/*
    *    Copyright 2010-2023 the original author or authors.
    *
    *    Licensed 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
    *
    *       https://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.ibatis.migration;
  
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.List;
  import java.util.Map;
  import java.util.Objects;
  import java.util.stream.Collectors;
  
  /**
   * @author Clinton Begin
   */
  public class VariableReplacer {
  
    private static final String OPEN_TOKEN = "${";
    private static final String CLOSE_TOKEN = "}";
    private final List<Map<? extends Object, ? extends Object>> variablesList;
  
    public VariableReplacer(Map<? extends Object, ? extends Object> variablesList) {
      this(Arrays.asList(variablesList));
    }
  
    public VariableReplacer(List<Map<? extends Object, ? extends Object>> variablesList) {
      this.variablesList = variablesList == null ? Collections.emptyList()
          : variablesList.stream().filter(Objects::nonNull).collect(Collectors.toList());
    }
  
    public String replace(String text) {
      if (text == null || text.isEmpty()) {
        return "";
      }
      // search open token
      int start = text.indexOf(OPEN_TOKEN);
      if (start == -1) {
        return text;
      }
      char[] src = text.toCharArray();
      int offset = 0;
      final StringBuilder builder = new StringBuilder();
      StringBuilder expression = null;
      while (start > -1) {
        if (start > 0 && src[start - 1] == '\\') {
          // this open token is escaped. remove the backslash and continue.
          builder.append(src, offset, start - offset - 1).append(OPEN_TOKEN);
          offset = start + OPEN_TOKEN.length();
        } else {
          // found open token. let's search close token.
          if (expression == null) {
            expression = new StringBuilder();
          } else {
            expression.setLength(0);
          }
          builder.append(src, offset, start - offset);
          offset = start + OPEN_TOKEN.length();
          int end = text.indexOf(CLOSE_TOKEN, offset);
          while (end > -1) {
            if (end <= offset || src[end - 1] != '\\') {
              expression.append(src, offset, end - offset);
              break;
            }
            // this close token is escaped. remove the backslash and continue.
            expression.append(src, offset, end - offset - 1).append(CLOSE_TOKEN);
            offset = end + CLOSE_TOKEN.length();
            end = text.indexOf(CLOSE_TOKEN, offset);
          }
          if (end == -1) {
            // close token was not found.
            builder.append(src, start, src.length - start);
            offset = src.length;
          } else {
            appendWithReplace(builder, expression.toString());
            offset = end + CLOSE_TOKEN.length();
          }
        }
        start = text.indexOf(OPEN_TOKEN, offset);
      }
      if (offset < src.length) {
        builder.append(src, offset, src.length - offset);
      }
      return builder.toString();
    }
  
    private StringBuilder appendWithReplace(StringBuilder builder, String key) {
      String value = null;
     for (Map<? extends Object, ? extends Object> variables : variablesList) {
       value = (String) variables.get(key);
       if (value != null) {
         builder.append(value);
         break;
       }
     }
     if (value == null) {
       builder.append(OPEN_TOKEN).append(key).append(CLOSE_TOKEN);
     }
     return builder;
   }
 }