wasm4pm_compat/

ocel.rs

//! Object-Centric Event Log (OCEL) shape — **first-class**, not "event log plus
//! extras".
//!
//! Classical event logs assume a *single case notion*: every event belongs to
//! exactly one case. OCEL drops that assumption: an event may relate to *many*
//! objects of *many* types, and objects relate to each other and change over
//! time. Modeling OCEL as "an [`crate::eventlog::EventLog`] with side tables"
//! would be a category error — so this module gives OCEL its own genuine canon:
//! [`crate::ocel::OcelObject`], [`crate::ocel::OcelEvent`], [`crate::ocel::EventObjectLink`] (E2O), [`crate::ocel::ObjectObjectLink`]
//! (O2O), and [`crate::ocel::ObjectChange`], collected in an [`crate::ocel::OcelLog`].
//!
//! ## Structure only
//!
//! [`crate::ocel::OcelLog::validate`] performs a **structural** integrity check: every link
//! must reference declared objects and events; ids must be unique. It does
//! **not** discover an object-centric Petri net, flatten the log, or check
//! conformance — those are engines and graduate to `wasm4pm`.
//!
//! ## The flattening trap
//!
//! Flattening OCEL to a single case notion is *lossy by construction* — it
//! drops convergence/divergence information. This crate treats that as a named
//! law, [`crate::ocel::OcelRefusal::FlatteningLoss`], so a flattening projection must carry a
//! loss policy and report rather than silently laundering object-centric truth
//! into case-centric shape.
//!
//! ## Graduation to `wasm4pm`
//!
//! Object-centric discovery (OC-Petri-nets, OC-DFG), object-centric conformance,
//! and OCPQ evaluation graduate to `wasm4pm`. This crate only guarantees the
//! OCEL is *well-shaped enough to mine*.

use std::collections::HashSet;

/// A typed attribute value on an [`OcelObject`] or [`OcelEvent`].
///
/// OCEL 2.0 attributes are typed: the key is a `&str`-named field and the value
/// is one of string, integer, float, boolean, timestamp, list, or map.
/// `OcelAttributeValue` models the value side; the key is always a `String`.
///
/// The `List` and `Map` variants reflect the OCEL 2.0 spec allowance for nested
/// attribute structures (e.g. a list of prices, a map of sub-attributes). Both
/// are structure-only containers — no evaluation or indexing occurs here; that
/// graduates to `wasm4pm`.
///
/// Structure-only: it stores the value, not a parser.
#[derive(Clone, Debug, PartialEq)]
pub enum OcelAttributeValue {
    /// A string-valued attribute.
    String(String),
    /// An integer-valued attribute.
    Integer(i64),
    /// A floating-point attribute.
    Float(f64),
    /// A boolean attribute.
    Boolean(bool),
    /// A timestamp attribute as nanoseconds since the Unix epoch.
    TimestampNs(i64),
    /// An ordered list of attribute values (OCEL 2.0 nested list).
    ///
    /// Structure-only: it is a container, not an indexed collection. Indexing
    /// and aggregation graduate to `wasm4pm`.
    List(Vec<OcelAttributeValue>),
    /// A key/value map of attribute values (OCEL 2.0 nested map).
    ///
    /// Structure-only: it is a named container, not a record system. Lookup
    /// and projection graduate to `wasm4pm`.
    Map(Vec<(String, OcelAttributeValue)>),
}

/// A named attribute (key + value) on an [`OcelObject`] or [`OcelEvent`].
///
/// Structure-only: it is a key/value pair, not a mined feature.
#[derive(Clone, Debug, PartialEq)]
pub struct OcelAttribute {
    /// The attribute key.
    pub key: String,
    /// The typed attribute value.
    pub value: OcelAttributeValue,
}

impl OcelAttribute {
    /// Construct a string attribute.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelAttribute, OcelAttributeValue};
    /// let a = OcelAttribute::string("status", "open");
    /// assert_eq!(a.key, "status");
    /// assert_eq!(a.value, OcelAttributeValue::String("open".into()));
    /// ```
    pub fn string(key: impl Into<String>, value: impl Into<String>) -> Self {
        OcelAttribute {
            key: key.into(),
            value: OcelAttributeValue::String(value.into()),
        }
    }

    /// Construct an integer attribute.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelAttribute, OcelAttributeValue};
    /// let a = OcelAttribute::integer("quantity", 3);
    /// assert_eq!(a.value, OcelAttributeValue::Integer(3));
    /// ```
    pub fn integer(key: impl Into<String>, value: i64) -> Self {
        OcelAttribute {
            key: key.into(),
            value: OcelAttributeValue::Integer(value),
        }
    }

    /// Construct a float attribute.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelAttribute, OcelAttributeValue};
    /// let a = OcelAttribute::float("price", 9.99);
    /// assert_eq!(a.value, OcelAttributeValue::Float(9.99));
    /// ```
    pub fn float(key: impl Into<String>, value: f64) -> Self {
        OcelAttribute {
            key: key.into(),
            value: OcelAttributeValue::Float(value),
        }
    }

    /// Construct a boolean attribute.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelAttribute, OcelAttributeValue};
    /// let a = OcelAttribute::boolean("active", true);
    /// assert_eq!(a.value, OcelAttributeValue::Boolean(true));
    /// ```
    pub fn boolean(key: impl Into<String>, value: bool) -> Self {
        OcelAttribute {
            key: key.into(),
            value: OcelAttributeValue::Boolean(value),
        }
    }

    /// Construct a nanosecond-timestamp attribute.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelAttribute, OcelAttributeValue};
    /// let a = OcelAttribute::timestamp_ns("created_at", 1_700_000_000_000_000_000);
    /// assert_eq!(a.value, OcelAttributeValue::TimestampNs(1_700_000_000_000_000_000));
    /// ```
    pub fn timestamp_ns(key: impl Into<String>, value: i64) -> Self {
        OcelAttribute {
            key: key.into(),
            value: OcelAttributeValue::TimestampNs(value),
        }
    }
}

/// An object: a typed, identified entity that events relate to, with OCEL 2.0
/// attributes.
///
/// In OCEL an object (e.g. an order, an item, a delivery) has a stable id, a
/// type, and a bag of typed attributes at creation time. Attribute evolution over
/// time is captured in [`ObjectChange`]. Multiple events may touch the same
/// object, and objects relate to one another via [`ObjectObjectLink`]s.
///
/// Structure-only: an `OcelObject` records identity, type, and initial
/// attributes; it does not compute object behavior. That graduates to `wasm4pm`.
#[derive(Clone, Debug, PartialEq)]
pub struct OcelObject {
    id: String,
    object_type: String,
    attributes: Vec<OcelAttribute>,
}

impl OcelObject {
    /// Construct an object with an id and a type, with no attributes.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::OcelObject;
    /// let o = OcelObject::new("ord-1", "order");
    /// assert_eq!(o.id(), "ord-1");
    /// assert_eq!(o.object_type(), "order");
    /// assert!(o.attributes().is_empty());
    /// ```
    pub fn new(id: impl Into<String>, object_type: impl Into<String>) -> Self {
        OcelObject {
            id: id.into(),
            object_type: object_type.into(),
            attributes: Vec::new(),
        }
    }

    /// Attach an attribute. Builder-style.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelObject, OcelAttribute};
    /// let o = OcelObject::new("ord-1", "order").with_attribute(OcelAttribute::string("status", "open"));
    /// assert_eq!(o.attributes().len(), 1);
    /// ```
    pub fn with_attribute(mut self, attr: OcelAttribute) -> Self {
        self.attributes.push(attr);
        self
    }

    /// The stable object identifier.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::OcelObject;
    /// assert_eq!(OcelObject::new("x", "t").id(), "x");
    /// ```
    pub fn id(&self) -> &str {
        &self.id
    }

    /// The object type (empty types are refused at validation time).
    ///
    /// ```
    /// use wasm4pm_compat::ocel::OcelObject;
    /// assert_eq!(OcelObject::new("x", "t").object_type(), "t");
    /// ```
    pub fn object_type(&self) -> &str {
        &self.object_type
    }

    /// The initial attributes of this object.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::OcelObject;
    /// assert!(OcelObject::new("x", "t").attributes().is_empty());
    /// ```
    pub fn attributes(&self) -> &[OcelAttribute] {
        &self.attributes
    }
}

/// A backwards-compatible alias for [`OcelObject`].
///
/// Existing code using `Object` continues to compile. New code should prefer
/// [`OcelObject`].
#[deprecated(
    since = "26.6.5",
    note = "use `OcelObject` — the unambiguous name for the OCEL object shape"
)]
pub type Object = OcelObject;

/// An object-centric event: an identified, named activity occurrence that may
/// relate to many objects, with OCEL 2.0 typed attributes.
///
/// Named `OcelEvent` (not `Event`) to stand clearly apart from the case-centric
/// [`crate::eventlog::Event`]: an `OcelEvent` carries no single case id, because
/// in OCEL there is no single case notion. Its object relationships live in the
/// [`OcelLog`]'s [`EventObjectLink`] table.
///
/// Structure-only: it records id, activity, optional time, and attributes; it
/// does not replay or mine.
#[derive(Clone, Debug, PartialEq)]
pub struct OcelEvent {
    id: String,
    activity: String,
    timestamp_ns: Option<i64>,
    attributes: Vec<OcelAttribute>,
}

impl OcelEvent {
    /// Construct an OCEL event with an id and activity name.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::OcelEvent;
    /// let e = OcelEvent::new("e1", "place_order");
    /// assert_eq!(e.id(), "e1");
    /// assert_eq!(e.activity(), "place_order");
    /// assert!(e.attributes().is_empty());
    /// ```
    pub fn new(id: impl Into<String>, activity: impl Into<String>) -> Self {
        OcelEvent {
            id: id.into(),
            activity: activity.into(),
            timestamp_ns: None,
            attributes: Vec::new(),
        }
    }

    /// Attach an attribute. Builder-style.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelEvent, OcelAttribute};
    /// let e = OcelEvent::new("e1", "ship").with_attribute(OcelAttribute::string("channel", "web"));
    /// assert_eq!(e.attributes().len(), 1);
    /// ```
    pub fn with_attribute(mut self, attr: OcelAttribute) -> Self {
        self.attributes.push(attr);
        self
    }

    /// The event attributes.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::OcelEvent;
    /// assert!(OcelEvent::new("e1", "a").attributes().is_empty());
    /// ```
    pub fn attributes(&self) -> &[OcelAttribute] {
        &self.attributes
    }

    /// Attach a nanosecond timestamp. Builder-style.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::OcelEvent;
    /// let e = OcelEvent::new("e1", "ship").at_ns(42);
    /// assert_eq!(e.timestamp_ns(), Some(42));
    /// ```
    pub fn at_ns(mut self, ts: i64) -> Self {
        self.timestamp_ns = Some(ts);
        self
    }

    /// The stable event identifier.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::OcelEvent;
    /// assert_eq!(OcelEvent::new("e1", "a").id(), "e1");
    /// ```
    pub fn id(&self) -> &str {
        &self.id
    }

    /// The activity name.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::OcelEvent;
    /// assert_eq!(OcelEvent::new("e1", "a").activity(), "a");
    /// ```
    pub fn activity(&self) -> &str {
        &self.activity
    }

    /// The optional timestamp in nanoseconds since the Unix epoch.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::OcelEvent;
    /// assert_eq!(OcelEvent::new("e1", "a").timestamp_ns(), None);
    /// ```
    #[must_use]
    pub fn timestamp_ns(&self) -> Option<i64> {
        self.timestamp_ns
    }
}

/// An event-to-object (E2O) link: which objects an event touched, and how.
///
/// The optional `qualifier` names the *role* of the object in the event (e.g.
/// `"item"`, `"customer"`). A dangling link — one pointing at an undeclared
/// event or object — is a structural defect, refused as
/// [`OcelRefusal::DanglingEventObjectLink`].
///
/// Structure-only: it is a typed edge in the OCEL graph, not a mined relation.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct EventObjectLink {
    event_id: String,
    object_id: String,
    qualifier: Option<String>,
}

impl EventObjectLink {
    /// Construct an unqualified E2O link.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::EventObjectLink;
    /// let l = EventObjectLink::new("e1", "ord-1");
    /// assert_eq!(l.event_id(), "e1");
    /// assert_eq!(l.object_id(), "ord-1");
    /// ```
    pub fn new(event_id: impl Into<String>, object_id: impl Into<String>) -> Self {
        EventObjectLink {
            event_id: event_id.into(),
            object_id: object_id.into(),
            qualifier: None,
        }
    }

    /// Attach a role qualifier. Builder-style.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::EventObjectLink;
    /// let l = EventObjectLink::new("e1", "ord-1").qualified("places");
    /// assert_eq!(l.qualifier(), Some("places"));
    /// ```
    pub fn qualified(mut self, qualifier: impl Into<String>) -> Self {
        self.qualifier = Some(qualifier.into());
        self
    }

    /// The referenced event id.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::EventObjectLink;
    /// assert_eq!(EventObjectLink::new("e", "o").event_id(), "e");
    /// ```
    pub fn event_id(&self) -> &str {
        &self.event_id
    }

    /// The referenced object id.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::EventObjectLink;
    /// assert_eq!(EventObjectLink::new("e", "o").object_id(), "o");
    /// ```
    pub fn object_id(&self) -> &str {
        &self.object_id
    }

    /// The optional role qualifier.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::EventObjectLink;
    /// assert_eq!(EventObjectLink::new("e", "o").qualifier(), None);
    /// ```
    #[must_use]
    pub fn qualifier(&self) -> Option<&str> {
        self.qualifier.as_deref()
    }
}

/// An object-to-object (O2O) link: a typed relationship between two objects.
///
/// The optional `qualifier` names the relationship (e.g. `"contains"`,
/// `"belongs_to"`). A link to an undeclared object is refused as
/// [`OcelRefusal::DanglingObjectObjectLink`].
///
/// Structure-only: a typed edge between objects, not a mined dependency.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct ObjectObjectLink {
    source_id: String,
    target_id: String,
    qualifier: Option<String>,
}

impl ObjectObjectLink {
    /// Construct an unqualified O2O link from `source` to `target`.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::ObjectObjectLink;
    /// let l = ObjectObjectLink::new("ord-1", "item-9");
    /// assert_eq!(l.source_id(), "ord-1");
    /// assert_eq!(l.target_id(), "item-9");
    /// ```
    pub fn new(source_id: impl Into<String>, target_id: impl Into<String>) -> Self {
        ObjectObjectLink {
            source_id: source_id.into(),
            target_id: target_id.into(),
            qualifier: None,
        }
    }

    /// Attach a relationship qualifier. Builder-style.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::ObjectObjectLink;
    /// let l = ObjectObjectLink::new("ord-1", "item-9").qualified("contains");
    /// assert_eq!(l.qualifier(), Some("contains"));
    /// ```
    pub fn qualified(mut self, qualifier: impl Into<String>) -> Self {
        self.qualifier = Some(qualifier.into());
        self
    }

    /// The source object id.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::ObjectObjectLink;
    /// assert_eq!(ObjectObjectLink::new("a", "b").source_id(), "a");
    /// ```
    pub fn source_id(&self) -> &str {
        &self.source_id
    }

    /// The target object id.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::ObjectObjectLink;
    /// assert_eq!(ObjectObjectLink::new("a", "b").target_id(), "b");
    /// ```
    pub fn target_id(&self) -> &str {
        &self.target_id
    }

    /// The optional relationship qualifier.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::ObjectObjectLink;
    /// assert_eq!(ObjectObjectLink::new("a", "b").qualifier(), None);
    /// ```
    #[must_use]
    pub fn qualifier(&self) -> Option<&str> {
        self.qualifier.as_deref()
    }
}

/// A recorded change to an object attribute (the OCEL 2.0 object-evolution
/// notion).
///
/// Objects are not static: an order's `status`, an item's `price`, may change
/// over the process. An `ObjectChange` records *which* object's *which*
/// attribute took *which* value, optionally *when*. A change naming no object
/// or no attribute is refused as [`OcelRefusal::InvalidObjectChange`].
///
/// Structure-only: it records the change tuple; it does not replay object
/// evolution.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct ObjectChange {
    object_id: String,
    attribute: String,
    value: String,
    timestamp_ns: Option<i64>,
}

impl ObjectChange {
    /// Construct an object change: `object_id.attribute = value`.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::ObjectChange;
    /// let c = ObjectChange::new("ord-1", "status", "paid");
    /// assert_eq!(c.object_id(), "ord-1");
    /// assert_eq!(c.attribute(), "status");
    /// assert_eq!(c.value(), "paid");
    /// ```
    pub fn new(
        object_id: impl Into<String>,
        attribute: impl Into<String>,
        value: impl Into<String>,
    ) -> Self {
        ObjectChange {
            object_id: object_id.into(),
            attribute: attribute.into(),
            value: value.into(),
            timestamp_ns: None,
        }
    }

    /// Attach a nanosecond timestamp to the change. Builder-style.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::ObjectChange;
    /// let c = ObjectChange::new("o", "a", "v").at_ns(7);
    /// assert_eq!(c.timestamp_ns(), Some(7));
    /// ```
    pub fn at_ns(mut self, ts: i64) -> Self {
        self.timestamp_ns = Some(ts);
        self
    }

    /// The changed object's id.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::ObjectChange;
    /// assert_eq!(ObjectChange::new("o", "a", "v").object_id(), "o");
    /// ```
    pub fn object_id(&self) -> &str {
        &self.object_id
    }

    /// The changed attribute name.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::ObjectChange;
    /// assert_eq!(ObjectChange::new("o", "a", "v").attribute(), "a");
    /// ```
    pub fn attribute(&self) -> &str {
        &self.attribute
    }

    /// The new attribute value.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::ObjectChange;
    /// assert_eq!(ObjectChange::new("o", "a", "v").value(), "v");
    /// ```
    pub fn value(&self) -> &str {
        &self.value
    }

    /// The optional timestamp of the change.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::ObjectChange;
    /// assert_eq!(ObjectChange::new("o", "a", "v").timestamp_ns(), None);
    /// ```
    #[must_use]
    pub fn timestamp_ns(&self) -> Option<i64> {
        self.timestamp_ns
    }
}

/// A complete object-centric event log: objects, events, E2O & O2O links, and
/// object changes.
///
/// This is the OCEL canon as one value. [`OcelLog::validate`] checks structural
/// integrity (no dangling links, no duplicate ids, no empty types); it does not
/// mine anything.
///
/// Structure-only: an admitted `OcelLog` is a substrate for object-centric
/// discovery and conformance, which graduate to `wasm4pm`.
#[doc(alias = "object-centric event log")]
#[doc(alias = "OCEL")]
#[derive(Clone, Debug, Default, PartialEq)]
pub struct OcelLog {
    objects: Vec<OcelObject>,
    events: Vec<OcelEvent>,
    e2o: Vec<EventObjectLink>,
    o2o: Vec<ObjectObjectLink>,
    changes: Vec<ObjectChange>,
}

impl OcelLog {
    /// Construct an OCEL log from its five constituent tables.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelObject, OcelEvent, EventObjectLink, OcelLog};
    /// let log = OcelLog::new(
    ///     [OcelObject::new("ord-1", "order")],
    ///     [OcelEvent::new("e1", "place_order")],
    ///     [EventObjectLink::new("e1", "ord-1")],
    ///     [],
    ///     [],
    /// );
    /// assert!(log.validate().is_ok());
    /// ```
    pub fn new(
        objects: impl IntoIterator<Item = OcelObject>,
        events: impl IntoIterator<Item = OcelEvent>,
        e2o: impl IntoIterator<Item = EventObjectLink>,
        o2o: impl IntoIterator<Item = ObjectObjectLink>,
        changes: impl IntoIterator<Item = ObjectChange>,
    ) -> Self {
        OcelLog {
            objects: objects.into_iter().collect(),
            events: events.into_iter().collect(),
            e2o: e2o.into_iter().collect(),
            o2o: o2o.into_iter().collect(),
            changes: changes.into_iter().collect(),
        }
    }

    /// The declared objects.
    pub fn objects(&self) -> &[OcelObject] {
        &self.objects
    }

    /// The declared events.
    pub fn events(&self) -> &[OcelEvent] {
        &self.events
    }

    /// The event-to-object (E2O) links.
    pub fn event_object_links(&self) -> &[EventObjectLink] {
        &self.e2o
    }

    /// The object-to-object (O2O) links.
    pub fn object_object_links(&self) -> &[ObjectObjectLink] {
        &self.o2o
    }

    /// The recorded object changes.
    pub fn object_changes(&self) -> &[ObjectChange] {
        &self.changes
    }

    /// Structurally validate the OCEL log.
    ///
    /// This is a **structure check, not mining**. It verifies, in order:
    /// - there is at least one object ([`OcelRefusal::MissingObject`]) and one
    ///   event ([`OcelRefusal::MissingEvent`]);
    /// - object and event ids are each unique
    ///   ([`OcelRefusal::DuplicateObjectId`], [`OcelRefusal::DuplicateEventId`]);
    /// - every object names a non-empty type ([`OcelRefusal::MissingObjectType`]);
    /// - at least one E2O link exists ([`OcelRefusal::EmptyEventObjectLinks`]);
    /// - every E2O link references a declared event and object
    ///   ([`OcelRefusal::DanglingEventObjectLink`]);
    /// - every O2O link references declared objects
    ///   ([`OcelRefusal::DanglingObjectObjectLink`]);
    /// - every object change references a declared object and names an attribute
    ///   ([`OcelRefusal::InvalidObjectChange`]).
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelObject, OcelEvent, EventObjectLink, OcelLog, OcelRefusal};
    /// // Dangling E2O link: references object "ghost" that was never declared.
    /// let log = OcelLog::new(
    ///     [OcelObject::new("ord-1", "order")],
    ///     [OcelEvent::new("e1", "a")],
    ///     [EventObjectLink::new("e1", "ghost")],
    ///     [],
    ///     [],
    /// );
    /// assert_eq!(log.validate(), Err(OcelRefusal::DanglingEventObjectLink));
    /// ```
    #[must_use = "check the shape-check result"]
    pub fn validate(&self) -> Result<(), OcelRefusal> {
        if self.objects.is_empty() {
            return Err(OcelRefusal::MissingObject);
        }
        if self.events.is_empty() {
            return Err(OcelRefusal::MissingEvent);
        }

        let mut object_ids: HashSet<&str> = HashSet::new();
        for o in &self.objects {
            if o.object_type().is_empty() {
                return Err(OcelRefusal::MissingObjectType);
            }
            if !object_ids.insert(o.id()) {
                return Err(OcelRefusal::DuplicateObjectId);
            }
        }

        let mut event_ids: HashSet<&str> = HashSet::new();
        for e in &self.events {
            if !event_ids.insert(e.id()) {
                return Err(OcelRefusal::DuplicateEventId);
            }
        }

        if self.e2o.is_empty() {
            return Err(OcelRefusal::EmptyEventObjectLinks);
        }
        for l in &self.e2o {
            if !event_ids.contains(l.event_id()) || !object_ids.contains(l.object_id()) {
                return Err(OcelRefusal::DanglingEventObjectLink);
            }
        }

        for l in &self.o2o {
            if !object_ids.contains(l.source_id()) || !object_ids.contains(l.target_id()) {
                return Err(OcelRefusal::DanglingObjectObjectLink);
            }
        }

        for c in &self.changes {
            if c.attribute().is_empty() || !object_ids.contains(c.object_id()) {
                return Err(OcelRefusal::InvalidObjectChange);
            }
        }

        Ok(())
    }
}

// ── IntoIterator for OcelLog ─────────────────────────────────────────────────

impl<'a> IntoIterator for &'a OcelLog {
    type Item = &'a OcelEvent;
    type IntoIter = core::slice::Iter<'a, OcelEvent>;

    /// Iterate over the [`OcelEvent`]s of this log.
    ///
    /// The idiomatic OCEL iteration surface. Objects, E2O links, and O2O links
    /// are accessible via [`OcelLog::objects`], [`OcelLog::event_object_links`],
    /// and [`OcelLog::object_object_links`] respectively.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelLog, OcelObject, OcelEvent, EventObjectLink};
    /// let log = OcelLog::new(
    ///     [OcelObject::new("o1", "order")],
    ///     [OcelEvent::new("e1", "place"), OcelEvent::new("e2", "ship")],
    ///     [EventObjectLink::new("e1", "o1"), EventObjectLink::new("e2", "o1")],
    ///     [],
    ///     [],
    /// );
    /// let activities: Vec<&str> = (&log).into_iter().map(|e| e.activity()).collect();
    /// assert_eq!(activities, ["place", "ship"]);
    /// ```
    fn into_iter(self) -> Self::IntoIter {
        self.events.iter()
    }
}

impl IntoIterator for OcelLog {
    type Item = OcelEvent;
    type IntoIter = std::vec::IntoIter<OcelEvent>;

    /// Consume the log and iterate over its [`OcelEvent`]s by value.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelLog, OcelObject, OcelEvent, EventObjectLink};
    /// let log = OcelLog::new(
    ///     [OcelObject::new("o1", "order")],
    ///     [OcelEvent::new("e1", "place")],
    ///     [EventObjectLink::new("e1", "o1")],
    ///     [],
    ///     [],
    /// );
    /// let v: Vec<OcelEvent> = log.into_iter().collect();
    /// assert_eq!(v.len(), 1);
    /// ```
    fn into_iter(self) -> Self::IntoIter {
        self.events.into_iter()
    }
}

/// The specific, named laws under which OCEL structure is refused.
///
/// Each variant cites a distinct structural law — never a bare "invalid input".
/// [`OcelRefusal::FlatteningLoss`] in particular guards the OCEL→case-centric
/// boundary: flattening is lossy and must go through a named projection with a
/// loss policy and report, not a silent re-shape.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
#[non_exhaustive]
pub enum OcelRefusal {
    /// The log declares no objects.
    MissingObject,
    /// The log declares no events.
    MissingEvent,
    /// The log declares no event-to-object links (an OCEL with no E2O is empty).
    EmptyEventObjectLinks,
    /// An E2O link references an undeclared event or object.
    DanglingEventObjectLink,
    /// An O2O link references an undeclared object.
    DanglingObjectObjectLink,
    /// Two objects share the same id.
    DuplicateObjectId,
    /// Two events share the same id.
    DuplicateEventId,
    /// Flattening to a single case notion would lose convergence/divergence
    /// information; requires a named projection with loss policy and report.
    FlatteningLoss,
    /// An object names an empty type.
    MissingObjectType,
    /// An object change references an undeclared object or names no attribute.
    InvalidObjectChange,
}

// ── OcelAttributeValue: Display + From conversions ───────────────────────────

impl core::fmt::Display for OcelAttributeValue {
    /// Human-readable representation of an OCEL attribute value.
    ///
    /// - `String(s)` → the string content directly (no quotes)
    /// - `Integer(n)` → decimal integer
    /// - `Float(f)` → decimal float
    /// - `Boolean(b)` → `"true"` or `"false"`
    /// - `TimestampNs(n)` → `"@<n>ns"` (nanoseconds since Unix epoch)
    /// - `List([…])` → `"[v1, v2, …]"`
    /// - `Map({…})` → `"{k1: v1, k2: v2, …}"`
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        match self {
            OcelAttributeValue::String(s) => f.write_str(s),
            OcelAttributeValue::Integer(n) => write!(f, "{n}"),
            OcelAttributeValue::Float(v) => write!(f, "{v}"),
            OcelAttributeValue::Boolean(b) => write!(f, "{b}"),
            OcelAttributeValue::TimestampNs(n) => write!(f, "@{n}ns"),
            OcelAttributeValue::List(items) => {
                f.write_str("[")?;
                for (i, item) in items.iter().enumerate() {
                    if i > 0 {
                        f.write_str(", ")?;
                    }
                    write!(f, "{item}")?;
                }
                f.write_str("]")
            }
            OcelAttributeValue::Map(pairs) => {
                f.write_str("{")?;
                for (i, (k, v)) in pairs.iter().enumerate() {
                    if i > 0 {
                        f.write_str(", ")?;
                    }
                    write!(f, "{k}: {v}")?;
                }
                f.write_str("}")
            }
        }
    }
}

impl From<String> for OcelAttributeValue {
    /// Infallible conversion: `String` → `OcelAttributeValue::String`.
    fn from(s: String) -> Self {
        OcelAttributeValue::String(s)
    }
}

impl From<&str> for OcelAttributeValue {
    /// Infallible conversion: `&str` → `OcelAttributeValue::String` (allocates, same as `String::from`).
    fn from(s: &str) -> Self {
        OcelAttributeValue::String(s.to_owned())
    }
}

impl From<i64> for OcelAttributeValue {
    /// Infallible conversion: `i64` → `OcelAttributeValue::Integer`.
    fn from(n: i64) -> Self {
        OcelAttributeValue::Integer(n)
    }
}

impl From<f64> for OcelAttributeValue {
    /// Infallible conversion: `f64` → `OcelAttributeValue::Float`.
    fn from(v: f64) -> Self {
        OcelAttributeValue::Float(v)
    }
}

impl From<bool> for OcelAttributeValue {
    /// Infallible conversion: `bool` → `OcelAttributeValue::Boolean`.
    fn from(b: bool) -> Self {
        OcelAttributeValue::Boolean(b)
    }
}

impl core::fmt::Display for OcelRefusal {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        let law = match self {
            OcelRefusal::MissingObject => "MissingObject",
            OcelRefusal::MissingEvent => "MissingEvent",
            OcelRefusal::EmptyEventObjectLinks => "EmptyEventObjectLinks",
            OcelRefusal::DanglingEventObjectLink => "DanglingEventObjectLink",
            OcelRefusal::DanglingObjectObjectLink => "DanglingObjectObjectLink",
            OcelRefusal::DuplicateObjectId => "DuplicateObjectId",
            OcelRefusal::DuplicateEventId => "DuplicateEventId",
            OcelRefusal::FlatteningLoss => "FlatteningLoss",
            OcelRefusal::MissingObjectType => "MissingObjectType",
            OcelRefusal::InvalidObjectChange => "InvalidObjectChange",
        };
        write!(f, "OCEL refused by law: {law}")
    }
}

/// Dimension summary for an OCEL log: the observed object types and activity
/// names.
///
/// `OcelDims` captures the *vocabulary* of an [`OcelLog`] — all object types and
/// activity names that appear — without materialising the log's relational
/// tables. It is useful as a fast header check before full admission.
///
/// Structure-only: it names dimensions; it does not count, mine, or index them.
/// Counting activities per object type, building object-type × activity
/// incidence tables, and computing object-type DFGs graduate to `wasm4pm`.
#[derive(Clone, Debug, Default, PartialEq, Eq)]
pub struct OcelDims {
    /// Distinct object types observed in this log.
    pub object_types: Vec<String>,
    /// Distinct activity names observed in this log.
    pub activities: Vec<String>,
}

impl OcelDims {
    /// Derive the dimension vocabulary from an [`OcelLog`].
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelDims, OcelLog, OcelObject, OcelEvent, EventObjectLink};
    /// let log = OcelLog::new(
    ///     [OcelObject::new("o1", "order"), OcelObject::new("i1", "item")],
    ///     [OcelEvent::new("e1", "place")],
    ///     [EventObjectLink::new("e1", "o1")],
    ///     [],
    ///     [],
    /// );
    /// let dims = OcelDims::from_log(&log);
    /// assert!(dims.object_types.contains(&"order".to_string()));
    /// assert!(dims.activities.contains(&"place".to_string()));
    /// ```
    #[must_use]
    pub fn from_log(log: &OcelLog) -> Self {
        use std::collections::BTreeSet;
        let object_types: BTreeSet<String> = log
            .objects()
            .iter()
            .map(|o| o.object_type().to_owned())
            .collect();
        let activities: BTreeSet<String> = log
            .events()
            .iter()
            .map(|e| e.activity().to_owned())
            .collect();
        OcelDims {
            object_types: object_types.into_iter().collect(),
            activities: activities.into_iter().collect(),
        }
    }

    /// Whether this log has any declared object types.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::OcelDims;
    /// assert!(OcelDims::default().is_empty());
    /// ```
    #[must_use]
    pub fn is_empty(&self) -> bool {
        self.object_types.is_empty() && self.activities.is_empty()
    }
}

// ── Object-type witness ───────────────────────────────────────────────────────

/// A phantom type-level object-type tag.
///
/// `ObjectTypeTag` is a zero-sized marker that threads a *named object type*
/// through generic typed surfaces. It prevents `TypedObject<OrderTag>` from
/// being silently coerced into `TypedObject<ItemTag>` at the type level.
///
/// Structure-only: it is a compile-time label. Object-type classification,
/// filtering, and DFG construction graduate to `wasm4pm`.
///
/// # Graduation
///
/// When an object-type distinction must be *enforced at runtime* (e.g. checking
/// that all events touching a given type appear only in a certain activity set),
/// the typed surface travels to `wasm4pm`.
pub trait ObjectTypeTag: core::fmt::Debug + Clone + PartialEq {
    /// The stable, lowercase, machine-facing object-type name (e.g. `"order"`).
    const TYPE_NAME: &'static str;
}

/// A typed wrapper around [`OcelObject`] that threads an [`ObjectTypeTag`] into
/// the type system.
///
/// `TypedObject<OT>` is a newtype around [`OcelObject`] whose phantom type
/// parameter `OT: ObjectTypeTag` makes the object's type visible at compile
/// time. It is not possible to mix `TypedObject<OrderTag>` and
/// `TypedObject<ItemTag>` without an explicit coercion through the inner
/// [`OcelObject`].
///
/// Structure-only: it carries identity, type tag, and attributes; it does not
/// compute object behavior or validate against a schema. That graduates to
/// `wasm4pm`.
#[derive(Clone, Debug, PartialEq)]
pub struct TypedObject<OT: ObjectTypeTag> {
    inner: OcelObject,
    _tag: core::marker::PhantomData<OT>,
}

impl<OT: ObjectTypeTag> TypedObject<OT> {
    /// Wrap an [`OcelObject`] with a compile-time object-type tag.
    ///
    /// The `object_type` field on the inner [`OcelObject`] is **not** replaced;
    /// callers should ensure it matches `OT::TYPE_NAME` if that consistency is
    /// required. The type-level tag is a compile-time claim, not a runtime check.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelObject, TypedObject, ObjectTypeTag};
    ///
    /// #[derive(Clone, Debug, PartialEq)]
    /// struct OrderTag;
    /// impl ObjectTypeTag for OrderTag { const TYPE_NAME: &'static str = "order"; }
    ///
    /// let obj = OcelObject::new("ord-1", "order");
    /// let typed = TypedObject::<OrderTag>::wrap(obj);
    /// assert_eq!(typed.inner().id(), "ord-1");
    /// ```
    pub fn wrap(inner: OcelObject) -> Self {
        TypedObject {
            inner,
            _tag: core::marker::PhantomData,
        }
    }

    /// Construct a [`TypedObject`] directly: id plus the tag's type name.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{TypedObject, ObjectTypeTag};
    ///
    /// #[derive(Clone, Debug, PartialEq)]
    /// struct ItemTag;
    /// impl ObjectTypeTag for ItemTag { const TYPE_NAME: &'static str = "item"; }
    ///
    /// let obj = TypedObject::<ItemTag>::new("item-7");
    /// assert_eq!(obj.inner().object_type(), "item");
    /// ```
    pub fn new(id: impl Into<String>) -> Self {
        TypedObject {
            inner: OcelObject::new(id, OT::TYPE_NAME),
            _tag: core::marker::PhantomData,
        }
    }

    /// The inner untyped [`OcelObject`].
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelObject, TypedObject, ObjectTypeTag};
    ///
    /// #[derive(Clone, Debug, PartialEq)]
    /// struct OrderTag;
    /// impl ObjectTypeTag for OrderTag { const TYPE_NAME: &'static str = "order"; }
    ///
    /// let typed = TypedObject::<OrderTag>::new("ord-3");
    /// assert_eq!(typed.inner().object_type(), "order");
    /// ```
    pub fn inner(&self) -> &OcelObject {
        &self.inner
    }

    /// Consume the wrapper and return the inner [`OcelObject`].
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{TypedObject, ObjectTypeTag};
    ///
    /// #[derive(Clone, Debug, PartialEq)]
    /// struct OrderTag;
    /// impl ObjectTypeTag for OrderTag { const TYPE_NAME: &'static str = "order"; }
    ///
    /// let obj = TypedObject::<OrderTag>::new("ord-5").into_inner();
    /// assert_eq!(obj.id(), "ord-5");
    /// ```
    pub fn into_inner(self) -> OcelObject {
        self.inner
    }
}

// ── Event-type witness ────────────────────────────────────────────────────────

/// A phantom type-level event-type tag.
///
/// `EventTypeTag` is a zero-sized marker that threads a *named activity type*
/// through generic typed surfaces. It prevents `TypedEvent<PlaceOrderTag>` from
/// being silently coerced into `TypedEvent<ShipTag>` at the type level.
///
/// Structure-only: it is a compile-time label. Activity-type classification
/// and typed process-tree construction graduate to `wasm4pm`.
pub trait EventTypeTag: core::fmt::Debug + Clone + PartialEq {
    /// The stable, lowercase, machine-facing activity-type name (e.g. `"place_order"`).
    const ACTIVITY_NAME: &'static str;
}

/// A typed wrapper around [`OcelEvent`] that threads an [`EventTypeTag`] into
/// the type system.
///
/// `TypedEvent<ET>` is a newtype around [`OcelEvent`] whose phantom type
/// parameter `ET: EventTypeTag` makes the event's activity visible at compile
/// time.
///
/// Structure-only: it carries identity, activity tag, timestamp, and
/// attributes; it does not replay, mine, or conform. That graduates to `wasm4pm`.
#[derive(Clone, Debug, PartialEq)]
pub struct TypedEvent<ET: EventTypeTag> {
    inner: OcelEvent,
    _tag: core::marker::PhantomData<ET>,
}

impl<ET: EventTypeTag> TypedEvent<ET> {
    /// Wrap an [`OcelEvent`] with a compile-time activity-type tag.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelEvent, TypedEvent, EventTypeTag};
    ///
    /// #[derive(Clone, Debug, PartialEq)]
    /// struct PlaceOrderTag;
    /// impl EventTypeTag for PlaceOrderTag { const ACTIVITY_NAME: &'static str = "place_order"; }
    ///
    /// let ev = OcelEvent::new("e1", "place_order");
    /// let typed = TypedEvent::<PlaceOrderTag>::wrap(ev);
    /// assert_eq!(typed.inner().activity(), "place_order");
    /// ```
    pub fn wrap(inner: OcelEvent) -> Self {
        TypedEvent {
            inner,
            _tag: core::marker::PhantomData,
        }
    }

    /// Construct a [`TypedEvent`] directly: id plus the tag's activity name.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{TypedEvent, EventTypeTag};
    ///
    /// #[derive(Clone, Debug, PartialEq)]
    /// struct ShipTag;
    /// impl EventTypeTag for ShipTag { const ACTIVITY_NAME: &'static str = "ship"; }
    ///
    /// let ev = TypedEvent::<ShipTag>::new("e2");
    /// assert_eq!(ev.inner().activity(), "ship");
    /// ```
    pub fn new(id: impl Into<String>) -> Self {
        TypedEvent {
            inner: OcelEvent::new(id, ET::ACTIVITY_NAME),
            _tag: core::marker::PhantomData,
        }
    }

    /// The inner untyped [`OcelEvent`].
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{TypedEvent, EventTypeTag};
    ///
    /// #[derive(Clone, Debug, PartialEq)]
    /// struct ShipTag;
    /// impl EventTypeTag for ShipTag { const ACTIVITY_NAME: &'static str = "ship"; }
    ///
    /// let ev = TypedEvent::<ShipTag>::new("e3");
    /// assert_eq!(ev.inner().id(), "e3");
    /// ```
    pub fn inner(&self) -> &OcelEvent {
        &self.inner
    }

    /// Consume the wrapper and return the inner [`OcelEvent`].
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{TypedEvent, EventTypeTag};
    ///
    /// #[derive(Clone, Debug, PartialEq)]
    /// struct ShipTag;
    /// impl EventTypeTag for ShipTag { const ACTIVITY_NAME: &'static str = "ship"; }
    ///
    /// let ev = TypedEvent::<ShipTag>::new("e4").into_inner();
    /// assert_eq!(ev.activity(), "ship");
    /// ```
    pub fn into_inner(self) -> OcelEvent {
        self.inner
    }
}

// ── Attribute-type witness ────────────────────────────────────────────────────

/// A phantom type-level attribute-type tag.
///
/// `AttributeTypeTag` is a zero-sized marker that threads a *named attribute
/// domain* (e.g. "status", "price", "quantity") through attribute-typed generic
/// surfaces. It prevents `TypedAttribute<StatusTag>` from being silently
/// coerced into `TypedAttribute<PriceTag>` at the type level.
///
/// Structure-only: it is a compile-time label. Attribute-domain validation,
/// aggregation, and normalization graduate to `wasm4pm`.
pub trait AttributeTypeTag: core::fmt::Debug + Clone + PartialEq {
    /// The stable, lowercase, machine-facing attribute name (e.g. `"status"`).
    const ATTR_NAME: &'static str;
}

/// A typed wrapper around [`OcelAttribute`] that threads an [`AttributeTypeTag`]
/// into the type system.
///
/// `TypedAttribute<AT>` is a newtype around [`OcelAttribute`] whose phantom
/// type parameter `AT: AttributeTypeTag` makes the attribute's domain visible
/// at compile time.
///
/// Structure-only: it wraps a key/value pair with a compile-time domain tag; it
/// does not interpret or validate the value. That graduates to `wasm4pm`.
#[derive(Clone, Debug, PartialEq)]
pub struct TypedAttribute<AT: AttributeTypeTag> {
    inner: OcelAttribute,
    _tag: core::marker::PhantomData<AT>,
}

impl<AT: AttributeTypeTag> TypedAttribute<AT> {
    /// Wrap an [`OcelAttribute`] with a compile-time attribute-type tag.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelAttribute, TypedAttribute, AttributeTypeTag};
    ///
    /// #[derive(Clone, Debug, PartialEq)]
    /// struct StatusTag;
    /// impl AttributeTypeTag for StatusTag { const ATTR_NAME: &'static str = "status"; }
    ///
    /// let attr = OcelAttribute::string("status", "open");
    /// let typed = TypedAttribute::<StatusTag>::wrap(attr);
    /// assert_eq!(typed.inner().key, "status");
    /// ```
    pub fn wrap(inner: OcelAttribute) -> Self {
        TypedAttribute {
            inner,
            _tag: core::marker::PhantomData,
        }
    }

    /// The inner untyped [`OcelAttribute`].
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelAttribute, TypedAttribute, AttributeTypeTag};
    ///
    /// #[derive(Clone, Debug, PartialEq)]
    /// struct PriceTag;
    /// impl AttributeTypeTag for PriceTag { const ATTR_NAME: &'static str = "price"; }
    ///
    /// let typed = TypedAttribute::<PriceTag>::wrap(OcelAttribute::float("price", 9.99));
    /// assert_eq!(typed.inner().key, "price");
    /// ```
    pub fn inner(&self) -> &OcelAttribute {
        &self.inner
    }

    /// Consume the wrapper and return the inner [`OcelAttribute`].
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{OcelAttribute, TypedAttribute, AttributeTypeTag};
    ///
    /// #[derive(Clone, Debug, PartialEq)]
    /// struct PriceTag;
    /// impl AttributeTypeTag for PriceTag { const ATTR_NAME: &'static str = "price"; }
    ///
    /// let attr = TypedAttribute::<PriceTag>::wrap(OcelAttribute::float("price", 1.5)).into_inner();
    /// assert_eq!(attr.key, "price");
    /// ```
    pub fn into_inner(self) -> OcelAttribute {
        self.inner
    }
}

// ── TypedObjectChange: object-change construction with typed value ────────────

/// A recorded change to an object attribute, with a typed [`OcelAttributeValue`].
///
/// `TypedObjectChange` is the typed companion to [`ObjectChange`]: instead of
/// storing the new value as a `String`, it stores an [`OcelAttributeValue`] so
/// the type of the change (integer, float, boolean, …) is visible without
/// parsing. A change naming no object or no attribute should be refused as
/// [`OcelRefusal::InvalidObjectChange`].
///
/// Structure-only: it records the typed change tuple; it does not replay object
/// evolution or compute a delta. That graduates to `wasm4pm`.
#[derive(Clone, Debug, PartialEq)]
pub struct TypedObjectChange {
    object_id: String,
    attribute: String,
    value: OcelAttributeValue,
    timestamp_ns: Option<i64>,
}

impl TypedObjectChange {
    /// Construct a typed object change: `object_id.attribute = value`.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{TypedObjectChange, OcelAttributeValue};
    /// let c = TypedObjectChange::new("ord-1", "price", OcelAttributeValue::Float(49.99));
    /// assert_eq!(c.object_id(), "ord-1");
    /// assert_eq!(c.attribute(), "price");
    /// assert_eq!(c.value(), &OcelAttributeValue::Float(49.99));
    /// ```
    pub fn new(
        object_id: impl Into<String>,
        attribute: impl Into<String>,
        value: OcelAttributeValue,
    ) -> Self {
        TypedObjectChange {
            object_id: object_id.into(),
            attribute: attribute.into(),
            value,
            timestamp_ns: None,
        }
    }

    /// Attach a nanosecond timestamp to the change. Builder-style.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{TypedObjectChange, OcelAttributeValue};
    /// let c = TypedObjectChange::new("o", "a", OcelAttributeValue::Boolean(true)).at_ns(42);
    /// assert_eq!(c.timestamp_ns(), Some(42));
    /// ```
    pub fn at_ns(mut self, ts: i64) -> Self {
        self.timestamp_ns = Some(ts);
        self
    }

    /// The changed object's id.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{TypedObjectChange, OcelAttributeValue};
    /// assert_eq!(TypedObjectChange::new("o", "a", OcelAttributeValue::Integer(1)).object_id(), "o");
    /// ```
    pub fn object_id(&self) -> &str {
        &self.object_id
    }

    /// The changed attribute name.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{TypedObjectChange, OcelAttributeValue};
    /// assert_eq!(TypedObjectChange::new("o", "a", OcelAttributeValue::Integer(1)).attribute(), "a");
    /// ```
    pub fn attribute(&self) -> &str {
        &self.attribute
    }

    /// The new typed attribute value.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{TypedObjectChange, OcelAttributeValue};
    /// let c = TypedObjectChange::new("o", "a", OcelAttributeValue::Integer(7));
    /// assert_eq!(c.value(), &OcelAttributeValue::Integer(7));
    /// ```
    pub fn value(&self) -> &OcelAttributeValue {
        &self.value
    }

    /// The optional timestamp of the change.
    ///
    /// ```
    /// use wasm4pm_compat::ocel::{TypedObjectChange, OcelAttributeValue};
    /// assert_eq!(TypedObjectChange::new("o", "a", OcelAttributeValue::Boolean(false)).timestamp_ns(), None);
    /// ```
    #[must_use]
    pub fn timestamp_ns(&self) -> Option<i64> {
        self.timestamp_ns
    }
}