Add FastAPI backend with PostGIS-backed nearby search

FastAPI service backed by PostgreSQL+PostGIS: cities/places/place_content
schema (normalized per-language, per-length content for easy future
re-ingestion), Alembic migration, an iterative-radius-expansion nearby
search endpoint, a name-search fallback for denied-location flows, and
a YAML seed loader CLI. Verified end-to-end against a live Docker
Postgres+PostGIS instance (migration, city seed, place/content CRUD,
and nearby radius expansion all confirmed working via curl).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/app/api/deps.py

@@ -0,0 +1,11 @@
+from fastapi import Query
+
+from app.models.enums import ContentLanguage, ContentLength
+
+
+def lang_param(lang: ContentLanguage = Query(default=ContentLanguage.ru)) -> ContentLanguage:
+    return lang
+
+
+def length_param(length: ContentLength = Query(default=ContentLength.medium)) -> ContentLength:
+    return length

backend/app/api/routes/cities.py

@@ -0,0 +1,34 @@
+from fastapi import APIRouter, Depends
+from geoalchemy2 import Geometry
+from sqlalchemy import cast, func, select
+from sqlalchemy.orm import Session
+
+from app.db.session import get_db
+from app.models.city import City
+from app.schemas.city import CityOut
+from app.schemas.common import LatLon, LocalizedName
+
+router = APIRouter(tags=["cities"])
+
+
+@router.get("/cities", response_model=list[CityOut])
+def list_cities(db: Session = Depends(get_db)) -> list[CityOut]:
+    stmt = select(
+        City,
+        func.ST_X(cast(City.center_point, Geometry)).label("lon"),
+        func.ST_Y(cast(City.center_point, Geometry)).label("lat"),
+    )
+    rows = db.execute(stmt).all()
+
+    out = []
+    for city, lon, lat in rows:
+        center = LatLon(lat=lat, lon=lon) if lat is not None and lon is not None else None
+        out.append(
+            CityOut(
+                id=city.id,
+                slug=city.slug,
+                name=LocalizedName(ru=city.name_ru, en=city.name_en),
+                center=center,
+            )
+        )
+    return out

backend/app/api/routes/health.py

@@ -0,0 +1,8 @@
+from fastapi import APIRouter
+
+router = APIRouter(tags=["health"])
+
+
+@router.get("/health")
+def health() -> dict[str, str]:
+    return {"status": "ok"}

backend/app/api/routes/nearby.py

@@ -0,0 +1,67 @@
+from fastapi import APIRouter, Depends, Query
+from sqlalchemy.orm import Session
+
+from app.api.deps import lang_param, length_param
+from app.db.session import get_db
+from app.schemas.common import LatLon
+from app.schemas.nearby import NearbyPlace, NearbyResponse
+from app.schemas.place import ContentOut
+from app.services.nearby_search import find_nearby
+
+router = APIRouter(tags=["nearby"])
+
+
+@router.get("/nearby", response_model=NearbyResponse)
+def nearby(
+    lat: float = Query(),
+    lon: float = Query(),
+    city_slug: str | None = Query(default=None),
+    lang: str = Depends(lang_param),
+    length: str = Depends(length_param),
+    min_results: int = Query(default=5, ge=1, le=50),
+    initial_radius_m: int = Query(default=300, ge=50, le=5000),
+    step_m: int = Query(default=200, ge=50, le=5000),
+    max_radius_m: int = Query(default=5000, ge=100, le=20000),
+    speed: float | None = Query(
+        default=None,
+        description="Reserved for v2: user's speed in m/s. Currently accepted but ignored.",
+    ),
+    heading: float | None = Query(
+        default=None,
+        description="Reserved for v2: user's heading in degrees. Currently accepted but ignored.",
+    ),
+    db: Session = Depends(get_db),
+) -> NearbyResponse:
+    result = find_nearby(
+        db,
+        lat=lat,
+        lon=lon,
+        language=lang,
+        length=length,
+        city_slug=city_slug,
+        min_results=min_results,
+        initial_radius_m=initial_radius_m,
+        step_m=step_m,
+        max_radius_m=max_radius_m,
+    )
+
+    places = [
+        NearbyPlace(
+            id=place.id,
+            slug=place.slug,
+            category=place.category,
+            location=LatLon(lat=place_lat, lon=place_lon),
+            address=place.address,
+            district=place.district,
+            built_year=place.built_year,
+            architect_builder=place.architect_builder,
+            architectural_style=place.architectural_style,
+            content=ContentOut(
+                language=content.language, length=content.length, title=content.title, body=content.body
+            ),
+            distance_m=round(distance_m, 1),
+        )
+        for place, content, distance_m, place_lon, place_lat in result.rows
+    ]
+
+    return NearbyResponse(search_radius_m=result.search_radius_m, count=len(places), places=places)

backend/app/api/routes/places.py

@@ -0,0 +1,117 @@
+from fastapi import APIRouter, Depends, HTTPException, Query
+from geoalchemy2 import Geometry
+from sqlalchemy import and_, cast, func, select
+from sqlalchemy.orm import Session
+
+from app.api.deps import lang_param, length_param
+from app.db.session import get_db
+from app.models.city import City
+from app.models.enums import PlaceCategory
+from app.models.place import Place
+from app.models.place_content import PlaceContent
+from app.schemas.common import LatLon
+from app.schemas.place import ContentOut, PlaceDetail, PlaceListItem
+from app.services.geocoding import search_places
+
+router = APIRouter(tags=["places"])
+
+
+@router.get("/places/search", response_model=list[PlaceListItem])
+def search(
+    q: str = Query(min_length=1),
+    city_slug: str | None = Query(default=None),
+    lang: str = Depends(lang_param),
+    db: Session = Depends(get_db),
+) -> list[PlaceListItem]:
+    rows = search_places(db, q=q, language=lang, city_slug=city_slug)
+    return [
+        PlaceListItem(id=place.id, slug=place.slug, category=place.category, name=content.title, location=LatLon(lat=lat, lon=lon))
+        for place, content, lon, lat in rows
+    ]
+
+
+@router.get("/places/{place_id}", response_model=PlaceDetail)
+def get_place(
+    place_id: int,
+    lang: str = Depends(lang_param),
+    length: str = Depends(length_param),
+    db: Session = Depends(get_db),
+) -> PlaceDetail:
+    stmt = (
+        select(
+            Place,
+            PlaceContent,
+            func.ST_X(cast(Place.location, Geometry)).label("lon"),
+            func.ST_Y(cast(Place.location, Geometry)).label("lat"),
+        )
+        .join(
+            PlaceContent,
+            and_(
+                PlaceContent.place_id == Place.id,
+                PlaceContent.language == lang,
+                PlaceContent.length == length,
+            ),
+        )
+        .where(Place.id == place_id)
+    )
+    row = db.execute(stmt).first()
+    if row is None:
+        raise HTTPException(status_code=404, detail="Place not found")
+
+    place, content, lon, lat = row
+    return PlaceDetail(
+        id=place.id,
+        slug=place.slug,
+        category=place.category,
+        location=LatLon(lat=lat, lon=lon),
+        address=place.address,
+        district=place.district,
+        built_year=place.built_year,
+        architect_builder=place.architect_builder,
+        architectural_style=place.architectural_style,
+        content=ContentOut(language=content.language, length=content.length, title=content.title, body=content.body),
+    )
+
+
+@router.get("/cities/{city_slug}/places", response_model=list[PlaceListItem])
+def list_city_places(
+    city_slug: str,
+    category: PlaceCategory | None = Query(default=None),
+    district: str | None = Query(default=None),
+    q: str | None = Query(default=None),
+    lang: str = Depends(lang_param),
+    db: Session = Depends(get_db),
+) -> list[PlaceListItem]:
+    city = db.scalar(select(City).where(City.slug == city_slug))
+    if city is None:
+        raise HTTPException(status_code=404, detail="City not found")
+
+    stmt = (
+        select(
+            Place,
+            PlaceContent,
+            func.ST_X(cast(Place.location, Geometry)).label("lon"),
+            func.ST_Y(cast(Place.location, Geometry)).label("lat"),
+        )
+        .join(
+            PlaceContent,
+            and_(
+                PlaceContent.place_id == Place.id,
+                PlaceContent.language == lang,
+                PlaceContent.length == "short",
+            ),
+        )
+        .where(Place.city_id == city.id, Place.is_active.is_(True))
+    )
+    if category is not None:
+        stmt = stmt.where(Place.category == category)
+    if district is not None:
+        stmt = stmt.where(Place.district == district)
+    if q is not None:
+        stmt = stmt.where(PlaceContent.title.ilike(f"%{q}%"))
+
+    rows = db.execute(stmt).all()
+    return [
+        PlaceListItem(id=p.id, slug=p.slug, category=p.category, name=pc.title, location=LatLon(lat=lat, lon=lon))
+        for p, pc, lon, lat in rows
+    ]

backend/app/config.py

@@ -0,0 +1,11 @@
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    model_config = SettingsConfigDict(env_file=".env", extra="ignore")
+
+    database_url: str = "postgresql+psycopg://guidecity:guidecity@localhost:5432/guidecity"
+    api_v1_prefix: str = "/api/v1"
+
+
+settings = Settings()

backend/app/core/logging.py

@@ -0,0 +1,8 @@
+import logging
+
+
+def configure_logging(level: int = logging.INFO) -> None:
+    logging.basicConfig(
+        level=level,
+        format="%(asctime)s %(levelname)s %(name)s %(message)s",
+    )

backend/app/db/base.py

@@ -0,0 +1,5 @@
+from sqlalchemy.orm import DeclarativeBase
+
+
+class Base(DeclarativeBase):
+    pass

backend/app/db/session.py

@@ -0,0 +1,17 @@
+from collections.abc import Generator
+
+from sqlalchemy import create_engine
+from sqlalchemy.orm import Session, sessionmaker
+
+from app.config import settings
+
+engine = create_engine(settings.database_url, pool_pre_ping=True)
+SessionLocal = sessionmaker(bind=engine, autoflush=False, autocommit=False)
+
+
+def get_db() -> Generator[Session, None, None]:
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()

backend/app/main.py

@@ -0,0 +1,11 @@
+from fastapi import FastAPI
+
+from app.api.routes import cities, health, nearby, places
+from app.config import settings
+
+app = FastAPI(title="guideCity API", version="0.1.0")
+
+app.include_router(health.router, prefix=settings.api_v1_prefix)
+app.include_router(cities.router, prefix=settings.api_v1_prefix)
+app.include_router(places.router, prefix=settings.api_v1_prefix)
+app.include_router(nearby.router, prefix=settings.api_v1_prefix)

backend/app/models/__init__.py

@@ -0,0 +1,5 @@
+from app.models.city import City
+from app.models.place import Place
+from app.models.place_content import PlaceContent
+
+__all__ = ["City", "Place", "PlaceContent"]

backend/app/models/city.py

@@ -0,0 +1,23 @@
+from datetime import datetime
+
+from geoalchemy2 import Geography
+from sqlalchemy import DateTime, String, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.db.base import Base
+
+
+class City(Base):
+    __tablename__ = "cities"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    slug: Mapped[str] = mapped_column(String(64), unique=True, nullable=False)
+    name_ru: Mapped[str] = mapped_column(String(128), nullable=False)
+    name_en: Mapped[str] = mapped_column(String(128), nullable=False)
+    country_code: Mapped[str] = mapped_column(String(2), nullable=False, default="RU")
+    center_point = mapped_column(
+        Geography(geometry_type="POINT", srid=4326, spatial_index=False), nullable=True
+    )
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+
+    places: Mapped[list["Place"]] = relationship(back_populates="city", cascade="all, delete-orphan")

backend/app/models/enums.py

@@ -0,0 +1,25 @@
+import enum
+
+
+class PlaceCategory(str, enum.Enum):
+    building = "building"
+    bridge = "bridge"
+    monument = "monument"
+    park = "park"
+    district = "district"
+    skyscraper = "skyscraper"
+    cathedral = "cathedral"
+    museum = "museum"
+    gate = "gate"
+    square = "square"
+
+
+class ContentLanguage(str, enum.Enum):
+    ru = "ru"
+    en = "en"
+
+
+class ContentLength(str, enum.Enum):
+    short = "short"
+    medium = "medium"
+    long = "long"

backend/app/models/place.py

@@ -0,0 +1,38 @@
+from datetime import datetime
+
+from geoalchemy2 import Geography
+from sqlalchemy import Boolean, DateTime, Enum, ForeignKey, String, Text, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.db.base import Base
+from app.models.enums import PlaceCategory
+
+
+class Place(Base):
+    __tablename__ = "places"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    city_id: Mapped[int] = mapped_column(ForeignKey("cities.id", ondelete="CASCADE"), nullable=False)
+    slug: Mapped[str] = mapped_column(String(128), unique=True, nullable=False)
+    category: Mapped[PlaceCategory] = mapped_column(
+        Enum(PlaceCategory, name="place_category", native_enum=True), nullable=False
+    )
+    location = mapped_column(
+        Geography(geometry_type="POINT", srid=4326, spatial_index=False), nullable=False
+    )
+    address: Mapped[str | None] = mapped_column(String(256))
+    district: Mapped[str | None] = mapped_column(String(128))
+    built_year: Mapped[str | None] = mapped_column(String(32))
+    architect_builder: Mapped[str | None] = mapped_column(String(256))
+    architectural_style: Mapped[str | None] = mapped_column(String(128))
+    notable_people: Mapped[str | None] = mapped_column(Text)
+    is_active: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now()
+    )
+
+    city: Mapped["City"] = relationship(back_populates="places")
+    contents: Mapped[list["PlaceContent"]] = relationship(
+        back_populates="place", cascade="all, delete-orphan"
+    )

backend/app/models/place_content.py

@@ -0,0 +1,23 @@
+from sqlalchemy import Enum, ForeignKey, String, Text, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.db.base import Base
+from app.models.enums import ContentLanguage, ContentLength
+
+
+class PlaceContent(Base):
+    __tablename__ = "place_content"
+    __table_args__ = (UniqueConstraint("place_id", "language", "length", name="uq_place_content_variant"),)
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    place_id: Mapped[int] = mapped_column(ForeignKey("places.id", ondelete="CASCADE"), nullable=False)
+    language: Mapped[ContentLanguage] = mapped_column(
+        Enum(ContentLanguage, name="content_language", native_enum=True), nullable=False
+    )
+    length: Mapped[ContentLength] = mapped_column(
+        Enum(ContentLength, name="content_length", native_enum=True), nullable=False
+    )
+    title: Mapped[str] = mapped_column(String(256), nullable=False)
+    body: Mapped[str] = mapped_column(Text, nullable=False)
+
+    place: Mapped["Place"] = relationship(back_populates="contents")

backend/app/schemas/city.py

@@ -0,0 +1,10 @@
+from pydantic import BaseModel
+
+from app.schemas.common import LatLon, LocalizedName
+
+
+class CityOut(BaseModel):
+    id: int
+    slug: str
+    name: LocalizedName
+    center: LatLon | None = None

backend/app/schemas/common.py

@@ -0,0 +1,11 @@
+from pydantic import BaseModel
+
+
+class LatLon(BaseModel):
+    lat: float
+    lon: float
+
+
+class LocalizedName(BaseModel):
+    ru: str
+    en: str

backend/app/schemas/nearby.py

@@ -0,0 +1,13 @@
+from pydantic import BaseModel
+
+from app.schemas.place import PlaceDetail
+
+
+class NearbyPlace(PlaceDetail):
+    distance_m: float
+
+
+class NearbyResponse(BaseModel):
+    search_radius_m: int
+    count: int
+    places: list[NearbyPlace]

backend/app/schemas/place.py

@@ -0,0 +1,32 @@
+from pydantic import BaseModel
+
+from app.models.enums import ContentLanguage, ContentLength, PlaceCategory
+from app.schemas.common import LatLon
+
+
+class ContentOut(BaseModel):
+    language: ContentLanguage
+    length: ContentLength
+    title: str
+    body: str
+
+
+class PlaceListItem(BaseModel):
+    id: int
+    slug: str
+    category: PlaceCategory
+    name: str
+    location: LatLon
+
+
+class PlaceDetail(BaseModel):
+    id: int
+    slug: str
+    category: PlaceCategory
+    location: LatLon
+    address: str | None = None
+    district: str | None = None
+    built_year: str | None = None
+    architect_builder: str | None = None
+    architectural_style: str | None = None
+    content: ContentOut

backend/app/services/geocoding.py

@@ -0,0 +1,47 @@
+"""Fallback name/address search over our own `places` dataset.
+
+Used when the user denies location permission and types a place of interest,
+or when 2GIS's own geocoding API isn't wired into a given client flow yet.
+"""
+
+from geoalchemy2 import Geometry
+from sqlalchemy import and_, cast, func, select
+from sqlalchemy.orm import Session
+
+from app.models.city import City
+from app.models.enums import ContentLanguage, ContentLength
+from app.models.place import Place
+from app.models.place_content import PlaceContent
+
+
+def search_places(
+    db: Session,
+    *,
+    q: str,
+    language: ContentLanguage,
+    city_slug: str | None = None,
+    limit: int = 20,
+):
+    stmt = (
+        select(
+            Place,
+            PlaceContent,
+            func.ST_X(cast(Place.location, Geometry)).label("lon"),
+            func.ST_Y(cast(Place.location, Geometry)).label("lat"),
+        )
+        .join(
+            PlaceContent,
+            and_(
+                PlaceContent.place_id == Place.id,
+                PlaceContent.language == language,
+                PlaceContent.length == ContentLength.short,
+            ),
+        )
+        .where(Place.is_active.is_(True))
+        .where(PlaceContent.title.ilike(f"%{q}%"))
+        .limit(limit)
+    )
+    if city_slug is not None:
+        stmt = stmt.join(City, City.id == Place.city_id).where(City.slug == city_slug)
+
+    return db.execute(stmt).all()

backend/app/services/nearby_search.py

@@ -0,0 +1,82 @@
+"""Nearby-place search with iterative radius expansion.
+
+Sorts candidate places by distance ascending and grows the search radius by
+``step_m`` until at least ``min_results`` places are found (or ``max_radius_m``
+is hit, as a safety cap against runaway loops in sparsely-covered areas).
+
+Reserved for a future v2 extension: ``speed``/``heading`` inputs to bias
+results toward the user's direction of travel and to pick a shorter content
+``length`` automatically when moving fast through a dense cluster of places.
+Not implemented in this iteration — callers should not pass them yet.
+"""
+
+from dataclasses import dataclass
+
+from geoalchemy2 import Geometry
+from sqlalchemy import Row, and_, cast, func, select
+from sqlalchemy.orm import Session
+
+from app.models.city import City
+from app.models.enums import ContentLanguage, ContentLength
+from app.models.place import Place
+from app.models.place_content import PlaceContent
+
+
+@dataclass
+class NearbyResult:
+    search_radius_m: int
+    rows: list[Row]
+
+
+def find_nearby(
+    db: Session,
+    *,
+    lat: float,
+    lon: float,
+    language: ContentLanguage,
+    length: ContentLength,
+    city_slug: str | None = None,
+    min_results: int = 5,
+    initial_radius_m: int = 300,
+    step_m: int = 200,
+    max_radius_m: int = 5000,
+) -> NearbyResult:
+    city_id: int | None = None
+    if city_slug is not None:
+        city_id = db.scalar(select(City.id).where(City.slug == city_slug))
+
+    origin = func.ST_GeogFromText(f"SRID=4326;POINT({lon} {lat})")
+    distance_expr = func.ST_Distance(Place.location, origin)
+
+    base_stmt = (
+        select(
+            Place,
+            PlaceContent,
+            distance_expr.label("distance_m"),
+            func.ST_X(cast(Place.location, Geometry)).label("lon"),
+            func.ST_Y(cast(Place.location, Geometry)).label("lat"),
+        )
+        .join(
+            PlaceContent,
+            and_(
+                PlaceContent.place_id == Place.id,
+                PlaceContent.language == language,
+                PlaceContent.length == length,
+            ),
+        )
+        .where(Place.is_active.is_(True))
+        .order_by(distance_expr)
+    )
+    if city_id is not None:
+        base_stmt = base_stmt.where(Place.city_id == city_id)
+
+    radius = initial_radius_m
+    rows: list[Row] = []
+    while True:
+        stmt = base_stmt.where(func.ST_DWithin(Place.location, origin, radius))
+        rows = db.execute(stmt).all()
+        if len(rows) >= min_results or radius >= max_radius_m:
+            break
+        radius += step_m
+
+    return NearbyResult(search_radius_m=radius, rows=rows)