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Configuration Utilities. NOTE: This module is deprecated and will be removed at the end of the v2.x versions of the utilities. Preferred config system after that is either to use true type-safe config with `net.morimekta.providence:providence-config` or to use a simple JSON or YAML library or java properties files. The semi-typesafe layered config did not really solve the problems I had hoped it would, and in essence this was just a helper for merging maps and getting pre-cast values out of it.

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/*
 * Copyright (c) 2016, Stein Eldar Johnsen
 *
 * 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 net.morimekta.config;

import net.morimekta.config.source.FileConfigSupplier;
import net.morimekta.config.source.RefreshingFileConfigSupplier;
import net.morimekta.config.source.ResourceConfigSupplier;

import java.util.function.Supplier;

/**
 * A config based on a layered set of configs. The config has four layer
 * groups, two above and two below the middle.
 *
 * 
 *     --fixed-top--
 *     [w] Layers: Lifo
 *     --top--
 *     [x] Layers: Lifo
 *     --middle--
 *     [y] Layers: Fifo
 *     --bottom--
 *     [z] Layers: Fifo
 *     --fixed-bottom--
 * 
 *
 * When layers are added, they are added to one of the four groups, and inserted
 * furthest away from the middle. The middle is actually just a theoretical
 * position, as the 'top' and 'bottom' groups insert away from that line.
 */
public interface LayeredConfig extends Config {
    /**
     * Add a new fixed top layer. The new config will be handled before all
     * other configs added before this.
     *
     * @param supplier The config supplier.
     * @return The config.
     */
    LayeredConfig addFixedTopLayer(Supplier supplier);

    /**
     * Add a new top layer. The new config will be handled before the
     * other top configs added before this, but after fixed-top configs.
     *
     * @param supplier The config supplier.
     * @return The config.
     */
    LayeredConfig addTopLayer(Supplier supplier);

    /**
     * Add a new bottom layer. The new config will be handled after the
     * other bottom configs added before this, but before fixed-bottom
     * configs.
     *
     * @param supplier The config supplier.
     * @return The config.
     */
    LayeredConfig addBottomLayer(Supplier supplier);

    /**
     * Add a new fixed bottom layer. The new config will be handled after all
     * other configs added before this.
     *
     * @param supplier The config supplier.
     * @return The config.
     */
    LayeredConfig addFixedBottomLayer(Supplier supplier);

    /**
     * Get the 'toString()' value for the config supplier for the layer that
     * contains the wanted key. If the supplier is a lambda expression we
     * assume it is just providing the config from memory.
     *
     * See the toString entries for the different config sources (See:
     * {@link FileConfigSupplier#toString()},
     * {@link RefreshingFileConfigSupplier#toString()},
     * {@link ResourceConfigSupplier#toString()}).
     *
     * @param key The key to get layer for.
     * @return The layer number and name.
     */
    String getLayerFor(String key);
}