using System.Diagnostics.CodeAnalysis;
using System.Reflection;
using InABox.Core;
using InABox.Database;

namespace PRS.Shared;

public class Update_7_06 : DatabaseUpdateScript
{

    public override VersionNumber Version => new (7,06);
        
    public override bool Update()
    {
        var deletions = DbFactory.NewProvider(Logger.Main).Query<Deletion>(
            new Filter<Deletion>(x => x.Data).IsEqualTo(""));
        Logger.Send(LogType.Information, "", "Updating Deletions");
        foreach (var deletion in deletions.ToObjects<Deletion>())
        {
            Purge(deletion);
        }
        Logger.Send(LogType.Information, "", "Finished updating Deletions");
        return true;
    }
    
    private static Dictionary<Type, List<Tuple<Type, string>>> _cascades = new();
    private static Dictionary<Type, List<Tuple<Type, List<string>>>> _setNulls = new();

    private static void LoadDeletions(Type type)
    {
        if (_cascades.ContainsKey(type)) return;

        // Get the EntityLink that is associated with this class
        var linkclass = CoreUtils.TypeList(
            new[] { type.Assembly },
            x => typeof(IEntityLink).GetTypeInfo().IsAssignableFrom(x) && x.GetInheritedGenericTypeArguments().FirstOrDefault() == type
        ).FirstOrDefault();

        // if The entitylink does not exist, we don't need to do anything
        if (linkclass == null)
            return;

        var cascades = new List<Tuple<Type, string>>();
        var setNulls = new List<Tuple<Type, List<string>>>();

        var childtypes = DbFactory.ProviderFactory.Types.Where(x => x.IsSubclassOf(typeof(Entity)) && x.GetCustomAttribute<AutoEntity>() == null);
        foreach (var childtype in childtypes)
        {
            // Get all registered types for this entitylink
            var fields = new List<string>();
            var bDelete = false;

            // Find any IEntityLink<> properties that refer back to this class
            var childprops = CoreUtils.PropertyList(childtype, x => x.PropertyType == linkclass);

            foreach (var childprop in childprops)
            {
                var fieldname = string.Format("{0}.ID", childprop.Name);
                var attr = childprop.GetCustomAttributes(typeof(EntityRelationshipAttribute), true).FirstOrDefault();
                if (attr != null && ((EntityRelationshipAttribute)attr).Action.Equals(DeleteAction.Cascade))
                {
                    cascades.Add(new(childtype, fieldname));
                    bDelete = true;
                    break;
                }

                fields.Add(fieldname);
            }
            if (!bDelete && fields.Any())
            {
                setNulls.Add(new(childtype, fields));
            }
        }

        _cascades[type] = cascades;
        _setNulls[type] = setNulls;
    }
    private static bool GetCascades(Type type, [NotNullWhen(true)] out List<Tuple<Type, string>>? cascades)
    {
        LoadDeletions(type);
        return _cascades.TryGetValue(type, out cascades);
    }
    private static bool GetSetNulls(Type type, [NotNullWhen(true)] out List<Tuple<Type, List<string>>>? setNulls)
    {
        LoadDeletions(type);
        return _setNulls.TryGetValue(type, out setNulls);
    }


    private static MethodInfo _deleteEntitiesMethod = typeof(Update_7_06).GetMethods(BindingFlags.NonPublic | BindingFlags.Static)
        .Single(x => x.Name == nameof(DeleteEntity) && x.IsGenericMethod);
    private static void DeleteEntity<T>(Deletion deletion, Guid parentID, string parentField, DeletionData deletionData) where T : Entity, new()
    {
        var columns = DeletionData.DeletionColumns<T>();
        var delEntities = DbFactory.NewProvider(Logger.Main).QueryDeleted(deletion, new Filter<T>(parentField).IsEqualTo(parentID), columns);
        var nDelntities = DbFactory.NewProvider(Logger.Main).Query(new Filter<T>(parentField).IsEqualTo(parentID), columns);
        foreach (var row in delEntities.Rows.Concat(nDelntities.Rows))
        {
            deletionData.DeleteEntity<T>(row);
            CascadeDelete(typeof(T), deletion, row.Get<T, Guid>(x => x.ID), deletionData);
        }
    }

    private static void DeleteEntity(Type T, Deletion deletion, Guid parentID, string parentField, DeletionData deletionData)
    {
        _deleteEntitiesMethod.MakeGenericMethod(T).Invoke(null, new object?[] { deletion, parentID, parentField, deletionData });
    }


    private static MethodInfo _setNullEntityMethod = typeof(Update_7_06).GetMethods(BindingFlags.NonPublic | BindingFlags.Static)
        .Single(x => x.Name == nameof(SetNullEntity) && x.IsGenericMethod);
    private static void SetNullEntity<T>(List<string> properties, Guid parentID, DeletionData deletionData) where T : Entity, new()
    {
        foreach (var property in properties)
        {
            var entities = DbFactory.NewProvider(Logger.Main).Query(new Filter<T>(property).IsEqualTo(parentID), Columns.None<T>().Add(x => x.ID));
            foreach (var row in entities.Rows)
            {
                deletionData.SetNullEntity<T>(row.Get<T, Guid>(x => x.ID), property, parentID);
            }
        }
    }

    private static void SetNullEntity(Type T, List<string> properties, Guid parentID, DeletionData deletionData)
    {
        _setNullEntityMethod.MakeGenericMethod(T).Invoke(null, new object?[] { properties, parentID, deletionData });
    }


    private static void CascadeDelete(Type type, Deletion deletion, Guid parentID, DeletionData deletionData)
    {
        if (GetCascades(type, out var cascades))
        {
            foreach (var cascade in cascades)
            {
                DeleteEntity(cascade.Item1, deletion, parentID, cascade.Item2, deletionData);
            }
        }
        if (GetSetNulls(type, out var setNulls))
        {
            foreach (var setNull in setNulls)
            {
                SetNullEntity(setNull.Item1, setNull.Item2, parentID, deletionData);
            }
        }
    }

    // Referenced via reflection.
    private static void PurgeEntityType<T>(Deletion deletion) where T : Entity, new()
    {
        var entities = DbFactory.NewProvider(Logger.Main).QueryDeleted(deletion, null, DeletionData.DeletionColumns<T>()).ToObjects<T>().ToList();

        var deletionData = new DeletionData();
        foreach (var entity in entities)
        {
            deletionData.DeleteEntity(entity);
            CascadeDelete(typeof(T), deletion, entity.ID, deletionData);
        }

        if (deletionData.Cascades.Count > 0 || deletionData.SetNulls.Count > 0)
        {
            var tableName = typeof(T).Name;
            var newDeletion = new Deletion()
            {
                DeletionDate = DateTime.Now,
                HeadTable = tableName,
                Description = $"Deleted {entities.Count} entries",
                DeletedBy = deletion.DeletedBy,
                Data = Serialization.Serialize(deletionData)
            };
            DbFactory.NewProvider(Logger.Main).Save(newDeletion);
        }
        DbFactory.NewProvider(Logger.Main).Purge(entities);
    }

    public static void Purge(Deletion deletion)
    {
        if (deletion.ID == Guid.Empty)
        {
            Logger.Send(LogType.Error, "", "Empty Deletion ID");
            return;
        }

        var entityType = CoreUtils.Entities.FirstOrDefault(x => x.Name == deletion.HeadTable);
        if (entityType is null)
        {
            Logger.Send(LogType.Error, "", $"Entity {deletion.HeadTable} does not exist");
            return;
        }
        var purgeMethod = typeof(Update_7_06).GetMethod(nameof(PurgeEntityType), BindingFlags.NonPublic | BindingFlags.Static)!;
        purgeMethod.MakeGenericMethod(entityType).Invoke(null, new object[] { deletion });

        DbFactory.NewProvider(Logger.Main).Purge<Deletion>(deletion);
    }


}