/*
 * 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 org.apache.jasper.runtime;

import java.util.ArrayList;
import java.util.List;

import jakarta.el.ELContext;
import jakarta.el.ELContextEvent;
import jakarta.el.ELContextListener;
import jakarta.el.ELResolver;
import jakarta.el.ExpressionFactory;
import jakarta.servlet.ServletContext;
import jakarta.servlet.jsp.JspApplicationContext;
import jakarta.servlet.jsp.JspContext;

import org.apache.jasper.compiler.Localizer;
import org.apache.jasper.el.ELContextImpl;
import org.apache.jasper.el.JasperELResolver;

/**
 * Implementation of JspApplicationContext.
 */
public class JspApplicationContextImpl implements JspApplicationContext {

    private static final String KEY = JspApplicationContextImpl.class.getName();

    private final ExpressionFactory expressionFactory = ExpressionFactory.newInstance();

    private final List<ELContextListener> contextListeners = new ArrayList<>();

    private final List<ELResolver> resolvers = new ArrayList<>();

    private boolean instantiated = false;

    private ELResolver resolver;

    /**
     * Constructs a new JspApplicationContextImpl instance.
     */
    public JspApplicationContextImpl() {

    }

    @Override
    public void addELContextListener(ELContextListener listener) {
        if (listener == null) {
            throw new IllegalArgumentException(Localizer.getMessage("jsp.error.nullArgument"));
        }
        this.contextListeners.add(listener);
    }

    /**
     * Returns the JspApplicationContextImpl singleton for the given ServletContext.
     * Creates a new instance if one does not yet exist.
     *
     * @param context The ServletContext
     * @return The JspApplicationContextImpl instance
     */
    public static JspApplicationContextImpl getInstance(ServletContext context) {
        if (context == null) {
            throw new IllegalArgumentException(Localizer.getMessage("jsp.error.nullArgument"));
        }
        JspApplicationContextImpl impl = (JspApplicationContextImpl) context.getAttribute(KEY);
        if (impl == null) {
            impl = new JspApplicationContextImpl();
            context.setAttribute(KEY, impl);
        }
        return impl;
    }

    /**
     * Creates an ELContext for the given JspContext.
     *
     * @param context The JspContext
     * @return The created ELContextImpl
     */
    public ELContextImpl createELContext(JspContext context) {
        if (context == null) {
            throw new IllegalArgumentException(Localizer.getMessage("jsp.error.nullArgument"));
        }

        // create ELContext for JspContext
        final ELResolver r = this.createELResolver();
        ELContextImpl ctx = new ELContextImpl(r);
        ctx.putContext(JspContext.class, context);

        // alert all ELContextListeners
        fireListeners(ctx);

        return ctx;
    }

    /**
     * Notifies all registered ELContextListeners that a new ELContext has been created.
     *
     * @param elContext The newly created ELContext
     */
    protected void fireListeners(ELContext elContext) {
        ELContextEvent event = new ELContextEvent(elContext);
        for (ELContextListener contextListener : this.contextListeners) {
            contextListener.contextCreated(event);
        }
    }

    private ELResolver createELResolver() {
        this.instantiated = true;
        if (this.resolver == null) {
            this.resolver = new JasperELResolver(this.resolvers, expressionFactory.getStreamELResolver());
        }
        return this.resolver;
    }

    @Override
    public void addELResolver(ELResolver resolver) throws IllegalStateException {
        if (resolver == null) {
            throw new IllegalArgumentException(Localizer.getMessage("jsp.error.nullArgument"));
        }
        if (this.instantiated) {
            throw new IllegalStateException(Localizer.getMessage("jsp.error.cannotAddResolver"));
        }
        this.resolvers.add(resolver);
    }

    @Override
    public ExpressionFactory getExpressionFactory() {
        return expressionFactory;
    }

}