namespace System.Web.ModelBinding {
    using System;
    using System.Collections.Generic;
    using System.Linq;

    public sealed class ModelValidationNode {

        public ModelValidationNode(ModelMetadata modelMetadata, string modelStateKey)
            : this(modelMetadata, modelStateKey, null) {
        }

        public ModelValidationNode(ModelMetadata modelMetadata, string modelStateKey, IEnumerable<ModelValidationNode> childNodes) {
            if (modelMetadata == null) {
                throw new ArgumentNullException("modelMetadata");
            }
            if (modelStateKey == null) {
                throw new ArgumentNullException("modelStateKey");
            }

            ModelMetadata = modelMetadata;
            ModelStateKey = modelStateKey;
            ChildNodes = (childNodes != null) ? childNodes.ToList() : new List<ModelValidationNode>();
        }

        public ICollection<ModelValidationNode> ChildNodes {
            get;
            private set;
        }

        public ModelMetadata ModelMetadata {
            get;
            private set;
        }

        public string ModelStateKey {
            get;
            private set;
        }

        public bool ValidateAllProperties {
            get;
            set;
        }

        public bool SuppressValidation {
            get;
            set;
        }

        public event EventHandler<ModelValidatedEventArgs> Validated;

        public event EventHandler<ModelValidatingEventArgs> Validating;

        public void CombineWith(ModelValidationNode otherNode) {
            if (otherNode != null && !otherNode.SuppressValidation) {
                Validated += otherNode.Validated;
                Validating += otherNode.Validating;
                foreach (ModelValidationNode childNode in otherNode.ChildNodes) {
                    ChildNodes.Add(childNode);
                }
            }
        }

        private void OnValidated(ModelValidatedEventArgs e) {
            EventHandler<ModelValidatedEventArgs> handler = Validated;
            if (handler != null) {
                handler(this, e);
            }
        }

        private void OnValidating(ModelValidatingEventArgs e) {
            EventHandler<ModelValidatingEventArgs> handler = Validating;
            if (handler != null) {
                handler(this, e);
            }
        }

        private object TryConvertContainerToMetadataType(ModelValidationNode parentNode) {
            if (parentNode != null) {
                object containerInstance = parentNode.ModelMetadata.Model;
                if (containerInstance != null) {
                    Type expectedContainerType = ModelMetadata.ContainerType;
                    if (expectedContainerType != null) {
                        if (expectedContainerType.IsInstanceOfType(containerInstance)) {
                            return containerInstance;
                        }
                    }
                }
            }

            return null;
        }

        public void Validate(ModelBindingExecutionContext modelBindingExecutionContext) {
            Validate(modelBindingExecutionContext, null /* parentNode */);
        }

        public void Validate(ModelBindingExecutionContext modelBindingExecutionContext, ModelValidationNode parentNode) {
            if (modelBindingExecutionContext == null) {
                throw new ArgumentNullException("modelBindingExecutionContext");
            }

            if (SuppressValidation) {
                // no-op
                return;
            }

            // pre-validation steps
            ModelValidatingEventArgs eValidating = new ModelValidatingEventArgs(modelBindingExecutionContext, parentNode);
            OnValidating(eValidating);
            if (eValidating.Cancel) {
                return;
            }

            ValidateChildren(modelBindingExecutionContext);
            ValidateThis(modelBindingExecutionContext, parentNode);

            // post-validation steps
            ModelValidatedEventArgs eValidated = new ModelValidatedEventArgs(modelBindingExecutionContext, parentNode);
            OnValidated(eValidated);
        }

        private void ValidateChildren(ModelBindingExecutionContext modelBindingExecutionContext) {
            foreach (ModelValidationNode child in ChildNodes) {
                child.Validate(modelBindingExecutionContext, this);
            }

            if (ValidateAllProperties) {
                ValidateProperties(modelBindingExecutionContext);
            }
        }

        private void ValidateProperties(ModelBindingExecutionContext modelBindingExecutionContext) {
            // Based off CompositeModelValidator.
            ModelStateDictionary modelState = modelBindingExecutionContext.ModelState;

            // DevDiv Bugs #227802 - Caching problem in ModelMetadata requires us to manually regenerate
            // the ModelMetadata.
            object model = ModelMetadata.Model;
            ModelMetadata updatedMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => model, ModelMetadata.ModelType);

            foreach (ModelMetadata propertyMetadata in updatedMetadata.Properties) {
                // Only want to add errors to ModelState if something doesn't already exist for the property node,
                // else we could end up with duplicate or irrelevant error messages.
                string propertyKeyRoot = ModelBinderUtil.CreatePropertyModelName(ModelStateKey, propertyMetadata.PropertyName);

                if (modelState.IsValidField(propertyKeyRoot)) {
                    foreach (ModelValidator propertyValidator in propertyMetadata.GetValidators(modelBindingExecutionContext)) {
                        foreach (ModelValidationResult propertyResult in propertyValidator.Validate(model)) {
                            string thisErrorKey = ModelBinderUtil.CreatePropertyModelName(propertyKeyRoot, propertyResult.MemberName);
                            modelState.AddModelError(thisErrorKey, propertyResult.Message);
                        }
                    }
                }
            }
        }

        private void ValidateThis(ModelBindingExecutionContext modelBindingExecutionContext, ModelValidationNode parentNode) {
            ModelStateDictionary modelState = modelBindingExecutionContext.ModelState;
            if (!modelState.IsValidField(ModelStateKey)) {
                return; // short-circuit
            }

            object container = TryConvertContainerToMetadataType(parentNode);
            foreach (ModelValidator validator in ModelMetadata.GetValidators(modelBindingExecutionContext)) {
                foreach (ModelValidationResult validationResult in validator.Validate(container)) {
                    string trueModelStateKey = ModelBinderUtil.CreatePropertyModelName(ModelStateKey, validationResult.MemberName);
                    modelState.AddModelError(trueModelStateKey, validationResult.Message);
                }
            }
        }

    }
}