/*
 * 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 javax.servlet.jsp.tagext;

/**
 * Optional class provided by the tag library author to describe additional translation-time information not described
 * in the TLD. The TagExtraInfo class is mentioned in the Tag Library Descriptor file (TLD).
 * <p>
 * This class can be used:
 * <ul>
 * <li>to indicate that the tag defines scripting variables
 * <li>to perform translation-time validation of the tag attributes.
 * </ul>
 * <p>
 * It is the responsibility of the JSP translator that the initial value to be returned by calls to getTagInfo()
 * corresponds to a TagInfo object for the tag being translated. If an explicit call to setTagInfo() is done, then the
 * object passed will be returned in subsequent calls to getTagInfo().
 * <p>
 * The only way to affect the value returned by getTagInfo() is through a setTagInfo() call, and thus,
 * TagExtraInfo.setTagInfo() is to be called by the JSP translator, with a TagInfo object that corresponds to the tag
 * being translated. The call should happen before any invocation on validate() and before any invocation on
 * getVariableInfo().
 * <p>
 * <b>NOTE:</b> It is a (translation time) error for a tag definition in a TLD with one or more variable subelements to
 * have an associated TagExtraInfo implementation that returns a VariableInfo array with one or more elements from a
 * call to getVariableInfo().
 */

public abstract class TagExtraInfo {

    /**
     * Sole constructor. (For invocation by subclass constructors, typically implicit.)
     */
    public TagExtraInfo() {
        // NOOP by default
    }

    /**
     * information on scripting variables defined by the tag associated with this TagExtraInfo instance. Request-time
     * attributes are indicated as such in the TagData parameter.
     *
     * @param data The TagData instance.
     *
     * @return An array of VariableInfo data, or null or a zero length array if no scripting variables are to be
     *             defined.
     */
    public VariableInfo[] getVariableInfo(TagData data) {
        return ZERO_VARIABLE_INFO;
    }

    /**
     * Translation-time validation of the attributes. Request-time attributes are indicated as such in the TagData
     * parameter. Note that the preferred way to do validation is with the validate() method, since it can return more
     * detailed information.
     *
     * @param data The TagData instance.
     *
     * @return Whether this tag instance is valid.
     *
     * @see TagExtraInfo#validate
     */

    public boolean isValid(TagData data) {
        return true;
    }

    /**
     * Translation-time validation of the attributes. Request-time attributes are indicated as such in the TagData
     * parameter. Because of the higher quality validation messages possible, this is the preferred way to do validation
     * (although isValid() still works).
     * <p>
     * JSP 2.0 and higher containers call validate() instead of isValid(). The default implementation of this method is
     * to call isValid(). If isValid() returns false, a generic ValidationMessage[] is returned indicating isValid()
     * returned false.
     * </p>
     *
     * @param data The TagData instance.
     *
     * @return A null object, or zero length array if no errors, an array of ValidationMessages otherwise.
     *
     * @since JSP 2.0
     */
    public ValidationMessage[] validate(TagData data) {
        ValidationMessage[] result = null;

        if (!isValid(data)) {
            result = new ValidationMessage[] { new ValidationMessage(data.getId(), "isValid() == false") };
        }

        return result;
    }

    /**
     * Set the TagInfo for this class.
     *
     * @param tagInfo The TagInfo this instance is extending
     */
    public final void setTagInfo(TagInfo tagInfo) {
        this.tagInfo = tagInfo;
    }

    /**
     * Get the TagInfo for this class.
     *
     * @return the taginfo instance this instance is extending
     */
    public final TagInfo getTagInfo() {
        return tagInfo;
    }

    // private data
    private TagInfo tagInfo;

    // zero length VariableInfo array
    private static final VariableInfo[] ZERO_VARIABLE_INFO = {};
}

