IfchangedTag.java

/**********************************************************************
 * Copyright (c) 2014 HubSpot Inc.
 *
 * 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 com.hubspot.jinjava.lib.tag;

import org.apache.commons.lang3.StringUtils;

import com.hubspot.jinjava.doc.annotations.JinjavaDoc;
import com.hubspot.jinjava.doc.annotations.JinjavaSnippet;
import com.hubspot.jinjava.interpret.JinjavaInterpreter;
import com.hubspot.jinjava.interpret.TemplateSyntaxException;
import com.hubspot.jinjava.tree.Node;
import com.hubspot.jinjava.tree.TagNode;

@JinjavaDoc(
    value = "Outputs the tag contents if the given variable has changed since a prior invocation of this tag",
    hidden = true,
    snippets = {
        @JinjavaSnippet(
            code = "{% ifchanged var %}\n" +
                "Variable to test if changed\n" +
                "{% endifchanged %}")
    })
public class IfchangedTag implements Tag {

  private static final long serialVersionUID = 3567908136629704724L;
  private static final String LASTKEY = "'IF\"CHG";
  private static final String TAGNAME = "ifchanged";
  private static final String ENDTAGNAME = "endifchanged";

  @Override
  public String interpret(TagNode tagNode, JinjavaInterpreter interpreter) {
    if (StringUtils.isBlank(tagNode.getHelpers())) {
      throw new TemplateSyntaxException(tagNode.getMaster().getImage(), "Tag 'ifchanged' expects a variable parameter", tagNode.getLineNumber());
    }
    boolean isChanged = true;
    String var = tagNode.getHelpers().trim();
    Object older = interpreter.getContext().get(LASTKEY + var);
    Object test = interpreter.retraceVariable(var, tagNode.getLineNumber());
    if (older == null) {
      if (test == null) {
        isChanged = false;
      }
    } else if (older.equals(test)) {
      isChanged = false;
    }
    interpreter.getContext().put(LASTKEY + var, test);
    if (isChanged) {
      StringBuilder sb = new StringBuilder();
      for (Node node : tagNode.getChildren()) {
        sb.append(node.render(interpreter));
      }
      return sb.toString();
    }
    return "";
  }

  @Override
  public String getEndTagName() {
    return ENDTAGNAME;
  }

  @Override
  public String getName() {
    return TAGNAME;
  }

}