feat(backend): expose GET /api/v1/sites/{site_id}/current pour l'issue #29

Ajoute la dernière mesure d'un site (SiteService.current), en réutilisant
la vérification d'existence déjà en place pour GET /sites/{site_id} :
SiteService gagne une dépendance ReadingRepository, sur le modèle de
composition déjà utilisé par StatsService/SensorService. Un site connu
sans lecture rend 200 avec les champs de mesure à null et
data_quality="critical" ; seul un site_id absent rend 404.

apps/backend/app/api/deps.py

@@ -140,7 +140,7 @@ UserServiceDep = Annotated[UserService, Depends(get_user_service)]
 
 
 def get_site_service(session: SessionDep) -> SiteService:
-    return SiteService(sites=SiteRepository(session))
+    return SiteService(sites=SiteRepository(session), readings=ReadingRepository(session))
 
 
 SiteServiceDep = Annotated[SiteService, Depends(get_site_service)]

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

@@ -3,7 +3,7 @@ from fastapi import APIRouter, HTTPException, status
 from app.api.deps import LecteurDep, SiteServiceDep
 from app.api.openapi import REPONSE_VALIDATION, Reponses
 from app.schemas.errors import ErrorResponse
-from app.schemas.site import SiteResponse
+from app.schemas.site import SiteCurrentResponse, SiteResponse
 from app.services.site import SiteNotFoundError
 
 router = APIRouter()
@@ -34,3 +34,21 @@ async def get_site(site_id: str, _: LecteurDep, service: SiteServiceDep) -> Site
             status_code=status.HTTP_404_NOT_FOUND, detail="Site introuvable"
         ) from erreur
     return SiteResponse.model_validate(site)
+
+
+@router.get(
+    "/{site_id}/current",
+    response_model=SiteCurrentResponse,
+    summary="Dernière mesure d'un site",
+    responses=REPONSES_INTROUVABLE,
+)
+async def get_current(
+    site_id: str, _: LecteurDep, service: SiteServiceDep
+) -> SiteCurrentResponse:
+    try:
+        actuel = await service.current(site_id)
+    except SiteNotFoundError as erreur:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND, detail="Site introuvable"
+        ) from erreur
+    return SiteCurrentResponse.model_validate(actuel)

apps/backend/app/repositories/reading.py

@@ -19,3 +19,12 @@ class ReadingRepository:
             .order_by(Reading.site_id, Reading.timestamp.desc())
         )
         return (await self._session.execute(requete)).scalars().all()
+
+    async def latest_for_site(self, site_id: str) -> Reading | None:
+        requete = (
+            select(Reading)
+            .where(Reading.site_id == site_id)
+            .order_by(Reading.timestamp.desc())
+            .limit(1)
+        )
+        return await self._session.scalar(requete)

apps/backend/app/schemas/site.py

@@ -1,3 +1,6 @@
+from datetime import datetime
+from typing import Literal
+
 from pydantic import BaseModel, ConfigDict
 
 
@@ -10,3 +13,20 @@ class SiteResponse(BaseModel):
     location: str | None
     capacity_kw: float | None
     status: str | None
+
+
+class SiteCurrentResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    timestamp: datetime | None
+    site_id: str
+    site_type: str
+    consumption_kw: float | None
+    consumption_kwh: float | None
+    voltage_v: float | None
+    current_a: float | None
+    power_factor: float | None
+    temperature_celsius: float | None
+    humidity_percent: float | None
+    null_reasons: list[str]
+    data_quality: Literal["good", "partial", "degraded", "critical"]

apps/backend/app/services/site.py

@@ -1,8 +1,16 @@
 from collections.abc import Sequence
+from dataclasses import dataclass
+from datetime import datetime
+from typing import Literal
 
 from app.models.energy import 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"})
+
 
 class SiteError(Exception):
     pass
@@ -12,9 +20,26 @@ class SiteNotFoundError(SiteError):
     pass
 
 
+@dataclass(frozen=True, slots=True)
+class SiteCurrentReading:
+    timestamp: datetime | None
+    site_id: str
+    site_type: str
+    consumption_kw: float | None
+    consumption_kwh: float | None
+    voltage_v: float | None
+    current_a: float | None
+    power_factor: float | None
+    temperature_celsius: float | None
+    humidity_percent: float | None
+    null_reasons: list[str]
+    data_quality: DataQuality
+
+
 class SiteService:
-    def __init__(self, *, sites: SiteRepository) -> None:
+    def __init__(self, *, sites: SiteRepository, readings: ReadingRepository) -> None:
         self._sites = sites
+        self._readings = readings
 
     async def list_all(self) -> Sequence[Site]:
         return await self._sites.list_all()
@@ -24,3 +49,41 @@ class SiteService:
         if site is None:
             raise SiteNotFoundError(site_id)
         return site
+
+    async def current(self, site_id: str) -> SiteCurrentReading:
+        site = await self.get_by_id(site_id)
+        derniere = await self._readings.latest_for_site(site_id)
+
+        if derniere is None:
+            return SiteCurrentReading(
+                timestamp=None,
+                site_id=site.site_id,
+                site_type=site.site_type,
+                consumption_kw=None,
+                consumption_kwh=None,
+                voltage_v=None,
+                current_a=None,
+                power_factor=None,
+                temperature_celsius=None,
+                humidity_percent=None,
+                null_reasons=[],
+                data_quality="critical",
+            )
+
+        qualite: DataQuality = (
+            derniere.data_quality if derniere.data_quality in QUALITES_CONNUES else "critical"
+        )
+        return SiteCurrentReading(
+            timestamp=derniere.timestamp,
+            site_id=site.site_id,
+            site_type=site.site_type,
+            consumption_kw=derniere.consumption_kw,
+            consumption_kwh=derniere.consumption_kwh,
+            voltage_v=derniere.voltage_v,
+            current_a=derniere.current_a,
+            power_factor=derniere.power_factor,
+            temperature_celsius=derniere.temperature_celsius,
+            humidity_percent=derniere.humidity_percent,
+            null_reasons=derniere.null_reasons or [],
+            data_quality=qualite,
+        )