#!/usr/bin/env python3
r"""chunk_dl.py — 分片并行下载器（断点续传），2026-11-03 CI 迁移批收编。

背景：GitHub 直连在本项目两台机器均不可用，加速镜像站速度慢且会掐连接/回错误页。
本件把大文件切成 N 片经镜像并行拉取（单片断了自动续传重试），全部齐后拼合。
已实证：74MB Godot Linux 包约 15 分钟拉完（2026-11-03 mac_setup 依赖此件拉 Godot macOS 包）。

用法: python3 tools/ci/chunk_dl.py <URL> <输出路径> [分片数=16]
镜像回落顺序：直连 → gh-proxy.net → gh-proxy.com（HEAD 探测 Content-Length 决定实际用的源）。
校验：分片按字节范围落盘、按序拼合；zip 结构校验由调用方（mac_setup.sh 的 unzip -tq）承担。
退出码：0=成功 1=失败。
"""
import concurrent.futures as cf
import os
import subprocess
import sys

MIRRORS = ["", "https://gh-proxy.net/", "https://gh-proxy.com/"]


def pick_mirror(url: str):
    """HEAD 探测取 Content-Length；返回（实际可用 URL, 字节数）或 (None, 0)。"""
    for m in MIRRORS:
        u = m + url
        r = subprocess.run(["curl", "-sIL", "-m", "30", u], capture_output=True, text=True)
        size = 0
        for line in r.stdout.splitlines():
            if line.lower().startswith("content-length:"):
                try:
                    size = int(line.split(":", 1)[1].strip())
                except ValueError:
                    size = 0
        if size > 0:
            return u, size
    return None, 0


def fetch(job) -> bool:
    i, s, e, url, out = job
    p = "%s.part%02d" % (out, i)
    want = e - s + 1
    for _attempt in range(200):
        have = os.path.getsize(p) if os.path.exists(p) else 0
        if have >= want:
            return True
        r0 = s + have
        subprocess.run(
            ["curl", "-sL", "--speed-limit", "1024", "--speed-time", "30",
             "-m", "600", "-r", "%d-%d" % (r0, e), "-o", p + ".new", url],
            capture_output=True)
        if os.path.exists(p + ".new"):
            with open(p, "ab") as f, open(p + ".new", "rb") as g:
                f.write(g.read())
            os.remove(p + ".new")
    return False


def main() -> int:
    if len(sys.argv) < 3:
        print("用法: python3 chunk_dl.py <URL> <输出路径> [分片数=16]")
        return 1
    url, out = sys.argv[1], sys.argv[2]
    n = int(sys.argv[3]) if len(sys.argv) > 3 else 16
    real, size = pick_mirror(url)
    if not real:
        print("全部下载源失败")
        return 1
    print("size=%d url=%s" % (size, real), flush=True)
    chunk = (size + n - 1) // n
    jobs = [(i, i * chunk, min((i + 1) * chunk, size) - 1, real, out)
            for i in range(n) if i * chunk < size]
    with cf.ThreadPoolExecutor(n) as ex:
        for ok in ex.map(fetch, jobs):
            if not ok:
                print("分片重试耗尽")
                return 1
    with open(out, "wb") as f:
        for i, _, _, _, _ in jobs:
            with open("%s.part%02d" % (out, i), "rb") as g:
                f.write(g.read())
    for i, _, _, _, _ in jobs:
        os.remove("%s.part%02d" % (out, i))
    print("done %d" % os.path.getsize(out))
    return 0


if __name__ == "__main__":
    sys.exit(main())