/*
 * Copyright 2002-2019 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
 *
 *      https://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.springframework.context.support;

import java.io.IOException;
import java.lang.reflect.Constructor;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.function.Supplier;

import org.springframework.beans.BeanUtils;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanDefinitionStoreException;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.beans.factory.config.AutowireCapableBeanFactory;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanDefinitionCustomizer;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.context.ApplicationContext;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.io.support.ResourcePatternResolver;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * Generic ApplicationContext implementation that holds a single internal
 * {@link org.springframework.beans.factory.support.DefaultListableBeanFactory}
 * instance and does not assume a specific bean definition format. Implements
 * the {@link org.springframework.beans.factory.support.BeanDefinitionRegistry}
 * interface in order to allow for applying any bean definition readers to it.
 *
 * <p>Typical usage is to register a variety of bean definitions via the
 * {@link org.springframework.beans.factory.support.BeanDefinitionRegistry}
 * interface and then call {@link #refresh()} to initialize those beans
 * with application context semantics (handling
 * {@link org.springframework.context.ApplicationContextAware}, auto-detecting
 * {@link org.springframework.beans.factory.config.BeanFactoryPostProcessor BeanFactoryPostProcessors},
 * etc).
 *
 * <p>In contrast to other ApplicationContext implementations that create a new
 * internal BeanFactory instance for each refresh, the internal BeanFactory of
 * this context is available right from the start, to be able to register bean
 * definitions on it. {@link #refresh()} may only be called once.
 *
 * <p>Usage example:
 *
 * <pre class="code">
 * GenericApplicationContext ctx = new GenericApplicationContext();
 * XmlBeanDefinitionReader xmlReader = new XmlBeanDefinitionReader(ctx);
 * xmlReader.loadBeanDefinitions(new ClassPathResource("applicationContext.xml"));
 * PropertiesBeanDefinitionReader propReader = new PropertiesBeanDefinitionReader(ctx);
 * propReader.loadBeanDefinitions(new ClassPathResource("otherBeans.properties"));
 * ctx.refresh();
 *
 * MyBean myBean = (MyBean) ctx.getBean("myBean");
 * ...</pre>
 *
 * For the typical case of XML bean definitions, simply use
 * {@link ClassPathXmlApplicationContext} or {@link FileSystemXmlApplicationContext},
 * which are easier to set up - but less flexible, since you can just use standard
 * resource locations for XML bean definitions, rather than mixing arbitrary bean
 * definition formats. The equivalent in a web environment is
 * {@link org.springframework.web.context.support.XmlWebApplicationContext}.
 *
 * <p>For custom application context implementations that are supposed to read
 * special bean definition formats in a refreshable manner, consider deriving
 * from the {@link AbstractRefreshableApplicationContext} base class.
 *
 * @author Juergen Hoeller
 * @author Chris Beams
 * @since 1.1.2
 * @see #registerBeanDefinition
 * @see #refresh()
 * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
 * @see org.springframework.beans.factory.support.PropertiesBeanDefinitionReader
 */
public class GenericApplicationContext extends AbstractApplicationContext implements BeanDefinitionRegistry {

        private final DefaultListableBeanFactory beanFactory;

        @Nullable
        private ResourceLoader resourceLoader;

        private boolean customClassLoader = false;

        private final AtomicBoolean refreshed = new AtomicBoolean();


        /**
         * Create a new GenericApplicationContext.
         * @see #registerBeanDefinition
         * @see #refresh
         */
        public GenericApplicationContext() {
                this.beanFactory = new DefaultListableBeanFactory();
        }

        /**
         * Create a new GenericApplicationContext with the given DefaultListableBeanFactory.
         * @param beanFactory the DefaultListableBeanFactory instance to use for this context
         * @see #registerBeanDefinition
         * @see #refresh
         */
        public GenericApplicationContext(DefaultListableBeanFactory beanFactory) {
                Assert.notNull(beanFactory, "BeanFactory must not be null");
                this.beanFactory = beanFactory;
        }

        /**
         * Create a new GenericApplicationContext with the given parent.
         * @param parent the parent application context
         * @see #registerBeanDefinition
         * @see #refresh
         */
        public GenericApplicationContext(@Nullable ApplicationContext parent) {
                this();
                setParent(parent);
        }

        /**
         * Create a new GenericApplicationContext with the given DefaultListableBeanFactory.
         * @param beanFactory the DefaultListableBeanFactory instance to use for this context
         * @param parent the parent application context
         * @see #registerBeanDefinition
         * @see #refresh
         */
        public GenericApplicationContext(DefaultListableBeanFactory beanFactory, ApplicationContext parent) {
                this(beanFactory);
                setParent(parent);
        }


        /**
         * Set the parent of this application context, also setting
         * the parent of the internal BeanFactory accordingly.
         * @see org.springframework.beans.factory.config.ConfigurableBeanFactory#setParentBeanFactory
         */
        @Override
        public void setParent(@Nullable ApplicationContext parent) {
                super.setParent(parent);
                this.beanFactory.setParentBeanFactory(getInternalParentBeanFactory());
        }

        /**
         * Set whether it should be allowed to override bean definitions by registering
         * a different definition with the same name, automatically replacing the former.
         * If not, an exception will be thrown. Default is "true".
         * @since 3.0
         * @see org.springframework.beans.factory.support.DefaultListableBeanFactory#setAllowBeanDefinitionOverriding
         */
        public void setAllowBeanDefinitionOverriding(boolean allowBeanDefinitionOverriding) {
                this.beanFactory.setAllowBeanDefinitionOverriding(allowBeanDefinitionOverriding);
        }

        /**
         * Set whether to allow circular references between beans - and automatically
         * try to resolve them.
         * <p>Default is "true". Turn this off to throw an exception when encountering
         * a circular reference, disallowing them completely.
         * @since 3.0
         * @see org.springframework.beans.factory.support.DefaultListableBeanFactory#setAllowCircularReferences
         */
        public void setAllowCircularReferences(boolean allowCircularReferences) {
                this.beanFactory.setAllowCircularReferences(allowCircularReferences);
        }

        /**
         * Set a ResourceLoader to use for this context. If set, the context will
         * delegate all {@code getResource} calls to the given ResourceLoader.
         * If not set, default resource loading will apply.
         * <p>The main reason to specify a custom ResourceLoader is to resolve
         * resource paths (without URL prefix) in a specific fashion.
         * The default behavior is to resolve such paths as class path locations.
         * To resolve resource paths as file system locations, specify a
         * FileSystemResourceLoader here.
         * <p>You can also pass in a full ResourcePatternResolver, which will
         * be autodetected by the context and used for {@code getResources}
         * calls as well. Else, default resource pattern matching will apply.
         * @see #getResource
         * @see org.springframework.core.io.DefaultResourceLoader
         * @see org.springframework.core.io.FileSystemResourceLoader
         * @see org.springframework.core.io.support.ResourcePatternResolver
         * @see #getResources
         */
        public void setResourceLoader(ResourceLoader resourceLoader) {
                this.resourceLoader = resourceLoader;
        }


        //---------------------------------------------------------------------
        // ResourceLoader / ResourcePatternResolver override if necessary
        //---------------------------------------------------------------------

        /**
         * This implementation delegates to this context's ResourceLoader if set,
         * falling back to the default superclass behavior else.
         * @see #setResourceLoader
         */
        @Override
        public Resource getResource(String location) {
                if (this.resourceLoader != null) {
                        return this.resourceLoader.getResource(location);
                }
                return super.getResource(location);
        }

        /**
         * This implementation delegates to this context's ResourceLoader if it
         * implements the ResourcePatternResolver interface, falling back to the
         * default superclass behavior else.
         * @see #setResourceLoader
         */
        @Override
        public Resource[] getResources(String locationPattern) throws IOException {
                if (this.resourceLoader instanceof ResourcePatternResolver) {
                        return ((ResourcePatternResolver) this.resourceLoader).getResources(locationPattern);
                }
                return super.getResources(locationPattern);
        }

        @Override
        public void setClassLoader(@Nullable ClassLoader classLoader) {
                super.setClassLoader(classLoader);
                this.customClassLoader = true;
        }

        @Override
        @Nullable
        public ClassLoader getClassLoader() {
                if (this.resourceLoader != null && !this.customClassLoader) {
                        return this.resourceLoader.getClassLoader();
                }
                return super.getClassLoader();
        }


        //---------------------------------------------------------------------
        // Implementations of AbstractApplicationContext's template methods
        //---------------------------------------------------------------------

        /**
         * Do nothing: We hold a single internal BeanFactory and rely on callers
         * to register beans through our public methods (or the BeanFactory's).
         * @see #registerBeanDefinition
         */
        @Override
        protected final void refreshBeanFactory() throws IllegalStateException {
                if (!this.refreshed.compareAndSet(false, true)) {
                        throw new IllegalStateException(
                                        "GenericApplicationContext does not support multiple refresh attempts: just call 'refresh' once");
                }
                this.beanFactory.setSerializationId(getId());
        }

        @Override
        protected void cancelRefresh(BeansException ex) {
                this.beanFactory.setSerializationId(null);
                super.cancelRefresh(ex);
        }

        /**
         * Not much to do: We hold a single internal BeanFactory that will never
         * get released.
         */
        @Override
        protected final void closeBeanFactory() {
                this.beanFactory.setSerializationId(null);
        }

        /**
         * Return the single internal BeanFactory held by this context
         * (as ConfigurableListableBeanFactory).
         */
        @Override
        public final ConfigurableListableBeanFactory getBeanFactory() {
                return this.beanFactory;
        }

        /**
         * Return the underlying bean factory of this context,
         * available for registering bean definitions.
         * <p><b>NOTE:</b> You need to call {@link #refresh()} to initialize the
         * bean factory and its contained beans with application context semantics
         * (autodetecting BeanFactoryPostProcessors, etc).
         * @return the internal bean factory (as DefaultListableBeanFactory)
         */
        public final DefaultListableBeanFactory getDefaultListableBeanFactory() {
                return this.beanFactory;
        }

        @Override
        public AutowireCapableBeanFactory getAutowireCapableBeanFactory() throws IllegalStateException {
                assertBeanFactoryActive();
                return this.beanFactory;
        }


        //---------------------------------------------------------------------
        // Implementation of BeanDefinitionRegistry
        //---------------------------------------------------------------------

        @Override
        public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
                        throws BeanDefinitionStoreException {

                this.beanFactory.registerBeanDefinition(beanName, beanDefinition);
        }

        @Override
        public void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
                this.beanFactory.removeBeanDefinition(beanName);
        }

        @Override
        public BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
                return this.beanFactory.getBeanDefinition(beanName);
        }

        @Override
        public boolean isBeanNameInUse(String beanName) {
                return this.beanFactory.isBeanNameInUse(beanName);
        }

        @Override
        public void registerAlias(String beanName, String alias) {
                this.beanFactory.registerAlias(beanName, alias);
        }

        @Override
        public void removeAlias(String alias) {
                this.beanFactory.removeAlias(alias);
        }

        @Override
        public boolean isAlias(String beanName) {
                return this.beanFactory.isAlias(beanName);
        }


        //---------------------------------------------------------------------
        // Convenient methods for registering individual beans
        //---------------------------------------------------------------------

        /**
         * Register a bean from the given bean class, optionally providing explicit
         * constructor arguments for consideration in the autowiring process.
         * @param beanClass the class of the bean
         * @param constructorArgs custom argument values to be fed into Spring's
         * constructor resolution algorithm, resolving either all arguments or just
         * specific ones, with the rest to be resolved through regular autowiring
         * (may be {@code null} or empty)
         * @since 5.2 (since 5.0 on the AnnotationConfigApplicationContext subclass)
         */
        public <T> void registerBean(Class<T> beanClass, Object... constructorArgs) {
                registerBean(null, beanClass, constructorArgs);
        }

        /**
         * Register a bean from the given bean class, optionally providing explicit
         * constructor arguments for consideration in the autowiring process.
         * @param beanName the name of the bean (may be {@code null})
         * @param beanClass the class of the bean
         * @param constructorArgs custom argument values to be fed into Spring's
         * constructor resolution algorithm, resolving either all arguments or just
         * specific ones, with the rest to be resolved through regular autowiring
         * (may be {@code null} or empty)
         * @since 5.2 (since 5.0 on the AnnotationConfigApplicationContext subclass)
         */
        public <T> void registerBean(@Nullable String beanName, Class<T> beanClass, Object... constructorArgs) {
                registerBean(beanName, beanClass, (Supplier<T>) null,
                                bd -> {
                                        for (Object arg : constructorArgs) {
                                                bd.getConstructorArgumentValues().addGenericArgumentValue(arg);
                                        }
                                });
        }

        /**
         * Register a bean from the given bean class, optionally customizing its
         * bean definition metadata (typically declared as a lambda expression).
         * @param beanClass the class of the bean (resolving a public constructor
         * to be autowired, possibly simply the default constructor)
         * @param customizers one or more callbacks for customizing the factory's
         * {@link BeanDefinition}, e.g. setting a lazy-init or primary flag
         * @since 5.0
         * @see #registerBean(String, Class, Supplier, BeanDefinitionCustomizer...)
         */
        public final <T> void registerBean(Class<T> beanClass, BeanDefinitionCustomizer... customizers) {
                registerBean(null, beanClass, null, customizers);
        }

        /**
         * Register a bean from the given bean class, optionally customizing its
         * bean definition metadata (typically declared as a lambda expression).
         * @param beanName the name of the bean (may be {@code null})
         * @param beanClass the class of the bean (resolving a public constructor
         * to be autowired, possibly simply the default constructor)
         * @param customizers one or more callbacks for customizing the factory's
         * {@link BeanDefinition}, e.g. setting a lazy-init or primary flag
         * @since 5.0
         * @see #registerBean(String, Class, Supplier, BeanDefinitionCustomizer...)
         */
        public final <T> void registerBean(
                        @Nullable String beanName, Class<T> beanClass, BeanDefinitionCustomizer... customizers) {

                registerBean(beanName, beanClass, null, customizers);
        }

        /**
         * Register a bean from the given bean class, using the given supplier for
         * obtaining a new instance (typically declared as a lambda expression or
         * method reference), optionally customizing its bean definition metadata
         * (again typically declared as a lambda expression).
         * @param beanClass the class of the bean
         * @param supplier a callback for creating an instance of the bean
         * @param customizers one or more callbacks for customizing the factory's
         * {@link BeanDefinition}, e.g. setting a lazy-init or primary flag
         * @since 5.0
         * @see #registerBean(String, Class, Supplier, BeanDefinitionCustomizer...)
         */
        public final <T> void registerBean(
                        Class<T> beanClass, Supplier<T> supplier, BeanDefinitionCustomizer... customizers) {

                registerBean(null, beanClass, supplier, customizers);
        }

        /**
         * Register a bean from the given bean class, using the given supplier for
         * obtaining a new instance (typically declared as a lambda expression or
         * method reference), optionally customizing its bean definition metadata
         * (again typically declared as a lambda expression).
         * <p>This method can be overridden to adapt the registration mechanism for
         * all {@code registerBean} methods (since they all delegate to this one).
         * @param beanName the name of the bean (may be {@code null})
         * @param beanClass the class of the bean
         * @param supplier a callback for creating an instance of the bean (in case
         * of {@code null}, resolving a public constructor to be autowired instead)
         * @param customizers one or more callbacks for customizing the factory's
         * {@link BeanDefinition}, e.g. setting a lazy-init or primary flag
         * @since 5.0
         */
        public <T> void registerBean(@Nullable String beanName, Class<T> beanClass,
                        @Nullable Supplier<T> supplier, BeanDefinitionCustomizer... customizers) {

                ClassDerivedBeanDefinition beanDefinition = new ClassDerivedBeanDefinition(beanClass);
                if (supplier != null) {
                        beanDefinition.setInstanceSupplier(supplier);
                }
                for (BeanDefinitionCustomizer customizer : customizers) {
                        customizer.customize(beanDefinition);
                }

                String nameToUse = (beanName != null ? beanName : beanClass.getName());
                registerBeanDefinition(nameToUse, beanDefinition);
        }


        /**
         * {@link RootBeanDefinition} marker subclass for {@code #registerBean} based
         * registrations with flexible autowiring for public constructors.
         */
        @SuppressWarnings("serial")
        private static class ClassDerivedBeanDefinition extends RootBeanDefinition {

                public ClassDerivedBeanDefinition(Class<?> beanClass) {
                        super(beanClass);
                }

                public ClassDerivedBeanDefinition(ClassDerivedBeanDefinition original) {
                        super(original);
                }

                @Override
                @Nullable
                public Constructor<?>[] getPreferredConstructors() {
                        Class<?> clazz = getBeanClass();
                        Constructor<?> primaryCtor = BeanUtils.findPrimaryConstructor(clazz);
                        if (primaryCtor != null) {
                                return new Constructor<?>[] {primaryCtor};
                        }
                        Constructor<?>[] publicCtors = clazz.getConstructors();
                        if (publicCtors.length > 0) {
                                return publicCtors;
                        }
                        return null;
                }

                @Override
                public RootBeanDefinition cloneBeanDefinition() {
                        return new ClassDerivedBeanDefinition(this);
                }
        }

}