#!/usr/bin/python3
# SPDX-License-Identifier: MIT
"""mdbp backend wrapper via ssh"""

import argparse
import contextlib
import io
import json
import pathlib
import random
import re
import subprocess
import sys
import tarfile
import typing
import urllib.parse

from .common import JsonObject, buildjson, get_dsc_files, tar_add


class RepoForward:
    def __init__(self):
        self.forwards = {}


    def get_forward(self, destination: str) -> str:
        try:
            return self.forwards[destination]
        except KeyError:
            forward = "localhost:%d" % random.randrange(1024, 65536)
            self.forwards[destination] = forward
            return forward


    def proxy(self, repoline: str) -> str:
        """Transform an extra repository line and to pass it through a ssh
        forward."""
        match = re.match(
            r"^(deb(?:-src)?(?:\s+\[[^]]*\])?)\s+(\S+)\s+(.*)$", repoline
        )
        if not match:
            raise ValueError(
                "failed to understand repository specification %r" % repoline
            )
        head, url, tail = match.groups()
        spliturl = urllib.parse.urlsplit(url)
        if spliturl.scheme != "http":
            raise ValueError("cannot proxy url of scheme %r" % spliturl.scheme)
        netloc = self.get_forward(
            "%s:%d" % (spliturl.hostname, spliturl.port or 80)
        )
        if spliturl.username:
            netloc = "@" + netloc
            if spliturl.password:
                netloc = ":" + spliturl.password + netloc
            netloc = spliturl.username + netloc
        url = urllib.parse.urlunsplit((spliturl.scheme, netloc) + spliturl[2:])
        return " ".join((head, url, tail))


    def ssh_options(self) -> typing.Iterable[str]:
        for dest, proxy in self.forwards.items():
            yield "-R"
            yield "%s:%s" % (proxy, dest)


def produce_request_tar(buildjsonobj: JsonObject,
                        fileobj: typing.IO[bytes]) -> None:
    """Write a tar file suitable for mdbp-streamapi into the given `fileobj`
    based on the given `buildjsonobj`.
     * An .output.directory is discarded.
     * A referenced .dsc file and its components is included.
    """
    sendjsonobj = buildjsonobj.copy()
    sendjsonobj["output"] = sendjsonobj["output"].copy()
    del sendjsonobj["output"]["directory"]
    dscpath: typing.Optional[pathlib.Path]
    try:
        dscpath = pathlib.Path(buildjsonobj["input"]["source_package_path"])
    except KeyError:
        dscpath = None
    else:
        sendjsonobj["input"] = sendjsonobj["input"].copy()
        sendjsonobj["input"]["source_package_path"] = dscpath.name
    with tarfile.open(mode="w|", fileobj=fileobj) as tar:
        info = tarfile.TarInfo("build.json")
        sendjsonfile = io.BytesIO()
        for chunk in json.JSONEncoder().iterencode(sendjsonobj):
            sendjsonfile.write(chunk.encode("utf8"))
        info.size = sendjsonfile.tell()
        sendjsonfile.seek(0)
        tar.addfile(info, sendjsonfile)
        if dscpath:
            for path in [dscpath] + get_dsc_files(dscpath):
                tar_add(tar, path)

def main() -> None:
    """Entry point for mdbp-ssh backend"""
    parser = argparse.ArgumentParser()
    parser.add_argument(
        "--proxyrepos",
        default=False,
        action="store_true",
        help="proxy http repositories over the ssh connection",
    )
    parser.add_argument("host", type=str)
    parser.add_argument("command", nargs=argparse.REMAINDER)
    args = parser.parse_args()
    if len(args.command) < 2:
        parser.error("missing command or json file")
    build = buildjson(args.command.pop())
    cmd = ["ssh"]
    if args.proxyrepos and "extrarepositories" in build:
        repoforward = RepoForward()
        build["extrarepositories"] = list(
            map(repoforward.proxy, build["extrarepositories"])
        )
        cmd.extend(repoforward.ssh_options())
    cmd.extend([args.host, "mdbp-streamapi", *args.command])
    with contextlib.ExitStack() as stack:
        proc = stack.enter_context(
            subprocess.Popen(
                cmd,
                stdin=subprocess.PIPE,
                stdout=subprocess.PIPE,
                stderr=sys.stdout if build["output"].get("log", True)
                                  else subprocess.DEVNULL
            ),
        )
        assert proc.stdin is not None
        produce_request_tar(build, proc.stdin)
        proc.stdin.close()
        exitcode = 0
        try:
            outtar = stack.enter_context(tarfile.open(fileobj=proc.stdout,
                                                      mode="r|"))
        except tarfile.ReadError as err:
            if str(err) != "empty file":
                raise
            exitcode = 1
        else:
            for member in outtar:
                if "/" in member.name or not member.isfile():
                    raise ValueError("expected flat tar as output")
                outtar.extract(member, build["output"]["directory"],
                               set_attrs=False)
        sys.exit(proc.wait() or exitcode)

if __name__ == "__main__":
    main()