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):
    digest: Digest16
    file: str
    size: int
    url: str


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


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.url, timeout=10)
    channel.channel_html = request.read()
    channel.forwarded_url = request.geturl()
    v.result(request.status == 200)
    v.check('Got forwarded', 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_commit = git_commit_node.firstChild.nodeValue
    v.status(channel.git_commit)
    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]
        url = urllib.parse.urljoin(channel.forwarded_url, fields.url)
        fields.file = fetch_with_nix_prefetch_url(v, 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_commit)


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.url.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)

    v.status('Checking if we already have this rev:')
    process = subprocess.run(
        ['git', '-C', channel.git_cachedir, 'cat-file', '-e', channel.git_commit])
    if process.returncode == 0:
        v.status('yes')
    if process.returncode == 1:
        v.status('no')
    v.result(process.returncode == 0 or process.returncode == 1)
    if process.returncode == 1:
        v.status('Fetching ref "%s"' % channel.git_ref)
        # 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)
        v.status('Verifying that fetch retrieved this rev')
        process = subprocess.run(
            ['git', '-C', channel.git_cachedir, 'cat-file', '-e', channel.git_commit])
        v.result(process.returncode == 0)

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


def check_channel_contents(v: Verification, channel: Channel) -> None:
    with tempfile.TemporaryDirectory() as channel_contents, \
            tempfile.TemporaryDirectory() as git_contents:
        v.status('Extracting tarball %s' %
                 channel.table['nixexprs.tar.xz'].file)
        shutil.unpack_archive(
            channel.table['nixexprs.tar.xz'].file,
            channel_contents)
        v.ok()
        v.status('Checking out corresponding git revision')
        git = subprocess.Popen(['git',
                                '-C',
                                channel.git_cachedir,
                                'archive',
                                channel.git_commit],
                               stdout=subprocess.PIPE)
        tar = subprocess.Popen(
            ['tar', 'x', '-C', git_contents, '-f', '-'], stdin=git.stdout)
        git.stdout.close()
        tar.wait()
        git.wait()
        v.result(git.returncode == 0 and tar.returncode == 0)
        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))
        v.status('Removing temporary directories')
    v.ok()


def main() -> None:
    v = Verification()
    channel = Channel(url='https://channels.nixos.org/nixos-20.03',
                      git_repo='https://github.com/NixOS/nixpkgs.git',
                      git_ref='nixos-20.03')
    fetch(v, channel)
    parse_channel(v, channel)
    fetch_resources(v, channel)
    git_fetch(v, channel)
    check_channel_contents(v, channel)
    print(channel)


main()