#!/usr/bin/env python3
"""Draw the pixel "9" of static/img/favicon.svg as PNGs and an ICO, with the standard library.

    python3 site/tools/make_favicons.py

Writes static/favicon.ico (32 and 48 px, PNG inside) and static/apple-touch-icon.png (180 px).
The 9 is a 7x7 grid, scaled by a whole number and centred on the background colour."""
import struct
import zlib
from pathlib import Path

BG = (0x00, 0x00, 0x55)
FG = (0x00, 0xDB, 0xFF)
# x, y, w, h: the same rectangles as favicon.svg
RECTS = [(1, 0, 3, 1), (0, 1, 1, 2), (4, 1, 1, 5), (1, 3, 3, 1), (0, 6, 3, 1)]
GRID = 7

STATIC = Path(__file__).resolve().parent.parent / "static"


def cells():
    on = set()
    for x, y, w, h in RECTS:
        on.update((x + i, y + j) for i in range(w) for j in range(h))
    return on


def png(size):
    scale = size // GRID
    pad = (size - scale * GRID) // 2
    on = cells()
    rows = bytearray()
    for py in range(size):
        rows.append(0)
        for px in range(size):
            cx, cy = (px - pad) // scale, (py - pad) // scale
            inside = 0 <= px - pad < scale * GRID and 0 <= py - pad < scale * GRID
            rows.extend(FG if inside and (cx, cy) in on else BG)

    def chunk(kind, data):
        body = kind + data
        return struct.pack(">I", len(data)) + body + struct.pack(">I", zlib.crc32(body))

    return (b"\x89PNG\r\n\x1a\n" + chunk(b"IHDR", struct.pack(">IIBBBBB", size, size, 8, 2, 0, 0, 0)) +
            chunk(b"IDAT", zlib.compress(bytes(rows), 9)) + chunk(b"IEND", b""))


def ico(sizes):
    images = [png(s) for s in sizes]
    out = struct.pack("<HHH", 0, 1, len(images))
    offset = 6 + 16 * len(images)
    for s, data in zip(sizes, images):
        out += struct.pack("<BBBBHHII", s, s, 0, 0, 1, 32, len(data), offset)
        offset += len(data)
    return out + b"".join(images)


if __name__ == "__main__":
    (STATIC / "favicon.ico").write_bytes(ico([32, 48]))
    (STATIC / "apple-touch-icon.png").write_bytes(png(180))
    print("wrote favicon.ico, apple-touch-icon.png")