"""仅为安装验收控制下载边界；工具链内容仍来自官方源。"""

from functools import partial
from http.server import SimpleHTTPRequestHandler, ThreadingHTTPServer
from pathlib import Path
import threading
import time


WORK = Path('/work')
lock = threading.Lock()
active = 0


class Handler(SimpleHTTPRequestHandler):
    def do_GET(self):
        global active
        environment = self.path.startswith(('/dist/', '/dever-native-'))
        if environment and (WORK / 'reject-environment').exists():
            self.send_error(404, 'intentional preparation failure')
            return
        archive = environment and self.path.endswith('.tar.xz')
        if archive:
            with lock:
                active += 1
                if active >= 2:
                    (WORK / 'parallel-downloads').touch()
            try:
                while (WORK / 'hold-environment').exists():
                    time.sleep(0.1)
                self.download()
            finally:
                with lock:
                    active -= 1
        else:
            self.download()

    def download(self):
        if self.path.startswith('/dist/'):
            self.send_response(302)
            self.send_header('Location', 'https://static.rust-lang.org' + self.path)
            self.end_headers()
            return
        resume = self.headers.get('Range')
        if resume and self.path.startswith('/dever-native-'):
            offset = int(resume.removeprefix('bytes=').removesuffix('-'))
            path = Path(self.translate_path(self.path))
            size = path.stat().st_size
            (WORK / 'resumed-offset').write_text(str(offset))
            self.send_response(206)
            self.send_header('Content-Range', f'bytes {offset}-{size - 1}/{size}')
            self.send_header('Content-Length', str(size - offset))
            self.end_headers()
            with path.open('rb') as source:
                source.seek(offset)
                self.copyfile(source, self.wfile)
            return
        super().do_GET()


ThreadingHTTPServer(('127.0.0.1', 18080), partial(Handler, directory='/work/assets')).serve_forever()