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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.impl;

import net.morimekta.config.Config;
import net.morimekta.config.KeyNotFoundException;
import net.morimekta.config.LayeredConfig;
import net.morimekta.config.util.ConfigUtil;
import net.morimekta.config.util.ValueConverter;
import net.morimekta.util.concurrent.ReadWriteMutex;
import net.morimekta.util.concurrent.ReentrantReadWriteMutex;

import com.google.common.collect.ImmutableList;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;
import java.util.function.Supplier;

import static net.morimekta.config.util.ConfigUtil.getLayerName;

/**
 * The SynchronizedLayeredConfig is a thread-safe layered config. It has an
 * internal synchronization mechanism using a read-write lock to avoid
 * tampering with data during read operations, and to ensure writes (layer
 * insertions) are atomic. Though it does not ensure that it's contained
 * configs are thread-safe, it has made a core part of the synchronization
 * available for callers.
 */
public class SynchronizedLayeredConfig implements Config, LayeredConfig, ReadWriteMutex {
    private final ArrayList> layers;
    private final ReadWriteMutex mutex;

    private volatile int top;
    private volatile int bottom;

    /**
     * Create a layered config with a predefined set of configs. The configs
     * supported are added as in-memory fixed configs in the two middle groups
     * (top and bottom).
     *
     * @param configs The configs.
     */
    public SynchronizedLayeredConfig(Config... configs) {
        this.mutex = new ReentrantReadWriteMutex();
        this.layers = new ArrayList<>();
        for (Config config : configs) {
            this.layers.add(() -> config);
        }
        this.top = 0;
        this.bottom = layers.size();
    }

    /**
     * Create a layered config with the given suppliers as the initial middle
     * two groups of layers.
     *
     * @param suppliers The config suppliers.
     */
    public SynchronizedLayeredConfig(Collection> suppliers) {
        this.mutex = new ReentrantReadWriteMutex();
        this.layers = new ArrayList<>();
        this.layers.addAll(suppliers);

        this.top = 0;
        this.bottom = layers.size();
    }

    @Override
    public void lockForReading(Runnable callable) {
        mutex.lockForReading(callable);
    }

    @Override
    public  V lockForReading(Supplier callable) {
        return mutex.lockForReading(callable);
    }

    @Override
    public void lockForWriting(Runnable runnable) {
        mutex.lockForWriting(runnable);
    }

    @Override
    public  V lockForWriting(Supplier callable) {
        return mutex.lockForWriting(callable);
    }

    @Override
    public SynchronizedLayeredConfig addFixedTopLayer(Supplier supplier) {
        lockForWriting(() -> {
            layers.add(0, supplier);
            ++top;
            ++bottom;
        });
        return this;
    }

    @Override
    public SynchronizedLayeredConfig addTopLayer(Supplier supplier) {
        lockForWriting(() -> {
            layers.add(top, supplier);
            ++bottom;
        });
        return this;
    }

    @Override
    public SynchronizedLayeredConfig addBottomLayer(Supplier supplier) {
        lockForWriting(() -> {
            layers.add(bottom, supplier);
            ++bottom;
        });
        return this;
    }

    @Override
    public SynchronizedLayeredConfig addFixedBottomLayer(Supplier supplier) {
        lockForWriting(() -> layers.add(supplier));
        return this;
    }

    @Override
    public String getLayerFor(String key) {
        return lockForReading(() -> {
            for (Supplier supplier : layers) {
                Config config = supplier.get();
                if (config.containsKey(key)) {
                    return getLayerName(supplier);
                }
            }

            return null;
        });
    }

    @Override
    public Object get(String key) {
        return getWithDefault(key, v -> v, null);
    }

    @Override
    @SuppressWarnings("unchecked")
    public  T getValue(String key) {
        return lockForReading(() -> {
            if (!containsKey(key)) {
                throw new KeyNotFoundException("No such config entry \"" + key + "\"");
            }
            return (T) get(key);
        });
    }

    @Override
    public  T getWithDefault(String key, ValueConverter converter, T def) {
        return lockForReading(() -> {
            for (Supplier supplier : layers) {
                Config config = supplier.get();
                if (config.containsKey(key)) {
                    return converter.convert(config.get(key));
                }
            }
            return def;
        });
    }

    @Override
    public boolean containsKey(String key) {
        return lockForReading(() -> {
            for (Supplier supplier : layers) {
                Config config = supplier.get();
                if (config.containsKey(key)) {
                    return true;
                }
            }
            return false;
        });
    }

    @Override
    public Set keySet() {
        return lockForReading(() -> {
            TreeSet set = new TreeSet<>();
            for (Supplier supplier : layers) {
                Config config = supplier.get();
                set.addAll(config.keySet());
            }
            return set;
        });
    }

    @Override
    public boolean equals(Object o) {
        if (o == this) {
            return true;
        } else if (o == null || !(o instanceof Config)) {
            return false;
        }
        return lockForReading(() -> ConfigUtil.equals(this, (Config) o));
    }

    @Override
    public int hashCode() {
        return lockForReading(() -> ConfigUtil.hashCode(this));
    }

    @Override
    public String toString() {
        return lockForReading(() -> ConfigUtil.toString(this));
    }

    /**
     * In case sub-classes need access to the layers (in some order).
     *
     * @return The layer list, ordered from top to bottom.
     */
    protected List> layers() {
        return lockForReading(() -> ImmutableList.copyOf(layers));
    }
}