/*
 * Copyright (c) 2002-2012 Alibaba Group Holding Limited.
 * All rights reserved.
 *
 * 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.alibaba.citrus.springext;

import static com.alibaba.citrus.util.Assert.*;
import static com.alibaba.citrus.util.ClassUtil.*;
import static com.alibaba.citrus.util.CollectionUtil.*;

import java.io.IOException;
import java.io.InputStream;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.core.io.InputStreamSource;

/**
 * 这个接口的目的是取得configuration point/contribution所需要的一切资源文件，例如定义文件、schema文件等。
 * 在不同的环境中，需要不同的实现。例如：
 * <ul>
 * <li>在应用程序的环境中，将从class loader来寻找和装载所有的资源文件。</li>
 * <li>在IDE开发环境中（IDE plugins），每个IDE有自己不同的装载资源的方法。
 * 每个IDE插件（例如Intellij IDE、Eclipse）需要实现自己的<code>ResourceResolver</code>来装载项目中的资源文件。</li>
 * </ul>
 * 默认的实现是用class loader来装载资源。
 *
 * @author Michael Zhou
 */
public abstract class ResourceResolver {
    protected final Logger log = LoggerFactory.getLogger(getClass());

    /**
     * 取得指定位置的一个资源。
     * 如果资源不存在，则返回<code>null</code>。
     */
    public abstract Resource getResource(String location);

    /**
     * 找到所有符合名称的资源。支持同名资源的查找，例如，查找所有jar包中的/META-INF/spring.schemas文件。该方法还支持通配符。
     *
     * @throws IOException 如果在寻找过程中出错
     */
    public abstract Resource[] getResources(String locationPattern) throws IOException;

    /** 从<code>ResourceResolver</code>中读取所有指定名称的资源文件，对每一个key/value调用handler。 */
    public final void loadAllProperties(String resourceName, PropertyHandler handler)
            throws ConfigurationPointException {
        assertNotNull(resourceName, "Resource name must not be null");
        assertNotNull(handler, "No handler provided");

        Map<String, Resource> keyToResources = createHashMap();

        try {
            for (Resource resource : getResources(resourceName)) {
                Properties props = new Properties();
                InputStream is = null;

                try {
                    is = resource.getInputStream();
                    props.load(is);

                    for (Entry<Object, Object> entry : props.entrySet()) {
                        String key = (String) entry.getKey();
                        String value = (String) entry.getValue();

                        if (keyToResources.containsKey(key)) {
                            log.warn("Duplicated key \"{}\" in {} and {}", new Object[] { key, resource, keyToResources.get(key) });
                        } else {
                            keyToResources.put(key, resource);
                            handler.handle(key, value, resource, -1); // no line number supported in this implementation
                        }
                    }
                } finally {
                    if (is != null) {
                        try {
                            is.close();
                        } catch (IOException ignored) {
                        }
                    }
                }
            }
        } catch (IOException e) {
            throw new ConfigurationPointException("Unable to load data from " + resourceName, e);
        }
    }

    public static abstract class Resource implements InputStreamSource {
        public abstract String getName();

        public abstract InputStream getInputStream() throws IOException;

        @Override
        public final String toString() {
            String desc = getName();
            return getSimpleClassName(getClass()) + (desc == null ? "" : "[" + desc + "]");
        }
    }

    public static interface PropertyHandler {
        void handle(String key, String value, Resource source, int lineNumber);
    }
}