#!/usr/bin/env python3
"""
torrent_tools.py — shared helpers for the TORRENT generic tools.

All functions talk to public agency services only (NWIS, NLDI, Iowa State MT
archive); nothing here depends on the authors' build machine.
"""
import gzip
import io
import json
import math
from datetime import datetime, timedelta, timezone
from pathlib import Path

import pandas as pd
import requests

NWIS_IV   = "https://waterservices.usgs.gov/nwis/iv/"
NWIS_SITE = "https://waterservices.usgs.gov/nwis/site/"
NLDI_BASIN = "https://api.water.usgs.gov/nldi/linked-data/nwissite/USGS-{site}/basin"
MTARCHIVE = "https://mtarchive.geol.iastate.edu"

UA = {"User-Agent": "TORRENT-tools/1.0 (flash-flood benchmark)"}


def haversine_km(lat1, lon1, lat2, lon2):
    r = 6371.0
    p1, p2 = math.radians(lat1), math.radians(lat2)
    dp = math.radians(lat2 - lat1)
    dl = math.radians(lon2 - lon1)
    a = math.sin(dp / 2) ** 2 + math.cos(p1) * math.cos(p2) * math.sin(dl / 2) ** 2
    return 2 * r * math.asin(math.sqrt(a))


def parse_utc(s):
    t = pd.to_datetime(s, utc=True)
    return t.to_pydatetime()


def sites_in_bbox(lat, lon, radius_km):
    """Active stream sites in a bounding box around (lat, lon)."""
    dlat = radius_km / 111.0
    dlon = radius_km / (111.0 * max(0.2, math.cos(math.radians(lat))))
    bbox = f"{lon-dlon:.4f},{lat-dlat:.4f},{lon+dlon:.4f},{lat+dlat:.4f}"
    r = requests.get(NWIS_SITE, params={
        "format": "rdb", "bBox": bbox, "siteType": "ST",
        "siteStatus": "all", "hasDataTypeCd": "iv"}, headers=UA, timeout=60)
    if r.status_code != 200:
        return []
    rows = []
    header = None
    for line in r.text.splitlines():
        if line.startswith("#"):
            continue
        parts = line.split("\t")
        if header is None:
            header = parts
            continue
        if parts and parts[0].endswith("s"):     # rdb format row ("5s 15s ...")
            continue
        d = dict(zip(header, parts))
        try:
            slat, slon = float(d["dec_lat_va"]), float(d["dec_long_va"])
        except (KeyError, ValueError):
            continue
        dist = haversine_km(lat, lon, slat, slon)
        if dist <= radius_km:
            rows.append(dict(site_no=d["site_no"], station_nm=d.get("station_nm", ""),
                             lat=slat, lon=slon, distance_km=round(dist, 2)))
    return sorted(rows, key=lambda x: x["distance_km"])


def fetch_iv(site, begin, end, parameter="00060"):
    """NWIS instantaneous values -> DataFrame(datetime_utc, value). Empty if none."""
    r = requests.get(NWIS_IV, params={
        "format": "json", "sites": site, "parameterCd": parameter,
        "startDT": begin.strftime("%Y-%m-%dT%H:%MZ"),
        "endDT": end.strftime("%Y-%m-%dT%H:%MZ")}, headers=UA, timeout=120)
    if r.status_code != 200:
        return pd.DataFrame(columns=["datetime_utc", "value"])
    try:
        ts = r.json()["value"]["timeSeries"]
        vals = ts[0]["values"][0]["value"]
    except (KeyError, IndexError, ValueError):
        return pd.DataFrame(columns=["datetime_utc", "value"])
    df = pd.DataFrame(vals)
    if df.empty:
        return pd.DataFrame(columns=["datetime_utc", "value"])
    df["datetime_utc"] = pd.to_datetime(df["dateTime"], utc=True)
    df["value"] = pd.to_numeric(df["value"], errors="coerce")
    df = df[df["value"] > -999990]
    return df[["datetime_utc", "value"]].reset_index(drop=True)


def fetch_basin(site):
    """NLDI contributing watershed as GeoJSON dict (retry twice: transient 5xx/404)."""
    url = NLDI_BASIN.format(site=site)
    last = None
    for _ in range(3):
        r = requests.get(url, headers=UA, timeout=90)
        last = r.status_code
        if r.status_code == 200:
            return r.json()
    raise RuntimeError(f"NLDI basin unavailable for {site} (HTTP {last}); "
                       "retry later — most NLDI failures are transient")


def mrms_precip_urls(begin, end):
    """2-min MRMS PrecipRate GRIB2 URLs on the Iowa State MT archive."""
    t = begin.replace(second=0, microsecond=0)
    t -= timedelta(minutes=t.minute % 2)
    out = []
    while t <= end:
        out.append((t, f"{MTARCHIVE}/{t:%Y/%m/%d}/mrms/ncep/PrecipRate/"
                       f"PrecipRate_00.00_{t:%Y%m%d-%H%M%S}.grib2.gz"))
        t += timedelta(minutes=2)
    return out


def episode_lookup(episode_id, data_dir):
    """Find an episode row (begin/end/coords) in the released L2, else L1, tables."""
    l2 = Path(data_dir) / "L2" / "l2_episodes.csv"
    l1 = Path(data_dir) / "L1" / "l1_ncei_flash_flood_episodes.csv"
    for src in (l2, l1):
        if not src.exists():
            continue
        df = pd.read_csv(src, low_memory=False)
        hit = df[df["ff_episode_id"] == episode_id]
        if len(hit):
            r = hit.iloc[0]
            lat = r.get("centroid_lat", r.get("begin_lat"))
            lon = r.get("centroid_lon", r.get("begin_lon"))
            return dict(begin=str(r["begin_dt"]), end=str(r["end_dt"]),
                        lat=float(lat), lon=float(lon), source=src.name)
    raise SystemExit(f"episode {episode_id} not found under {data_dir}")


def save_json(obj, path):
    Path(path).parent.mkdir(parents=True, exist_ok=True)
    with open(path, "w") as f:
        json.dump(obj, f, indent=2)