/*
 * 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.beans.factory.config;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.Map;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.InjectionPoint;
import org.springframework.beans.factory.NoUniqueBeanDefinitionException;
import org.springframework.core.GenericTypeResolver;
import org.springframework.core.MethodParameter;
import org.springframework.core.ParameterNameDiscoverer;
import org.springframework.core.ResolvableType;

/**
 * Descriptor for a specific dependency that is about to be injected.
 * Wraps a constructor parameter, a method parameter or a field,
 * allowing unified access to their metadata.
 *
 * @author Juergen Hoeller
 * @since 2.5
 */
@SuppressWarnings("serial")
public class DependencyDescriptor extends InjectionPoint implements Serializable {

        private final Class<?> declaringClass;

        private String methodName;

        private Class<?>[] parameterTypes;

        private int parameterIndex;

        private String fieldName;

        private final boolean required;

        private final boolean eager;

        private int nestingLevel = 1;

        private Class<?> containingClass;

        private volatile ResolvableType resolvableType;


        /**
         * Create a new descriptor for a method or constructor parameter.
         * Considers the dependency as 'eager'.
         * @param methodParameter the MethodParameter to wrap
         * @param required whether the dependency is required
         */
        public DependencyDescriptor(MethodParameter methodParameter, boolean required) {
                this(methodParameter, required, true);
        }

        /**
         * Create a new descriptor for a method or constructor parameter.
         * @param methodParameter the MethodParameter to wrap
         * @param required whether the dependency is required
         * @param eager whether this dependency is 'eager' in the sense of
         * eagerly resolving potential target beans for type matching
         */
        public DependencyDescriptor(MethodParameter methodParameter, boolean required, boolean eager) {
                super(methodParameter);

                this.declaringClass = methodParameter.getDeclaringClass();
                if (methodParameter.getMethod() != null) {
                        this.methodName = methodParameter.getMethod().getName();
                        this.parameterTypes = methodParameter.getMethod().getParameterTypes();
                }
                else {
                        this.parameterTypes = methodParameter.getConstructor().getParameterTypes();
                }
                this.parameterIndex = methodParameter.getParameterIndex();
                this.containingClass = methodParameter.getContainingClass();
                this.required = required;
                this.eager = eager;
        }

        /**
         * Create a new descriptor for a field.
         * Considers the dependency as 'eager'.
         * @param field the field to wrap
         * @param required whether the dependency is required
         */
        public DependencyDescriptor(Field field, boolean required) {
                this(field, required, true);
        }

        /**
         * Create a new descriptor for a field.
         * @param field the field to wrap
         * @param required whether the dependency is required
         * @param eager whether this dependency is 'eager' in the sense of
         * eagerly resolving potential target beans for type matching
         */
        public DependencyDescriptor(Field field, boolean required, boolean eager) {
                super(field);

                this.declaringClass = field.getDeclaringClass();
                this.fieldName = field.getName();
                this.required = required;
                this.eager = eager;
        }

        /**
         * Copy constructor.
         * @param original the original descriptor to create a copy from
         */
        public DependencyDescriptor(DependencyDescriptor original) {
                super(original);

                this.declaringClass = original.declaringClass;
                this.methodName = original.methodName;
                this.parameterTypes = original.parameterTypes;
                this.parameterIndex = original.parameterIndex;
                this.fieldName = original.fieldName;
                this.containingClass = original.containingClass;
                this.required = original.required;
                this.eager = original.eager;
                this.nestingLevel = original.nestingLevel;
        }


        /**
         * Return whether this dependency is required.
         */
        public boolean isRequired() {
                return this.required;
        }

        /**
         * Return whether this dependency is 'eager' in the sense of
         * eagerly resolving potential target beans for type matching.
         */
        public boolean isEager() {
                return this.eager;
        }

        /**
         * Resolve the specified not-unique scenario: by default,
         * throwing a {@link NoUniqueBeanDefinitionException}.
         * <p>Subclasses may override this to select one of the instances or
         * to opt out with no result at all through returning {@code null}.
         * @param type the requested bean type
         * @param matchingBeans a map of bean names and corresponding bean
         * instances which have been pre-selected for the given type
         * (qualifiers etc already applied)
         * @return a bean instance to proceed with, or {@code null} for none
         * @throws BeansException in case of the not-unique scenario being fatal
         * @since 4.3
         */
        public Object resolveNotUnique(Class<?> type, Map<String, Object> matchingBeans) throws BeansException {
                throw new NoUniqueBeanDefinitionException(type, matchingBeans.keySet());
        }

        /**
         * Resolve a shortcut for this dependency against the given factory, for example
         * taking some pre-resolved information into account.
         * <p>The resolution algorithm will first attempt to resolve a shortcut through this
         * method before going into the regular type matching algorithm across all beans.
         * Subclasses may override this method to improve resolution performance based on
         * pre-cached information while still receiving {@link InjectionPoint} exposure etc.
         * @param beanFactory the associated factory
         * @return the shortcut result if any, or {@code null} if none
         * @throws BeansException if the shortcut could not be obtained
         * @since 4.3.1
         */
        public Object resolveShortcut(BeanFactory beanFactory) throws BeansException {
                return null;
        }

        /**
         * Resolve the specified bean name, as a candidate result of the matching
         * algorithm for this dependency, to a bean instance from the given factory.
         * <p>The default implementation calls {@link BeanFactory#getBean(String)}.
         * Subclasses may provide additional arguments or other customizations.
         * @param beanName the bean name, as a candidate result for this dependency
         * @param requiredType the expected type of the bean (as an assertion)
         * @param beanFactory the associated factory
         * @return the bean instance (never {@code null})
         * @throws BeansException if the bean could not be obtained
         * @since 4.3.2
         * @see BeanFactory#getBean(String)
         */
        public Object resolveCandidate(String beanName, Class<?> requiredType, BeanFactory beanFactory)
                        throws BeansException {

                return beanFactory.getBean(beanName, requiredType);
        }


        /**
         * Increase this descriptor's nesting level.
         * @see MethodParameter#increaseNestingLevel()
         */
        public void increaseNestingLevel() {
                this.nestingLevel++;
                this.resolvableType = null;
                if (this.methodParameter != null) {
                        this.methodParameter.increaseNestingLevel();
                }
        }

        /**
         * Optionally set the concrete class that contains this dependency.
         * This may differ from the class that declares the parameter/field in that
         * it may be a subclass thereof, potentially substituting type variables.
         * @since 4.0
         */
        public void setContainingClass(Class<?> containingClass) {
                this.containingClass = containingClass;
                this.resolvableType = null;
                if (this.methodParameter != null) {
                        GenericTypeResolver.resolveParameterType(this.methodParameter, containingClass);
                }
        }

        /**
         * Build a {@link ResolvableType} object for the wrapped parameter/field.
         * @since 4.0
         */
        public ResolvableType getResolvableType() {
                ResolvableType resolvableType = this.resolvableType;
                if (resolvableType == null) {
                        resolvableType = (this.field != null ?
                                        ResolvableType.forField(this.field, this.nestingLevel, this.containingClass) :
                                        ResolvableType.forMethodParameter(this.methodParameter));
                        this.resolvableType = resolvableType;
                }
                return resolvableType;
        }

        /**
         * Return whether a fallback match is allowed.
         * <p>This is {@code false} by default but may be overridden to return {@code true} in order
         * to suggest to an {@link org.springframework.beans.factory.support.AutowireCandidateResolver}
         * that a fallback match is acceptable as well.
         * @since 4.0
         */
        public boolean fallbackMatchAllowed() {
                return false;
        }

        /**
         * Return a variant of this descriptor that is intended for a fallback match.
         * @since 4.0
         * @see #fallbackMatchAllowed()
         */
        public DependencyDescriptor forFallbackMatch() {
                return new DependencyDescriptor(this) {
                        @Override
                        public boolean fallbackMatchAllowed() {
                                return true;
                        }
                };
        }

        /**
         * Initialize parameter name discovery for the underlying method parameter, if any.
         * <p>This method does not actually try to retrieve the parameter name at
         * this point; it just allows discovery to happen when the application calls
         * {@link #getDependencyName()} (if ever).
         */
        public void initParameterNameDiscovery(ParameterNameDiscoverer parameterNameDiscoverer) {
                if (this.methodParameter != null) {
                        this.methodParameter.initParameterNameDiscovery(parameterNameDiscoverer);
                }
        }

        /**
         * Determine the name of the wrapped parameter/field.
         * @return the declared name (never {@code null})
         */
        public String getDependencyName() {
                return (this.field != null ? this.field.getName() : this.methodParameter.getParameterName());
        }

        /**
         * Determine the declared (non-generic) type of the wrapped parameter/field.
         * @return the declared type (never {@code null})
         */
        public Class<?> getDependencyType() {
                if (this.field != null) {
                        if (this.nestingLevel > 1) {
                                Type type = this.field.getGenericType();
                                for (int i = 2; i <= this.nestingLevel; i++) {
                                        if (type instanceof ParameterizedType) {
                                                Type[] args = ((ParameterizedType) type).getActualTypeArguments();
                                                type = args[args.length - 1];
                                        }
                                }
                                if (type instanceof Class) {
                                        return (Class<?>) type;
                                }
                                else if (type instanceof ParameterizedType) {
                                        Type arg = ((ParameterizedType) type).getRawType();
                                        if (arg instanceof Class) {
                                                return (Class<?>) arg;
                                        }
                                }
                                return Object.class;
                        }
                        else {
                                return this.field.getType();
                        }
                }
                else {
                        return this.methodParameter.getNestedParameterType();
                }
        }

        /**
         * Determine the generic element type of the wrapped Collection parameter/field, if any.
         * @return the generic type, or {@code null} if none
         * @deprecated as of 4.3.6, in favor of direct {@link ResolvableType} usage
         */
        @Deprecated
        public Class<?> getCollectionType() {
                return (this.field != null ?
                                org.springframework.core.GenericCollectionTypeResolver.getCollectionFieldType(this.field, this.nestingLevel) :
                                org.springframework.core.GenericCollectionTypeResolver.getCollectionParameterType(this.methodParameter));
        }

        /**
         * Determine the generic key type of the wrapped Map parameter/field, if any.
         * @return the generic type, or {@code null} if none
         * @deprecated as of 4.3.6, in favor of direct {@link ResolvableType} usage
         */
        @Deprecated
        public Class<?> getMapKeyType() {
                return (this.field != null ?
                                org.springframework.core.GenericCollectionTypeResolver.getMapKeyFieldType(this.field, this.nestingLevel) :
                                org.springframework.core.GenericCollectionTypeResolver.getMapKeyParameterType(this.methodParameter));
        }

        /**
         * Determine the generic value type of the wrapped Map parameter/field, if any.
         * @return the generic type, or {@code null} if none
         * @deprecated as of 4.3.6, in favor of direct {@link ResolvableType} usage
         */
        @Deprecated
        public Class<?> getMapValueType() {
                return (this.field != null ?
                                org.springframework.core.GenericCollectionTypeResolver.getMapValueFieldType(this.field, this.nestingLevel) :
                                org.springframework.core.GenericCollectionTypeResolver.getMapValueParameterType(this.methodParameter));
        }


        @Override
        public boolean equals(Object other) {
                if (this == other) {
                        return true;
                }
                if (!super.equals(other)) {
                        return false;
                }
                DependencyDescriptor otherDesc = (DependencyDescriptor) other;
                return (this.required == otherDesc.required && this.eager == otherDesc.eager &&
                                this.nestingLevel == otherDesc.nestingLevel && this.containingClass == otherDesc.containingClass);
        }


        //---------------------------------------------------------------------
        // Serialization support
        //---------------------------------------------------------------------

        private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
                // Rely on default serialization; just initialize state after deserialization.
                ois.defaultReadObject();

                // Restore reflective handles (which are unfortunately not serializable)
                try {
                        if (this.fieldName != null) {
                                this.field = this.declaringClass.getDeclaredField(this.fieldName);
                        }
                        else {
                                if (this.methodName != null) {
                                        this.methodParameter = new MethodParameter(
                                                        this.declaringClass.getDeclaredMethod(this.methodName, this.parameterTypes), this.parameterIndex);
                                }
                                else {
                                        this.methodParameter = new MethodParameter(
                                                        this.declaringClass.getDeclaredConstructor(this.parameterTypes), this.parameterIndex);
                                }
                                for (int i = 1; i < this.nestingLevel; i++) {
                                        this.methodParameter.increaseNestingLevel();
                                }
                        }
                }
                catch (Throwable ex) {
                        throw new IllegalStateException("Could not find original class structure", ex);
                }
        }

}