Line data    Source code

       1             : #region Copyright
       2             : // // -----------------------------------------------------------------------
       3             : // // <copyright company="Chinchilla Software Limited">
       4             : // //   Copyright Chinchilla Software Limited. All rights reserved.
       5             : // // </copyright>
       6             : // // -----------------------------------------------------------------------
       7             : #endregion
       8             : 
       9             : using System;
      10             : using System.Collections.Generic;
      11             : using System.Linq;
      12             : using Cqrs.Domain;
      13             : using Cqrs.Events;
      14             : 
      15             : namespace Cqrs.Snapshots
      16             : {
      17             :         /// <summary>
      18             :         /// An <see cref="ISnapshotStrategy{TAuthenticationToken}"/> that takes a snapshot every 15 versions.
      19             :         /// </summary>
      20             :         /// <typeparam name="TAuthenticationToken">The <see cref="Type"/> of the authentication token.</typeparam>
      21             :         public class DefaultSnapshotStrategy<TAuthenticationToken>
      22             :                 : ISnapshotStrategy<TAuthenticationToken>
      23           1 :         {
      24             :                 private const int SnapshotInterval = 15;
      25             : 
      26             :                 /// <summary>
      27             :                 /// Indicates if the <paramref name="aggregateType"/> is able to be snapshotted by checking if the <paramref name="aggregateType"/>
      28             :                 /// directly inherits <see cref="SnapshotAggregateRoot{TAuthenticationToken,TSnapshot}"/>
      29             :                 /// </summary>
      30             :                 /// <param name="aggregateType">The <see cref="Type"/> of <see cref="IAggregateRoot{TAuthenticationToken}"/> to check.</param>
      31           1 :                 public virtual bool IsSnapshotable(Type aggregateType)
      32             :                 {
      33             :                         if (aggregateType.BaseType == null)
      34             :                                 return false;
      35             :                         if (aggregateType.BaseType.IsGenericType && aggregateType.BaseType.GetGenericTypeDefinition() == typeof(SnapshotAggregateRoot<,>))
      36             :                                 return true;
      37             :                         return IsSnapshotable(aggregateType.BaseType);
      38             :                 }
      39             : 
      40             :                 /// <summary>
      41             :                 /// Checks <see cref="IsSnapshotable"/> and if it is, also checks if the calculated version number would be exactly dividable by <see cref="GetSnapshotInterval"/>.
      42             :                 /// </summary>
      43             :                 /// <param name="aggregate">The <see cref="IAggregateRoot{TAuthenticationToken}"/> to check.</param>
      44             :                 /// <param name="uncommittedChanges">A collection of uncommited changes to assess. If null the aggregate will be asked to provide them.</param>
      45           1 :                 public virtual bool ShouldMakeSnapShot(IAggregateRoot<TAuthenticationToken> aggregate, IEnumerable<IEvent<TAuthenticationToken>> uncommittedChanges = null)
      46             :                 {
      47             :                         if (!IsSnapshotable(aggregate.GetType()))
      48             :                                 return false;
      49             : 
      50             :                         // The reason this isn't as simple as `(aggregate.Version + aggregate.GetUncommittedChanges().Count()) % SnapshotInterval` is
      51             :                         // because if there are enough uncommited events that this would result in a snapshot, plus some left over, the final state is what will be generated
      52             :                         // when the snapshot is taken, thus this is a faster and more accurate assessment.
      53             :                         int limit = (uncommittedChanges ?? aggregate.GetUncommittedChanges()).Count();
      54             :                         int i = aggregate.Version - limit;
      55             :                         int snapshotInterval = GetSnapshotInterval();
      56             :                         
      57             :                         for (int j = 0; j < limit; j++)
      58             :                                 if (++i % snapshotInterval == 0 && i != 0)
      59             :                                         return true;
      60             :                         return false;
      61             :                 }
      62             : 
      63             :                 /// <summary>
      64             :                 /// Returns the value of <see cref="SnapshotInterval"/>.
      65             :                 /// </summary>
      66           1 :                 protected virtual int GetSnapshotInterval()
      67             :                 {
      68             :                         return SnapshotInterval;
      69             :                 }
      70             :         }
      71             : }