using System;
using System.Collections.Generic;
using System.Linq;

namespace ln.http.rest
{
    public delegate void CRUDEvent(CRUDObjectContainer sender, CRUDEventArgs args);
    public enum CRUDEventType { CREATE, READ, UPDATE, DELETE }

    public class CRUDEventArgs : EventArgs
    {
        public CRUDEventType EventType { get; }
        public Type ObjectType { get; }
        public object ObjectIdentity { get; }
        public object ObjectInstance { get; }
        public FieldValueList FieldValues { get; }

        public CRUDEventArgs(CRUDEventType eventType, Type objectType, object objectIdentity, object objectInstance, FieldValueList fieldValues)
        {
            EventType = eventType;
            ObjectType = objectType;
            ObjectIdentity = objectIdentity;
            ObjectInstance = objectInstance;
            FieldValues = fieldValues;
        }
    }

    public abstract partial class CRUDObjectContainer
    {
        public event CRUDEvent OnCRUDEvent;


        Dictionary<Type, RegisteredType> registeredTypes = new Dictionary<Type, RegisteredType>();

        public CRUDObjectContainer()
        { }

        public abstract bool TryGetObjectIdentifier(object objectInstance, out object objectIdentifier);

        public abstract bool TryCreateObject(Type objectType, FieldValueList fieldValues, out object objectInstance);
        public abstract bool TryLookupObject(Type objectType, object objectIdentifier, out object objectInstance);
        public abstract bool TryUpdateObject(Type objectType, object objectIdentifier, FieldValueList fieldValues);
        public abstract bool TryDeleteObject(Type objectType, object objectIdentifier);

        public virtual bool TryUpdateObject(object objectInstance, FieldValueList fieldValues)
        {
            if (TryGetObjectIdentifier(objectInstance, out object objectIdentifier))
                return TryUpdateObject(objectInstance.GetType(), objectIdentifier, fieldValues);
            return false;
        }
        public virtual bool TryDeleteObject(object objectInstance)
        {
            if (TryGetObjectIdentifier(objectInstance, out object objectIdentifier))
                return TryDeleteObject(objectInstance.GetType(), objectIdentifier);
            return false;
        }

        protected void FireCRUDEvent(CRUDEventArgs args) => OnCRUDEvent?.Invoke(this, args);
        protected void FireCRUDEVent(CRUDEventType EventType, Type ObjectType, object ObjectIdentity, object ObjectInstance, FieldValueList FieldValues)
            => FireCRUDEvent(new CRUDEventArgs(EventType, ObjectType, ObjectIdentity, ObjectInstance, FieldValues));

        public virtual IEnumerable<Type> RegisteredTypes => registeredTypes.Keys;
        public virtual bool ContainsRegisteredType(Type objectType) => registeredTypes.ContainsKey(objectType);

        public virtual bool TryRegisterType(Type objectType) => TryRegisterType(objectType, null);
        public virtual bool TryRegisterType(Type objectType, Func<object,object> idGetter)
        {
            if (ContainsRegisteredType(objectType))
                throw new ArgumentException("objectType already registered", nameof(objectType));

            RegisteredType registeredType = new RegisteredType(this, objectType, idGetter);

            registeredTypes.Add(objectType, registeredType);

            return true;
        }
        public virtual bool TryGetFieldDescriptors(Type objectType, out FieldDescriptor[] fieldDescriptors)
        {
            if (registeredTypes.TryGetValue(objectType, out RegisteredType registeredType))
            {
                fieldDescriptors = registeredType.FieldDescriptors.ToArray();
                return true;
            }
            fieldDescriptors = null;
            return false;
        }

        public virtual IEnumerable<object> EnumerateObjectInstances(Type objectType) => EnumerateObjectInstances(objectType, null);
        public abstract IEnumerable<object> EnumerateObjectInstances(Type objectType, FieldValueList conditionalFieldValues);

        public abstract bool AddForeignObjectInstance(object objectInstance);
    }
}