"""Read and write .thr (theta-rho) pattern files.

Each line holds "<theta> <rho>":
  theta: angle in radians, continuous (it keeps counting past 2*pi; it is not wrapped)
  rho:   distance from the centre, 0 (centre) to 1 (edge)
Lines starting with '#' or '//' are comments. This is the format used by Sandify,
Sisyphus and Dune Weaver.
"""
import math

Pattern = list  # list of (theta_rad, rho) tuples


def loads(text):
    pts = []
    for raw in text.splitlines():
        line = raw.strip()
        if not line or line.startswith('#') or line.startswith('//'):
            continue
        parts = line.replace(',', ' ').split()
        if len(parts) < 2:
            continue
        try:
            th, rho = float(parts[0]), float(parts[1])
        except ValueError:
            continue
        if math.isfinite(th) and math.isfinite(rho):
            pts.append((th, min(1.0, max(0.0, rho))))
    return pts


def load(path):
    with open(path, encoding='utf-8', errors='replace') as f:
        pts = loads(f.read())
    if len(pts) < 2:
        raise ValueError(f'{path}: no theta-rho points found')
    return pts


def dumps(pts, header=None):
    out = []
    if header:
        out += [f'# {h}' for h in header.splitlines()]
    out += [f'{th:.5f} {rho:.5f}' for th, rho in pts]
    return '\n'.join(out) + '\n'


def save(path, pts, header=None):
    with open(path, 'w') as f:
        f.write(dumps(pts, header))