/*
 * Copyright 2002-2018 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.expression.spel.support;

import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.springframework.core.convert.TypeDescriptor;
import org.springframework.expression.BeanResolver;
import org.springframework.expression.ConstructorResolver;
import org.springframework.expression.EvaluationContext;
import org.springframework.expression.MethodFilter;
import org.springframework.expression.MethodResolver;
import org.springframework.expression.OperatorOverloader;
import org.springframework.expression.PropertyAccessor;
import org.springframework.expression.TypeComparator;
import org.springframework.expression.TypeConverter;
import org.springframework.expression.TypeLocator;
import org.springframework.expression.TypedValue;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * A powerful and highly configurable {@link EvaluationContext} implementation.
 * This context uses standard implementations of all applicable strategies,
 * based on reflection to resolve properties, methods and fields.
 *
 * <p>For a simpler builder-style context variant for data-binding purposes,
 * consider using {@link SimpleEvaluationContext} instead which allows for
 * opting into several SpEL features as needed by specific evaluation cases.
 *
 * @author Andy Clement
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @since 3.0
 * @see SimpleEvaluationContext
 * @see ReflectivePropertyAccessor
 * @see ReflectiveConstructorResolver
 * @see ReflectiveMethodResolver
 * @see StandardTypeLocator
 * @see StandardTypeConverter
 * @see StandardTypeComparator
 * @see StandardOperatorOverloader
 */
public class StandardEvaluationContext implements EvaluationContext {

	private TypedValue rootObject;

	@Nullable
	private volatile List<PropertyAccessor> propertyAccessors;

	@Nullable
	private volatile List<ConstructorResolver> constructorResolvers;

	@Nullable
	private volatile List<MethodResolver> methodResolvers;

	@Nullable
	private volatile ReflectiveMethodResolver reflectiveMethodResolver;

	@Nullable
	private BeanResolver beanResolver;

	@Nullable
	private TypeLocator typeLocator;

	@Nullable
	private TypeConverter typeConverter;

	private TypeComparator typeComparator = new StandardTypeComparator();

	private OperatorOverloader operatorOverloader = new StandardOperatorOverloader();

	private final Map<String, Object> variables = new ConcurrentHashMap<>();


	/**
	 * Create a {@code StandardEvaluationContext} with a null root object.
	 */
	public StandardEvaluationContext() {
		this.rootObject = TypedValue.NULL;
	}

	/**
	 * Create a {@code StandardEvaluationContext} with the given root object.
	 * @param rootObject the root object to use
	 * @see #setRootObject
	 */
	public StandardEvaluationContext(@Nullable Object rootObject) {
		this.rootObject = new TypedValue(rootObject);
	}


	public void setRootObject(@Nullable Object rootObject, TypeDescriptor typeDescriptor) {
		this.rootObject = new TypedValue(rootObject, typeDescriptor);
	}

	public void setRootObject(@Nullable Object rootObject) {
		this.rootObject = (rootObject != null ? new TypedValue(rootObject) : TypedValue.NULL);
	}

	@Override
	public TypedValue getRootObject() {
		return this.rootObject;
	}

	public void setPropertyAccessors(List<PropertyAccessor> propertyAccessors) {
		this.propertyAccessors = propertyAccessors;
	}

	@Override
	public List<PropertyAccessor> getPropertyAccessors() {
		return initPropertyAccessors();
	}

	public void addPropertyAccessor(PropertyAccessor accessor) {
		addBeforeDefault(initPropertyAccessors(), accessor);
	}

	public boolean removePropertyAccessor(PropertyAccessor accessor) {
		return initPropertyAccessors().remove(accessor);
	}

	public void setConstructorResolvers(List<ConstructorResolver> constructorResolvers) {
		this.constructorResolvers = constructorResolvers;
	}

	@Override
	public List<ConstructorResolver> getConstructorResolvers() {
		return initConstructorResolvers();
	}

	public void addConstructorResolver(ConstructorResolver resolver) {
		addBeforeDefault(initConstructorResolvers(), resolver);
	}

	public boolean removeConstructorResolver(ConstructorResolver resolver) {
		return initConstructorResolvers().remove(resolver);
	}

	public void setMethodResolvers(List<MethodResolver> methodResolvers) {
		this.methodResolvers = methodResolvers;
	}

	@Override
	public List<MethodResolver> getMethodResolvers() {
		return initMethodResolvers();
	}

	public void addMethodResolver(MethodResolver resolver) {
		addBeforeDefault(initMethodResolvers(), resolver);
	}

	public boolean removeMethodResolver(MethodResolver methodResolver) {
		return initMethodResolvers().remove(methodResolver);
	}

	public void setBeanResolver(BeanResolver beanResolver) {
		this.beanResolver = beanResolver;
	}

	@Override
	@Nullable
	public BeanResolver getBeanResolver() {
		return this.beanResolver;
	}

	public void setTypeLocator(TypeLocator typeLocator) {
		Assert.notNull(typeLocator, "TypeLocator must not be null");
		this.typeLocator = typeLocator;
	}

	@Override
	public TypeLocator getTypeLocator() {
		if (this.typeLocator == null) {
			this.typeLocator = new StandardTypeLocator();
		}
		return this.typeLocator;
	}

	public void setTypeConverter(TypeConverter typeConverter) {
		Assert.notNull(typeConverter, "TypeConverter must not be null");
		this.typeConverter = typeConverter;
	}

	@Override
	public TypeConverter getTypeConverter() {
		if (this.typeConverter == null) {
			this.typeConverter = new StandardTypeConverter();
		}
		return this.typeConverter;
	}

	public void setTypeComparator(TypeComparator typeComparator) {
		Assert.notNull(typeComparator, "TypeComparator must not be null");
		this.typeComparator = typeComparator;
	}

	@Override
	public TypeComparator getTypeComparator() {
		return this.typeComparator;
	}

	public void setOperatorOverloader(OperatorOverloader operatorOverloader) {
		Assert.notNull(operatorOverloader, "OperatorOverloader must not be null");
		this.operatorOverloader = operatorOverloader;
	}

	@Override
	public OperatorOverloader getOperatorOverloader() {
		return this.operatorOverloader;
	}

	@Override
	public void setVariable(@Nullable String name, @Nullable Object value) {
		// For backwards compatibility, we ignore null names here...
		// And since ConcurrentHashMap cannot store null values, we simply take null
		// as a remove from the Map (with the same result from lookupVariable below).
		if (name != null) {
			if (value != null) {
				this.variables.put(name, value);
			}
			else {
				this.variables.remove(name);
			}
		}
	}

	public void setVariables(Map<String, Object> variables) {
		variables.forEach(this::setVariable);
	}

	public void registerFunction(String name, Method method) {
		this.variables.put(name, method);
	}

	@Override
	@Nullable
	public Object lookupVariable(String name) {
		return this.variables.get(name);
	}

	/**
	 * Register a {@code MethodFilter} which will be called during method resolution
	 * for the specified type.
	 * <p>The {@code MethodFilter} may remove methods and/or sort the methods which
	 * will then be used by SpEL as the candidates to look through for a match.
	 * @param type the type for which the filter should be called
	 * @param filter a {@code MethodFilter}, or {@code null} to unregister a filter for the type
	 * @throws IllegalStateException if the {@link ReflectiveMethodResolver} is not in use
	 */
	public void registerMethodFilter(Class<?> type, MethodFilter filter) throws IllegalStateException {
		initMethodResolvers();
		ReflectiveMethodResolver resolver = this.reflectiveMethodResolver;
		if (resolver == null) {
			throw new IllegalStateException(
					"Method filter cannot be set as the reflective method resolver is not in use");
		}
		resolver.registerMethodFilter(type, filter);
	}


	private List<PropertyAccessor> initPropertyAccessors() {
		List<PropertyAccessor> accessors = this.propertyAccessors;
		if (accessors == null) {
			accessors = new ArrayList<>(5);
			accessors.add(new ReflectivePropertyAccessor());
			this.propertyAccessors = accessors;
		}
		return accessors;
	}

	private List<ConstructorResolver> initConstructorResolvers() {
		List<ConstructorResolver> resolvers = this.constructorResolvers;
		if (resolvers == null) {
			resolvers = new ArrayList<>(1);
			resolvers.add(new ReflectiveConstructorResolver());
			this.constructorResolvers = resolvers;
		}
		return resolvers;
	}

	private List<MethodResolver> initMethodResolvers() {
		List<MethodResolver> resolvers = this.methodResolvers;
		if (resolvers == null) {
			resolvers = new ArrayList<>(1);
			this.reflectiveMethodResolver = new ReflectiveMethodResolver();
			resolvers.add(this.reflectiveMethodResolver);
			this.methodResolvers = resolvers;
		}
		return resolvers;
	}

	private static <T> void addBeforeDefault(List<T> resolvers, T resolver) {
		resolvers.add(resolvers.size() - 1, resolver);
	}

}
