feat(backend): expose GET /api/v1/stats/summary

Ajoute le resume instantane de consommation du parc attendu par le
frontend (deja developpe contre ce contrat en mode mock). Nouveaux
SiteRepository et ReadingRepository (derniere lecture par site via
DISTINCT ON), StatsService pour l'agregation et les cas de repli
(capacite nulle, absence de lecture, data_quality inconnue), et le
endpoint lecteur-seul correspondant. Documentation des routes et du
schema des couches mises a jour.

apps/backend/app/api/deps.py

@@ -23,9 +23,12 @@ from app.core.security import decode_access_token as decode_token
 from app.db.session import get_session
 from app.repositories.audit_log import AuditLogRepository
 from app.repositories.login_attempt import LoginAttemptRepository
+from app.repositories.reading import ReadingRepository
 from app.repositories.refresh_token import RefreshTokenRepository
+from app.repositories.site import SiteRepository
 from app.repositories.user import UserRepository
 from app.services.auth import AuthService, LoginPolicy
+from app.services.stats import StatsService
 from app.services.user import UserService
 
 SessionDep = Annotated[AsyncSession, Depends(get_session)]
@@ -131,6 +134,13 @@ def get_user_service(
 UserServiceDep = Annotated[UserService, Depends(get_user_service)]
 
 
+def get_stats_service(session: SessionDep) -> StatsService:
+    return StatsService(sites=SiteRepository(session), readings=ReadingRepository(session))
+
+
+StatsServiceDep = Annotated[StatsService, Depends(get_stats_service)]
+
+
 async def get_current_principal(
     credentials: CredentialsDep,
     session: SessionDep,

apps/backend/app/api/v1/endpoints/stats.py

@@ -0,0 +1,16 @@
+from fastapi import APIRouter
+
+from app.api.deps import LecteurDep, StatsServiceDep
+from app.schemas.stats import StatsSummaryResponse
+
+router = APIRouter()
+
+
+@router.get(
+    "/summary",
+    response_model=StatsSummaryResponse,
+    summary="Résume la consommation instantanée du parc",
+)
+async def get_summary(_: LecteurDep, service: StatsServiceDep) -> StatsSummaryResponse:
+    resume = await service.summary()
+    return StatsSummaryResponse.model_validate(resume)

apps/backend/app/api/v1/router.py

@@ -1,8 +1,9 @@
 from fastapi import APIRouter
 
-from app.api.v1.endpoints import auth, health, users
+from app.api.v1.endpoints import auth, health, stats, users
 
 api_router = APIRouter()
 api_router.include_router(health.router, prefix="/health", tags=["health"])
 api_router.include_router(auth.router, prefix="/auth", tags=["auth"])
 api_router.include_router(users.router, prefix="/users", tags=["users"])
+api_router.include_router(stats.router, prefix="/stats", tags=["stats"])

apps/backend/app/repositories/reading.py

@@ -0,0 +1,21 @@
+from collections.abc import Sequence
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.energy import Reading
+
+
+class ReadingRepository:
+    def __init__(self, session: AsyncSession) -> None:
+        self._session = session
+
+    async def latest_by_site(self) -> Sequence[Reading]:
+        # `.distinct(site_id)` compile en `DISTINCT ON (site_id)` sous PostgreSQL : une seule
+        # ligne par site, la plus récente grâce à l'ordre composite qui suit.
+        requete = (
+            select(Reading)
+            .distinct(Reading.site_id)
+            .order_by(Reading.site_id, Reading.timestamp.desc())
+        )
+        return (await self._session.execute(requete)).scalars().all()

apps/backend/app/repositories/site.py

@@ -0,0 +1,15 @@
+from collections.abc import Sequence
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.energy import Site
+
+
+class SiteRepository:
+    def __init__(self, session: AsyncSession) -> None:
+        self._session = session
+
+    async def list_all(self) -> Sequence[Site]:
+        requete = select(Site).order_by(Site.site_id)
+        return (await self._session.execute(requete)).scalars().all()

apps/backend/app/schemas/stats.py

@@ -0,0 +1,26 @@
+from datetime import datetime
+from typing import Literal
+
+from pydantic import BaseModel, ConfigDict
+
+
+class SiteSummaryResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    site_id: str
+    site_name: str
+    current_consumption_kw: float | None
+    capacity_kw: float
+    load_percent: float | None
+    data_quality: Literal["good", "partial", "degraded", "critical"]
+
+
+class StatsSummaryResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    timestamp: datetime
+    total_sites: int
+    total_consumption_kw: float
+    total_capacity_kw: float
+    average_load_percent: float
+    sites: list[SiteSummaryResponse]

apps/backend/app/services/stats.py

@@ -0,0 +1,81 @@
+from dataclasses import dataclass
+from datetime import UTC, datetime
+from typing import Literal
+
+from app.models.energy import Reading, Site
+from app.repositories.reading import ReadingRepository
+from app.repositories.site import SiteRepository
+
+DataQuality = Literal["good", "partial", "degraded", "critical"]
+
+QUALITES_CONNUES: frozenset[str] = frozenset({"good", "partial", "degraded", "critical"})
+
+
+@dataclass(frozen=True, slots=True)
+class SiteConsumption:
+    site_id: str
+    site_name: str
+    current_consumption_kw: float | None
+    capacity_kw: float
+    load_percent: float | None
+    data_quality: DataQuality
+
+
+@dataclass(frozen=True, slots=True)
+class ConsumptionSummary:
+    timestamp: datetime
+    total_sites: int
+    total_consumption_kw: float
+    total_capacity_kw: float
+    average_load_percent: float
+    sites: list[SiteConsumption]
+
+
+class StatsService:
+    def __init__(self, sites: SiteRepository, readings: ReadingRepository) -> None:
+        self._sites = sites
+        self._readings = readings
+
+    async def summary(self) -> ConsumptionSummary:
+        sites = await self._sites.list_all()
+        dernieres = {lecture.site_id: lecture for lecture in await self._readings.latest_by_site()}
+
+        resumes = [self._resume_site(site, dernieres.get(site.site_id)) for site in sites]
+        consommation_totale = sum(r.current_consumption_kw or 0 for r in resumes)
+        capacite_totale = sum(r.capacity_kw for r in resumes)
+
+        return ConsumptionSummary(
+            timestamp=datetime.now(UTC),
+            total_sites=len(resumes),
+            total_consumption_kw=consommation_totale,
+            total_capacity_kw=capacite_totale,
+            average_load_percent=(
+                consommation_totale / capacite_totale * 100 if capacite_totale > 0 else 0
+            ),
+            sites=resumes,
+        )
+
+    @staticmethod
+    def _resume_site(site: Site, derniere: Reading | None) -> SiteConsumption:
+        capacite = site.capacity_kw or 0
+        # Piège : `data_quality` est nul dès qu'un site n'a jamais reçu de lecture, ou que le
+        # producteur n'a pas su la qualifier. Le contrat frontend n'a pas de valeur pour ce cas,
+        # `critical` est la seule des quatre qui n'induit pas une confiance qu'on n'a pas.
+        qualite: DataQuality = "critical"
+        consommation = None
+        if derniere is not None and derniere.data_quality in QUALITES_CONNUES:
+            qualite = derniere.data_quality  # type: ignore[assignment]
+            consommation = derniere.consumption_kw
+
+        charge = (
+            consommation / capacite * 100 if consommation is not None and capacite > 0 else None
+        )
+
+        return SiteConsumption(
+            site_id=site.site_id,
+            site_name=site.site_name,
+            current_consumption_kw=consommation,
+            capacity_kw=capacite,
+            load_percent=charge,
+            data_quality=qualite,
+        )