li>
   * <li>Each paragraph but the first has &lt;p&gt; immediately
   * before the first word, with no space after.</li>
   * <li>The outer most paragraph tags should not precede
   * <a href="https://www.w3schools.com/html/html_blocks.asp">HTML block-tag</a>.
   * Nested paragraph tags are allowed to do that. This check only supports following block-tags:
   * &lt;address&gt;,&lt;blockquote&gt;
   * ,&lt;div&gt;,&lt;dl&gt;
   * ,&lt;h1&gt;,&lt;h2&gt;,&lt;h3&gt;,&lt;h4&gt;,&lt;h5&gt;,&lt;h6&gt;,&lt;hr&gt;
   * ,&lt;ol&gt;,&lt;p&gt;,&lt;pre&gt;
   * ,&lt;table&gt;,&lt;ul&gt;.
   * </li>
   * </ul>
   *
   * <p><b>ATTENTION:</b></p>
   *
   * <p>This Check ignores HTML comments.</p>
   *
   * <p>The Check ignores all the nested paragraph tags,
   * it will not give any kind of violation if the paragraph tag is nested.
   * It also ignores paragraph tags inside block tags.</p>
   *
   * @since 6.0
   */
  @StatelessCheck
  public class JavadocParagraphCheck extends AbstractJavadocCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_TAG_AFTER = "javadoc.paragraph.tag.after";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_LINE_BEFORE = "javadoc.paragraph.line.before";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_REDUNDANT_PARAGRAPH = "javadoc.paragraph.redundant.paragraph";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_MISPLACED_TAG = "javadoc.paragraph.misplaced.tag";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_PRECEDED_BLOCK_TAG = "javadoc.paragraph.preceded.block.tag";
  
      /**
       * Constant for the paragraph tag name.
      */
     private static final String PARAGRAPH_TAG = "p";
 
     /**
      * Set of block tags supported by this check.
      */
     private static final Set<String> BLOCK_TAGS =
             Set.of("address", "blockquote", "div", "dl",
                    "h1", "h2", "h3", "h4", "h5", "h6", "hr",
                    "ol", PARAGRAPH_TAG, "pre", "table", "ul");
 
     /**
      * Control whether the &lt;p&gt; tag should be placed immediately before the first word.
      */
     private boolean allowNewlineParagraph = true;
 
     /**
      * Setter to control whether the &lt;p&gt; tag should be placed
      * immediately before the first word.
      *
      * @param value value to set.
      * @since 6.9
      */
     public void setAllowNewlineParagraph(boolean value) {
         allowNewlineParagraph = value;
     }
 
     @Override
     public int[] getDefaultJavadocTokens() {
         return new int[] {
             JavadocCommentsTokenTypes.NEWLINE,
             JavadocCommentsTokenTypes.HTML_ELEMENT,
         };
     }
 
     @Override
     public int[] getRequiredJavadocTokens() {
         return getAcceptableJavadocTokens();
     }
 
     @Override
     public void visitJavadocToken(DetailNode ast) {
         if (ast.getType() == JavadocCommentsTokenTypes.NEWLINE && isEmptyLine(ast)) {
             checkEmptyLine(ast);
         }
         else if (JavadocUtil.isTag(ast, PARAGRAPH_TAG)) {
             checkParagraphTag(ast);
         }
     }
 
     /**
      * Determines whether or not the next line after empty line has paragraph tag in the beginning.
      *
      * @param newline NEWLINE node.
      */
     private void checkEmptyLine(DetailNode newline) {
         final DetailNode nearestToken = getNearestNode(newline);
         if (nearestToken != null && nearestToken.getType() == JavadocCommentsTokenTypes.TEXT
                 && !CommonUtil.isBlank(nearestToken.getText())) {
             log(newline.getLineNumber(), newline.getColumnNumber(), MSG_TAG_AFTER);
         }
     }
 
     /**
      * Determines whether or not the line with paragraph tag has previous empty line.
      *
      * @param tag html tag.
      */
     private void checkParagraphTag(DetailNode tag) {
         if (!isNestedParagraph(tag) && !isInsideBlockTag(tag)) {
             final DetailNode newLine = getNearestEmptyLine(tag);
             if (isFirstParagraph(tag)) {
                 log(tag.getLineNumber(), tag.getColumnNumber(), MSG_REDUNDANT_PARAGRAPH);
             }
             else if (newLine == null || tag.getLineNumber() - newLine.getLineNumber() != 1) {
                 log(tag.getLineNumber(), tag.getColumnNumber(), MSG_LINE_BEFORE);
             }
 
             final String blockTagName = findFollowedBlockTagName(tag);
             if (blockTagName != null) {
                 log(tag.getLineNumber(), tag.getColumnNumber(),
                         MSG_PRECEDED_BLOCK_TAG, blockTagName);
             }
 
             if (!allowNewlineParagraph && isImmediatelyFollowedByNewLine(tag)) {
                 log(tag.getLineNumber(), tag.getColumnNumber(), MSG_MISPLACED_TAG);
             }
             if (isImmediatelyFollowedByText(tag)) {
                 log(tag.getLineNumber(), tag.getColumnNumber(), MSG_MISPLACED_TAG);
             }
         }
     }
 
     /**
      * Determines whether the paragraph tag is nested.
      *
      * @param tag html tag.
      * @return true, if the paragraph tag is nested.
      */
     private static boolean isNestedParagraph(DetailNode tag) {
         boolean nested = false;
         DetailNode parent = tag.getParent();
 
         while (parent != null) {
             if (parent.getType() == JavadocCommentsTokenTypes.HTML_ELEMENT) {
                 nested = true;
                 break;
             }
             parent = parent.getParent();
         }
 
         return nested;
     }
 
     /**
      * Determines whether the paragraph tag is inside javadoc block tag.
      *
      * @param tag html tag.
      * @return true, if the paragraph tag is inside javadoc block tag.
      */
     private static boolean isInsideBlockTag(DetailNode tag) {
         boolean result = false;
         DetailNode parent = tag;
 
         while (parent != null) {
             if (parent.getType() == JavadocCommentsTokenTypes.JAVADOC_BLOCK_TAG) {
                 result = true;
                 break;
             }
             parent = parent.getParent();
         }
 
         return result;
     }
 
     /**
      * Determines whether or not the paragraph tag is followed by block tag.
      *
      * @param tag html tag.
      * @return block tag if the paragraph tag is followed by block tag or null if not found.
      */
     @Nullable
     private static String findFollowedBlockTagName(DetailNode tag) {
         final DetailNode htmlElement = findFirstHtmlElementAfter(tag);
         String blockTagName = null;
 
         if (htmlElement != null) {
             blockTagName = getHtmlElementName(htmlElement);
         }
 
         return blockTagName;
     }
 
     /**
      * Finds and returns first html element after the tag.
      *
      * @param tag html tag.
      * @return first html element after the paragraph tag or null if not found.
      */
     @Nullable
     private static DetailNode findFirstHtmlElementAfter(DetailNode tag) {
         DetailNode htmlElement = getNextSibling(tag);
 
         while (htmlElement != null
                 && htmlElement.getType() != JavadocCommentsTokenTypes.HTML_ELEMENT) {
             if (htmlElement.getType() == JavadocCommentsTokenTypes.HTML_CONTENT) {
                 htmlElement = htmlElement.getFirstChild();
             }
             else if (htmlElement.getType() == JavadocCommentsTokenTypes.TEXT
                     && !CommonUtil.isBlank(htmlElement.getText())) {
                 htmlElement = null;
                 break;
             }
             else {
                 htmlElement = htmlElement.getNextSibling();
             }
         }
         if (htmlElement != null
                 && JavadocUtil.findFirstToken(htmlElement,
                         JavadocCommentsTokenTypes.HTML_TAG_END) == null) {
             htmlElement = null;
         }
 
         return htmlElement;
     }
 
     /**
      * Finds and returns first block-level html element name.
      *
      * @param htmlElement block-level html tag.
      * @return block-level html element name or null if not found.
      */
     @Nullable
     private static String getHtmlElementName(DetailNode htmlElement) {
         final DetailNode htmlTagStart = htmlElement.getFirstChild();
         final DetailNode htmlTagName =
                 JavadocUtil.findFirstToken(htmlTagStart, JavadocCommentsTokenTypes.TAG_NAME);
         String blockTagName = null;
         if (BLOCK_TAGS.contains(htmlTagName.getText())) {
             blockTagName = htmlTagName.getText();
         }
 
         return blockTagName;
     }
 
     /**
      * Returns nearest node.
      *
      * @param node DetailNode node.
      * @return nearest node.
      */
     private static DetailNode getNearestNode(DetailNode node) {
         DetailNode currentNode = node;
         while (currentNode != null
                 && (currentNode.getType() == JavadocCommentsTokenTypes.LEADING_ASTERISK
                     || currentNode.getType() == JavadocCommentsTokenTypes.NEWLINE)) {
             currentNode = currentNode.getNextSibling();
         }
         if (currentNode != null
                 && currentNode.getType() == JavadocCommentsTokenTypes.HTML_CONTENT) {
             currentNode = currentNode.getFirstChild();
         }
         return currentNode;
     }
 
     /**
      * Determines whether or not the line is empty line.
      *
      * @param newLine NEWLINE node.
      * @return true, if line is empty line.
      */
     private static boolean isEmptyLine(DetailNode newLine) {
         boolean result = false;
         DetailNode previousSibling = newLine.getPreviousSibling();
         if (previousSibling != null && (previousSibling.getParent().getType()
                 == JavadocCommentsTokenTypes.JAVADOC_CONTENT
                 || insideNonTightHtml(previousSibling))) {
             if (previousSibling.getType() == JavadocCommentsTokenTypes.TEXT
                     && CommonUtil.isBlank(previousSibling.getText())) {
                 previousSibling = previousSibling.getPreviousSibling();
             }
             result = previousSibling != null
                     && previousSibling.getType() == JavadocCommentsTokenTypes.LEADING_ASTERISK;
         }
         return result;
     }
 
     /**
      * Checks whether the given node is inside a non-tight HTML element.
      *
      * @param previousSibling the node to check
      * @return true if inside non-tight HTML, false otherwise
      */
     private static boolean insideNonTightHtml(DetailNode previousSibling) {
         final DetailNode parent = previousSibling.getParent();
         DetailNode htmlElement = parent;
         if (parent.getType() == JavadocCommentsTokenTypes.HTML_CONTENT) {
             htmlElement = parent.getParent();
         }
         return htmlElement.getType() == JavadocCommentsTokenTypes.HTML_ELEMENT
                 && JavadocUtil.findFirstToken(htmlElement,
                     JavadocCommentsTokenTypes.HTML_TAG_END) == null;
     }
 
     /**
      * Determines whether or not the line with paragraph tag is first line in javadoc.
      *
      * @param paragraphTag paragraph tag.
      * @return true, if line with paragraph tag is first line in javadoc.
      */
     private static boolean isFirstParagraph(DetailNode paragraphTag) {
         boolean result = true;
         DetailNode previousNode = paragraphTag.getPreviousSibling();
         while (previousNode != null) {
             if (previousNode.getType() == JavadocCommentsTokenTypes.TEXT
                     && !CommonUtil.isBlank(previousNode.getText())
                 || previousNode.getType() != JavadocCommentsTokenTypes.LEADING_ASTERISK
                     && previousNode.getType() != JavadocCommentsTokenTypes.NEWLINE
                     && previousNode.getType() != JavadocCommentsTokenTypes.TEXT) {
                 result = false;
                 break;
             }
             previousNode = previousNode.getPreviousSibling();
         }
         return result;
     }
 
     /**
      * Finds and returns nearest empty line in javadoc.
      *
      * @param node DetailNode node.
      * @return Some nearest empty line in javadoc.
      */
     private static DetailNode getNearestEmptyLine(DetailNode node) {
         DetailNode newLine = node;
         while (newLine != null) {
             final DetailNode previousSibling = newLine.getPreviousSibling();
             if (newLine.getType() == JavadocCommentsTokenTypes.NEWLINE && isEmptyLine(newLine)) {
                 break;
             }
             newLine = previousSibling;
         }
         return newLine;
     }
 
     /**
      * Tests whether the paragraph tag is immediately followed by the text.
      *
      * @param tag html tag.
      * @return true, if the paragraph tag is immediately followed by the text.
      */
     private static boolean isImmediatelyFollowedByText(DetailNode tag) {
         final DetailNode nextSibling = getNextSibling(tag);
 
         return nextSibling == null || nextSibling.getText().startsWith(" ");
     }
 
     /**
      * Tests whether the paragraph tag is immediately followed by the new line.
      *
      * @param tag html tag.
      * @return true, if the paragraph tag is immediately followed by the new line.
      */
     private static boolean isImmediatelyFollowedByNewLine(DetailNode tag) {
         final DetailNode sibling = getNextSibling(tag);
         return sibling != null && sibling.getType() == JavadocCommentsTokenTypes.NEWLINE;
     }
 
     /**
      * Custom getNextSibling method to handle different types of paragraph tag.
      * It works for both {@code <p>} and {@code <p></p>} tags.
      *
      * @param tag HTML_ELEMENT tag.
      * @return next sibling of the tag.
      */
     private static DetailNode getNextSibling(DetailNode tag) {
         DetailNode nextSibling;
         final DetailNode paragraphStartTagToken = tag.getFirstChild();
         final DetailNode nextNode = paragraphStartTagToken.getNextSibling();
 
         if (nextNode == null) {
             nextSibling = tag.getNextSibling();
         }
         else if (nextNode.getType() == JavadocCommentsTokenTypes.HTML_CONTENT) {
             nextSibling = nextNode.getFirstChild();
         }
         else {
             nextSibling = nextNode;
         }
 
         if (nextSibling != null
                 && nextSibling.getType() == JavadocCommentsTokenTypes.HTML_COMMENT) {
             nextSibling = nextSibling.getNextSibling();
         }
         return nextSibling;
     }
 }