actpub-activitystreams 0.2.0

//! The universal Activity Streams 2.0 [`Object`] container.
//!
//! AS 2.0 defines a rich vocabulary of object types (Actor, Activity,
//! Collection, Note, …) that share the majority of their properties.
//! Rather than materialize every specialisation as an independent Rust
//! struct, this crate models all of them through a single [`Object`] type
//! with every standard property represented directly as a typed field.
//! The [`kind`](crate::kind) module provides string constants for
//! distinguishing variants, and [`Object::is_kind`] gives an ergonomic
//! check against them.
//!
//! This mirrors the design of the popular `activitystreams` Rust crate and
//! of reference implementations such as `activitypub-federation-rust`; it
//! is the most interoperable style for a Fediverse where many
//! implementations emit structurally ambiguous JSON-LD.

use std::collections::BTreeMap;

use chrono::{DateTime, FixedOffset};
use serde::{Deserialize, Serialize};
use url::Url;

use crate::actor::{Endpoints, PublicKey};
use crate::kind;
use crate::multikey::AssertionMethod;
use crate::proof::Proof;
use crate::value::{HasId, OneOrMany, Public, UrlOr};

/// A reference-valued property that may appear as a bare URL or as an
/// inlined [`Object`].
///
/// [`Object`] is recursive in its own properties, so the inline arm is
/// boxed to keep the struct size predictable.
pub type ObjectRef = UrlOr<Box<Object>>;

/// A language map keyed by BCP-47 language tag, as used by `contentMap`,
/// `summaryMap`, and `nameMap`.
pub type LanguageMap = BTreeMap<String, String>;

/// The universal Activity Streams 2.0 object container.
///
/// Every specification-defined property across [Object][obj],
/// [Activity][act], [Collection][coll], and [CollectionPage][page] is
/// represented as a typed field. Properties that are absent on the wire
/// are deserialised as `None` (for scalar fields) or an empty
/// [`OneOrMany`] (for array fields). Unknown properties are preserved
/// verbatim in [`extra`](Self::extra), ensuring lossless round-trips
/// across implementations that emit non-standard extensions.
///
/// [obj]: https://www.w3.org/TR/activitystreams-core/#object
/// [act]: https://www.w3.org/TR/activitystreams-core/#activities
/// [coll]: https://www.w3.org/TR/activitystreams-core/#collections
/// [page]: https://www.w3.org/TR/activitystreams-core/#dfn-collectionpage
#[derive(Debug, Clone, PartialEq, Default, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
#[allow(
    clippy::struct_field_names,
    reason = "the `object`, `relationship`, `subject` etc. field names are all mandated verbatim by the Activity Streams 2.0 vocabulary and cannot be renamed without breaking interoperability"
)]
pub struct Object {
    /// Globally unique identifier of this object.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub id: Option<Url>,

    /// Type(s) of this object. Multiple types are permitted; most
    /// Fediverse implementations emit exactly one.
    #[serde(rename = "type", default, skip_serializing_if = "OneOrMany::is_empty")]
    pub kind: OneOrMany<String>,

    /// Files or media objects attached to this object.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub attachment: OneOrMany<ObjectRef>,

    /// The actors attributed as creators of this object.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub attributed_to: OneOrMany<ObjectRef>,

    /// Intended audience for this object.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub audience: OneOrMany<ObjectRef>,

    /// Plain-text or HTML content of this object.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub content: Option<String>,

    /// Localised content variants keyed by BCP-47 language tag.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub content_map: Option<LanguageMap>,

    /// AS 2.0 application-level `context` property.
    ///
    /// Note: this is *not* the JSON-LD `@context` — that is handled by
    /// [`WithContext`](crate::WithContext).
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub context: OneOrMany<ObjectRef>,

    /// Plain-text display name.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub name: Option<String>,

    /// Localised display names keyed by BCP-47 language tag.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub name_map: Option<LanguageMap>,

    /// End time for an interval-valued object (`xsd:dateTime`).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub end_time: Option<DateTime<FixedOffset>>,

    /// Entity that generated this object.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub generator: OneOrMany<ObjectRef>,

    /// Small iconic representation of this object.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub icon: OneOrMany<ObjectRef>,

    /// Primary image associated with this object.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub image: OneOrMany<ObjectRef>,

    /// Objects this object is in reply to.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub in_reply_to: OneOrMany<ObjectRef>,

    /// Associated physical or virtual location.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub location: OneOrMany<ObjectRef>,

    /// Preview resource associated with this object.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub preview: OneOrMany<ObjectRef>,

    /// Publication timestamp (`xsd:dateTime`).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub published: Option<DateTime<FixedOffset>>,

    /// Collection of replies to this object.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub replies: Option<Box<ObjectRef>>,

    /// Start time for an interval-valued object (`xsd:dateTime`).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub start_time: Option<DateTime<FixedOffset>>,

    /// Plain-text or HTML summary of this object.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub summary: Option<String>,

    /// Localised summary variants keyed by BCP-47 language tag.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub summary_map: Option<LanguageMap>,

    /// Tags (mentions, hashtags, emoji) linked to this object.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub tag: OneOrMany<ObjectRef>,

    /// Last-updated timestamp (`xsd:dateTime`).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub updated: Option<DateTime<FixedOffset>>,

    /// URL(s) providing alternate representations of this object.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub url: OneOrMany<ObjectRef>,

    /// Public primary recipients.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub to: OneOrMany<ObjectRef>,

    /// Private primary recipients (stripped before delivery).
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub bto: OneOrMany<ObjectRef>,

    /// Public secondary recipients.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub cc: OneOrMany<ObjectRef>,

    /// Private secondary recipients (stripped before delivery).
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub bcc: OneOrMany<ObjectRef>,

    /// MIME type of this object's payload.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub media_type: Option<String>,

    /// `xsd:duration` lexical form (e.g. `"PT5M"`).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub duration: Option<String>,

    /// One or more actors performing the activity.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub actor: OneOrMany<ObjectRef>,

    /// Object of the activity. Omitted for `IntransitiveActivity`.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub object: OneOrMany<ObjectRef>,

    /// Indirect target of the activity.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub target: OneOrMany<ObjectRef>,

    /// Result of the activity.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub result: OneOrMany<ObjectRef>,

    /// Origin from which the activity proceeds.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub origin: OneOrMany<ObjectRef>,

    /// Instrument used to perform the activity.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub instrument: OneOrMany<ObjectRef>,

    /// Number of items in the collection.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub total_items: Option<u64>,

    /// Current page of a paged collection.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub current: Option<Box<ObjectRef>>,

    /// First page of a paged collection.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub first: Option<Box<ObjectRef>>,

    /// Last page of a paged collection.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub last: Option<Box<ObjectRef>>,

    /// Items in an unordered collection.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub items: OneOrMany<ObjectRef>,

    /// Items in an ordered collection.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub ordered_items: OneOrMany<ObjectRef>,

    /// Collection this page is part of.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub part_of: Option<Box<ObjectRef>>,

    /// Next page.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub next: Option<Box<ObjectRef>>,

    /// Previous page.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub prev: Option<Box<ObjectRef>>,

    /// Starting index (`OrderedCollectionPage` only).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub start_index: Option<u64>,

    /// Place: accuracy of the position coordinates in percent
    /// `[0.0, 100.0]`.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub accuracy: Option<f64>,

    /// Place: altitude of the position in [`units`](Self::units).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub altitude: Option<f64>,

    /// Place: latitude of the position in decimal degrees.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub latitude: Option<f64>,

    /// Place: longitude of the position in decimal degrees.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub longitude: Option<f64>,

    /// Place: radius of the position in [`units`](Self::units).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub radius: Option<f64>,

    /// Place: measurement units for [`altitude`](Self::altitude) and
    /// [`radius`](Self::radius). The AS2.0 vocabulary defines a fixed set
    /// (`"cm"`, `"feet"`, `"inches"`, `"km"`, `"m"`, `"miles"`) but any URI
    /// is permitted as an extension, so the raw string is preserved.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub units: Option<String>,

    /// Question: exclusive list of options (only one may be selected).
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub one_of: OneOrMany<ObjectRef>,

    /// Question: inclusive list of options (any subset may be selected).
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub any_of: OneOrMany<ObjectRef>,

    /// Question: indicates a question has closed. Per AS2.0 this property
    /// is polymorphic (`xsd:dateTime` | `Object` | `Link` | `xsd:boolean`),
    /// so the raw JSON value is preserved verbatim.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub closed: Option<serde_json::Value>,

    /// Tombstone: the `type` of the object that was deleted.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub former_type: Option<String>,

    /// Tombstone: timestamp of when the object was deleted.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub deleted: Option<DateTime<FixedOffset>>,

    /// Relationship: the subject individual in the relationship.
    ///
    /// Renamed on the wire to avoid clashing with
    /// [`attributed_to`](Self::attributed_to); the property name in AS2.0
    /// is `subject`.
    #[serde(rename = "subject", default, skip_serializing_if = "Option::is_none")]
    pub relationship_subject: Option<Box<ObjectRef>>,

    /// Relationship: kind of relationship between
    /// [`relationship_subject`](Self::relationship_subject) and
    /// [`object`](Self::object). May be a URI or an inlined `Relationship`
    /// vocabulary term.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub relationship: OneOrMany<ObjectRef>,

    /// Profile: the object this profile describes.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub describes: Option<Box<ObjectRef>>,

    /// `ActivityPub` §4.1: short, mention-friendly handle (e.g. `"alice"`).
    /// Mandatory on every Mastodon-style actor.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub preferred_username: Option<String>,

    /// `ActivityPub` §4.1: actor's inbox URL. Servers POST activities here
    /// to deliver them to this actor.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub inbox: Option<Url>,

    /// `ActivityPub` §4.1: actor's outbox URL containing the
    /// `OrderedCollection` of activities they have authored.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub outbox: Option<Url>,

    /// `ActivityPub` §4.1: collection of actors following this actor.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub followers: Option<Url>,

    /// `ActivityPub` §4.1: collection of actors this actor follows.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub following: Option<Url>,

    /// `ActivityPub` §4.1: collection of objects this actor has liked.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub liked: Option<Url>,

    /// `ActivityPub` §4.1: list of additional collections owned by this
    /// actor (e.g. groups, lists). Rarely used in practice but defined
    /// in the spec.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub streams: Vec<Url>,

    /// W3C Security v1 / ActivityPub-via-Mastodon: legacy Cavage-style
    /// HTTP-Signature verification key. See [`PublicKey`].
    #[serde(skip_serializing_if = "Option::is_none")]
    pub public_key: Option<PublicKey>,

    /// `ActivityPub` §4.1 `endpoints` block (shared inbox, OAuth
    /// endpoints, …). See [`Endpoints`].
    #[serde(skip_serializing_if = "Option::is_none")]
    pub endpoints: Option<Endpoints>,

    /// Mastodon `toot:featured` collection of pinned posts.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub featured: Option<Url>,

    /// Mastodon `toot:featuredTags` collection of pinned hashtags.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub featured_tags: Option<Url>,

    /// AS 2.0: whether the actor's follow requests require manual
    /// approval (i.e. private profile).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub manually_approves_followers: Option<bool>,

    /// Mastodon `toot:discoverable`: whether the actor opts in to
    /// inclusion in directory listings.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub discoverable: Option<bool>,

    /// Mastodon `toot:indexable`: whether posts may be indexed by
    /// full-text search engines.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub indexable: Option<bool>,

    /// Mastodon `toot:memorial`: whether this account has been
    /// memorialised (read-only after death).
    #[serde(skip_serializing_if = "Option::is_none")]
    pub memorial: Option<bool>,

    /// FEP-521a `assertionMethod` array of verification methods used
    /// for content-signing (FEP-8b32 proofs and similar).
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub assertion_method: Vec<AssertionMethod>,

    /// W3C Controlled Identifiers `authentication` array of
    /// verification methods used for proving control of the actor URL
    /// (challenge-response auth, signed delete tombstones, …).
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub authentication: Vec<AssertionMethod>,

    /// FEP-8b32: zero or more Object Integrity Proofs attached to this
    /// document. Multiple entries form a proof chain.
    #[serde(default, skip_serializing_if = "OneOrMany::is_empty")]
    pub proof: OneOrMany<Proof>,

    /// Unknown or extension properties preserved verbatim.
    ///
    /// This captures any JSON property that does not map to a typed field,
    /// ensuring lossless round-tripping through non-standard extensions
    /// (e.g. Mastodon's `toot:` namespace fields, Lemmy's moderation
    /// metadata, Misskey reactions).
    #[serde(flatten)]
    pub extra: BTreeMap<String, serde_json::Value>,
}

impl Object {
    /// Creates an empty [`Object`] with no properties set.
    #[must_use]
    pub fn new() -> Self {
        Self::default()
    }

    /// Creates an [`Object`] with the given type.
    #[must_use]
    pub fn with_kind(kind: impl Into<String>) -> Self {
        Self {
            kind: OneOrMany::one(kind.into()),
            ..Self::default()
        }
    }

    /// Sets the [`id`](Self::id).
    #[must_use]
    pub fn with_id(mut self, id: Url) -> Self {
        self.id = Some(id);
        self
    }

    /// Returns `true` if any of this object's declared types equals `kind`.
    #[must_use]
    pub fn is_kind(&self, kind: &str) -> bool {
        self.kind.iter().any(|k| k == kind)
    }

    /// Returns the primary (first) type name, if any.
    #[must_use]
    pub fn primary_kind(&self) -> Option<&str> {
        self.kind.first().map(String::as_str)
    }

    /// Returns `true` if this object is any of the five standard actor
    /// types (Person, Group, Organization, Application, Service).
    #[must_use]
    pub fn is_actor(&self) -> bool {
        self.is_kind(kind::actor::PERSON)
            || self.is_kind(kind::actor::GROUP)
            || self.is_kind(kind::actor::ORGANIZATION)
            || self.is_kind(kind::actor::APPLICATION)
            || self.is_kind(kind::actor::SERVICE)
    }

    /// Returns `true` if this object is any kind of collection or page.
    #[must_use]
    pub fn is_collection(&self) -> bool {
        self.is_kind(kind::core::COLLECTION)
            || self.is_kind(kind::core::ORDERED_COLLECTION)
            || self.is_kind(kind::core::COLLECTION_PAGE)
            || self.is_kind(kind::core::ORDERED_COLLECTION_PAGE)
    }

    /// Returns `true` if any of the **public** audience properties
    /// address the `ActivityPub` `Public` pseudo-actor in any of its
    /// spellings.
    ///
    /// Per [ActivityPub §5.6][public] only the public-facing addressing
    /// fields ([`to`](Self::to), [`cc`](Self::cc),
    /// [`audience`](Self::audience)) participate in the public-visibility
    /// check. The [`bto`](Self::bto) and [`bcc`](Self::bcc) fields MUST be
    /// stripped by the server before delivery to remote inboxes, so
    /// including them here would produce incorrect results on the receiver
    /// side.
    ///
    /// [public]: https://www.w3.org/TR/activitypub/#public-addressing
    #[must_use]
    pub fn is_public(&self) -> bool {
        fn any_public(refs: &OneOrMany<ObjectRef>) -> bool {
            refs.iter().any(|r| match r {
                UrlOr::Url(u) => Public::is_public(u.as_str()),
                UrlOr::Object(o) => o.id.as_ref().is_some_and(|u| Public::is_public(u.as_str())),
            })
        }

        any_public(&self.to) || any_public(&self.cc) || any_public(&self.audience)
    }
}

impl HasId for Object {
    fn id(&self) -> Option<&Url> {
        self.id.as_ref()
    }
}

#[cfg(test)]
mod tests {
    use pretty_assertions::assert_eq;
    use serde_json::json;

    use super::*;

    #[test]
    fn empty_object_roundtrips_as_empty_json() {
        let obj = Object::new();
        let v = serde_json::to_value(&obj).unwrap();
        assert_eq!(v, json!({}));
    }

    #[test]
    fn with_kind_emits_type() {
        let obj = Object::with_kind("Note");
        let v = serde_json::to_value(&obj).unwrap();
        assert_eq!(v, json!({ "type": "Note" }));
    }

    #[test]
    fn kind_helpers_work() {
        let note = Object::with_kind("Note");
        assert!(note.is_kind("Note"));
        assert_eq!(note.primary_kind(), Some("Note"));
        assert!(!note.is_actor());
        assert!(!note.is_collection());
    }

    #[test]
    fn actor_detection_covers_all_standard_types() {
        for t in [
            kind::actor::PERSON,
            kind::actor::GROUP,
            kind::actor::ORGANIZATION,
            kind::actor::APPLICATION,
            kind::actor::SERVICE,
        ] {
            let a = Object::with_kind(t);
            assert!(a.is_actor(), "{t} should be an actor");
        }
    }

    #[test]
    fn is_public_detects_bare_url_in_to() {
        let mut obj = Object::with_kind("Note");
        obj.to = OneOrMany::one(UrlOr::Url(
            Url::parse(Public::URI).expect("Public::URI must parse"),
        ));
        assert!(obj.is_public());
    }

    #[test]
    fn is_public_detects_inlined_object_in_cc() {
        let mut obj = Object::with_kind("Note");
        let public_obj =
            Object::new().with_id(Url::parse(Public::URI).expect("Public::URI must parse"));
        obj.cc = OneOrMany::one(UrlOr::Object(Box::new(public_obj)));
        assert!(obj.is_public());
    }

    #[test]
    fn is_public_detects_target_in_audience() {
        // `audience` is one of the three public-addressing fields per
        // ActivityPub §5.6.
        let mut obj = Object::with_kind("Note");
        obj.audience = OneOrMany::one(UrlOr::Url(
            Url::parse(Public::URI).expect("Public::URI must parse"),
        ));
        assert!(obj.is_public());
    }

    #[test]
    fn is_public_ignores_bto_and_bcc() {
        // Per ActivityPub §5.6, `bto`/`bcc` MUST be stripped before
        // delivery, so they must not contribute to public visibility.
        let mut obj = Object::with_kind("Note");
        obj.bto = OneOrMany::one(UrlOr::Url(Url::parse(Public::URI).unwrap()));
        assert!(!obj.is_public(), "bto must not be considered public");

        let mut obj2 = Object::with_kind("Note");
        obj2.bcc = OneOrMany::one(UrlOr::Url(Url::parse(Public::URI).unwrap()));
        assert!(!obj2.is_public(), "bcc must not be considered public");
    }

    #[test]
    fn place_properties_roundtrip() {
        let raw = json!({
            "type": "Place",
            "name": "Work Office",
            "latitude": 36.75,
            "longitude": 119.7726,
            "altitude": 90.0,
            "accuracy": 94.5,
            "radius": 10.5,
            "units": "m"
        });
        let obj: Object = serde_json::from_value(raw.clone()).unwrap();
        assert_eq!(obj.latitude, Some(36.75));
        assert_eq!(obj.longitude, Some(119.7726));
        assert_eq!(obj.altitude, Some(90.0));
        assert_eq!(obj.accuracy, Some(94.5));
        assert_eq!(obj.radius, Some(10.5));
        assert_eq!(obj.units.as_deref(), Some("m"));
        let back = serde_json::to_value(&obj).unwrap();
        assert_eq!(back, raw);
    }

    #[test]
    fn question_properties_roundtrip() {
        let raw = json!({
            "type": "Question",
            "name": "What is your favourite colour?",
            "oneOf": [
                { "type": "Note", "name": "Red" },
                { "type": "Note", "name": "Blue" }
            ],
            "closed": "2026-01-01T00:00:00Z"
        });
        let obj: Object = serde_json::from_value(raw.clone()).unwrap();
        assert_eq!(obj.one_of.len(), 2);
        assert!(obj.closed.is_some());
        let back = serde_json::to_value(&obj).unwrap();
        assert_eq!(back, raw);
    }

    #[test]
    fn tombstone_properties_roundtrip() {
        let raw = json!({
            "id": "https://mastodon.social/users/alice/statuses/1",
            "type": "Tombstone",
            "formerType": "Note",
            "deleted": "2026-04-20T12:00:00Z"
        });
        let obj: Object = serde_json::from_value(raw.clone()).unwrap();
        assert!(obj.is_kind("Tombstone"));
        assert_eq!(obj.former_type.as_deref(), Some("Note"));
        assert!(obj.deleted.is_some());
        let back = serde_json::to_value(&obj).unwrap();
        assert_eq!(back, raw);
    }

    #[test]
    fn relationship_properties_roundtrip() {
        let raw = json!({
            "type": "Relationship",
            "subject": "https://example.com/users/alice",
            "relationship": "http://purl.org/vocab/relationship/acquaintanceOf",
            "object": "https://example.com/users/bob"
        });
        let obj: Object = serde_json::from_value(raw.clone()).unwrap();
        assert!(obj.relationship_subject.is_some());
        assert_eq!(obj.relationship.len(), 1);
        assert_eq!(obj.object.len(), 1);
        let back = serde_json::to_value(&obj).unwrap();
        assert_eq!(back, raw);
    }

    #[test]
    fn profile_describes_roundtrip() {
        let raw = json!({
            "type": "Profile",
            "describes": {
                "type": "Person",
                "name": "Alice"
            }
        });
        let obj: Object = serde_json::from_value(raw.clone()).unwrap();
        assert!(obj.describes.is_some());
        let back = serde_json::to_value(&obj).unwrap();
        assert_eq!(back, raw);
    }

    #[test]
    fn mastodon_note_roundtrips() {
        let raw = json!({
            "id": "https://mastodon.social/users/alice/statuses/1",
            "type": "Note",
            "attributedTo": "https://mastodon.social/users/alice",
            "content": "<p>Hello, Fediverse</p>",
            "published": "2026-04-20T10:00:00+00:00",
            "to": ["https://www.w3.org/ns/activitystreams#Public"],
            "cc": ["https://mastodon.social/users/alice/followers"],
            "sensitive": false,
            "inReplyTo": null
        });

        let obj: Object = serde_json::from_value(raw).unwrap();
        assert!(obj.is_kind("Note"));
        assert_eq!(obj.content.as_deref(), Some("<p>Hello, Fediverse</p>"));
        assert!(obj.is_public());
        assert_eq!(obj.attributed_to.len(), 1);
        assert!(obj.extra.contains_key("sensitive"));
        // `inReplyTo: null` should be absorbed without failure
    }

    #[test]
    fn extension_fields_roundtrip() {
        let raw = json!({
            "type": "Note",
            "_misskey_quote": "https://misskey.example/note/abc",
            "blurhash": "LEHV6nWB2yk8pyo0adR*.7kCMdnj"
        });
        let obj: Object = serde_json::from_value(raw.clone()).unwrap();
        assert_eq!(obj.extra.len(), 2);
        let back = serde_json::to_value(&obj).unwrap();
        assert_eq!(back, raw);
    }
}