import argparse
import configparser
import filecmp
import functools
import hashlib
import operator
import os
import os.path
import shutil
import subprocess
import tempfile
import types
import urllib.parse
import urllib.request
import xml.dom.minidom

from typing import (
    Dict,
    Iterable,
    List,
    NewType,
    Tuple,
)

Digest16 = NewType('Digest16', str)
Digest32 = NewType('Digest32', str)


class ChannelTableEntry(types.SimpleNamespace):
    absolute_url: str
    digest: Digest16
    file: str
    size: int
    url: str


class Channel(types.SimpleNamespace):
    channel_html: bytes
    channel_url: str
    forwarded_url: str
    git_cachedir: str
    git_ref: str
    git_repo: str
    git_revision: str
    old_git_revision: str
    release_name: str
    table: Dict[str, ChannelTableEntry]


class VerificationError(Exception):
    pass


class Verification:

    def __init__(self) -> None:
        self.line_length = 0

    def status(self, s: str) -> None:
        print(s, end=' ', flush=True)
        self.line_length += 1 + len(s)  # Unicode??

    @staticmethod
    def _color(s: str, c: int) -> str:
        return '\033[%2dm%s\033[00m' % (c, s)

    def result(self, r: bool) -> None:
        message, color = {True: ('OK ', 92), False: ('FAIL', 91)}[r]
        length = len(message)
        cols = shutil.get_terminal_size().columns
        pad = (cols - (self.line_length + length)) % cols
        print(' ' * pad + self._color(message, color))
        self.line_length = 0
        if not r:
            raise VerificationError()

    def check(self, s: str, r: bool) -> None:
        self.status(s)
        self.result(r)

    def ok(self) -> None:
        self.result(True)


def compare(a: str, b: str) -> Tuple[List[str], List[str], List[str]]:

    def throw(error: OSError) -> None:
        raise error

    def join(x: str, y: str) -> str:
        return y if x == '.' else os.path.join(x, y)

    def recursive_files(d: str) -> Iterable[str]:
        all_files: List[str] = []
        for path, dirs, files in os.walk(d, onerror=throw):
            rel = os.path.relpath(path, start=d)
            all_files.extend(join(rel, f) for f in files)
            for dir_or_link in dirs:
                if os.path.islink(join(path, dir_or_link)):
                    all_files.append(join(rel, dir_or_link))
        return all_files

    def exclude_dot_git(files: Iterable[str]) -> Iterable[str]:
        return (f for f in files if not f.startswith('.git/'))

    files = functools.reduce(
        operator.or_, (set(
            exclude_dot_git(
                recursive_files(x))) for x in [a, b]))
    return filecmp.cmpfiles(a, b, files, shallow=False)


def fetch(v: Verification, channel: Channel) -> None:
    v.status('Fetching channel')
    request = urllib.request.urlopen(channel.channel_url, timeout=10)
    channel.channel_html = request.read()
    channel.forwarded_url = request.geturl()
    v.result(request.status == 200)
    v.check('Got forwarded', channel.channel_url != channel.forwarded_url)


def parse_channel(v: Verification, channel: Channel) -> None:
    v.status('Parsing channel description as XML')
    d = xml.dom.minidom.parseString(channel.channel_html)
    v.ok()

    v.status('Extracting release name:')
    title_name = d.getElementsByTagName(
        'title')[0].firstChild.nodeValue.split()[2]
    h1_name = d.getElementsByTagName('h1')[0].firstChild.nodeValue.split()[2]
    v.status(title_name)
    v.result(title_name == h1_name)
    channel.release_name = title_name

    v.status('Extracting git commit:')
    git_commit_node = d.getElementsByTagName('tt')[0]
    channel.git_revision = git_commit_node.firstChild.nodeValue
    v.status(channel.git_revision)
    v.ok()
    v.status('Verifying git commit label')
    v.result(git_commit_node.previousSibling.nodeValue == 'Git commit ')

    v.status('Parsing table')
    channel.table = {}
    for row in d.getElementsByTagName('tr')[1:]:
        name = row.childNodes[0].firstChild.firstChild.nodeValue
        url = row.childNodes[0].firstChild.getAttribute('href')
        size = int(row.childNodes[1].firstChild.nodeValue)
        digest = Digest16(row.childNodes[2].firstChild.firstChild.nodeValue)
        channel.table[name] = ChannelTableEntry(
            url=url, digest=digest, size=size)
    v.ok()


def digest_string(s: bytes) -> Digest16:
    return Digest16(hashlib.sha256(s).hexdigest())


def digest_file(filename: str) -> Digest16:
    hasher = hashlib.sha256()
    with open(filename, 'rb') as f:
        # pylint: disable=cell-var-from-loop
        for block in iter(lambda: f.read(4096), b''):
            hasher.update(block)
    return Digest16(hasher.hexdigest())


def to_Digest16(v: Verification, digest32: Digest32) -> Digest16:
    v.status('Converting digest to base16')
    process = subprocess.run(
        ['nix', 'to-base16', '--type', 'sha256', digest32], capture_output=True)
    v.result(process.returncode == 0)
    return Digest16(process.stdout.decode().strip())


def to_Digest32(v: Verification, digest16: Digest16) -> Digest32:
    v.status('Converting digest to base32')
    process = subprocess.run(
        ['nix', 'to-base32', '--type', 'sha256', digest16], capture_output=True)
    v.result(process.returncode == 0)
    return Digest32(process.stdout.decode().strip())


def fetch_with_nix_prefetch_url(
        v: Verification,
        url: str,
        digest: Digest16) -> str:
    v.status('Fetching %s' % url)
    process = subprocess.run(
        ['nix-prefetch-url', '--print-path', url, digest], capture_output=True)
    v.result(process.returncode == 0)
    prefetch_digest, path, empty = process.stdout.decode().split('\n')
    assert empty == ''
    v.check("Verifying nix-prefetch-url's digest",
            to_Digest16(v, Digest32(prefetch_digest)) == digest)
    v.status("Verifying file digest")
    file_digest = digest_file(path)
    v.result(file_digest == digest)
    return path


def fetch_resources(v: Verification, channel: Channel) -> None:
    for resource in ['git-revision', 'nixexprs.tar.xz']:
        fields = channel.table[resource]
        fields.absolute_url = urllib.parse.urljoin(
            channel.forwarded_url, fields.url)
        fields.file = fetch_with_nix_prefetch_url(
            v, fields.absolute_url, fields.digest)
    v.status('Verifying git commit on main page matches git commit in table')
    v.result(
        open(
            channel.table['git-revision'].file).read(999) == channel.git_revision)


def git_fetch(v: Verification, channel: Channel) -> None:
    # It would be nice if we could share the nix git cache, but as of the time
    # of writing it is transitioning from gitv2 (deprecated) to gitv3 (not ready
    # yet), and trying to straddle them both is too far into nix implementation
    # details for my comfort.  So we re-implement here half of nix.fetchGit.
    # :(

    # TODO: Consider using pyxdg to find this path.
    channel.git_cachedir = os.path.expanduser(
        '~/.cache/nix-pin-channel/git/%s' %
        digest_string(
            channel.git_repo.encode()))
    if not os.path.exists(channel.git_cachedir):
        v.status("Initializing git repo")
        process = subprocess.run(
            ['git', 'init', '--bare', channel.git_cachedir])
        v.result(process.returncode == 0)

    have_rev = False
    if hasattr(channel, 'git_revision'):
        v.status('Checking if we already have this rev:')
        process = subprocess.run(
            ['git', '-C', channel.git_cachedir, 'cat-file', '-e', channel.git_revision])
        if process.returncode == 0:
            v.status('yes')
        if process.returncode == 1:
            v.status('no')
        v.result(process.returncode == 0 or process.returncode == 1)
        have_rev = process.returncode == 0

    if not have_rev:
        v.status(
            'Fetching ref "%s" from %s' %
            (channel.git_ref, channel.git_repo))
        # We don't use --force here because we want to abort and freak out if forced
        # updates are happening.
        process = subprocess.run(['git',
                                  '-C',
                                  channel.git_cachedir,
                                  'fetch',
                                  channel.git_repo,
                                  '%s:%s' % (channel.git_ref,
                                             channel.git_ref)])
        v.result(process.returncode == 0)
        if hasattr(channel, 'git_revision'):
            v.status('Verifying that fetch retrieved this rev')
            process = subprocess.run(
                ['git', '-C', channel.git_cachedir, 'cat-file', '-e', channel.git_revision])
            v.result(process.returncode == 0)

    if not hasattr(channel, 'git_revision'):
        channel.git_revision = open(
            os.path.join(
                channel.git_cachedir,
                'refs',
                'heads',
                channel.git_ref)).read(999).strip()

    v.status('Verifying rev is an ancestor of ref')
    process = subprocess.run(['git',
                              '-C',
                              channel.git_cachedir,
                              'merge-base',
                              '--is-ancestor',
                              channel.git_revision,
                              channel.git_ref])
    v.result(process.returncode == 0)

    if hasattr(channel, 'old_git_revision'):
        v.status(
            'Verifying rev is an ancestor of previous rev %s' %
            channel.old_git_revision)
        process = subprocess.run(['git',
                                  '-C',
                                  channel.git_cachedir,
                                  'merge-base',
                                  '--is-ancestor',
                                  channel.old_git_revision,
                                  channel.git_revision])
        v.result(process.returncode == 0)


def compare_tarball_and_git(
        v: Verification,
        channel: Channel,
        channel_contents: str,
        git_contents: str) -> None:
    v.status('Comparing channel tarball with git checkout')
    match, mismatch, errors = compare(os.path.join(
        channel_contents, channel.release_name), git_contents)
    v.ok()
    v.check('%d files match' % len(match), len(match) > 0)
    v.check('%d files differ' % len(mismatch), len(mismatch) == 0)
    expected_errors = [
        '.git-revision',
        '.version-suffix',
        'nixpkgs',
        'programs.sqlite',
        'svn-revision']
    benign_errors = []
    for ee in expected_errors:
        if ee in errors:
            errors.remove(ee)
            benign_errors.append(ee)
    v.check(
        '%d unexpected incomparable files' %
        len(errors),
        len(errors) == 0)
    v.check(
        '(%d of %d expected incomparable files)' %
        (len(benign_errors),
         len(expected_errors)),
        len(benign_errors) == len(expected_errors))


def extract_tarball(v: Verification, channel: Channel, dest: str) -> None:
    v.status('Extracting tarball %s' %
             channel.table['nixexprs.tar.xz'].file)
    shutil.unpack_archive(
        channel.table['nixexprs.tar.xz'].file,
        dest)
    v.ok()


def git_checkout(v: Verification, channel: Channel, dest: str) -> None:
    v.status('Checking out corresponding git revision')
    git = subprocess.Popen(['git',
                            '-C',
                            channel.git_cachedir,
                            'archive',
                            channel.git_revision],
                           stdout=subprocess.PIPE)
    tar = subprocess.Popen(
        ['tar', 'x', '-C', dest, '-f', '-'], stdin=git.stdout)
    git.stdout.close()
    tar.wait()
    git.wait()
    v.result(git.returncode == 0 and tar.returncode == 0)


def check_channel_metadata(
        v: Verification,
        channel: Channel,
        channel_contents: str) -> None:
    v.status('Verifying git commit in channel tarball')
    v.result(
        open(
            os.path.join(
                channel_contents,
                channel.release_name,
                '.git-revision')).read(999) == channel.git_revision)

    v.status(
        'Verifying version-suffix is a suffix of release name %s:' %
        channel.release_name)
    version_suffix = open(
        os.path.join(
            channel_contents,
            channel.release_name,
            '.version-suffix')).read(999)
    v.status(version_suffix)
    v.result(channel.release_name.endswith(version_suffix))


def check_channel_contents(v: Verification, channel: Channel) -> None:
    with tempfile.TemporaryDirectory() as channel_contents, \
            tempfile.TemporaryDirectory() as git_contents:

        extract_tarball(v, channel, channel_contents)
        check_channel_metadata(v, channel, channel_contents)

        git_checkout(v, channel, git_contents)

        compare_tarball_and_git(v, channel, channel_contents, git_contents)

        v.status('Removing temporary directories')
    v.ok()


def pin_channel(v: Verification, channel: Channel) -> None:
    fetch(v, channel)
    parse_channel(v, channel)
    fetch_resources(v, channel)
    git_fetch(v, channel)
    check_channel_contents(v, channel)


def make_channel(conf: configparser.SectionProxy) -> Channel:
    channel = Channel(**dict(conf.items()))
    if hasattr(channel, 'git_revision'):
        channel.old_git_revision = channel.git_revision
        del channel.git_revision
    return channel


def pin(args: argparse.Namespace) -> None:
    v = Verification()
    config = configparser.ConfigParser()
    config.read_file(open(args.channels_file), args.channels_file)
    for section in config.sections():
        channel = make_channel(config[section])
        if 'channel_url' in config[section]:
            pin_channel(v, channel)
            config[section]['name'] = channel.release_name
            config[section]['tarball_url'] = channel.table['nixexprs.tar.xz'].absolute_url
            config[section]['tarball_sha256'] = channel.table['nixexprs.tar.xz'].digest
        else:
            git_fetch(v, channel)
        config[section]['git_revision'] = channel.git_revision

    with open(args.channels_file, 'w') as configfile:
        config.write(configfile)


def main() -> None:
    parser = argparse.ArgumentParser(prog='pinch')
    subparsers = parser.add_subparsers(dest='mode', required=True)
    parser_pin = subparsers.add_parser('pin')
    parser_pin.add_argument('channels_file', type=str)
    parser_pin.set_defaults(func=pin)
    args = parser.parse_args()
    args.func(args)


main()