style:use restful api

app/database.py

@@ -123,3 +123,81 @@ async def get_history_by_station(
             *params,
         )
         return [dict(r) for r in rows]
+
+
+async def list_all_stations() -> list[dict]:
+    """Return all distinct station names with observation counts and latest timestamps.
+
+    Derives stations from weather_data since there is no separate stations table.
+    """
+    pool = await get_pool()
+    async with pool.acquire() as conn:
+        rows = await conn.fetch("""
+            SELECT
+                station_name AS name,
+                COUNT(*)::int AS observation_count,
+                MAX(received_at) AS latest_observation_at
+            FROM weather_data
+            GROUP BY station_name
+            ORDER BY station_name
+        """)
+        return [dict(r) for r in rows]
+
+
+async def get_station_exists(station_name: str) -> bool:
+    """Check whether a station has any observations."""
+    pool = await get_pool()
+    async with pool.acquire() as conn:
+        row = await conn.fetchrow(
+            "SELECT 1 FROM weather_data WHERE station_name = $1 LIMIT 1",
+            station_name,
+        )
+        return row is not None
+
+
+async def get_history_by_station_paginated(
+    station_name: str,
+    start_time: datetime | None = None,
+    end_time: datetime | None = None,
+    limit: int | None = None,
+    offset: int = 0,
+) -> list[dict]:
+    """Return observations for a station within the given time range, with pagination.
+
+    Returns an empty list if no records match.
+    """
+    pool = await get_pool()
+    async with pool.acquire() as conn:
+        conditions = ["station_name = $1"]
+        params: list = [station_name]
+        idx = 2
+
+        if start_time is not None:
+            conditions.append(f"received_at >= ${idx}")
+            params.append(start_time)
+            idx += 1
+
+        if end_time is not None:
+            conditions.append(f"received_at <= ${idx}")
+            params.append(end_time)
+            idx += 1
+
+        where_clause = " AND ".join(conditions)
+
+        query = f"""
+            SELECT id, station_name, temperature, pressure, relative_humidity, received_at
+            FROM weather_data
+            WHERE {where_clause}
+            ORDER BY received_at DESC
+        """
+
+        if limit is not None:
+            query += f" LIMIT ${idx}"
+            params.append(limit)
+            idx += 1
+
+        query += f" OFFSET ${idx}"
+        params.append(offset)
+
+        rows = await conn.fetch(query, *params)
+        return [dict(r) for r in rows]