#!/usr/bin/env python3
"""Estrae singoli file da uno ZIP remoto via HTTP Range (senza scaricare 1,28 GB).

Il tpz dei template Godot e' uno zip: serve solo templates/linux_release.arm64.
Legge EOCD + central directory con Range, poi scarica solo il membro richiesto.
"""
import binascii
import struct
import sys
import urllib.request
import zlib

URL = ("https://github.com/godotengine/godot-builds/releases/download/"
       "4.7.1-stable/Godot_v4.7.1-stable_export_templates.tpz")


def get_range(url, start, end=None):
    if end is None:
        rng = f"bytes={start}-"
    else:
        rng = f"bytes={start}-{end}"
    req = urllib.request.Request(url, headers={"Range": rng})
    with urllib.request.urlopen(req, timeout=90) as r:
        return r.read(), r.status


def main(wanted, dest_dir):
    # 1. dimensione totale
    req = urllib.request.Request(URL, method="HEAD")
    with urllib.request.urlopen(req, timeout=60) as r:
        total = int(r.headers["Content-Length"])
    print(f"zip remoto: {total} byte")

    # 2. EOCD negli ultimi 64 KiB
    tail_len = min(65536, total)
    tail, _ = get_range(URL, total - tail_len)
    pos = tail.rfind(b"PK\x05\x06")
    if pos < 0:
        sys.exit("EOCD non trovato (zip64?)")
    (_, _, _, _, n_entries, cd_size, cd_off, _) = struct.unpack(
        "<IHHHHIIH", tail[pos:pos + 22])
    print(f"voci: {n_entries}, central directory: {cd_off}+{cd_size}")

    # 3. central directory
    cd, _ = get_range(URL, cd_off, cd_off + cd_size - 1)

    entries = {}
    i = 0
    while i + 46 <= len(cd) and cd[i:i + 4] == b"PK\x01\x02":
        (method, csize, usize, name_len, extra_len, comment_len,
         local_off) = (struct.unpack("<H", cd[i + 10:i + 12])[0],
                       struct.unpack("<I", cd[i + 20:i + 24])[0],
                       struct.unpack("<I", cd[i + 24:i + 28])[0],
                       struct.unpack("<H", cd[i + 28:i + 30])[0],
                       struct.unpack("<H", cd[i + 30:i + 32])[0],
                       struct.unpack("<H", cd[i + 32:i + 34])[0],
                       struct.unpack("<I", cd[i + 42:i + 46])[0])
        name = cd[i + 46:i + 46 + name_len].decode("utf-8", "replace")
        entries[name] = (method, csize, usize, local_off)
        i += 46 + name_len + extra_len + comment_len

    print(f"membri indicizzati: {len(entries)}")
    if wanted not in entries:
        candidati = [n for n in entries if "arm64" in n]
        sys.exit(f"'{wanted}' non presente. Candidati arm64: {candidati}")

    method, csize, usize, local_off = entries[wanted]
    print(f"{wanted}: metodo={method} compresso={csize} originale={usize}")

    # 4. header locale per sapere dove iniziano davvero i dati
    lh, _ = get_range(URL, local_off, local_off + 29)
    if lh[:4] != b"PK\x03\x04":
        sys.exit("header locale inatteso")
    name_len = struct.unpack("<H", lh[26:28])[0]
    extra_len = struct.unpack("<H", lh[28:30])[0]
    data_start = local_off + 30 + name_len + extra_len

    # 5. dati compressi del solo membro
    print(f"scarico {csize} byte da offset {data_start} ...")
    data, status = get_range(URL, data_start, data_start + csize - 1)
    print(f"ricevuti {len(data)} byte (http {status})")

    if method == 8:
        raw = zlib.decompress(data, -15)
    elif method == 0:
        raw = data
    else:
        sys.exit(f"metodo di compressione non gestito: {method}")

    print(f"decompresso: {len(raw)} byte (atteso {usize})")
    if len(raw) != usize:
        sys.exit("dimensione non corrispondente")
    out = f"{dest_dir}/{wanted.split('/')[-1]}"
    with open(out, "wb") as fh:
        fh.write(raw)
    print(f"scritto {out}")


if __name__ == "__main__":
    target = sys.argv[1] if len(sys.argv) > 1 else "templates/linux_release.arm64"
    dest = sys.argv[2] if len(sys.argv) > 2 else "/tmp/godot-dl"
    main(target, dest)