using System;
using System.Reflection;
using System.Collections.Generic;
using ln.logging;
using System.Linq;
using ln.types.collections;
using ln.objects.catalog;

namespace ln.types.odb.ng.mappings
{

    public class ClassMapping : IODBMapping
    {
        public delegate object GetID(object o);
        public delegate object SetID(object o, object id);

        public Type MappedType { get; }
        public bool IsReferenceType => !MappedType.IsValueType;

        List<FieldInfo> mappedFields = new List<FieldInfo>();

        Func<Mapper, Document, object> createObjectHook;
        Func<FieldInfo, bool> filterFieldsHook;

        private ClassMapping() { }

        public ClassMapping(Type type) : this(type, null, null) { }

        public ClassMapping(Type type, Func<Mapper, Document, object> createObjectHook, Func<FieldInfo, bool> filterFieldsHook)
        {
            Logging.Log(LogLevel.DEBUG, "Constructing ClassMapping for {0}", type);
            MappedType = type;

            this.createObjectHook = createObjectHook;
            this.filterFieldsHook = filterFieldsHook;

            AddFields(type);
        }

        private void AddFields(Type type)
        {
            foreach (FieldInfo fieldinfo in type.GetFields(BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public))
            {
                if ((filterFieldsHook == null) || filterFieldsHook(fieldinfo))
                    mappedFields.Add(fieldinfo);
            }

            if ((type != null) && !type.IsValueType && (!typeof(object).Equals(type.BaseType)))
            {
                AddFields(type.BaseType);
            }
        }

        public bool HasField(String name)
        {
            foreach (FieldInfo fieldInfo in mappedFields)
                if (fieldInfo.Name.Equals(name))
                    return true;
            return false;
        }

        private object GetObjectForDocument(Mapper mapper,Document document)
        {
            if (IsReferenceType)
            {
                if (mapper.IdentityCache.TryGetValue(document.ID, out object o, () => (createObjectHook != null) ? createObjectHook(mapper, document) : Activator.CreateInstance(MappedType, true) ))
                    return o;
            }

            return (createObjectHook != null) ? createObjectHook(mapper,document) : Activator.CreateInstance(MappedType, true);
        }

        public object UnmapValue(Mapper mapper,ODBEntity oval)
        {
            Document document = oval as Document;
            object o = GetObjectForDocument(mapper,document);

            Apply(mapper, document, o);

            return o;
        }

        public void Apply(Mapper mapper,Document document,object o)
        {
            foreach (FieldInfo fieldInfo in mappedFields)
            {
                object fv = mapper.UnmapValue(fieldInfo.FieldType, document[fieldInfo.Name]);
                if (!object.ReferenceEquals(fv, null))
                {
                    Type st = fv.GetType();
                    if (st != fieldInfo.FieldType)
                    {
                        fv = mapper.TryImplicitMapping(fv, fieldInfo.FieldType);
                        st = fv.GetType();
                    }
                    if (st != fieldInfo.FieldType)
                        fv = Convert.ChangeType(fv, fieldInfo.FieldType);
                }
                if (!object.ReferenceEquals(null, fv))
                    fieldInfo.SetValue(o, fv);
            }
        }

        public Document MapDocument(Mapper mapper,Guid documentID,object value)
		{
			Document document = new Document(documentID);
			document["__asm__"] = new ODBStringValue(value.GetType().Assembly.GetName().Name);
			document["__type__"] = new ODBStringValue(value.GetType().FullName);

			foreach (FieldInfo fieldInfo in mappedFields)
			{
				object fv = fieldInfo.GetValue(value);
				ODBEntity ov = null;

				ov = mapper.MapValue(fv);

				document[fieldInfo.Name] = ov;
			}

            if (IsReferenceType)
            {
                mapper.IdentityCache.Ensure(documentID, value);
            }

            return document;
		}

		public ODBEntity MapValue(Mapper mapper,object value)
        {
            if (Object.ReferenceEquals(value, null))
                return ODBNull.Instance;

            if (!mapper.IdentityCache.TryGetIdentity(value, out Guid documentID))
                documentID = Guid.NewGuid();

            return MapDocument(mapper, documentID, value);
        }

        public Type GetFieldType(Mapper mapper,string fieldName)
        {
            foreach (FieldInfo fieldInfo in mappedFields)
                if (fieldInfo.Name.Equals(fieldName))
                    return fieldInfo.FieldType;

            throw new KeyNotFoundException();
        }

    }

    public class ObjectMapping : IODBMapping
    {

        public ODBEntity MapValue(Mapper mapper, object value)
        {
            return new Document();
        }

        public object UnmapValue(Mapper mapper, ODBEntity oval)
        {
            if (oval is Document)
            {
                Document document = oval as Document;
                if (!document.Contains(new ODBStringValue("__type__")))
                    return new object();

                Type dType = Type.GetType(String.Format("{0}, {1}",document["__type__"].As<String>(), document["__asm__"].As<String>()));
                return mapper.UnmapValue(dType, oval);
            } else if (oval is ODBList)
            {
                ODBList list = oval as ODBList;
                Array array = (Array)mapper.UnmapValue(typeof(object[]), list);

                if (array.Length > 0)
                {
                    /* Magic: Try to find out about the arrays real element type */
                    HashSet<Type> eTypes = null;

                    foreach (object v in array)
                    {
                        HashSet<Type> myTypes = new HashSet<Type>();

                        Type eType = v?.GetType();
                        while (eType != null)
                        {
                            myTypes.Add(eType);
                            eType = eType.BaseType;
                        }

                        if (eTypes == null)
                        {
                            eTypes = myTypes;
                        }
                        else
                        {
                            eTypes.IntersectWith(myTypes);
                        }
                    }

                    foreach (Type t in eTypes.ToArray())
                    {
                        if (eTypes.Contains(t.BaseType))
                            eTypes.Remove(t.BaseType);
                    }

                    Type baseElementType = eTypes.First();
                    if (!array.GetType().GetElementType().Equals(baseElementType))
                    {
                        Array tarray = Array.CreateInstance(baseElementType, array.Length);
                        Array.Copy(array, tarray, array.Length);
                        array = tarray;
                    }
                }

                return array;
            }
            else if (oval is ODBValue)
            {
                return (oval as ODBValue).Value;
            }

            throw new NotImplementedException();
        }
    }

}