"""Fetch the official Dota 2 emblem icon (no wordmark) for the preview header.

Source (discovered, not guessed) from the dota2.com.cn site HTML:
  <link rel="Shortcut Icon" href="//www.dota2.com.cn/favicon.ico"/>

That .ico is a multi-frame container whose largest frames are 256x256 PNGs of
the red Dota 2 map-marker emblem with a transparent background — i.e. the
brand icon alone, no "DOTA 2" text. We extract the first 256x256 PNG frame,
decode with OpenCV, and write it to assets/ui_icons/dota2_logo.png so it rides
the existing /ui-icon/ route + static-export glob pipeline.
"""
import struct
import sys

import cv2
import numpy as np

from common import UI_ICONS
from http_utils import http_bytes

FAVICON_URL = "https://www.dota2.com.cn/favicon.ico"
OUT = UI_ICONS / "dota2_logo.png"
TARGET_SIZE = 256


def _extract_largest_png_frame(data: bytes) -> bytes | None:
    """Return the bytes of the largest PNG-embedded frame in an ICO blob."""
    if len(data) < 6 or data[:4] != b"\x00\x00\x01\x00":
        return None
    count = struct.unpack("<H", data[4:6])[0]
    best: tuple[int, bytes] | None = None
    for i in range(count):
        off = 6 + 16 * i
        if off + 16 > len(data):
            break
        w = data[off]
        size = struct.unpack("<I", data[off + 8 : off + 12])[0]
        img_off = struct.unpack("<I", data[off + 12 : off + 16])[0]
        width = 256 if w == 0 else w
        blob = data[img_off : img_off + size]
        if blob[:8] != b"\x89PNG\r\n\x1a\n":
            continue
        if best is None or width * width > best[0]:
            best = (width * width, blob)
    return best[1] if best else None


def main() -> int:
    if OUT.is_file() and OUT.stat().st_size >= 512:
        print(f"exists: {OUT} ({OUT.stat().st_size} bytes)")
        return 0
    data = http_bytes(FAVICON_URL, timeout=30)
    if not data or len(data) < 16:
        print("empty favicon download", file=sys.stderr)
        return 1
    png = _extract_largest_png_frame(data)
    if png is None:
        print("no PNG frame in .ico", file=sys.stderr)
        return 1
    arr = cv2.imdecode(np.frombuffer(png, dtype=np.uint8), cv2.IMREAD_UNCHANGED)
    if arr is None:
        print("decode failed", file=sys.stderr)
        return 1
    UI_ICONS.mkdir(parents=True, exist_ok=True)
    ok = cv2.imwrite(str(OUT), arr)
    if not ok:
        print("write failed", file=sys.stderr)
        return 1
    h, w = arr.shape[:2]
    channels = arr.shape[2] if arr.ndim == 3 else 1
    transparent = int(np.count_nonzero(arr[:, :, 3] == 0)) if channels == 4 else 0
    print(f"saved {OUT} ({w}x{h}, {OUT.stat().st_size} bytes, {transparent} px transparent)")
    return 0


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