/*
    *    Copyright 2009-2021 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
    *
    *       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.ibatis.parsing;
  
  import java.util.Properties;
  
  /**
   * @author Clinton Begin
   * @author Kazuki Shimizu
   */
  public class PropertyParser {
  
    private static final String KEY_PREFIX = "org.apache.ibatis.parsing.PropertyParser.";
    /**
     * The special property key that indicate whether enable a default value on placeholder.
     * <p>
     *   The default value is {@code false} (indicate disable a default value on placeholder)
     *   If you specify the {@code true}, you can specify key and default value on placeholder (e.g. {@code ${db.username:postgres}}).
     * </p>
     * @since 3.4.2
     */
    public static final String KEY_ENABLE_DEFAULT_VALUE = KEY_PREFIX + "enable-default-value";
  
    /**
     * The special property key that specify a separator for key and default value on placeholder.
     * <p>
     *   The default separator is {@code ":"}.
     * </p>
     * @since 3.4.2
     */
    public static final String KEY_DEFAULT_VALUE_SEPARATOR = KEY_PREFIX + "default-value-separator";
  
    private static final String ENABLE_DEFAULT_VALUE = "false";
    private static final String DEFAULT_VALUE_SEPARATOR = ":";
  
    private PropertyParser() {
      // Prevent Instantiation
    }
  
    public static String parse(String string, Properties variables) {
      VariableTokenHandler handler = new VariableTokenHandler(variables);
      GenericTokenParser parser = new GenericTokenParser("${", "}", handler);
      return parser.parse(string);
    }
  
    private static class VariableTokenHandler implements TokenHandler {
      private final Properties variables;
      private final boolean enableDefaultValue;
      private final String defaultValueSeparator;
  
      private VariableTokenHandler(Properties variables) {
        this.variables = variables;
        this.enableDefaultValue = Boolean.parseBoolean(getPropertyValue(KEY_ENABLE_DEFAULT_VALUE, ENABLE_DEFAULT_VALUE));
        this.defaultValueSeparator = getPropertyValue(KEY_DEFAULT_VALUE_SEPARATOR, DEFAULT_VALUE_SEPARATOR);
      }
  
      private String getPropertyValue(String key, String defaultValue) {
        return (variables == null) ? defaultValue : variables.getProperty(key, defaultValue);
      }
  
      @Override
      public String handleToken(String content) {
        if (variables != null) {
          String key = content;
          if (enableDefaultValue) {
            final int separatorIndex = content.indexOf(defaultValueSeparator);
            String defaultValue = null;
            if (separatorIndex >= 0) {
              key = content.substring(0, separatorIndex);
              defaultValue = content.substring(separatorIndex + defaultValueSeparator.length());
            }
            if (defaultValue != null) {
              return variables.getProperty(key, defaultValue);
            }
          }
          if (variables.containsKey(key)) {
            return variables.getProperty(key);
          }
        }
        return "${" + content + "}";
      }
    }
  
  }