/**
 * 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.pulsar.io.flume.node;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.HashMap;
import java.util.Properties;

import org.apache.flume.conf.FlumeConfiguration;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * <p>
 * A configuration provider that uses properties file for specifying
 * configuration. The configuration files follow the Java properties file syntax
 * rules specified at {@link java.util.Properties#load(java.io.Reader)}. Every
 * configuration value specified in the properties file is prefixed by an
 * <em>Agent Name</em> which helps isolate an individual agent&apos;s namespace.
 * </p>
 * <p>
 * Valid configuration files must observe the following rules for every agent
 * namespace.
 * <ul>
 * <li>For every &lt;agent name&gt; there must be three lists specified that
 * include <tt>&lt;agent name&gt;.sources</tt>,
 * <tt>&lt;agent name&gt;.sinks</tt>, and <tt>&lt;agent name&gt;.channels</tt>.
 * Each of these lists must contain a space separated list of names
 * corresponding to that particular entity.</li>
 * <li>For each source named in <tt>&lt;agent name&gt;.sources</tt>, there must
 * be a non-empty <tt>type</tt> attribute specified from the valid set of source
 * types. For example:
 * <tt>&lt;agent name&gt;.sources.&lt;source name&gt;.type = event</tt></li>
 * <li>For each source named in <tt>&lt;agent name&gt;.sources</tt>, there must
 * be a space-separated list of channel names that the source will associate
 * with during runtime. Each of these names must be contained in the channels
 * list specified by <tt>&lt;agent name&gt;.channels</tt>. For example:
 * <tt>&lt;agent name&gt;.sources.&lt;source name&gt;.channels =
 * &lt;channel-1 name&gt; &lt;channel-2 name&gt;</tt></li>
 * <li>For each source named in the <tt>&lt;agent name&gt;.sources</tt>, there
 * must be a <tt>runner</tt> namespace of configuration that configures the
 * associated source runner. For example:
 * <tt>&lt;agent name&gt;.sources.&lt;source name&gt;.runner.type = avro</tt>.
 * This namespace can also be used to configure other configuration of the
 * source runner as needed. For example:
 * <tt>&lt;agent name&gt;.sources.&lt;source name&gt;.runner.port = 10101</tt>
 * </li>
 * <li>For each source named in <tt>&lt;sources&gt;.sources</tt> there can
 * be an optional <tt>selector.type</tt> specified that identifies the type
 * of channel selector associated with the source. If not specified, the
 * default replicating channel selector is used.
 * </li><li>For each channel named in the <tt>&lt;agent name&gt;.channels</tt>,
 * there must be a non-empty <tt>type</tt> attribute specified from the valid
 * set of channel types. For example:
 * <tt>&lt;agent name&gt;.channels.&lt;channel name&gt;.type = mem</tt></li>
 * <li>For each sink named in the <tt>&lt;agent name&gt;.sinks</tt>, there must
 * be a non-empty <tt>type</tt> attribute specified from the valid set of sink
 * types. For example:
 * <tt>&lt;agent name&gt;.sinks.&lt;sink name&gt;.type = hdfs</tt></li>
 * <li>For each sink named in the <tt>&lt;agent name&gt;.sinks</tt>, there must
 * be a non-empty single-valued channel name specified as the value of the
 * <tt>channel</tt> attribute. This value must be contained in the channels list
 * specified by <tt>&lt;agent name&gt;.channels</tt>. For example:
 * <tt>&lt;agent name&gt;.sinks.&lt;sink name&gt;.channel =
 * &lt;channel name&gt;</tt></li>
 * <li>For each sink named in the <tt>&lt;agent name&gt;.sinks</tt>, there must
 * be a <tt>runner</tt> namespace of configuration that configures the
 * associated sink runner. For example:
 * <tt>&lt;agent name&gt;.sinks.&lt;sink name&gt;.runner.type = polling</tt>.
 * This namespace can also be used to configure other configuration of the sink
 * runner as needed. For example:
 * <tt>&lt;agent name&gt;.sinks.&lt;sink name&gt;.runner.polling.interval =
 * 60</tt></li>
 * <li>A fourth optional list <tt>&lt;agent name&gt;.sinkgroups</tt>
 * may be added to each agent, consisting of unique space separated names
 * for groups</li>
 * <li>Each sinkgroup must specify sinks, containing a list of all sinks
 * belonging to it. These cannot be shared by multiple groups.
 * Further, one can set a processor and behavioral parameters to determine
 * how sink selection is made via <tt>&lt;agent name&gt;.sinkgroups.&lt;
 * group name&lt.processor</tt>. For further detail refer to individual processor
 * documentation</li>
 * <li>Sinks not assigned to a group will be assigned to default single sink
 * groups.</li>
 * </ul>
 *
 * Apart from the above required configuration values, each source, sink or
 * channel can have its own set of arbitrary configuration as required by the
 * implementation. Each of these configuration values are expressed by fully
 * namespace qualified configuration keys. For example, the configuration
 * property called <tt>capacity</tt> for a channel called <tt>ch1</tt> for the
 * agent named <tt>host1</tt> with value <tt>1000</tt> will be expressed as:
 * <tt>host1.channels.ch1.capacity = 1000</tt>.
 * </p>
 * <p>
 * Any information contained in the configuration file other than what pertains
 * to the configured agents, sources, sinks and channels via the explicitly
 * enumerated list of sources, sinks and channels per agent name are ignored by
 * this provider. Moreover, if any of the required configuration values are not
 * present in the configuration file for the configured entities, that entity
 * and anything that depends upon it is considered invalid and consequently not
 * configured. For example, if a channel is missing its <tt>type</tt> attribute,
 * it is considered misconfigured. Also, any sources or sinks that depend upon
 * this channel are also considered misconfigured and not initialized.
 * </p>
 * <p>
 * Example configuration file:
 *
 * <pre>
 * #
 * # Flume Configuration
 * # This file contains configuration for one Agent identified as host1.
 * #
 *
 * host1.sources = avroSource thriftSource
 * host1.channels = jdbcChannel
 * host1.sinks = hdfsSink
 *
 * # avroSource configuration
 * host1.sources.avroSource.type = org.apache.flume.source.AvroSource
 * host1.sources.avroSource.runner.type = avro
 * host1.sources.avroSource.runner.port = 11001
 * host1.sources.avroSource.channels = jdbcChannel
 * host1.sources.avroSource.selector.type = replicating
 *
 * # thriftSource configuration
 * host1.sources.thriftSource.type = org.apache.flume.source.ThriftSource
 * host1.sources.thriftSource.runner.type = thrift
 * host1.sources.thriftSource.runner.port = 12001
 * host1.sources.thriftSource.channels = jdbcChannel
 *
 * # jdbcChannel configuration
 * host1.channels.jdbcChannel.type = jdbc
 * host1.channels.jdbcChannel.jdbc.driver = com.mysql.jdbc.Driver
 * host1.channels.jdbcChannel.jdbc.connect.url = http://localhost/flumedb
 * host1.channels.jdbcChannel.jdbc.username = flume
 * host1.channels.jdbcChannel.jdbc.password = flume
 *
 * # hdfsSink configuration
 * host1.sinks.hdfsSink.type = hdfs
 * host1.sinks.hdfsSink.hdfs.path = hdfs://localhost/
 * host1.sinks.hdfsSink.batchsize = 1000
 * host1.sinks.hdfsSink.runner.type = polling
 * host1.sinks.hdfsSink.runner.polling.interval = 60
 * </pre>
 *
 * </p>
 *
 * @see java.util.Properties#load(java.io.Reader)
 */
public class PropertiesFileConfigurationProvider extends
        AbstractConfigurationProvider {

    private static final Logger LOGGER = LoggerFactory
            .getLogger(PropertiesFileConfigurationProvider.class);
    private static final String DEFAULT_PROPERTIES_IMPLEMENTATION = "java.util.Properties";

    private final File file;

    public PropertiesFileConfigurationProvider(String agentName, File file) {
        super(agentName);
        this.file = file;
    }

    @Override
    public FlumeConfiguration getFlumeConfiguration() {
        BufferedReader reader = null;
        try {
            reader = new BufferedReader(new FileReader(file));
            String resolverClassName = System.getProperty("propertiesImplementation",
                    DEFAULT_PROPERTIES_IMPLEMENTATION);
            Class<? extends Properties> propsclass = Class.forName(resolverClassName)
                    .asSubclass(Properties.class);
            Properties properties = propsclass.newInstance();
            properties.load(reader);
            return new FlumeConfiguration(toMap(properties));
        } catch (IOException ex) {
            LOGGER.error("Unable to load file:" + file
                    + " (I/O failure) - Exception follows.", ex);
        } catch (ClassNotFoundException | NoClassDefFoundError e) {
            LOGGER.error("Configuration resolver class not found", e);
        } catch (InstantiationException e) {
            LOGGER.error("Instantiation exception", e);
        } catch (IllegalAccessException e) {
            LOGGER.error("Illegal access exception", e);
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException ex) {
                    LOGGER.warn(
                            "Unable to close file reader for file: " + file, ex);
                }
            }
        }
        return new FlumeConfiguration(new HashMap<String, String>());
    }
}
