"""EventEnvelope — schema for state-hub lifecycle events published to NATS.

Mirrors the EventEnvelope contract defined in activity-core
(`src/activity_core/models.py`). The state-hub publishes; activity-core
consumes and routes to ActivityDefinitions.

Subject naming convention (see docs/nats-event-subjects.md):

    org.statehub.{noun}.{verb}

Examples:
    org.statehub.repo.registered
    org.statehub.workstream.completed
    org.statehub.decision.resolved
    org.statehub.domain.goal.activated
    org.statehub.task.stale
"""

from __future__ import annotations

import uuid
from datetime import datetime, timezone
from typing import Any

from pydantic import BaseModel, Field

PUBLISHER = "state-hub"


class EventEnvelope(BaseModel):
    """Standard envelope shared with activity-core. Do not break compatibility.

    All inbound events on activity-core's side are normalised into this shape.
    """

    id: str = Field(description="UUID v4 — stable unique ID for deduplication.")
    type: str = Field(description="Dot-namespaced event type, e.g. 'org.statehub.repo.registered'.")
    version: str = Field(default="1.0", description="Schema version string.")
    timestamp: datetime = Field(description="When the event occurred (UTC).")
    publisher: str = Field(default=PUBLISHER, description="Originating service.")
    attributes: dict[str, Any] = Field(
        default_factory=dict,
        description="Event-specific attributes; structure varies by event type.",
    )

    @classmethod
    def new(cls, event_type: str, attributes: dict[str, Any] | None = None) -> "EventEnvelope":
        """Construct an envelope with a fresh UUID and current UTC timestamp."""
        return cls(
            id=str(uuid.uuid4()),
            type=event_type,
            timestamp=datetime.now(tz=timezone.utc),
            publisher=PUBLISHER,
            attributes=attributes or {},
        )
