#!/usr/bin/env python3
"""Generate OpenMapClassic's edge-feather masks.

A feather is a mask over a map sheet's whole rect: opaque in the middle, falling to nothing at
the border, so the sheet blends into what is around it instead of ending in a straight line.
Upstream's own NOTICE calls these "generated from noise" rather than cut from art -- they are
parametric, so this reproduces them rather than approximating an artist.

1.12 needs them where Classic Era does not. Era's `C_Map` zone textures carry a transparent
surround; the 1.12 sheets in this client's archives are **fully opaque** (measured: alpha 255
everywhere) and paint their own sea, lettering and a torn parchment border right to the edge. So
a zone drawn without a mask covers its neighbours with a rectangle -- which is what
`OpenMapClassic/Map/Stitch.lua`'s own comment predicts, and what the Gilneas sheet does over
Silverpine.

Writes 256x256 uncompressed 32-bit TGA, matching the shipped `MapZoneDilate` masks: RGB black,
alpha the coverage.
"""
import sys
from pathlib import Path

import numpy as np
from PIL import Image

SIZE = 256
# Margin as a fraction of the sheet, per variant. The parchment border on a 1002-px sheet runs
# ~35 px (3.5%); a feather has to clear that and then blend, so the plain one takes 9%.
VARIANTS = {"MapFeather": 0.09, "MapFeatherThin": 0.045, "MapFeatherWide": 0.16}


def ramp(n: int, margin: float) -> np.ndarray:
    """1 in the middle, 0 at both ends, smoothstep across `margin` of the span."""
    x = (np.arange(n) + 0.5) / n
    d = np.minimum(x, 1.0 - x) / margin  # distance from the nearer edge, in margins
    t = np.clip(d, 0.0, 1.0)
    return t * t * (3.0 - 2.0 * t)


def feather(margin: float) -> Image.Image:
    a = np.outer(ramp(SIZE, margin), ramp(SIZE, margin))
    rgba = np.zeros((SIZE, SIZE, 4), dtype=np.uint8)
    rgba[:, :, 3] = np.round(a * 255.0).astype(np.uint8)
    return Image.fromarray(rgba, "RGBA")


def main() -> int:
    if len(sys.argv) != 2:
        print("usage: make-map-feather.py <OpenMapClassic/Media/Textures>", file=sys.stderr)
        return 2
    out = Path(sys.argv[1])
    if not out.is_dir():
        print(f"not a directory: {out}", file=sys.stderr)
        return 2
    for name, margin in VARIANTS.items():
        path = out / f"{name}.tga"
        feather(margin).save(path)
        print(f"wrote {path} ({margin:.0%} margin)")
    return 0


if __name__ == "__main__":
    raise SystemExit(main())