mastodon-backup-filter/Activity.cs

using System.Text.Json.Nodes;

namespace MastodonBackupFilter
{
    public class MastodonOutboxNodeReader
    {
        public static OutboxObject ReadNodes(JsonNode? node)
        {
            if (node == null)
            {
                throw new ArgumentNullException();
            }

            var baseObj = new OutboxObject
            {
                Node = node,
                Recipients = VisibilityExtractor.ExtractRecipients(node)
            };

            return baseObj.TypeString switch
            {
                "Create" => new CreateActivityJsonNode
                {
                    Node = node,
                    Recipients = baseObj.Recipients,
                    Payload = node["object"] switch
                    {
                        null => throw new InvalidDataException("Create has a null object"),
                        JsonObject o => ReadContentNode(o),
                        _ => throw new InvalidDataException("Can't handle a create payload that isn't a JsonObject")
                    }
                },
                "Announce" => node["object"] switch
                {
                    JsonValue v => new AnnounceActivityJsonNode<string>()
                    {
                        Node = node,
                        Recipients = baseObj.Recipients,
                        BoostTarget = v.GetValue<string>()
                    },
                    JsonObject o => new AnnounceActivityJsonNode<OutboxObject>()
                    {
                        Node = node,
                        Recipients = baseObj.Recipients,
                        BoostTarget = ReadContentNode(o),
                    },
                    _ => throw new InvalidDataException("Unhandled announce node type")
                },
                _ => baseObj // No special handling...
            };
        }

        public static UrlObject ReadContentNode(JsonObject node)
        {
            return node["type"] switch
            {
                null => throw new InvalidDataException("Created post object has null type"),
                JsonValue v => v.GetValue<string>() switch
                {
                    "Note" => new NoteObject
                    {
                        Node = node,
                        Recipients = VisibilityExtractor.ExtractRecipients(node)
                    },
                    "Question" => new QuestionObject
                    {
                        Node = node,
                        Recipients = VisibilityExtractor.ExtractRecipients(node)
                    },
                    _ => throw new InvalidDataException($"Unhandled kind of content {node}")
                },
                _ => throw new InvalidDataException("Object type should be a JsonValue")
            };
        }

    }

    public record MastodonObject
    {
        public required JsonNode Node { get; init; }
        public string Id => Node["id"]!.GetValue<string>();
        public string Published => Node["published"]!.GetValue<string>();
        public string TypeString => Node["type"]!.GetValue<string>();
    }

    public record OutboxObject : MastodonObject
    {
        public required PostRecipients Recipients { get; init; }
        public JsonArray To => Node["to"]!.AsArray();
        public JsonArray Cc => Node["to"]!.AsArray();

        public Visibility Visibility => Recipients.AsVisibility();
    }

    public record CreateActivityJsonNode : OutboxObject
    {
        public required OutboxObject Payload { get; init; }
    }

    public record AnnounceActivityJsonNode<T> : OutboxObject
    {
        public required T BoostTarget { get; init; }
    }

    public record UrlObject : OutboxObject
    {
        public string Url => Node["url"]!.GetValue<string>();

    }

    public record NoteObject : UrlObject
    {

    }

    public record QuestionObject : UrlObject
    {

    }
}