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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) 2008-2011, 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.tensorbacked;

import static org.tensorics.core.util.InstantiatorType.CONSTRUCTOR;
import static org.tensorics.core.util.Instantiators.instantiatorFor;

import java.util.ArrayList;
import java.util.List;
import java.util.Set;

import org.tensorics.core.tensor.Tensor;
import org.tensorics.core.tensorbacked.annotation.Dimensions;

import com.google.common.collect.ImmutableSet;

/**
 * This class gives an access to the methods for {@link Tensorbacked} object support.
 * 
 * @author agorzaws, kfuchsbe
 */
public final class TensorbackedInternals {

    private TensorbackedInternals() {
        /* Only static methods */
    }

    /**
     * Retrieves the dimensions from the given class inheriting from tensor backed. This is done by inspecting the
     * {@link Dimensions} annotation.
     * 
     * @param tensorBackedClass the class for which to determine the dimensions
     * @return the set of dimentions (classses of coordinates) which are required to create an instance of the given
     *         class.
     */
    public static Set> dimensionsOf(Class> tensorBackedClass) {
        Dimensions dimensionAnnotation = tensorBackedClass.getAnnotation(Dimensions.class);
        if (dimensionAnnotation == null) {
            throw new IllegalArgumentException("No annotation of type '" + Dimensions.class
                    + "' is present on the class '" + tensorBackedClass
                    + "'. Therefore, the dimensions of this tensorbacked type cannot be determined.");
        }
        return ImmutableSet.copyOf(dimensionAnnotation.value());
    }

    /**
     * Creates an instance of a class backed by a tensor.
     * 
     * @param tensorBackedClass the type of the class for which to create an instance.
     * @param tensor the tensor to back the instance
     * @return a new instance of the given class, backed by the given tensor
     */
    public static > T createBackedByTensor(Class tensorBackedClass, Tensor tensor) {
        verifyDimensions(tensorBackedClass, tensor);
        return instantiatorFor(tensorBackedClass).ofType(CONSTRUCTOR).withArgumentType(Tensor.class).create(tensor);
    }

    private static , V> void verifyDimensions(Class tensorBackedClass, Tensor tensor) {
        Set> targetDimensions = dimensionsOf(tensorBackedClass);
        Set> tensorDimensions = tensor.shape().dimensionSet();
        if (!targetDimensions.equals(tensorDimensions)) {
            throw new IllegalArgumentException("Dimensions of target class (" + targetDimensions
                    + ") do not match dimensions of given tensor (" + tensorDimensions + "). Cannot create object.");
        }
    }

    public static  Iterable> tensorsOf(Iterable> tensorbackeds) {
        List> tensors = new ArrayList<>();
        for (Tensorbacked tensorbacked : tensorbackeds) {
            tensors.add(tensorbacked.tensor());
        }
        return tensors;
    }

}