import re
from subprocess import run, CalledProcessError, PIPE
from getpass import getuser
from os.path import isdir
from os.path import join as joinpath
from uuid import uuid4

from dateutil import parser as dateparser


class SnapshotProvider:
    def __init__(self, directory, git_dir, exclude_unix_patterns=None):
        self._classname = self.__class__.__name__
        author = f'{getuser()} via TFW {self._classname}'
        self.gitenv = {
            'GIT_DIR': git_dir,
            'GIT_WORK_TREE': directory,
            'GIT_AUTHOR_NAME': author,
            'GIT_AUTHOR_EMAIL': '',
            'GIT_COMMITTER_NAME': author,
            'GIT_COMMITTER_EMAIL': '',
            'GIT_PAGER': 'cat'
        }

        self._init_repo()
        self.__last_valid_branch = self._branch
        if exclude_unix_patterns:
            self.exclude = exclude_unix_patterns

    def _init_repo(self):
        self._check_environment()

        if not self._repo_is_initialized:
            self._run(('git', 'init'))

        if self._number_of_commits == 0:
            try:
                self._snapshot()
            except CalledProcessError:
                raise EnvironmentError(f'{self._classname} cannot init on empty directories!')

        self._check_head_not_detached()

    def _check_environment(self):
        if not isdir(self.gitenv['GIT_DIR']) or not isdir(self.gitenv['GIT_WORK_TREE']):
            raise EnvironmentError(f'{self._classname}: "directory" and "git_dir" must exist!')

    @property
    def _repo_is_initialized(self):
        return self._run(
            ('git', 'status'),
            check=False
        ).returncode == 0

    @property
    def _number_of_commits(self):
        return int(
            self._get_stdout((
                'git', 'rev-list',
                '--all',
                '--count'
            ))
        )

    def _snapshot(self):
        self._run((
            'git', 'add',
            '-A'
        ))
        try:
            self._get_stdout((
                'git', 'commit',
                '-m', 'Snapshot'
            ))
        except CalledProcessError as err:
            if b'nothing to commit, working tree clean' not in err.output:
                raise

    def _check_head_not_detached(self):
        if self._head_detached:
            raise EnvironmentError(f'{self._classname} cannot init from detached HEAD state!')

    @property
    def _head_detached(self):
        return self._branch == 'HEAD'

    @property
    def _branch(self):
        return self._get_stdout((
            'git', 'rev-parse',
            '--abbrev-ref', 'HEAD'
        ))

    def _get_stdout(self, *args, **kwargs):
        kwargs['stdout'] = PIPE
        kwargs['stderr'] = PIPE
        stdout_bytes = self._run(*args, **kwargs).stdout
        return stdout_bytes.decode().rstrip('\n')

    def _run(self, *args, **kwargs):
        if 'check' not in kwargs:
            kwargs['check'] = True
        if 'env' not in kwargs:
            kwargs['env'] = self.gitenv
        return run(*args, **kwargs)

    @property
    def exclude(self):
        with open(self._exclude_path, 'r') as ofile:
            return ofile.read()

    @exclude.setter
    def exclude(self, exclude_patterns):
        with open(self._exclude_path, 'w') as ifile:
            ifile.write('\n'.join(exclude_patterns))

    @property
    def _exclude_path(self):
        return joinpath(
            self.gitenv['GIT_DIR'],
            'info',
            'exclude'
        )

    def take_snapshot(self):
        if self._head_detached:
            self._checkout_new_branch_from_head()
        self._snapshot()

    def _checkout_new_branch_from_head(self):
        branch_name = str(uuid4())
        self._run((
            'git', 'branch',
            branch_name
        ))
        self._checkout(branch_name)

    def _checkout(self, what):
        self._run((
            'git', 'checkout',
            what
        ))

    def restore_snapshot(self, date):
        commit = self._get_commit_from_timestamp(date)
        branch = self._last_valid_branch
        if commit == self._latest_commit_on_branch(branch):
            commit = branch
        self._checkout(commit)

    def _get_commit_from_timestamp(self, date):
        commit = self._get_stdout((
            'git', 'rev-list',
            '--date=iso',
            '-n', '1',
            f'--before="{date.isoformat()}"',
            self._last_valid_branch
        ))
        if not commit:
            commit = self._get_oldest_parent_of_head()
        return commit

    def _get_oldest_parent_of_head(self):
        return self._get_stdout((
            'git',
            'rev-list',
            '--max-parents=0',
            'HEAD'
        ))

    @property
    def _last_valid_branch(self):
        if not self._head_detached:
            self.__last_valid_branch = self._branch
        return self.__last_valid_branch

    def _latest_commit_on_branch(self, branch):
        return self._get_stdout((
            'git', 'log',
            '-n', '1',
            '--pretty=format:%H',
            branch
        ))

    @property
    def all_timelines(self):
        return self._branches

    @property
    def _branches(self):
        git_branch_output = self._get_stdout(('git', 'branch'))
        regex_pattern = re.compile(r'(?:[^\S\n]|[*])')  # matches '*' and non-newline whitespace chars
        return re.sub(regex_pattern, '', git_branch_output).splitlines()

    @property
    def timeline(self):
        return self._last_valid_branch

    @timeline.setter
    def timeline(self, value):
        self._checkout(value)

    @property
    def snapshots(self):
        return self._pretty_log_branch()

    def _pretty_log_branch(self):
        git_log_output = self._get_stdout((
            'git', 'log',
            '--pretty=%H@%aI'
        ))

        commits = []
        for line in git_log_output.splitlines():
            commit_hash, timestamp = line.split('@')
            commits.append({
                'hash': commit_hash,
                'timestamp': dateparser.parse(timestamp)
            })

        return commits