[utils] / system / general / src / main / java / org / wamblee / system / adapters / ConstructorConfiguration.java

/*
 * Copyright 2008 the original author or authors.
 *
 * 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 org.wamblee.system.adapters;

import org.wamblee.collections.CollectionFilter;

import org.wamblee.conditions.Condition;

import org.wamblee.system.core.RequiredInterface;
import org.wamblee.system.core.Scope;
import org.wamblee.system.core.SystemAssemblyException;

import java.lang.reflect.Constructor;
import java.lang.reflect.Modifier;

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


/**
 * Class that allows configuration of the constructor to use.   In
 * particular, it provides:
 *  <ul>
 *      <li>Selection of a constructor using explicit selection  {@link
 *      #select(Class...)} or using the most greedy constructor  {@link
 *      #greedy()}.</li>
 *      <li>Selection of methods to invoke to inject other objects into
 *      the object.</li>
 *      <li>Selection of fields to set.</li>
 *  </ul>
 */
public class ConstructorConfiguration {
    /**
     * DOCUMENT ME!
     */
    private Class clazz;

    /**
     * DOCUMENT ME!
     */
    private Constructor<?> constructor;

    /**
     * DOCUMENT ME!
     */
    private ParameterValues values;

    /**
     * DOCUMENT ME!
     */
    private boolean publicOnly;

/**
         * Constructs the configuration. By default the public constructor with the 
         * most arguments will be used.   
         * @param aClass Class to construct. 
         */
    public ConstructorConfiguration(Class aClass) {
        clazz           = aClass;
        constructor     = null;
        publicOnly      = true;
    }

    /**
     * Sets whether or no non public constructors are also considered.
     * Reset the choice of a constructor to its default.
     *
     * @param aNonPublic
     *
     * @return
     */
    public ConstructorConfiguration setNonPublic(boolean aNonPublic) {
        publicOnly      = !aNonPublic;
        constructor     = null;
        values          = null;

        return this;
    }

    /**
     * Selects an explicit constructor.
     *
     * @return Return the injector to allow call chaining.
     *
     * @throws SystemAssemblyException DOCUMENT ME!
     */
    public ConstructorConfiguration select(Class... aTypes) {
        try {
            constructor = clazz.getDeclaredConstructor(aTypes);
        } catch (Exception e) {
            throw new SystemAssemblyException(e.getMessage(), e);
        }

        resetValues();

        return this;
    }

    /**
     * Selects the greediest constructor.
     *
     * @return The injector to allow call chaining.
     *
     * @throws SystemAssemblyException if the greediest constructor cannot be
     *         uniquely  identified.
     */
    public ConstructorConfiguration greedy() {
        Constructor<?>[] declared = clazz.getDeclaredConstructors();

        if (declared.length == 0) {
            throw new SystemAssemblyException("Class '" + clazz
                + " is an interface, primitive type, or array");
        }

        int                  max     = -1;
        List<Constructor<?>> checked = new ArrayList<Constructor<?>>();
        CollectionFilter.filter(Arrays.asList(declared), checked,
            new Condition<Constructor<?>>() {
                @Override
                public boolean matches(Constructor<?> aObject) {
                    if (!publicOnly) {
                        return true;
                    } else {
                        return Modifier.isPublic(aObject.getModifiers());
                    }
                }
            });

        for (Constructor ctor : checked) {
            if (ctor.getParameterTypes().length > max) {
                max = ctor.getParameterTypes().length;
            }
        }

        final int            max2    = max;
        List<Constructor<?>> ctors   = checked;
        List<Constructor<?>> longest = new ArrayList<Constructor<?>>();
        CollectionFilter.filter(ctors, longest,
            new Condition<Constructor<?>>() {
                @Override
                public boolean matches(Constructor<?> aObject) {
                    return aObject.getParameterTypes().length == max2;
                }
            });

        if (longest.size() > 1) {
            throw new SystemAssemblyException(
                "Greediest constructor cannot be uniquely determined");
        }

        constructor = longest.get(0);
        resetValues();

        return this;
    }

    public ParameterValues getParameters() {
        getConstructor(); // initialize constructor if needed.

        return values;
    }

    /**
     * Resets the values.
     */
    private void resetValues() {
        constructor.setAccessible(true);
        values = new ParameterValues(constructor.getParameterTypes());
    }

    /**
     * Creates the object in the given scope.
     *
     * @param aScope Scope containing required interfaces for this object.
     *
     * @return object.
     *
     * @throws SystemAssemblyException DOCUMENT ME!
     */
    public Object create(Scope aScope) {
        Object[] valueArray = values.values(aScope);

        try {
            return getConstructor().newInstance(valueArray);
        } catch (Exception e) {
            throw new SystemAssemblyException("Could not construct object "
                + getConstructor() + " " + Arrays.asList(valueArray), e);
        }
    }

    public List<RequiredInterface> getRequiredInterfaces() {
        getConstructor(); // initialize constructor if needed.

        return values.getRequiredInterfaces();
    }

    private Constructor getConstructor() {
        if (constructor == null) {
            greedy();
        }

        return constructor;
    }
}