/*
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 1999 The Apache Software Foundation.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowlegement:  
 *       "This product includes software developed by the 
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 *
 * 4. The names "The Jakarta Project", "Tomcat", and "Apache Software
 *    Foundation" must not be used to endorse or promote products derived
 *    from this software without prior written permission. For written 
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache"
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 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */ 

package javax.servlet.jsp.jstl.core;

import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;

/**
 * <p>ConditionalTagSupport は、
 * 条件判定タグを実装しやすくするための抽象クラスです。
 * -- 条件判定タグは、&lt;if&gt;といった形式のタグです。</p>
 *
 * <p>この基本クラスは次の項目をサポートします:</p>
 * 
 * <ul>
 *  <li> <tt>condition()</tt>メソッドのオーバーライドを前提とする排他論理</li>
 *  <li> サブクラスによって実行される論理結果(Boolean値)
 *       を保持するスコープ付きの属性．(属性指定によるオプション)</li>
 * </ul>
 *
 * <p>このメソッドは、２値論理をサポートするタグに関しての標準で
 * 要求されると思われる振る舞いを実装するので、
 *  JSTL APIの一部となると思われます。
 * </p>
 * 
 * @author Shawn Bayern
 */

public abstract class ConditionalTagSupport
    extends TagSupport
{
    //*********************************************************************
    // Abstract methods

    /**
     * <p>特定のサブクラスが条件判定論理を活用するのに利用する
     * 状態を表す<tt>boolean値</tt>を返却します。
     *
     * @return タグの振る舞いの活用に利用される任意の論理結果を表すboolean値
     */
    protected abstract boolean condition() throws JspTagException;


    //*********************************************************************
    // Constructor

    /**
     * ローカル状態を初期化する基本コンストラクタ。タグサポートをするために、
     * サブクラスは他のコンストラクタをサポートすべきでないし、
     * スーパークラスのコンストラクタを呼ぶことが要求されます。
     */
    public ConditionalTagSupport() {
        super();
        init();
    }


    //*********************************************************************
    // Lifecycle management and implementation of conditional behavior

    /**
     * <tt>condition()</tt>の評価結果がtrueの場合にボディ部へ挿入します。
     */
    public int doStartTag() throws JspException {

        // execute our condition() method once per invocation
        result = condition();

        // expose variables if appropriate
        exposeVariables();

        // handle conditional behavior
        if (result)
            return EVAL_BODY_INCLUDE;
        else
            return SKIP_BODY;
    }

    /**
     * このConditionalTagSupportが持つ（継承する）リソースをすべて解放します。
     */
    public void release() {
        super.release();
        init();
    }

    //*********************************************************************
    // Private state

    private boolean result;             // the saved result of condition()
    private String var;			// scoped attribute name
    private int scope;			// scoped attribute scope


    //*********************************************************************
    // Accessors

    /**
     * 'var' 属性を設定します。
     *
     * @param var <tt>condition()</tt>の結果を保持するスコープありの変数の名前
     * 
     */
    public void setVar(String var) {
	this.var = var;
    }

    /**
     * 'scope' 属性を設定します。
     *
     * @param scope 'var' 属性のスコープ
     */
    public void setScope(String scope) {
	if (scope.equalsIgnoreCase("request"))
	    this.scope = PageContext.REQUEST_SCOPE;
	else if (scope.equalsIgnoreCase("session"))
	    this.scope = PageContext.SESSION_SCOPE;
	else if (scope.equalsIgnoreCase("application"))
	    this.scope = PageContext.APPLICATION_SCOPE;
	// TODO: Add error handling?  Needs direction from spec.
    }


    //*********************************************************************
    // Utility methods

    // expose attributes if we have a non-null 'var'
    private void exposeVariables() {
        if (var != null)
            pageContext.setAttribute(var, new Boolean(result), scope);
    }

    // initializes internal state
    private void init() {
        result = false;                 // not really necessary
	var = null;
	scope = PageContext.PAGE_SCOPE;
    }
}