code: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   *
   */
  
  package org.apache.skywalking.oap.server.core.config.group.uri.quickmatch;
  
  import java.util.ArrayList;
  import java.util.List;
  import lombok.EqualsAndHashCode;
  import lombok.ToString;
  import org.apache.skywalking.oap.server.library.util.StringFormatGroup;
  
  @EqualsAndHashCode
  @ToString
  public class PatternTree {
      private final List<PatternToken> roots;
  
      public PatternTree() {
          roots = new ArrayList<>();
      }
  
      /**
       * The pattern is split by /, and each token is a node in the tree. Each node either a literal string or "{var}"
       * representing a variable.
       *
       * @param pattern of URIs
       */
      public void addPattern(String pattern) {
          final List<String> tokens = splitByCharacter(pattern);
  
          PatternToken current = null;
          for (final PatternToken patternToken : roots) {
              if (patternToken.isMatch(tokens.get(0))) {
                  current = patternToken;
                  break;
              }
          }
  
          if (current == null) {
              current = new StringToken(tokens.get(0));
              roots.add(current);
          }
  
          if (tokens.size() == 1) {
              current.setExpression(pattern);
              return;
          }
  
          for (int i = 1; i < tokens.size(); i++) {
              final String token = tokens.get(i);
              PatternToken newToken;
              if (VarToken.VAR_TOKEN.equals(token)) {
                  newToken = new VarToken();
              } else {
                  newToken = new StringToken(token);
              }
              final PatternToken found = current.find(newToken);
              if (found == null) {
                  current = current.add(newToken);
              } else {
                  current = found;
              }
          }
          current.setExpression(pattern);
      }
  
      List<String> splitByCharacter(String input) {
          List<String> parts = new ArrayList<>();
          int length = input.length();
          int start = 0;
  
          for (int i = 0; i < length; i++) {
              if (input.charAt(i) == '/') {
                  if (i == 0) {
                      start = i + 1;
                      continue;
                  }
                  parts.add(input.substring(start, i));
                  start = i + 1;
              }
          }
  
          // Add the last part if necessary
          if (start < length) {
              parts.add(input.substring(start));
          }
  
          return parts;
      }
  
      public StringFormatGroup.FormatResult match(String uri) {
          final List<String> slices = splitByCharacter(uri);
          if (slices.size() == 1) {
              // Special case handling, since if a URI is just length one
              // itself will never be a variable, so simply return true and itself
              // trailing slashes, if ever encountered will be kept as is
              return new StringFormatGroup.FormatResult(true, uri, uri);
          }
          List<PatternToken> current = roots;
          PatternToken matchedToken = null;
          for (final String slice : slices) {
              boolean matched = false;
              for (final PatternToken patternToken : current) {
                  if (patternToken.isMatch(slice)) {
                      matchedToken = patternToken;
                      matched = true;
                      break;
                  }
              }
              if (!matched) {
                  return new StringFormatGroup.FormatResult(false, uri, uri);
              }
              current = matchedToken.children();
          }
          if (matchedToken.isLeaf()) {
              return new StringFormatGroup.FormatResult(true, uri, matchedToken.expression());
          } else {
              return new StringFormatGroup.FormatResult(false, uri, uri);
          }
      }
  
      @SuppressWarnings("unused")
      // Utility method to visualize the full tree for debugging purposes
      public String printTree() {
          StringBuilder sb = new StringBuilder();
          for (PatternToken root : roots) {
              sb.append(printNode(root, 0));
          }
          return sb.toString();
      }
  
      private String printNode(PatternToken node, int depth) {
          StringBuilder sb = new StringBuilder();
  
          sb.append("  ".repeat(Math.max(0, depth)));
  
          sb.append(node.toString()).append("\n");
  
          // Append expression if not null
          if (node.expression() != null) {
              sb.append("  ").append(node.expression()).append("\n");
          }
  
          if (node instanceof StringToken) {
              StringToken stringToken = (StringToken) node;
              for (PatternToken child : stringToken.children()) {
                  sb.append(printNode(child, depth + 1));
              }
          } else if (node instanceof VarToken) {
              VarToken varToken = (VarToken) node;
              for (PatternToken child : varToken.children()) {
                  sb.append(printNode(child, depth + 1));
              }
          }
  
          return sb.toString();
      }
  
  }
  