/*
 * 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;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * Translation-time validator class for a JSP page. A validator operates on the XML view associated with the JSP page.
 * <p>
 * The TLD file associates a TagLibraryValidator class and some init arguments with a tag library.
 * <p>
 * The JSP container is responsible for locating an appropriate instance of the appropriate subclass by
 * <ul>
 * <li>new a fresh instance, or reuse an available one
 * <li>invoke the setInitParams(Map) method on the instance
 * </ul>
 * once initialized, the validate(String, String, PageData) method will be invoked, where the first two arguments are
 * the prefix and uri for this tag library in the XML View. The prefix is intended to make it easier to produce an error
 * message. However, it is not always accurate. In the case where a single URI is mapped to more than one prefix in the
 * XML view, the prefix of the first URI is provided. Therefore, to provide high quality error messages in cases where
 * the tag elements themselves are checked, the prefix parameter should be ignored and the actual prefix of the element
 * should be used instead. TagLibraryValidators should always use the uri to identify elements as belonging to the tag
 * library, not the prefix.
 * <p>
 * A TagLibraryValidator instance may create auxiliary objects internally to perform the validation (e.g. an XSchema
 * validator) and may reuse it for all the pages in a given translation run.
 * <p>
 * The JSP container is not guaranteed to serialize invocations of validate() method, and TagLibraryValidators should
 * perform any synchronization they may require.
 * <p>
 * As of JSP 2.0, a JSP container must provide a jsp:id attribute to provide higher quality validation errors. The
 * container will track the JSP pages as passed to the container, and will assign to each element a unique "id", which
 * is passed as the value of the jsp:id attribute. Each XML element in the XML view available will be extended with this
 * attribute. The TagLibraryValidator can then use the attribute in one or more ValidationMessage objects. The container
 * then, in turn, can use these values to provide more precise information on the location of an error.
 * <p>
 * The actual prefix of the <code>id</code> attribute may or may not be <code>jsp</code> but it will always map to the
 * namespace <code>http://java.sun.com/JSP/Page</code>. A TagLibraryValidator implementation must rely on the uri, not
 * the prefix, of the <code>id</code> attribute.
 */

public abstract class TagLibraryValidator {

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

    /**
     * Set the init data in the TLD for this validator. Parameter names are keys, and parameter values are the values.
     *
     * @param map A Map describing the init parameters
     */
    public void setInitParameters(Map<String,Object> map) {
        initParameters = Collections.unmodifiableMap(new HashMap<>(map));
    }


    /**
     * Get the init parameters data as an immutable Map. Parameter names are keys, and parameter values are the values.
     *
     * @return The init parameters as an immutable map.
     */
    public Map<String,Object> getInitParameters() {
        return initParameters;
    }

    /**
     * Validate a JSP page. This will get invoked once per unique tag library URI in the XML view. This method will
     * return null if the page is valid; otherwise the method should return an array of ValidationMessage objects. An
     * array of length zero is also interpreted as no errors.
     *
     * @param prefix the first prefix with which the tag library is associated, in the XML view. Note that some tags may
     *                   use a different prefix if the namespace is redefined.
     * @param uri    the tag library's unique identifier
     * @param page   the JspData page object
     *
     * @return A null object, or zero length array if no errors, an array of ValidationMessages otherwise.
     */
    public ValidationMessage[] validate(String prefix, String uri, PageData page) {
        return null;
    }

    /**
     * Release any data kept by this instance for validation purposes.
     */
    public void release() {
        initParameters = null;
    }

    // Private data
    private Map<String,Object> initParameters;

}
