Deduplicate picture flows: shared upload issuer, cover query and picture source change

backend/Core/Musify.Application/Pictures/PictureSourceChange.cs

@@ -0,0 +1,35 @@
+using ErrorOr;
+using Musify.Application.Configuration;
+using Musify.Application.Services;
+using Musify.Application.Shared;
+using Musify.Domain.Entities;
+using Musify.Domain.ValueObjects;
+
+namespace Musify.Application.Pictures;
+
+/// <summary>What an album or playlist needs to switch to a freshly uploaded picture.</summary>
+public sealed record PreparedPicture(UploadIntent Intent, EntityPictures Pictures, string FinalKey, ImageSizes Sizes);
+
+public static class PictureSourceChange
+{
+    public static async Task<ErrorOr<PreparedPicture>> PrepareAsync(
+        UploadIntentValidator uploadIntentValidator,
+        Guid intentId,
+        long userId,
+        UploadIntentPurpose purpose,
+        IPictureOwnerConfiguration owner,
+        CancellationToken cancellationToken)
+    {
+        var validation = await uploadIntentValidator.ValidateAndLoadAsync(intentId, userId, purpose, cancellationToken);
+        if (validation.IsError)
+            return validation.Errors;
+
+        var intent = validation.Value;
+
+        return new PreparedPicture(
+            intent,
+            EntityPictures.Pending(intent.ObjectName),
+            owner.Routes.BuildOriginalPicturePath(userId, intent.ObjectName),
+            owner.PicturesSizes.ToImageSizes(owner.Routes));
+    }
+}