#!/usr/bin/env python
"""Idempotently download, extract, and serve a mirror of <docs.python.org>."""

import argparse
import http.client
import shlex
import subprocess
import sys
import tarfile
from pathlib import Path

import requests
from send2trash import send2trash

HERE = Path(__file__).parent

# Something other than the default 8000 used by python -m http.server
PORT = "8004"


def get_options():
    """Parse command line options."""
    parser = argparse.ArgumentParser(
        description="Idempotently download and serve Python docs from a local copy"
    )
    parser.add_argument(
        "--systemd",
        action="store_true",
        help="Also create, enable, and start a systemd service",
    )
    parser.add_argument(
        "--clean",
        action="store_true",
        help="Clean out past downloads and unit files (uninstall)",
    )
    return parser.parse_args()


def clean():
    """Clean (trash) past downloads and unit files."""
    print("Cleaning past downloads and unit files")
    trash_targets = []
    if (
        p := Path.home() / ".config" / "systemd" / "user" / "python-docs.service"
    ).exists():
        cmd = ["systemctl", "--user", "disable", "--now", "python-docs.service"]
        print(f"  {shlex.join(cmd)}")
        subprocess.run(cmd).check_returncode()
        trash_targets.append(p)

    trash_targets.extend(HERE.glob("python-*.*-docs*/"))
    trash_targets.extend(HERE.glob("python-*.*-docs*.tar.bz2"))
    for p in trash_targets:
        print(f"  Trashing {p}")
    send2trash(trash_targets)


def download_extract():
    """Download and extract Python docs to `HERE`."""
    major, minor, *_ = sys.version_info
    url = f"https://docs.python.org/{major}.{minor}/archives/python-{major}.{minor}-docs-html.tar.bz2"
    outfile = HERE / f"python-{major}.{minor}-docs-html.tar.bz2"

    print(f"Downloading {url}")
    if outfile.is_file():
        print(f"  Already exists: {outfile}")
    else:
        with requests.get(url) as r, open(outfile, "wb") as f:
            if r.status_code != 200:
                descr = http.client.responses[r.status_code]
                raise RuntimeError(f"{r.status_code = } ({descr})")
            f.write(r.content)
            print(f"  Downloaded: {outfile} ({len(r.content)} bytes)")

    print(f"Extracting {outfile}")
    assert outfile.is_file()
    outdir = HERE / f"python-{major}.{minor}-docs-html"
    if (outdir / "index.html").is_file():
        print(f"  Already exists: {outdir}/index.html")
    else:
        with tarfile.open(outfile) as f:
            f.extractall(path=HERE, filter="data")  # Extracting HERE creates outdir
        assert (outdir / "index.html").is_file()

    return outdir


def define_user_service(outdir):
    """Create a systemd unit file to serve docs as a user service."""
    print("Creating systemd unit file")
    if not Path("/run/systemd/system").exists():
        raise ValueError("Host appears not to use systemd")

    dest = Path.home() / ".config" / "systemd" / "user" / "python-docs.service"
    dest.parent.mkdir(parents=True, exist_ok=True)
    cmd = shlex.join(
        [sys.executable, "-m", "http.server", "-d", str(outdir.absolute()), PORT]
    )
    body = f"""\
# Autogenerated by {__file__}

[Service]
Type=simple
Description=Serve Python docs on port {PORT}
ExecStart={cmd}

[Install]
WantedBy=default.target
"""
    if dest.is_file():
        with open(dest) as f:
            contents = f.read()
        if contents == body:
            print(f"  Already defined: {dest}")
            return

    with open(dest, "w") as f:
        f.write(body)
        print(f"  Saved: {dest}")


def enable_user_service():
    """Start and enable the systemd unit service."""
    print("Enabling and starting systemd user service")

    cmd = ["systemctl", "--user", "daemon-reload"]
    print(f"  {shlex.join(cmd)}")
    subprocess.run(cmd).check_returncode()

    cmd = ["systemctl", "--user", "enable", "--now", "python-docs"]
    print(f"  {shlex.join(cmd)}")
    subprocess.run(cmd).check_returncode()


if __name__ == "__main__":
    options = get_options()

    if options.clean:
        clean()
        exit()

    outdir = download_extract()

    if options.systemd:
        define_user_service(outdir)
        enable_user_service()