feat: required outer services for agent accessor chain (#40)

* feat: required outer services for agent accessor chain

this feature allows access to required services from the service provider that constructed the agent accessor chain

* refactor: appease codacy gods

also move the method which builds a service provider to a private static method, keep ctor tidy

src/EntityDb.Common/Agents/AgentAccessorChain.cs

@@ -21,21 +21,52 @@ public class AgentAccessorChain : IAgentAccessor
     private readonly IAgentAccessor[] _agentAccessors;
 
     /// <ignore/>
-    public AgentAccessorChain(ILogger<AgentAccessorChain> logger, IOptions<AgentAccessorChainOptions> options) : this(logger, options.Value)
+    public AgentAccessorChain
+    (
+        ILogger<AgentAccessorChain> logger,
+        IOptions<AgentAccessorChainOptions> options,
+        IServiceProvider outerServiceProvider
+    ) : this(logger, options.Value, outerServiceProvider)
     {
     }
 
-    internal AgentAccessorChain(ILogger<AgentAccessorChain> logger, AgentAccessorChainOptions options)
+    internal AgentAccessorChain
+    (
+        ILogger<AgentAccessorChain> logger,
+        AgentAccessorChainOptions options,
+        IServiceProvider outerServiceProvider
+    )
     {
-        var serviceProvider = options.ServiceCollection
-            .BuildServiceProvider();
+        var serviceProvider = GetServiceProvider(outerServiceProvider, options);
 
         _logger = logger;
         _agentAccessors = serviceProvider
             .GetServices<IAgentAccessor>()
             .ToArray();
     }
 
+    private static IServiceProvider GetServiceProvider(IServiceProvider outerServiceProvider, AgentAccessorChainOptions options)
+    {
+        IServiceCollection serviceCollectionCopy = new ServiceCollection();
+
+        foreach (var (outerServiceType, innerServiceLifetime) in options.RequiredOuterServices)
+        {
+            serviceCollectionCopy.Add(new ServiceDescriptor
+            (
+                outerServiceType,
+                _ => outerServiceProvider.GetRequiredService(outerServiceType),
+                innerServiceLifetime
+            ));
+        }
+
+        foreach (var serviceDescriptor in options.ServiceCollection)
+        {
+            serviceCollectionCopy.Add(serviceDescriptor);
+        }
+
+        return serviceCollectionCopy.BuildServiceProvider();
+    }
+
     /// <inheritdoc />
     public IAgent GetAgent()
     {

src/EntityDb.Common/Agents/AgentAccessorChainOptions.cs

@@ -1,5 +1,7 @@
 using EntityDb.Abstractions.Agents;
 using Microsoft.Extensions.DependencyInjection;
+using System;
+using System.Collections.Generic;
 
 namespace EntityDb.Common.Agents;
 
@@ -9,7 +11,19 @@ namespace EntityDb.Common.Agents;
 public sealed class AgentAccessorChainOptions
 {
     /// <summary>
-    ///     A service collection used to resolve multiple instances of <see cref="IAgentAccessor"/>.
+    ///     An inner service collection used to configure and resolve multiple instances of <see cref="IAgentAccessor"/>.
     /// </summary>
     public IServiceCollection ServiceCollection { get; } = new ServiceCollection();
+
+    /// <summary>
+    ///     If any of the instances of <see cref="IAgentAccessor"/> which are added to <see cref="ServiceCollection"/>
+    ///     have required dependencies that live in the outer service provider (the one constructing <see cref="AgentAccessorChainOptions"/>),
+    ///     then you can specify them here.
+    /// </summary>
+    /// <remarks>
+    ///     Note that the <see cref="ServiceLifetime.Scoped">ServiceLifetime.Scoped</see> is not supported,
+    ///     and if the outer service is itself scoped, the agent accessor will not be able to receive it
+    ///     because it is, itself, registered as a singleton service.
+    /// </remarks>
+    public Dictionary<Type, ServiceLifetime> RequiredOuterServices { get; } = new();
 }