"""Shared paths and helpers for the `silurian` study."""
import os, ssl, time, json, urllib.request, urllib.parse

STUDY = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
CODE = os.path.join(STUDY, "code")
DATA = os.path.join(STUDY, "data")
FIGS = os.path.join(STUDY, "figures")
RAW = os.environ.get("SILURIAN_RAW", "fermi_raw/silurian")
for d in (DATA, FIGS, RAW):
    os.makedirs(d, exist_ok=True)

SEED = 20261012
UA = "fermi-silurian-study/1.0 (research; python-urllib)"

# Physical / geographic constants used throughout
A_EARTH = 510.1e6      # km2
A_LAND = 148.9e6       # km2 present land area (incl. Antarctica, Greenland)
A_OCEAN = A_EARTH - A_LAND


def fetch(url, dest, timeout=600, retries=4, min_bytes=1):
    """Download url to dest unless it is already cached. Returns dest."""
    if os.path.exists(dest) and os.path.getsize(dest) >= min_bytes:
        return dest
    os.makedirs(os.path.dirname(dest), exist_ok=True)
    last = None
    for k in range(retries):
        try:
            req = urllib.request.Request(url, headers={"User-Agent": UA})
            with urllib.request.urlopen(req, timeout=timeout) as r, open(dest + ".part", "wb") as f:
                while True:
                    b = r.read(1 << 16)
                    if not b:
                        break
                    f.write(b)
            if os.path.getsize(dest + ".part") < min_bytes:
                raise IOError("short download")
            os.replace(dest + ".part", dest)
            return dest
        except Exception as e:  # noqa
            last = e
            time.sleep(3 + 5 * k)
    raise IOError(f"download failed: {url}: {last}")


def save_json(obj, name):
    p = os.path.join(DATA, name)
    with open(p, "w") as f:
        json.dump(obj, f, indent=1, sort_keys=True, default=float)
    return p


def load_json(name):
    with open(os.path.join(DATA, name)) as f:
        return json.load(f)