YouTube-Manager/Manager.Data/Contexts/AuditInterceptor.cs

using System.Text.Json;
using System.Text.Json.Serialization;
using Manager.Data.Entities.Audit;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.ChangeTracking;
using Microsoft.EntityFrameworkCore.Diagnostics;

namespace Manager.Data.Contexts;

public class AuditInterceptor : SaveChangesInterceptor
{
    public override InterceptionResult<int> SavingChanges(DbContextEventData eventData, InterceptionResult<int> result)
    {
        AddAudit(eventData.Context);
        return base.SavingChanges(eventData, result);
    }

    public override ValueTask<InterceptionResult<int>> SavingChangesAsync(
        DbContextEventData eventData,
        InterceptionResult<int> result,
        CancellationToken cancellationToken = default)
    {
        AddAudit(eventData.Context);
        return base.SavingChangesAsync(eventData, result, cancellationToken);
    }

    private void AddAudit(DbContext? context)
    {
        if (context == null) return;

        var entries = context.ChangeTracker.Entries()
            .Where(e => e.State is EntityState.Modified or EntityState.Deleted or EntityState.Added && Attribute.IsDefined(e.Entity.GetType(),
                typeof(AuditableAttribute)));

        var audits = new List<EntityAudit>();

        foreach (var entry in entries)
        {
            var primaryKey = entry.Properties.First(p => p.Metadata.IsPrimaryKey()).CurrentValue?.ToString();
            
            var declaredProperties = entry.Entity.GetType()
                .GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance)
                .Where(p => !Attribute.IsDefined(p.DeclaringType!, typeof(NoAuditAttribute), false))
                .Select(p => p.Name)
                .ToHashSet();

            var allowedProperties = entry.Properties.Where(p => declaredProperties.Contains(p.Metadata.Name));

            switch (entry.State)
            {
                case EntityState.Added:
                    audits.AddRange(allowedProperties
                            .Where(p => p.CurrentValue != null)
                            .Select(p => CreateAudit(entry, p, entry.State, primaryKey))
                    );
                    break;
                case EntityState.Modified:
                    audits.AddRange(allowedProperties
                            .Where(p => p.IsModified)
                            .Select(p => CreateAudit(entry, p, entry.State, primaryKey))
                    );
                    break;
                case EntityState.Deleted:
                    audits.AddRange(allowedProperties
                            .Select(p => CreateAudit(entry, p, entry.State, primaryKey))
                    );
                    break;
            }
        }

        if (audits.Count != 0)
        {
            context.Set<EntityAudit>().AddRange(audits);
        }
    }

    private EntityAudit CreateAudit(EntityEntry entry, PropertyEntry prop, EntityState changeType, string? primaryKey)
    {
        return new EntityAudit
        {
            Id = Guid.NewGuid(),
            EntityName = entry.Entity.GetType().Name,
            EntityId = primaryKey ?? "Unknown",
            PropertyName = prop.Metadata.Name,
            OldValue = SerializeValue(prop.OriginalValue),
            NewValue = SerializeValue(prop.CurrentValue),
            ModifiedUtc = DateTime.UtcNow,
            ChangedBy = "SYSTEM",
            ChangeType = changeType
        };
    }

    private readonly JsonSerializerOptions _jsonSerializerOptions = new()
    {
        WriteIndented = false,
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
    };
    
    private string? SerializeValue(object? value)
    {
        if (value == null) return null;

        var type = value.GetType();

        if (type.IsPrimitive || type == typeof(string) || type == typeof(DateTime) || type == typeof(decimal))
        {
            return value.ToString();
        }

        return JsonSerializer.Serialize(value, _jsonSerializerOptions);
    }
}