// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.tensor.functions;

import com.yahoo.tensor.Tensor;
import com.yahoo.tensor.TensorType;
import com.yahoo.tensor.evaluation.EvaluationContext;
import com.yahoo.tensor.evaluation.MapEvaluationContext;
import com.yahoo.tensor.evaluation.Name;
import com.yahoo.tensor.evaluation.TypeContext;

import java.util.List;
import java.util.Optional;
import java.util.function.Function;

/**
 * A representation of a tensor function which is able to be translated to a set of primitive
 * tensor functions if necessary.
 * All tensor functions are immutable.
 *
 * @author bratseth
 */
public abstract class TensorFunction<NAMETYPE extends Name> {

    /** Returns the function arguments of this node in the order they are applied */
    public abstract List<TensorFunction<NAMETYPE>> arguments();

    /**
     * Returns a copy of this tensor function with the arguments replaced by the given list of arguments.
     *
     * @throws IllegalArgumentException if the argument list has the wrong size for this function
     */
    public abstract TensorFunction<NAMETYPE> withArguments(List<TensorFunction<NAMETYPE>> arguments);

    /**
     * Translate this function - and all of its arguments recursively -
     * to a tree of primitive functions only.
     *
     * @return a tree of primitive functions implementing this
     */
    public abstract PrimitiveTensorFunction<NAMETYPE> toPrimitive();

    /**
     * Evaluates this tensor.
     *
     * @param context a context which must be passed to all nested functions when evaluating
     */
    public abstract Tensor evaluate(EvaluationContext<NAMETYPE>  context);

    /**
     * Returns the type of the tensor this produces given the input types in the context
     *
     * @param context a context which must be passed to all nexted functions when evaluating
     */
    public abstract TensorType type(TypeContext<NAMETYPE> context);

    /** Evaluate with no context */
    public final Tensor evaluate() { return evaluate(new MapEvaluationContext<>()); }

    /**
     * Return a string representation of this context.
     *
     * @param context a context which must be passed to all nested functions when requesting the string value
     */
    public abstract String toString(ToStringContext<NAMETYPE> context);

    /** Returns this as a scalar function, or empty if it cannot be represented as a scalar function */
    public Optional<ScalarFunction<NAMETYPE>> asScalarFunction() { return Optional.empty(); }

    @Override
    public String toString() { return toString(ToStringContext.empty()); }

    /** Returns a hashcode computed from the data in this */
    @Override
    public abstract int hashCode();

    public TensorFunction<NAMETYPE> withTransformedFunctions(
            Function<ScalarFunction<NAMETYPE>, ScalarFunction<NAMETYPE>> transformer)
    {
        return this;
    }
}