#!/usr/bin/env python3
"""fetch a stage3 from Gentoo's mirror"""

import argparse
import urllib.request
import os
import re
import sys
from collections import namedtuple

MIRROR = 'http://gentoo.osuosl.org/'
Stage3 = namedtuple('Stage3', 'url cpu specialty minimal nomultilib systemd size')
MINIMAL = re.compile(r'[\+-]minimal-')
NOMULTILIB = re.compile(r'[\+-]nomultilib-')
SYSTEMD = re.compile(r'[\+-]systemd-')


def parse_args():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('--cpu', type=str, default=None)
    parser.add_argument('--specialty', type=str, default=None)
    parser.add_argument('--no-multilib', action='store_true', default=False)
    parser.add_argument('--systemd', action='store_true', default=False)
    parser.add_argument('--minimal', action='store_true', default=False)
    parser.add_argument('--outfile', type=str, default=None)
    parser.add_argument('arch', type=str)

    return parser.parse_args()


def get_manifest(arch, mirror=MIRROR):
    manifest = []
    url = mirror + '/releases/{0}/autobuilds/latest-stage3.txt'.format(arch)
    base_url = mirror + '/releases/{0}/autobuilds/'.format(arch)

    with urllib.request.urlopen(url) as fp:
        text = fp.read()
        text = text.decode('ascii')

    for line in text.split('\n'):
        line = line.strip()

        if not line or line[0] == '#':
            continue

        filename, size = line.split()
        size = int(size)
        dirname, rest = filename.split('/', 1)

        if '/' in rest:
            specialty, rest = rest.split('/', 1)
        else:
            specialty = None

        cpu = rest.split('-', 2)[1]
        nomultilib = 'nomultilib-' in rest
        nomultilib = bool(NOMULTILIB.search(rest))
        systemd = 'systemd-' in rest
        systemd = bool(SYSTEMD.search(rest))
        minimal = bool(MINIMAL.search(rest))

        stage3 = Stage3(
            cpu=cpu,
            minimal=minimal,
            nomultilib=nomultilib,
            systemd=systemd,
            size=size,
            specialty=specialty,
            url=base_url + filename,
        )

        manifest.append(stage3)

    return manifest


def fetch(url, outfile):
    """fetch url and write it to outfile"""
    with urllib.request.urlopen(url) as infile, open(outfile, 'wb') as outfile:
        while True:
            data = infile.read(512)

            if not data:
                break

            outfile.write(data)


def main():
    args = parse_args()
    manifest = get_manifest(args.arch)
    manifest.reverse()
    stage3 = None

    for item in manifest:
        if args.cpu and item.cpu != args.cpu:
            continue

        if not all([
            args.minimal == item.minimal,
            args.no_multilib == item.nomultilib,
            args.systemd == item.systemd,
            args.specialty == item.specialty,
        ]):
            continue

        stage3 = item
        break

    if not stage3:
        msg = 'No stage3 found matching your criteria\n'
        sys.stderr.write(msg)
        sys.exit(404)

    filename = os.path.basename(stage3.url)
    if args.outfile:
        outfile = args.outfile
    else:
        outfile = filename

    print(filename)
    fetch(stage3.url, outfile)
    stat = os.stat(outfile)

    assert stat.st_size == stage3.size, 'File size does not match manifest'

main()