/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.wicket.bean.validation;

import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

import javax.validation.ConstraintViolation;
import javax.validation.Validator;
import javax.validation.groups.Default;
import javax.validation.metadata.ConstraintDescriptor;

import org.apache.wicket.Component;
import org.apache.wicket.behavior.Behavior;
import org.apache.wicket.markup.ComponentTag;
import org.apache.wicket.markup.html.form.FormComponent;
import org.apache.wicket.model.IModel;
import org.apache.wicket.model.PropertyModel;
import org.apache.wicket.validation.INullAcceptingValidator;
import org.apache.wicket.validation.IValidatable;

/**
 * Validator that delegates to the bean validation framework. The integration has to be first
 * configured using {@link BeanValidationConfiguration}.
 * 
 * <p>
 * The validator must be provided a {@link Property}, unless one can be resolved from the component
 * implicitly. By default the configuration contains the {@link DefaultPropertyResolver} so
 * {@link PropertyModel}s are supported out of the box - when attached to a component with a
 * property model the property does not need to be specified explicitly.
 * </p>
 * 
 * <p>
 * The validator will set the required flag on the form component it is attached to based on the
 * presence of the @NotNull annotation, see {@link BeanValidationContext#isRequiredConstraint(ConstraintDescriptor)}
 * for details. Notice, the required flag will only be set to {@code true},
 * components with the required flag already set to {@code true} will not have the flag set to
 * {@code false} by this validator.
 * </p>
 * 
 * <p>
 * The validator will allow {@link ITagModifier}s registered on {@link BeanValidationContext}
 * to mutate the markup tag of the component it is attached to, e.g. add a <code>maxlength</code> attribute.
 * </p>
 * 
 * <p>
 * The validator specifies default error messages in the {@code PropertyValidator.properties} file.
 * These values can be overridden in the application subclass' property files globally or in the
 * page or panel properties locally. See this file for the default messages supported.
 * </p>
 * 
 * @author igor
 * 
 * @param <T>
 */
public class PropertyValidator<T> extends Behavior implements INullAcceptingValidator<T>
{
        private static final Class<?>[] EMPTY = new Class<?>[0];

        private FormComponent<T> component;

        // the trailing underscore means that these members should not be used
        // directly. ALWAYS use the respective getter instead.
        private Property property_;

        private final IModel<Class<?>[]> groups_;

        /**
         * A flag indicating whether the component has been configured at least once.
         */
        private boolean requiredFlagSet;

        public PropertyValidator(Class<?>... groups)
        {
                this(null, groups);
        }

        public PropertyValidator(IModel<Class<?>[]> groups)
        {
                this(null, groups);
        }

        public PropertyValidator(Property property, Class<?>... groups)
        {
                this(property, new GroupsModel(groups));
        }

        public PropertyValidator(Property property, IModel<Class<?>[]> groups)
        {
                this.property_ = property;
                this.groups_ = groups;
        }

        /**
         * To support debugging, trying to provide useful information where possible
         * 
         * @return
         */
        private String createUnresolvablePropertyMessage(FormComponent<T> component)
        {
                String baseMessage = "Could not resolve Bean Property from component: " + component
                        + ". (Hints:) Possible causes are a typo in the PropertyExpression, a null reference or a model that does not work in combination with a "
                        + IPropertyResolver.class.getSimpleName() + ".";
                IModel<?> model = ValidationModelResolver.resolvePropertyModelFrom(component);
                if (model != null)
                {
                        baseMessage += " Model : " + model;
                }
                return baseMessage;
        }

        private Property getProperty()
        {
                if (property_ == null)
                {
                        BeanValidationContext config = BeanValidationConfiguration.get();
                        property_ = config.resolveProperty(component);
                        if (property_ == null)
                        {
                                throw new IllegalStateException(createUnresolvablePropertyMessage(component));
                        }
                }
                return property_;
        }

        private Class<?>[] getGroups()
        {
                if (groups_ == null)
                {
                        return EMPTY;
                }
                return groups_.getObject();
        }

        @SuppressWarnings("unchecked")
        @Override
        public void bind(Component component)
        {
                if (this.component != null)
                {
                        throw new IllegalStateException( //
                                "This validator has already been added to component: " + this.component
                                        + ". This validator does not support reusing instances, please create a new one");
                }

                if (!(component instanceof FormComponent))
                {
                        throw new IllegalStateException(
                                getClass().getSimpleName() + " can only be added to FormComponents");
                }

                // TODO add a validation key that appends the type so we can have
                // different messages for
                // @Size on String vs Collection - done but need to add a key for each
                // superclass/interface

                this.component = (FormComponent<T>)component;
        }

        @Override
        public void onConfigure(Component component)
        {
                super.onConfigure(component);
                if (requiredFlagSet == false)
                {
                        // "Required" flag is calculated upon component's model property, so
                        // we must ensure,
                        // that model object is accessible (i.e. component is already added
                        // in a page).
                        requiredFlagSet = true;

                        if (isRequired())
                        {
                                this.component.setRequired(true);
                        }
                }
        }

        @Override
        public void detach(Component component)
        {
                super.detach(component);
                if (groups_ != null)
                {
                        groups_.detach();
                }
        }

        /**
         * Should this property make the owning component required.
         * 
         * @return <code>true</code> if required
         * 
         * @see BeanValidationContext#isRequiredConstraint(ConstraintDescriptor)
         */
        protected boolean isRequired()
        {
                BeanValidationContext config = BeanValidationConfiguration.get();

                HashSet<Class<?>> groups = new HashSet<Class<?>>(Arrays.asList(getGroups()));

                Iterator<ConstraintDescriptor<?>> it = new ConstraintIterator(config.getValidator(), getProperty());
                while (it.hasNext())
                {
                        ConstraintDescriptor<?> constraint = it.next();
                        
                        if (config.isRequiredConstraint(constraint))
                        {
                                if (canApplyToDefaultGroup(constraint) && groups.size() == 0)
                                {
                                        return true;
                                }
                
                                for (Class<?> constraintGroup : constraint.getGroups())
                                {
                                        if (groups.contains(constraintGroup))
                                        {
                                                return true;
                                        }
                                }
                        }
                }

                return false;
        }

        private boolean canApplyToDefaultGroup(ConstraintDescriptor<?> constraint)
        {
                Set<Class<?>> groups = constraint.getGroups();
                //the constraint can be applied to default group either if its group array is empty
                //or if it contains javax.validation.groups.Default
                return groups.size() == 0 || groups.contains(Default.class);
        }

        @Override
        @SuppressWarnings({ "rawtypes", "unchecked" })
        public void onComponentTag(Component component, ComponentTag tag)
        {
                super.onComponentTag(component, tag);

                BeanValidationContext config = BeanValidationConfiguration.get();
                Validator validator = config.getValidator();
                Property property = getProperty();

                // find any tag modifiers that apply to the constraints of the property
                // being validated
                // and allow them to modify the component tag

                Iterator<ConstraintDescriptor<?>> it = new ConstraintIterator(validator, property,
                        getGroups());

                while (it.hasNext())
                {
                        ConstraintDescriptor<?> desc = it.next();

                        ITagModifier modifier = config.getTagModifier(desc.getAnnotation().annotationType());

                        if (modifier != null)
                        {
                                modifier.modify((FormComponent<?>)component, tag, desc.getAnnotation());
                        }
                }
        }

        @SuppressWarnings("unchecked")
        @Override
        public void validate(IValidatable<T> validatable)
        {
                BeanValidationContext config = BeanValidationConfiguration.get();
                Validator validator = config.getValidator();

                Property property = getProperty();

                // validate the value using the bean validator

                Set<?> violations = validator.validateValue(property.getOwner(), property.getName(),
                        validatable.getValue(), getGroups());

                // iterate over violations and report them

                for (ConstraintViolation<?> violation : (Set<ConstraintViolation<?>>)violations)
                {
                        validatable.error(config.getViolationTranslator().convert(violation));
                }
        }

}