bambuddy/backend/app/models/active_print_session.py

"""Durable copy of the filament-attribution context for an in-flight print."""

from datetime import datetime

from sqlalchemy import JSON, DateTime, ForeignKey
from sqlalchemy.orm import Mapped, mapped_column

from backend.app.core.database import Base


class ActivePrintSession(Base):
    """Print-start context the completion path needs, persisted per printer.

    ``usage_tracker._active_sessions`` holds the same data in memory, and the
    tray-change log lives on ``PrinterState``. Both are lost when Bambuddy
    restarts mid-print, which on a long print silently destroys filament
    attribution: without the plate the 3MF parser sums every plate, without the
    assignment snapshot a spool unlinked at runout can't be resolved, and
    without the tray-change log an AMS-backup switch charges the whole print to
    whichever tray happened to finish it.

    One row per printer — a printer runs one print at a time. Written at print
    start, appended to on every tray change, deleted at completion. A leaked
    row (completion missed entirely) is harmless: print start overwrites it,
    and the completion path ignores a row whose ``started_at`` doesn't line up
    with the print it is closing.

    The Spoolman writer has had an equivalent durable row since #1820
    (``active_print_spoolman``); this is the internal-inventory counterpart.
    """

    __tablename__ = "active_print_sessions"

    printer_id: Mapped[int] = mapped_column(ForeignKey("printers.id", ondelete="CASCADE"), primary_key=True)

    print_name: Mapped[str] = mapped_column(default="")
    started_at: Mapped[datetime] = mapped_column(DateTime)

    # tray_now at print start — reliable, unlike at completion where the
    # printer has usually retracted and reports 255.
    tray_now_at_start: Mapped[int] = mapped_column(default=-1)

    # Queue item's plate for multi-plate 3MFs dispatched one plate at a time.
    plate_id: Mapped[int | None] = mapped_column(nullable=True)

    # Slicer slot -> global tray, as dispatched: [2]
    ams_mapping: Mapped[list | None] = mapped_column(JSON, nullable=True)

    # {"<ams_id>-<tray_id>": spool_id} — the assignment map as it stood before
    # the print could disturb it.
    spool_assignments: Mapped[dict | None] = mapped_column(JSON, nullable=True)

    # {"<ams_id>-<tray_id>": remain%} for the remain-delta fallback path.
    tray_remain_start: Mapped[dict | None] = mapped_column(JSON, nullable=True)

    # [[global_tray_id, layer_num], ...] mirroring PrinterState.tray_change_log.
    tray_change_log: Mapped[list | None] = mapped_column(JSON, nullable=True)