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Tensorics is a java framework which uses a tensor as a central object. A tensor represents a set of values placed in an N-dimensional space. Wherever you are tempted to use maps of maps, a tensor might be a good choice ;-) Tensorics provides methods to create, transform and performing calculations with those tensors.

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// @formatter:off
 /*******************************************************************************
 *
 * This file is part of tensorics.
 * 
 * Copyright (c) 2008-2016, CERN. 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.
 * 
 ******************************************************************************/
// @formatter:on

package org.tensorics.core.function;

import java.io.Serializable;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import com.google.common.collect.ImmutableMap;

/**
 * Implementation of {@link DiscreteFunction} backed by a {@link Map}
 * 
 * @author caguiler
 * @see DiscreteFunction
 * @param  the type of the values in x-direction (Independent variable)
 * @param  the type of the values in y-direction (Dependent variable)
 */
public class MapBackedDiscreteFunction implements DiscreteFunction, Serializable {
    private static final long serialVersionUID = 1L;
    private final ImmutableMap function;

    MapBackedDiscreteFunction(Builder builder) {
        this.function = builder.mapBuilder.build();
    }

    @Override
    public Y apply(X input) {
        if (!function.containsKey(input)) {
            throw new IllegalDiscreteFunctionUsageException("No value can be found for given argument: " + input);
        }

        return function.get(input);
    }

    public static final  DiscreteFunction fromMap(Map function) {
        return MapBackedDiscreteFunction. builder().putAll(function).build();
    }

    @Override
    public Set definedXValues() {
        return function.keySet();
    }

    @Override
    public int hashCode() {
        return 31 + ((function == null) ? 0 : function.hashCode());
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (!(obj instanceof MapBackedDiscreteFunction)) {
            return false;
        }
        @SuppressWarnings("rawtypes")
        MapBackedDiscreteFunction other = (MapBackedDiscreteFunction) obj;
        if (function == null) {
            if (other.function != null) {
                return false;
            }
        } else if (!function.equals(other.function)) {
            return false;
        }
        return true;
    }
    
    

    @Override
    public String toString() {
        return "MapBackedDiscreteFunction [function=" + function + "]";
    }

    /**
     * The builder for the function based on a map. This class provides methods to add values to the function.
     * 
     * @author kfuchsbe, caguiler
     * @param  the type of the independent variable (input)
     * @param  the type of the dependent variable (output)
     */
    public static final class Builder implements DiscreteFunctionBuilder {

        private final ImmutableMap.Builder mapBuilder = ImmutableMap.builder();

        Builder() {
            /* Should only be instantiated from the static method */
        }

        public DiscreteFunctionBuilder put(Entry entry) {
            mapBuilder.put(entry);
            return this;
        }

        @Override
        public DiscreteFunctionBuilder put(X key, Y value) {
            mapBuilder.put(key, value);
            return this;
        }

        public DiscreteFunctionBuilder putAll(Map values) {
            mapBuilder.putAll(values);
            return this;
        }

        @Override
        public MapBackedDiscreteFunction build() {
            return new MapBackedDiscreteFunction<>(this);
        }
    }

    public static final  Builder builder() {
        return new Builder<>();
    }

}