/*
 * 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.spark.internal.config

import java.util.{Map => JMap}

/**
 * A source of configuration values.
 */
private[spark] trait ConfigProvider {

  def get(key: String): Option[String]

}

private[spark] class EnvProvider extends ConfigProvider {

  override def get(key: String): Option[String] = sys.env.get(key)

}

private[spark] class SystemProvider extends ConfigProvider {

  override def get(key: String): Option[String] = sys.props.get(key)

}

private[spark] class MapProvider(conf: JMap[String, String]) extends ConfigProvider {

  override def get(key: String): Option[String] = Option(conf.get(key))

}

/**
 * A config provider that only reads Spark config keys, and considers default values for known
 * configs when fetching configuration values.
 */
private[spark] class SparkConfigProvider(conf: JMap[String, String]) extends ConfigProvider {

  import ConfigEntry._

  override def get(key: String): Option[String] = {
    if (key.startsWith("spark.")) {
      Option(conf.get(key)).orElse(defaultValueString(key))
    } else {
      None
    }
  }

  private def defaultValueString(key: String): Option[String] = {
    findEntry(key) match {
      case e: ConfigEntryWithDefault[_] => Option(e.defaultValueString)
      case e: ConfigEntryWithDefaultString[_] => Option(e.defaultValueString)
      case e: FallbackConfigEntry[_] => get(e.fallback.key)
      case _ => None
    }
  }

}
