M8-T08: add WarmteLink reading schema

app/models/meter_source.py

@@ -4,10 +4,12 @@ from __future__ import annotations
 
 import uuid as _uuid
 from datetime import datetime
+from decimal import Decimal
 from typing import TYPE_CHECKING
 
 from sqlalchemy import (
     Boolean,
+    CheckConstraint,
     DateTime,
     ForeignKey,
     Index,
@@ -93,12 +95,48 @@ class MeterSourceChannel(Base):
     bindings: Mapped[list["MeterSourceBinding"]] = relationship(
         back_populates="channel", cascade="save-update, merge"
     )
+    warmtelink_readings: Mapped[list["WarmteLinkReading"]] = relationship(
+        back_populates="channel", cascade="save-update, merge"
+    )
 
     __table_args__ = (
         UniqueConstraint("source_id", "channel_key", name="uq_meter_source_channel_source_key"),
     )
 
 
+class WarmteLinkReading(Base):
+    """One accepted scalar cumulative reading from a WarmteLink channel."""
+
+    __tablename__ = "warmtelink_reading"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+    channel_id: Mapped[int] = mapped_column(
+        ForeignKey("meter_source_channel.id", ondelete="RESTRICT"), nullable=False
+    )
+    # These timestamps retain their UTC-aware application semantics.  SQLite
+    # stores them without an offset, so callers must always supply aware UTC.
+    recorded_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False)
+    received_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False)
+    # SQLite's ORM Numeric path can exactly round-trip this 12-integer-digit
+    # range at scale 3. That is ample for a long-lived cumulative meter while
+    # retaining the protocol's 0.001 resolution without float conversion.
+    value: Mapped[Decimal] = mapped_column(Numeric(15, 3), nullable=False)
+    unit: Mapped[str] = mapped_column(String(32), nullable=False)
+    quality: Mapped[str] = mapped_column(String(32), nullable=False)
+    equipment_fingerprint: Mapped[str] = mapped_column(String(64), nullable=False)
+
+    channel: Mapped["MeterSourceChannel"] = relationship(back_populates="warmtelink_readings")
+
+    __table_args__ = (
+        CheckConstraint(
+            "quality IN ('valid', 'invalid', 'unverifiable')",
+            name="ck_warmtelink_reading_quality",
+        ),
+        UniqueConstraint("channel_id", "recorded_at", name="uq_warmtelink_reading_channel_recorded_at"),
+        Index("ix_warmtelink_reading_recorded_at", "recorded_at"),
+    )
+
+
 class MeterSourceBinding(Base):
     """Connect one source channel to one physical meter for a half-open window."""