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,
+        )

apps/backend/openapi.json

@@ -921,6 +921,93 @@
         }
       }
     },
+    "/api/v1/sites/{site_id}/current": {
+      "get": {
+        "tags": [
+          "sites"
+        ],
+        "summary": "Dernière mesure d'un site",
+        "operationId": "get_current_api_v1_sites__site_id__current_get",
+        "security": [
+          {
+            "Jeton d'accès": []
+          }
+        ],
+        "parameters": [
+          {
+            "name": "site_id",
+            "in": "path",
+            "required": true,
+            "schema": {
+              "type": "string",
+              "title": "Site Id"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "Successful Response",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/SiteCurrentResponse"
+                }
+              }
+            }
+          },
+          "500": {
+            "description": "Erreur interne. `correlation` identifie la trace côté serveur, qui n'est pas renvoyée au client.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/InternalErrorResponse"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Jeton absent, illisible, périmé, ou rendu caduc par un changement de rôle ou une désactivation. L'en-tête `WWW-Authenticate` porte la cause dans `error=`.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ErrorResponse"
+                }
+              }
+            }
+          },
+          "403": {
+            "description": "Mot de passe provisoire à changer (`detail` vaut `password_change_required`).",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ErrorResponse"
+                }
+              }
+            }
+          },
+          "422": {
+            "description": "Corps invalide. Le détail nomme le champ fautif et le type d'erreur, jamais la valeur envoyée.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ValidationErrorResponse"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Aucun site ne porte cet identifiant.",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ErrorResponse"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/api/v1/alerts": {
       "get": {
         "tags": [
@@ -1572,6 +1659,140 @@
         ],
         "title": "Role"
       },
+      "SiteCurrentResponse": {
+        "properties": {
+          "timestamp": {
+            "anyOf": [
+              {
+                "type": "string",
+                "format": "date-time"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Timestamp"
+          },
+          "site_id": {
+            "type": "string",
+            "title": "Site Id"
+          },
+          "site_type": {
+            "type": "string",
+            "title": "Site Type"
+          },
+          "consumption_kw": {
+            "anyOf": [
+              {
+                "type": "number"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Consumption Kw"
+          },
+          "consumption_kwh": {
+            "anyOf": [
+              {
+                "type": "number"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Consumption Kwh"
+          },
+          "voltage_v": {
+            "anyOf": [
+              {
+                "type": "number"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Voltage V"
+          },
+          "current_a": {
+            "anyOf": [
+              {
+                "type": "number"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Current A"
+          },
+          "power_factor": {
+            "anyOf": [
+              {
+                "type": "number"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Power Factor"
+          },
+          "temperature_celsius": {
+            "anyOf": [
+              {
+                "type": "number"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Temperature Celsius"
+          },
+          "humidity_percent": {
+            "anyOf": [
+              {
+                "type": "number"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Humidity Percent"
+          },
+          "null_reasons": {
+            "items": {
+              "type": "string"
+            },
+            "type": "array",
+            "title": "Null Reasons"
+          },
+          "data_quality": {
+            "type": "string",
+            "enum": [
+              "good",
+              "partial",
+              "degraded",
+              "critical"
+            ],
+            "title": "Data Quality"
+          }
+        },
+        "type": "object",
+        "required": [
+          "timestamp",
+          "site_id",
+          "site_type",
+          "consumption_kw",
+          "consumption_kwh",
+          "voltage_v",
+          "current_a",
+          "power_factor",
+          "temperature_celsius",
+          "humidity_percent",
+          "null_reasons",
+          "data_quality"
+        ],
+        "title": "SiteCurrentResponse"
+      },
       "SiteResponse": {
         "properties": {
           "site_id": {

apps/backend/tests/api/test_openapi.py

@@ -31,6 +31,7 @@ ROUTES_A_ROLE = {
     ("POST", "/api/v1/users/{id}/password-reset"),
     ("GET", "/api/v1/sites"),
     ("GET", "/api/v1/sites/{site_id}"),
+    ("GET", "/api/v1/sites/{site_id}/current"),
     ("GET", "/api/v1/alerts"),
     ("GET", "/api/v1/recommendations"),
     ("GET", "/api/v1/recommendations/{recommendation_id}"),

apps/backend/tests/api/test_sites.py

@@ -1,4 +1,5 @@
 from collections.abc import Callable, Iterator
+from datetime import UTC, datetime
 from uuid import uuid4
 
 import pytest
@@ -9,7 +10,9 @@ from app.api.deps import get_current_principal, get_site_service
 from app.core.principal import Principal
 from app.core.roles import AccountKind, Role
 from app.models.energy import Site
-from app.services.site import SiteNotFoundError
+from app.services.site import SiteCurrentReading, SiteNotFoundError
+
+TIMESTAMP = datetime(2026, 9, 16, 12, 0, tzinfo=UTC)
 
 
 def principal(role: Role = Role.LECTEUR) -> Principal:
@@ -33,10 +36,28 @@ def site(site_id: str = "site-1") -> Site:
     )
 
 
+def lecture_actuelle(site_id: str = "site-1") -> SiteCurrentReading:
+    return SiteCurrentReading(
+        timestamp=TIMESTAMP,
+        site_id=site_id,
+        site_type="industriel",
+        consumption_kw=87.34,
+        consumption_kwh=87.34,
+        voltage_v=401.2,
+        current_a=132.5,
+        power_factor=0.923,
+        temperature_celsius=22.1,
+        humidity_percent=58.4,
+        null_reasons=[],
+        data_quality="good",
+    )
+
+
 class FauxService:
     def __init__(self, erreur: Exception | None = None) -> None:
         self._erreur = erreur
         self.site = site()
+        self.actuel = lecture_actuelle()
 
     async def list_all(self) -> list[Site]:
         return [self.site]
@@ -46,6 +67,11 @@ class FauxService:
             raise self._erreur
         return self.site
 
+    async def current(self, site_id: str) -> SiteCurrentReading:
+        if self._erreur is not None:
+            raise self._erreur
+        return self.actuel
+
 
 @pytest.fixture
 def lecteur_connecte(app: FastAPI) -> Iterator[None]:
@@ -109,6 +135,30 @@ async def test_get_site_returns_404_for_an_unknown_site(
     assert response.status_code == 404
 
 
+async def test_get_current_returns_the_latest_reading(
+    servi: Callable[..., FauxService], client: AsyncClient
+) -> None:
+    servi()
+
+    response = await client.get("/api/v1/sites/site-1/current")
+
+    assert response.status_code == 200
+    corps = response.json()
+    assert corps["site_id"] == "site-1"
+    assert corps["data_quality"] == "good"
+    assert corps["consumption_kw"] == 87.34
+
+
+async def test_get_current_returns_404_for_an_unknown_site(
+    servi: Callable[..., FauxService], client: AsyncClient
+) -> None:
+    servi(SiteNotFoundError("site-inconnu"))
+
+    response = await client.get("/api/v1/sites/site-inconnu/current")
+
+    assert response.status_code == 404
+
+
 async def test_list_sites_reaches_the_repository_through_the_session(
     lecteur_connecte: None, fake_session: Callable[..., None], client: AsyncClient
 ) -> None:

apps/backend/tests/services/test_site.py

@@ -1,8 +1,13 @@
+from dataclasses import dataclass, field
+from datetime import UTC, datetime
+
 import pytest
 
 from app.models.energy import Site
 from app.services.site import SiteNotFoundError, SiteService
 
+TIMESTAMP = datetime(2026, 9, 16, 12, 0, tzinfo=UTC)
+
 
 def site(site_id: str = "site-1") -> Site:
     return Site(
@@ -15,6 +20,21 @@ def site(site_id: str = "site-1") -> Site:
     )
 
 
+@dataclass
+class FauxLecture:
+    site_id: str
+    timestamp: datetime = TIMESTAMP
+    consumption_kw: float | None = 87.34
+    consumption_kwh: float | None = 87.34
+    voltage_v: float | None = 401.2
+    current_a: float | None = 132.5
+    power_factor: float | None = 0.923
+    temperature_celsius: float | None = 22.1
+    humidity_percent: float | None = 58.4
+    null_reasons: list[str] | None = field(default_factory=list)
+    data_quality: str | None = "good"
+
+
 class FakeRepository:
     def __init__(self, sites: list[Site]) -> None:
         self._sites = sites
@@ -26,24 +46,79 @@ class FakeRepository:
         return next((s for s in self._sites if s.site_id == site_id), None)
 
 
-async def test_list_all_returns_the_repository_sites() -> None:
+class FauxDepotLectures:
-    service = SiteService(sites=FakeRepository([site("a"), site("b")]))
+    def __init__(self, lectures: dict[str, FauxLecture]) -> None:
+        self._lectures = lectures
 
-    sites = await service.list_all()
+    async def latest_for_site(self, site_id: str) -> FauxLecture | None:
+        return self._lectures.get(site_id)
+
+
+def service(
+    sites: list[Site], lectures: dict[str, FauxLecture] | None = None
+) -> SiteService:
+    return SiteService(
+        sites=FakeRepository(sites),  # type: ignore[arg-type]
+        readings=FauxDepotLectures(lectures or {}),  # type: ignore[arg-type]
+    )
+
+
+async def test_list_all_returns_the_repository_sites() -> None:
+    svc = service([site("a"), site("b")])
+
+    sites = await svc.list_all()
 
     assert [s.site_id for s in sites] == ["a", "b"]
 
 
 async def test_get_by_id_returns_the_matching_site() -> None:
-    service = SiteService(sites=FakeRepository([site("a")]))
+    svc = service([site("a")])
 
-    trouve = await service.get_by_id("a")
+    trouve = await svc.get_by_id("a")
 
     assert trouve.site_id == "a"
 
 
 async def test_get_by_id_raises_when_the_site_is_unknown() -> None:
-    service = SiteService(sites=FakeRepository([]))
+    svc = service([])
 
     with pytest.raises(SiteNotFoundError):
-        await service.get_by_id("inconnu")
+        await svc.get_by_id("inconnu")
+
+
+async def test_current_raises_when_the_site_is_unknown() -> None:
+    svc = service([])
+
+    with pytest.raises(SiteNotFoundError):
+        await svc.current("inconnu")
+
+
+async def test_current_returns_every_field_as_null_when_the_site_has_no_reading() -> None:
+    svc = service([site("a")])
+
+    actuel = await svc.current("a")
+
+    assert actuel.timestamp is None
+    assert actuel.consumption_kw is None
+    assert actuel.data_quality == "critical"
+    assert actuel.null_reasons == []
+
+
+async def test_current_copies_every_field_from_the_latest_reading() -> None:
+    svc = service([site("a")], {"a": FauxLecture(site_id="a")})
+
+    actuel = await svc.current("a")
+
+    assert actuel.timestamp == TIMESTAMP
+    assert actuel.site_type == "industriel"
+    assert actuel.consumption_kw == 87.34
+    assert actuel.voltage_v == 401.2
+    assert actuel.data_quality == "good"
+
+
+async def test_current_treats_an_unknown_data_quality_as_critical() -> None:
+    svc = service([site("a")], {"a": FauxLecture(site_id="a", data_quality=None)})
+
+    actuel = await svc.current("a")
+
+    assert actuel.data_quality == "critical"

docs/architecture/20-backend.md

@@ -142,6 +142,7 @@ Deux fichiers d'environnement, deux usages : `.env` à la racine alimente `docke
 | POST | `/api/v1/users/{id}/password-reset` | Réinitialise et ferme les sessions. `admin` | 401, 403, 404, 422, 500 |
 | GET | `/api/v1/sites` | Liste les sites. `lecteur` | 401, 403, 500 |
 | GET | `/api/v1/sites/{site_id}` | Décrit un site. `lecteur` | 401, 403, 404, 422, 500 |
+| GET | `/api/v1/sites/{site_id}/current` | Dernière mesure d'un site. `lecteur` | 401, 403, 404, 422, 500 |
 | GET | `/api/v1/alerts` | Liste les alertes, filtrable par `site_id` et `severity`. `lecteur` | 401, 403, 422, 500 |
 | GET | `/api/v1/recommendations` | Liste les recommandations. `lecteur` | 401, 403, 500 |
 | GET | `/api/v1/recommendations/{recommendation_id}` | Décrit une recommandation. `lecteur` | 401, 403, 404, 422, 500 |
@@ -169,7 +170,11 @@ gabarit à la lettre, `recommendation_id` étant un entier plutôt qu'un texte.
 porte pas `site_id` : elle remonte à un site par sa seule `alert_id`, `alert` n'étant pas encore
 exposée. `GET /stats/summary` agrège deux repositories (`SiteRepository`, `ReadingRepository`)
 dans un service dédié plutôt que d'exposer une table : elle n'entre donc pas dans ce gabarit
-route-par-table. Le contrat détaillé pour le frontend est dans
+route-par-table. `GET /sites/{site_id}/current` reste sur le gabarit `sites`, mais
+`SiteService` gagne la même seconde dépendance (`ReadingRepository`) pour restituer la
+dernière `Reading` du site : un site connu sans lecture rend `200` avec tous les champs de
+mesure à `null` et `data_quality="critical"`, seul un `site_id` absent de la base rend `404`.
+Le contrat détaillé pour le frontend est dans
 [31-contrat-authentification.md](31-contrat-authentification.md).
 
 ### `/health/ready`