#!/usr/bin/env python3
#
# Copyright 2021 Johannes Schauer Marin Rodrigues <josch@debian.org>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.

# This tool is similar to debootstrap but is able to recreate a chroot tarball
# containing precisely the given package and version selection. The package
# list is expected on standard input and may be of the format produced by:
#
#     dpkg-query --showformat '${binary:Package}=${Version}\n' --show

# The name was suggested by Adrian Bunk as a portmanteau of debootstrap and
# snapshot.debian.org.

# TODO: Address invalid names
# pylint: disable=invalid-name

import argparse
import atexit
import dataclasses
import difflib
import http.server
import os
import pathlib
import re
import shutil
import subprocess
import sys
import tempfile
import threading
from collections import defaultdict
from contextlib import contextmanager
from functools import partial
from operator import itemgetter

import apt
import requests
from debian.deb822 import BuildInfo

from devscripts.proxy import setupcache


class MyHTTPException(Exception):
    pass


class MyHTTP404Exception(Exception):
    pass


class MyHTTPTimeoutException(Exception):
    pass


class RetryCountExceeded(Exception):
    pass


@dataclasses.dataclass
class Source:
    archive: str
    timestamp: str
    suite: str
    components: list[str]

    def deb_line(self) -> str:
        if self.timestamp:
            return (
                "deb [check-valid-until=no]"
                f" http://snapshot.debian.org/archive/{self.archive}/{self.timestamp}/"
                f" {self.suite} {' '.join(self.components)}\n"
            )

        return (
            "deb [signed-by=/usr/share/keyrings/debian-archive-keyring.gpg]"
            f" http://deb.debian.org/{self.archive}"
            f" {self.suite} {' '.join(self.components)}\n"
        )


def parse_buildinfo(val):
    with open(val, encoding="utf8") as f:
        buildinfo = BuildInfo(f)
    pkgs = []
    for dep in buildinfo.relations["installed-build-depends"]:
        assert len(dep) == 1
        dep = dep[0]
        assert dep["arch"] is None
        assert dep["restrictions"] is None
        assert len(dep["version"]) == 2
        rel, version = dep["version"]
        assert rel == "="
        pkgs.append((dep["name"], dep["archqual"], version))
    return pkgs, buildinfo.get("Build-Architecture")


def parse_pkgs(val):
    if val == "-":
        val = sys.stdin.read()
    if val.startswith("./") or val.startswith("/"):
        val = pathlib.Path(val)
        if not val.exists():
            print(f"{val} does not exist", file=sys.stderr)
            sys.exit(1)
        val = val.read_text(encoding="utf8")
    pkgs = []
    pattern = re.compile(
        r"""
            ^[^a-z0-9]*                    # garbage at the beginning
            ([a-z0-9][a-z0-9+.-]+)         # package name
            (?:[^a-z0-9+.-]+([a-z0-9-]+))? # optional version
            [^A-Za-z0-9.+~:-]+             # optional garbage
            ([A-Za-z0-9.+~:-]+)            # version
            [^A-Za-z0-9.+~:-]*$            # garbage at the end
            """,
        re.VERBOSE,
    )
    for line in re.split(r"[,\r\n]+", val):
        if not line:
            continue
        match = pattern.fullmatch(line)
        if match is None:
            print(f"cannot parse: {line}", file=sys.stderr)
            sys.exit(1)
        pkgs.append(match.groups())
    return [pkgs]


def get_parser() -> argparse.ArgumentParser:
    parser = argparse.ArgumentParser(
        formatter_class=argparse.RawDescriptionHelpFormatter,
        description="""\

Combines debootstrap and snapshot.debian.org to create a chroot tarball with
exact package versions from the past either to reproduce bugs or to test source
package reproducibility.

To obtain a list of packages run the following command on one machine:

    $ dpkg-query --showformat '${binary:Package}=${Version}\\n' --show

And pass the output to debootsnap with the --packages argument. The result
will be a chroot tarball with precisely the package versions as they were
found on the system that ran dpkg-query.
""",
        epilog="""\

*EXAMPLES*

On one system run:

    $ dpkg-query --showformat '${binary:Package}=${Version}\\n' --show > pkglist

Then copy over "pkglist" and on another system run:

    $ debootsnap --pkgs=./pkglist > ./chroot.tar

Or use a buildinfo file as input:

    $ debootsnap --buildinfo=./package.buildinfo > ./chroot.tar

A tarball of a chroot with precisely the requested package versions then be
found in the file `./chroot.tar`.

""",
    )
    parser.add_argument(
        "--architecture",
        "--nativearch",
        help="native architecture of the chroot. Ignored if --buildinfo is"
        " used. Foreign architectures are inferred from the package list."
        " Not required if packages are architecture qualified.",
    )
    parser.add_argument(
        "--ignore-notfound",
        action="store_true",
        help="only warn about packages that cannot be found on "
        "snapshot.debian.org instead of exiting",
    )
    parser.add_argument(
        "--cache", help="cache directory -- by default $TMPDIR is used", type=str
    )
    parser.add_argument(
        "--port",
        help="manually choose port number for the apt cache instead of "
        "automatically choosing a free port",
        type=int,
        default=0,
    )
    parser.add_argument("--nocache", help="disable cache", action="store_true")
    group = parser.add_mutually_exclusive_group(required=True)
    group.add_argument(
        "--buildinfo",
        type=parse_buildinfo,
        help="use packages from a buildinfo file. Read buildinfo file from "
        'standard input if value is "-".',
    )
    group.add_argument(
        "--packages",
        "--pkgs",
        action="extend",
        type=parse_pkgs,
        help="list of packages, optional architecture and version, separated "
        "by comma or linebreak. Read list from standard input if value is "
        '"-". Read list from a file if value starts with "./" or "/". The '
        "option can be specified multiple times. Package name, "
        "version and architecture are separated by one or more characters "
        "that are not legal in the respective adjacent field. Leading and "
        "trailing illegal characters are allowed. Example: "
        "pkg1:arch=ver1,pkg2:arch=ver2",
    )
    group = parser.add_mutually_exclusive_group()
    group.add_argument(
        "--sources-list-only",
        action="store_true",
        help="only query metasnap.debian.net and print the sources.list "
        "needed to create chroot and exit",
    )
    group.add_argument(
        "output",
        nargs="?",
        default="-",
        help="path to output chroot tarball",
    )
    return parser


def query_apt_repo(pkgs, nativearch, repo, sources: list[Source]):
    missing = []
    found_packages = False

    with tempfile.TemporaryDirectory() as tmpdirname:
        apt.apt_pkg.config.set("Apt::Architecture", nativearch)
        apt.apt_pkg.config.clear("APT::Default-Release")
        cache = apt.Cache(rootdir=tmpdirname)
        apt_sources = pathlib.Path(f"{tmpdirname}/etc/apt/sources.list")
        apt_sources.write_text(repo.deb_line(), encoding="utf8")
        cache.open()  # needed for new apt sources
        cache.update()
        cache.open()  # needed after apt update

        for name, arch, version in pkgs:
            qual_name = f"{name}:{arch}"
            if qual_name in cache and version in cache[qual_name].versions:
                found_packages = True
            else:
                missing.append((name, arch, version))

    if found_packages:
        sources.append(repo)

    return missing


# pylint: disable=too-many-locals
def query_metasnap(pkgsleft, archive, nativearch, foreignarches):
    handled_pkgs = set(pkgsleft)
    r = requests.post(
        "http://metasnap.debian.net/cgi-bin/api",
        files={
            "archive": archive,
            "arch": nativearch,
            "pkgs": ",".join([n + ":" + a + "=" + v for n, a, v in handled_pkgs]),
        },
        timeout=60,
    )
    if r.status_code == 404:
        for line in r.text.splitlines():
            n, a, v = line.split()
            if a == "all" and (n, nativearch, v) in handled_pkgs:
                handled_pkgs.remove((n, nativearch, v))
            else:
                handled_pkgs.remove((n, a, v))
        r = requests.post(
            "http://metasnap.debian.net/cgi-bin/api",
            files={
                "archive": archive,
                "arch": nativearch,
                "pkgs": ",".join([n + ":" + a + "=" + v for n, a, v in handled_pkgs]),
            },
            timeout=60,
        )
    assert r.status_code == 200, r.text

    suite2pkgs = defaultdict(set)
    pkg2range = {}
    for line in r.text.splitlines():
        n, a, v, s, c, b, e = line.split()
        # in case the package was only part of arch:all and not added to the
        # arch specific Packages file metasnap.d.n will return arch:all.
        # Use that instead and make sure apt downloads the arch:all Packages
        # file in addition.
        if a == "all" and (n, nativearch, v) in handled_pkgs:
            foreignarches.add("all")
            handled_pkgs.remove((n, nativearch, v))
            handled_pkgs.add((n, a, v))
            pkgsleft.remove((n, nativearch, v))
            pkgsleft.add((n, a, v))
        assert (n, a, v) in handled_pkgs
        suite2pkgs[s].add((n, a, v))
        # this will only keep one range of packages with multiple
        # ranges but we don't care because we only need one
        pkg2range[((n, a, v), s)] = (c, b, e)

    return handled_pkgs, suite2pkgs, pkg2range


def comp_ts(ranges):
    last = "19700101T000000Z"  # impossibly early date
    res = []
    for c, b, e in ranges:
        if last >= b:
            # add the component the current timestamp needs
            res[-1][1].add(c)
            continue
        # add new timestamp with initial component
        last = e
        res.append((last, set([c])))
    return res


# pylint: disable=too-many-locals
def compute_sources(
    pkgs, nativearch, ignore_notfound, sources: list[Source], foreignarches
):
    pkgsleft = set(pkgs)
    for archive in [
        "debian",
        "debian-debug",
        "debian-security",
        "debian-ports",
        "debian-volatile",
        "debian-backports",
    ]:
        if len(pkgsleft) == 0:
            break

        handled_pkgs, suite2pkgs, pkg2range = query_metasnap(
            pkgsleft, archive, nativearch, foreignarches
        )

        # greedy algorithm:
        # pick the suite covering most packages first
        while len(handled_pkgs) > 0:
            bestsuite = sorted(suite2pkgs.items(), key=lambda v: len(v[1]))[-1][0]
            ranges = [pkg2range[nav, bestsuite] for nav in suite2pkgs[bestsuite]]
            # sort by end-time
            ranges.sort(key=itemgetter(2))

            for ts, comps in comp_ts(ranges):
                sources.append(Source(archive, ts, bestsuite, comps))

            for nav in suite2pkgs[bestsuite]:
                handled_pkgs.remove(nav)
                pkgsleft.remove(nav)
                for suite in suite2pkgs:
                    if suite == bestsuite:
                        continue
                    if nav in suite2pkgs[suite]:
                        suite2pkgs[suite].remove(nav)
            del suite2pkgs[bestsuite]
    if pkgsleft:
        print("cannot find:", file=sys.stderr)
        print(
            "\n".join([f"{pkg[0]}:{pkg[1]}={pkg[2]}" for pkg in pkgsleft]),
            file=sys.stderr,
        )
        if not ignore_notfound:
            sys.exit(1)


def create_install_hook(tmpdirname, deb_files):
    # manually feed apt install the complete package list
    # to be sure that the apt solver did not change it.
    hook = pathlib.Path(tmpdirname) / "apt_install.sh"
    hook.write_text(
        "\n".join(
            [
                "#!/bin/sh",
                "cat << END | APT_CONFIG=$MMDEBSTRAP_APT_CONFIG"
                " xargs apt-get install --yes",
                "\n".join(deb_files),
                "END",
            ]
        )
    )
    hook.chmod(0o755)


def create_repo(tmpdirname, pkgs):
    with open(tmpdirname + "/control", "w", encoding="utf8") as f:

        def pkg2name(n, a, v):
            if a is None:
                return f"{n} (= {v})"
            return f"{n}:{a} (= {v})"

        f.write("Package: debootsnap-dummy\n")
        f.write(f"Depends: {', '.join([pkg2name(*pkg) for pkg in pkgs])}\n")
    subprocess.check_call(
        ["equivs-build", tmpdirname + "/control"],
        cwd=tmpdirname + "/cache",
        # equivs-build behaves differently depending on whether TMPDIR is set
        # or not, so to force the same behaviour independent on whether the
        # user has TMPDIR set, we set or override that variable with our own
        # (which is a path below the user's $TMPDIR anyways, if it was set)
        env={**os.environ, "TMPDIR": tmpdirname + "/cache"},
    )

    packages_content = subprocess.check_output(
        ["apt-ftparchive", "packages", "."], cwd=tmpdirname + "/cache"
    )
    with open(tmpdirname + "/cache/Packages", "wb") as f:
        f.write(packages_content)
    release_content = subprocess.check_output(
        [
            "apt-ftparchive",
            "release",
            "-oAPT::FTPArchive::Release::Suite=dummysuite",
            ".",
        ],
        cwd=tmpdirname + "/cache",
    )
    with open(tmpdirname + "/cache/Release", "wb") as f:
        f.write(release_content)


@contextmanager
def serve_repo(tmpdirname):
    httpd = http.server.HTTPServer(
        ("localhost", 0),
        partial(http.server.SimpleHTTPRequestHandler, directory=tmpdirname + "/cache"),
    )
    # run server in a new thread
    server_thread = threading.Thread(target=httpd.serve_forever)
    server_thread.daemon = True
    # start thread
    server_thread.start()
    # retrieve port (in case it was generated automatically)
    _, port = httpd.server_address
    try:
        yield port
    finally:
        httpd.shutdown()
        httpd.server_close()
        server_thread.join()


def run_mmdebstrap(
    tmpdirname, sources: list[Source], nativearch, foreignarches, output
):
    with open(tmpdirname + "/sources.list", "w", encoding="utf8") as f:
        for source in sources:
            f.write(source.deb_line())
    # we serve the directory via http instead of using a copy:// mirror
    # because the temporary directory is not accessible to the unshared
    # user
    with serve_repo(tmpdirname) as port:
        cmd = [
            "mmdebstrap",
            f"--architectures={','.join([nativearch] + list(foreignarches))}",
            "--variant=essential",
            "--include=debootsnap-dummy",
            "--format=tar",
            "--skip=cleanup/reproducible",
            '--aptopt=Apt::Key::gpgvcommand "/usr/libexec/mmdebstrap/gpgvnoexpkeysig"',
            "--hook-dir=/usr/share/mmdebstrap/hooks/maybe-merged-usr",
            f"--customize={tmpdirname}/apt_install.sh",
            '--customize-hook=chroot "$1" dpkg -r debootsnap-dummy',
            '--customize-hook=chroot "$1" dpkg-query --showformat '
            "'${binary:Package}=${Version}\\n' --show > \"$1/pkglist\"",
            "--customize-hook=download /pkglist ./pkglist",
            '--customize-hook=rm "$1/pkglist"',
            "--customize-hook=upload sources.list /etc/apt/sources.list",
            "dummysuite",
            output,
            f"deb [trusted=yes] http://localhost:{port}/ ./",
        ]
        subprocess.check_call(cmd, cwd=tmpdirname)

    newpkgs = set()
    with open(tmpdirname + "/pkglist", encoding="utf8") as f:
        for line in f:
            line = line.rstrip()
            n, v = line.split("=")
            a = nativearch
            if ":" in n:
                n, a = n.split(":")
            newpkgs.add((n, a, v))

    return newpkgs


# pylint: disable=too-many-locals
def download_packages(
    tmpdirname,
    sources: list[Source],
    pkgs,
    nativearch,
    foreignarches,
    cache,
    nocache,
    port,
):
    for d in [
        "/etc/apt/apt.conf.d",
        "/etc/apt/sources.list.d",
        "/etc/apt/preferences.d",
        "/var/cache/apt",
        "/var/lib/apt/lists/partial",
        "/var/lib/dpkg",
    ]:
        os.makedirs(tmpdirname + "/" + d)
    # apt-get update requires /var/lib/dpkg/status
    with open(tmpdirname + "/var/lib/dpkg/status", "w", encoding="utf8") as f:
        pass
    with open(tmpdirname + "/apt.conf", "w", encoding="utf8") as f:
        f.write(f'Apt::Architecture "{nativearch}";\n')
        f.write("Apt::Architectures { " + f'"{nativearch}"; ')
        for a in foreignarches:
            f.write(f'"{a}"; ')
        f.write("};\n")
        f.write('Dir "' + tmpdirname + '";\n')
        f.write('Dir::Etc::Trusted "/etc/apt/trusted.gpg";\n')
        f.write('Dir::Etc::TrustedParts "/usr/share/keyrings/";\n')
        f.write('Acquire::Languages "none";\n')
        # f.write("Acquire::http::Dl-Limit \"1000\";\n")
        # f.write("Acquire::https::Dl-Limit \"1000\";\n")
        f.write('Acquire::Retries "5";\n')
        # work around proxy.py only supports one connection at a time
        f.write('Acquire::Queue-Mode "access";\n')
        # ignore expired signatures
        f.write('Apt::Key::gpgvcommand "/usr/libexec/mmdebstrap/gpgvnoexpkeysig";\n')

    os.makedirs(tmpdirname + "/cache")

    apt_env = {"APT_CONFIG": tmpdirname + "/apt.conf"}
    if not nocache:
        port, teardown = setupcache(cache, port)
        apt_env["http_proxy"] = f"http://127.0.0.1:{port}"
        atexit.register(teardown)

    with open(tmpdirname + "/etc/apt/sources.list", "w", encoding="utf8") as f:
        for source in sources:
            f.write(source.deb_line())
    subprocess.check_call(["apt-get", "update", "--error-on=any"], env=apt_env)

    deb_files = []
    cache = pathlib.Path(tmpdirname, "cache")
    for i, (name, arch, version) in enumerate(pkgs):
        pkg = f"{name}:{arch}={version}"
        print(f"Downloading dependency {i + 1} of {len(pkgs)}: {pkg}")
        with tempfile.TemporaryDirectory() as tmpdir2:
            subprocess.check_call(
                ["apt-get", "download", "--yes", pkg],
                cwd=tmpdir2,
                env=apt_env,
            )
            debs = os.listdir(tmpdir2)
            assert len(debs) == 1
            # Normalize the package name to how it appears in the archive.
            # Mainly this removes the epoch from the filename, see
            # https://bugs.debian.org/645895
            # This avoids apt bugs connected with a percent sign in the
            # filename as they occasionally appear, for example as
            # introduced in apt 2.1.15 and later fixed by DonKult:
            # https://salsa.debian.org/apt-team/apt/-/merge_requests/175
            subprocess.check_call(["dpkg-name", tmpdir2 + "/" + debs[0]])
            debs = os.listdir(tmpdir2)
            assert len(debs) == 1
            shutil.move(tmpdir2 + "/" + debs[0], cache)
            deb_files.append((cache / debs[0]).as_posix())
    return deb_files


def handle_packages(architecture, packages):
    pkgs = [v for sublist in packages for v in sublist]
    if architecture is None:
        arches = {a for _, a, _ in pkgs if a is not None}
        if len(arches) == 0:
            print("packages are not architecture qualified", file=sys.stderr)
            print("use --architecture to set the native architecture", file=sys.stderr)
            sys.exit(1)
        elif len(arches) > 1:
            print("more than one architecture in the package list", file=sys.stderr)
            print("use --architecture to set the native architecture", file=sys.stderr)
            sys.exit(1)
        nativearch = arches.pop()
        assert arches == set()
    else:
        nativearch = architecture
    return pkgs, nativearch


def main(arguments: list[str]) -> None:
    parser = get_parser()
    args = parser.parse_args(arguments)

    if not args.sources_list_only and args.output == "-" and sys.stdout.isatty():
        parser.print_usage()
        print(
            "E: Refusing to write tarball to interactive tty. "
            "Redirect stdout to a file or pass the output tarball filename "
            "as the positional argument [output]."
        )
        sys.exit(1)

    if args.packages:
        pkgs, nativearch = handle_packages(args.architecture, args.packages)
    else:
        pkgs, nativearch = args.buildinfo
    # unknown architectures are the native architecture
    pkgs = [(n, a if a is not None else nativearch, v) for n, a, v in pkgs]
    # make package list unique
    pkgs = list(set(pkgs))
    # compute foreign architectures
    foreignarches = set()
    for _, a, _ in pkgs:
        if a != nativearch:
            foreignarches.add(a)

    for tool in [
        "equivs-build",
        "apt-ftparchive",
        "mmdebstrap",
        "apt-get",
        "dpkg-name",
    ]:
        if shutil.which(tool) is None:
            print(f"{tool} is required but not installed", file=sys.stderr)
            sys.exit(1)

    sources = []
    pkgs_notfound = pkgs

    unstable = Source("debian", None, "unstable", ["main"])
    pkgs_notfound = query_apt_repo(pkgs_notfound, nativearch, unstable, sources)

    compute_sources(
        pkgs_notfound, nativearch, args.ignore_notfound, sources, foreignarches
    )

    if args.sources_list_only:
        for source in sources:
            print(source.deb_line(), end="")
        sys.exit(0)

    with tempfile.TemporaryDirectory() as tmpdirname:
        # chmod so mmdebstrap can run the generated install hook
        os.chmod(tmpdirname, 0o711)

        deb_files = download_packages(
            tmpdirname,
            sources,
            pkgs,
            nativearch,
            foreignarches,
            args.cache,
            args.nocache,
            args.port,
        )

        create_install_hook(tmpdirname, deb_files)

        create_repo(tmpdirname, pkgs)

        newpkgs = run_mmdebstrap(
            tmpdirname, sources, nativearch, foreignarches, args.output
        )

    # make sure that the installed packages match the requested package
    # list
    if set(newpkgs) != set(pkgs):
        diff = "\n".join(
            difflib.unified_diff(
                ["_".join(pkg) for pkg in sorted(pkgs)],
                ["_".join(pkg) for pkg in sorted(newpkgs)],
                fromfile="buildinfo",
                tofile="bootstrapped",
                lineterm="",
            )
        )
        raise AssertionError(
            "environment bootstrapped from buildinfo file does not match "
            "environment in buildinfo file:\n\n" + diff
        )


if __name__ == "__main__":
    main(sys.argv[1:])
