rfcp/backend/app/services/water_service.py

"""
OSM water bodies service for RF reflection calculations.

Water surfaces produce strong specular reflections that can boost
or create multipath interference for RF signals.
"""

import os
import httpx
import json
from typing import List, Tuple, Optional
from pydantic import BaseModel
from pathlib import Path
from datetime import datetime, timedelta


class WaterBody(BaseModel):
    """Water body from OSM"""
    id: int
    geometry: List[Tuple[float, float]]  # [(lon, lat), ...]
    water_type: str  # river, lake, pond, reservoir
    name: Optional[str] = None


class WaterCache:
    """Local cache for water body data with expiry"""

    CACHE_EXPIRY_DAYS = 30

    def __init__(self):
        self.data_path = Path(os.environ.get('RFCP_DATA_PATH', './data'))
        self.cache_path = self.data_path / 'osm' / 'water'
        self.cache_path.mkdir(parents=True, exist_ok=True)

    def _get_cache_key(self, min_lat: float, min_lon: float, max_lat: float, max_lon: float) -> str:
        return f"{min_lat:.2f}_{min_lon:.2f}_{max_lat:.2f}_{max_lon:.2f}"

    def _get_cache_file(self, cache_key: str) -> Path:
        return self.cache_path / f"{cache_key}.json"

    def get(self, min_lat: float, min_lon: float, max_lat: float, max_lon: float) -> Optional[list]:
        cache_key = self._get_cache_key(min_lat, min_lon, max_lat, max_lon)
        cache_file = self._get_cache_file(cache_key)

        if not cache_file.exists():
            return None

        try:
            data = json.loads(cache_file.read_text())
            cached_at = datetime.fromisoformat(data.get('_cached_at', '2000-01-01'))
            if datetime.now() - cached_at > timedelta(days=self.CACHE_EXPIRY_DAYS):
                return None
            return data.get('data')
        except Exception as e:
            print(f"[WaterCache] Failed to read cache: {e}")
            return None

    def set(self, min_lat: float, min_lon: float, max_lat: float, max_lon: float, data):
        cache_key = self._get_cache_key(min_lat, min_lon, max_lat, max_lon)
        cache_file = self._get_cache_file(cache_key)

        try:
            cache_data = {
                '_cached_at': datetime.now().isoformat(),
                '_bbox': [min_lat, min_lon, max_lat, max_lon],
                'data': data
            }
            cache_file.write_text(json.dumps(cache_data))
        except Exception as e:
            print(f"[WaterCache] Failed to write cache: {e}")

    def clear(self):
        for f in self.cache_path.glob("*.json"):
            f.unlink()

    def get_size_mb(self) -> float:
        total = sum(f.stat().st_size for f in self.cache_path.glob("*.json"))
        return total / (1024 * 1024)


class WaterService:
    """OSM water bodies for reflection calculations"""

    OVERPASS_URL = "https://overpass-api.de/api/interpreter"

    # Reflection coefficients by water type
    REFLECTION_COEFF = {
        "lake": 0.8,
        "reservoir": 0.8,
        "river": 0.7,
        "pond": 0.75,
        "water": 0.7,
    }

    def __init__(self):
        self.cache = WaterCache()
        self._memory_cache: dict[str, List[WaterBody]] = {}

    async def fetch_water_bodies(
        self,
        min_lat: float, min_lon: float,
        max_lat: float, max_lon: float
    ) -> List[WaterBody]:
        """Fetch water bodies in bounding box, using cache if available"""

        cache_key = f"{min_lat:.2f}_{min_lon:.2f}_{max_lat:.2f}_{max_lon:.2f}"

        # Memory cache
        if cache_key in self._memory_cache:
            return self._memory_cache[cache_key]

        # Disk cache with expiry
        cached = self.cache.get(min_lat, min_lon, max_lat, max_lon)
        if cached is not None:
            print(f"[Water] Cache hit for bbox")
            bodies = [WaterBody(**w) for w in cached]
            self._memory_cache[cache_key] = bodies
            return bodies

        # Fetch from Overpass
        print(f"[Water] Fetching from Overpass API...")

        query = f"""
        [out:json][timeout:30];
        (
          way["natural"="water"]({min_lat},{min_lon},{max_lat},{max_lon});
          relation["natural"="water"]({min_lat},{min_lon},{max_lat},{max_lon});
          way["waterway"]({min_lat},{min_lon},{max_lat},{max_lon});
        );
        out body;
        >;
        out skel qt;
        """

        try:
            async with httpx.AsyncClient(timeout=60.0) as client:
                response = await client.post(self.OVERPASS_URL, data={"data": query})
                response.raise_for_status()
                data = response.json()
        except Exception as e:
            print(f"[Water] Fetch error: {e}")
            return []

        bodies = self._parse_response(data)

        # Save to disk cache
        if bodies:
            self.cache.set(min_lat, min_lon, max_lat, max_lon,
                           [w.model_dump() for w in bodies])

        self._memory_cache[cache_key] = bodies
        return bodies

    def _parse_response(self, data: dict) -> List[WaterBody]:
        """Parse Overpass response"""
        nodes = {}
        for element in data.get("elements", []):
            if element["type"] == "node":
                nodes[element["id"]] = (element["lon"], element["lat"])

        bodies = []
        for element in data.get("elements", []):
            if element["type"] != "way":
                continue

            tags = element.get("tags", {})
            water_type = tags.get("water", tags.get("waterway", tags.get("natural", "water")))

            geometry = []
            for node_id in element.get("nodes", []):
                if node_id in nodes:
                    geometry.append(nodes[node_id])

            if len(geometry) < 3:
                continue

            bodies.append(WaterBody(
                id=element["id"],
                geometry=geometry,
                water_type=water_type,
                name=tags.get("name")
            ))

        return bodies

    def get_reflection_coefficient(self, water_type: str) -> float:
        """Get reflection coefficient for water type"""
        return self.REFLECTION_COEFF.get(water_type, 0.7)

    def point_over_water(
        self, lat: float, lon: float, water_bodies: List[WaterBody]
    ) -> Optional[WaterBody]:
        """Check if point is over water"""
        for body in water_bodies:
            if self._point_in_polygon(lat, lon, body.geometry):
                return body
        return None

    @staticmethod
    def _point_in_polygon(
        lat: float, lon: float, polygon: List[Tuple[float, float]]
    ) -> bool:
        """Ray casting algorithm -- polygon coords are (lon, lat)"""
        n = len(polygon)
        inside = False

        j = n - 1
        for i in range(n):
            xi, yi = polygon[i]  # lon, lat
            xj, yj = polygon[j]

            if ((yi > lat) != (yj > lat)) and (lon < (xj - xi) * (lat - yi) / (yj - yi) + xi):
                inside = not inside
            j = i

        return inside


water_service = WaterService()