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/*
 * 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.
 */
package com.github.dm.jrt.function;

import com.github.dm.jrt.util.Reflection;

import org.jetbrains.annotations.NotNull;

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

/**
 * Class wrapping a function instance.
 * 
 * Created by davide-maestroni on 10/11/2015.
 *
 * @param   the input data type.
 * @param  the output data type.
 */
public class FunctionWrapper implements Function {

    private final List> mFunctions;

    /**
     * Constructor.
     *
     * @param functions the list of wrapped functions.
     */
    FunctionWrapper(@NotNull final List> functions) {

        if (functions.isEmpty()) {

            throw new IllegalArgumentException("the list of functions must not be empty");
        }

        mFunctions = functions;
    }

    /**
     * Returns a composed function wrapper that first applies this function to its input, and then
     * applies the after function to the result.
     *
     * @param after   the function to apply after this function is applied.
     * @param  the type of output of the after function.
     * @return the composed function.
     */
    @NotNull
    public  FunctionWrapper andThen(
            @NotNull final Function after) {

        final Class functionClass = after.getClass();
        final List> functions = mFunctions;
        final ArrayList> newFunctions =
                new ArrayList>(functions.size() + 1);
        newFunctions.addAll(functions);

        if (functionClass == FunctionWrapper.class) {

            newFunctions.addAll(((FunctionWrapper) after).mFunctions);

        } else {

            newFunctions.add(after);
        }

        return new FunctionWrapper(newFunctions);
    }

    @SuppressWarnings("unchecked")
    public OUT apply(final IN in) {

        Object result = in;

        for (final Function function : mFunctions) {

            result = ((Function) function).apply(result);
        }

        return (OUT) result;
    }

    /**
     * Returns a composed function wrapper that first applies the before function to its input,
     * and then applies this function to the result.
     *
     * @param before   the function to apply before this function is applied.
     * @param  the type of input to the before function.
     * @return the composed function.
     */
    @NotNull
    public  FunctionWrapper compose(
            @NotNull final Function before) {

        final Class functionClass = before.getClass();
        final List> functions = mFunctions;
        final ArrayList> newFunctions =
                new ArrayList>(functions.size() + 1);

        if (functionClass == FunctionWrapper.class) {

            newFunctions.addAll(((FunctionWrapper) before).mFunctions);

        } else {

            newFunctions.add(before);
        }

        newFunctions.addAll(functions);
        return new FunctionWrapper(newFunctions);
    }

    /**
     * Checks if the functions wrapped by this instance have a static context.
     *
     * @return whether the functions have a static context.
     */
    public boolean hasStaticContext() {

        for (final Function function : mFunctions) {

            if (!Reflection.hasStaticContext(function.getClass())) {

                return false;
            }
        }

        return true;
    }

    @Override
    public int hashCode() {

        int result = 0;

        for (final Function function : mFunctions) {

            result = 31 * result + function.getClass().hashCode();
        }

        return result;
    }

    @Override
    public boolean equals(final Object o) {

        if (this == o) {

            return true;
        }

        if ((o == null) || (getClass() != o.getClass())) {

            return false;
        }

        final FunctionWrapper that = (FunctionWrapper) o;
        final List> thisFunctions = mFunctions;
        final List> thatFunctions = that.mFunctions;
        final int size = thisFunctions.size();

        if (size != thatFunctions.size()) {

            return false;
        }

        for (int i = 0; i < size; ++i) {

            if (thisFunctions.get(i).getClass() != thatFunctions.get(i).getClass()) {

                return false;
            }
        }

        return true;
    }
}