using System;
using System.Collections;
using System.Dynamic;
using System.Linq;
using System.Linq.Expressions;
using MongoDB.Bson.IO;
using MongoDB.Bson.Serialization;
using MongoDB.Bson.Serialization.Serializers;
using MongoDB.Bson;
using MongoDB.Bson.Serialization.IdGenerators;
using System.Collections.Generic;
using log4net;

namespace MongoData
{
  public class MongoDynamicBsonSerializer : SerializerBase<MongoDynamic>, IBsonIdProvider //, IBsonDocumentSerializer//, IBsonArraySerializer
  {
    private static readonly ILog log= LogManager.GetLogger("DynMongoSer");

    public static MongoDynamicBsonSerializer Instance { get; } = new MongoDynamicBsonSerializer();

    private static readonly IBsonSerializer<string> stringSerializer = new StringSerializer();

    public override MongoDynamic Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
    {
      log.Debug($"Deserializing ... {args.NominalType}");
      var bsonReader = context.Reader;
      Type nominalType = args.NominalType;

      var bsonType = bsonReader.GetCurrentBsonType();
      if (bsonType == BsonType.Null)
      {
        bsonReader.ReadNull();
        return null;
      }
      else if (bsonType == BsonType.Document)
      {
        MongoDynamic md = new MongoDynamic();
        bsonReader.ReadStartDocument();

        // Scan document first to find interfaces and id fields
        Dictionary<string, Type> typeMap = ScanToLoadTypeMapFromInterfaces(context, bsonReader, md, nominalType);

        while (bsonReader.ReadBsonType() != BsonType.EndOfDocument)
        {
          var name = bsonReader.ReadName();
          log.Debug($"Reading field {name}");

          if (name == "_id")
          {
            md[name] = bsonReader.ReadObjectId();
            log.Debug($"  {name} = {md[name]}");
          }
          else if (name == MongoDynamic.InterfacesField)
          {
            // Read it and ignore it, we already have it
            bsonReader.SkipValue();
            log.Debug("  Skipping int field");
          }
          else if (name == "_t")
          {
            log.Debug("  Skipping _t field, don't need that for interfaces");
            bsonReader.SkipValue();
          }
          else if (name == "Entity")
          {
            log.Debug("  Skipping Entity field");
            // Read it and ignore it, this was a broken earlier attempt at serialization
            bsonReader.SkipValue();
          }
          else if (bsonReader.CurrentBsonType == BsonType.Null)
          {
            bsonReader.ReadNull();
            md[name] = null;
            log.Debug($"  {name} = null");
          }
          else
          {
            if (typeMap == null)
            {
              throw new FormatException("No interfaces defined for this dynamic object - can't deserialize [" + md["_id"] + "]");
            }

            // lookup the type for this element according to the interfaces
            Type elementType;
            if (typeMap.TryGetValue(name, out elementType))
            {
              if (elementType.IsArray)
              {
                var subElementType = elementType.GetElementType();

                if (subElementType.IsInterface)
                {
                  bsonReader.ReadStartArray();
                  var listType = typeof (List<>).MakeGenericType(subElementType);
                  var elements = (IList) Activator.CreateInstance(listType);

                  while (bsonReader.ReadBsonType() != BsonType.EndOfDocument)
                  {
                    var subargs = new BsonDeserializationArgs {NominalType = subElementType};
                    MongoDynamic o = this.Deserialize(context, subargs);
                    elements.Add(o.ActLikeAllInterfacesPresent());
                  }
                  bsonReader.ReadEndArray();

                  var array = Array.CreateInstance(subElementType, elements.Count);
                  for (int i = 0; i < array.Length; i++)
                  {
                    try
                    {
                      array.SetValue(elements[i], i);
                    }
                    catch (InvalidCastException)
                    {
                      log.Error(
                        $"Cannot cast {elements[i].GetType().Name} to {subElementType}");
                    }
                  }
                  md[name] = array;
                  log.Debug($"  {name} = {md[name]}");
                }
                else
                {
                  md[name] = BsonSerializer.LookupSerializer(elementType).Deserialize(context, args);
                  log.Debug($"  {name} = {md[name]}");
                }
              }
              else if (elementType.IsInterface)
              {
                //log.Debug("Recursing on an interface " + elementType.Name);
                var subargs = new BsonDeserializationArgs {NominalType = elementType};
                var value = this.Deserialize(context, subargs);
                md[name] = value.ActLikeAllInterfacesPresent();
                log.Debug($"  {name} = {md[name]}");
              }
              else
              {
                // Not an interface type, call the normal deserializer
                try
                {
                  IBsonSerializer serializer = BsonSerializer.LookupSerializer(elementType);
                  var value = serializer.Deserialize(context);
                  md[name] = value;
                }
                catch (FormatException fex)
                {
                  log.Error($"Unrecoverable error reading a {elementType}", fex);
                  log.Error(md.ToStringValues());
                  throw;
                }
                catch (Exception ex)
                {
                  log.Error($"Could not Deserialize a {elementType}", ex);
                  log.Error(md.ToStringValues());
                }

                log.Debug($"  {name} = {md[name]}");
              }
            }
            else
            {
              log.Debug("Trying to deserialize field " + name + " which was not found in the type map");
              log.Debug("TypeMap contains " + string.Join(", ", typeMap.Select(x => x.Key + "=" + x.Value)));
              try
              {
                // This is a value that is no longer in the interface, maybe a column you removed
                // not really much we can do with it ... but we need to read it and move on
                var value = BsonSerializer.Deserialize(bsonReader, typeof (object));
                md[name] = value;
                log.Debug($"  {name} = {md[name]}");
              }
              catch (Exception ex)
              {
                ex.Data.Add("Explanation",
                  "As with all databases, removing elements from the schema is going to cause problems");
                throw;
              }
            }
          }
        }
        bsonReader.ReadEndDocument();
        log.Debug($"--------");
        return md;
      }
      else
      {
        var message = $"Can't deserialize a {nominalType.FullName} from BsonType {bsonType}.";
        throw new FormatException(message);
      }
    }


    static Dictionary<string, Type> ScanToLoadTypeMapFromInterfaces(BsonDeserializationContext context, IBsonReader bsonReader,
      MongoDynamic md, Type nominalType)
    {
      Dictionary<string, Type> typeMap = null;
      var bookMark = bsonReader.GetBookmark();
      if (bsonReader.FindElement(MongoDynamic.InterfacesField))
      {
        bsonReader.ReadStartArray();
        var innerList = new List<string>();
        while (bsonReader.ReadBsonType() != BsonType.EndOfDocument)
        {
          innerList.Add(stringSerializer.Deserialize(context));
        }
        bsonReader.ReadEndArray();
        md[MongoDynamic.InterfacesField] = innerList;
        typeMap = md.GetTypeMap();
        log.Debug($"  Interfaces = {md.InterfacesAsText}");
        log.Debug($"  Properties = {string.Join(", ", typeMap.Keys)}");
      }
      else
      {
        log.Debug($"No 'int' field on this dynamic object - switching to use nominal type {nominalType}");
        var interfaces = nominalType.GetInterfaces();
        List<string> interfaceNames = new List<string>();
        if (nominalType.IsInterface) interfaceNames.Add(nominalType.FullName);
        interfaceNames.AddRange(interfaces.Select(i => i.FullName));
        // What about concrete types? Well, they are deserialized by normal MongoDB deserializer
        md[MongoDynamic.InterfacesField] = interfaceNames;
        typeMap = md.GetTypeMap();
      }
      bsonReader.ReturnToBookmark(bookMark);
      return typeMap;
    }

    public bool GetDocumentId(object document, out object id, out Type idNominalType, out IIdGenerator idGenerator)
    {
      log.Debug("GetDocumentId");
      MongoDynamic x = (MongoDynamic)document;
      id = x._id;
      idNominalType = typeof(ObjectId);
      idGenerator = new ObjectIdGenerator();
      return true;
    }

    public void SetDocumentId(object document, object id)
    {
      MongoDynamic x = (MongoDynamic)document;
      x._id = (ObjectId)id;
    }

    public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args,
      MongoDynamic value)
    {
      var bsonWriter = context.Writer;
      log.Debug("Serialize " + value);
      if (value == null)
      {
        bsonWriter.WriteNull();
        return;
      }

      // ------------------- NEW WAY --- WE KNOW IT'S A MONGODYNAMIC, NO NEED TO GO ALL IDynamicMetaObjectProvider ON IT
      MongoDynamic mongoDynamic = value as MongoDynamic;

      bsonWriter.WriteStartDocument();

      // And now write the fields according to the interface map
      var typeMap = mongoDynamic.GetTypeMap();

      var metaObject = ((IDynamicMetaObjectProvider)value).GetMetaObject(Expression.Constant(value));
      var memberNames = metaObject.GetDynamicMemberNames().ToList();
      if (memberNames.Count == 0)
      {
        bsonWriter.WriteNull();
        return;
      }

      foreach (var memberName in memberNames)
      {
        log.Debug("Examining " + memberName);
        // Get the value
        object memberValue;
        Type memberType;

        if (memberName == "_id")
        {
          memberValue = mongoDynamic._id;
          memberType = typeof(ObjectId);
        }
        else if (memberName == "int")
        {
          memberValue = mongoDynamic.@int;
          memberType = memberValue.GetType();   // A Hashset<string>
        }
        else
        {
          memberValue = mongoDynamic[memberName]; /// Could also use ... Impromptu.InvokeGet(value, memberName);
          // Lookup the intended type for that field because it
          // may be different from the typeof(memberValue) which
          // is likely a Proxy type. If we can't find it, go ahead
          // and use the type of the object - for some reason it's not in the interfaces
          if (!typeMap.TryGetValue(memberName, out memberType))
            memberType = memberValue?.GetType();
        }

        bsonWriter.WriteName(memberName);
        WriteValue(context, args, memberValue, bsonWriter, memberType);

        if (memberName == "Name" && memberType == typeof(string))
        {
          string cleanedName = ITagExtensions.RemoveDiacritics(((string)memberValue).ToLowerInvariant());
          // Normalize the name field, lower case, replace special characters (TODO)
          bsonWriter.WriteName("name");
          WriteValue(context, args, cleanedName, bsonWriter, memberType);
        }
      }

      bsonWriter.WriteEndDocument();

      return;
    }

    private void WriteValue(BsonSerializationContext context, BsonSerializationArgs args, object memberValue,
      IBsonWriter bsonWriter, Type memberType)
    {
      if (memberValue == null)
        bsonWriter.WriteNull();
      else
      {
        if (memberType.IsArray)
        {
          context.Writer.WriteStartArray();

          memberType = memberType.GetElementType();
          foreach (var item in memberValue as IEnumerable)
          {
            // It could be a normal type here, or it could be an interface
            var iid = item as IId;
            var type = item.GetType();
            if (iid != null)
            {
              var mdInner = iid.Entity;
              this.Serialize(context, mdInner);
            }
            else
            {
              var serializer = BsonSerializer.LookupSerializer(memberType);
              serializer.Serialize(context, item);
            }
          }
          context.Writer.WriteEndArray();
        }
        else if (memberType.IsInterface)
        {
//        log.Debug("Serializing " + memberName + " : " + memberValue.GetType().Name + " a " + memberType.Name + " from a " + args.NominalType.Name + " by using another MongoDynamic!");

          // Make it into a MongoDynamic object so we can read it back using only its interface
          MongoDynamic expanded = new MongoDynamic(memberType, memberValue);
          // Recursively call ourself to serialize this embedded interface which will again embed another interfaces field
          // to identify the interface type to load back in
          Serialize(context, args, expanded);
        }
        else
        {
//            log.Debug("Serializing " + memberName + " : " + memberValue.GetType() + " a " + memberType.Name + " from a " + args.NominalType.Name + " using normal lookup");
          var serializer = BsonSerializer.LookupSerializer(memberType);
          serializer.Serialize(context, memberValue);
        }
      }
    }
  }
}