# Copyright (C) 2018 Avatao.com Innovative Learning Kft.
# All Rights Reserved. See LICENSE file for details.

import re
from subprocess import run
from getpass import getuser
from os.path import isdir
from datetime import datetime


class SnapshotProvider:
    def __init__(self, directory, git_dir):
        author = f'{getuser()} via TFW {self.__class__.__name__}'
        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._check_environment()
        self.__last_valid_branch = self._branch
        self._init_repo_if_needed()

    def _check_environment(self):
        if not isdir(self.gitenv['GIT_DIR']) or not isdir(self.gitenv['GIT_WORK_TREE']):
            raise EnvironmentError('Directories "directory" and "git_dir" must exist!')
        if self._head_detached:
            raise EnvironmentError(f'{self.__class__.__name__} cannot init from detached HEAD state!')

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

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

    def take_snapshot(self):
        if self._head_detached:
            self._checkout_new_branch_from_head()
        self._run((
            'git', 'add',
            '-A'
        ))
        self._run((
            'git', 'commit',
            '-m', 'Snapshot'
        ))

    def _checkout_new_branch_from_head(self):
        head_hash = self._get_head_hash()
        self._run((
            'git', 'branch',
            head_hash
        ))
        self._checkout(head_hash)

    def _get_head_hash(self):
        return self._get_stdout((
            'git', 'rev-parse',
            'HEAD'
        ))

    def restore_snapshot(self, date):
        commit = self._get_commit_from_timestamp(date)
        self._checkout(commit)

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

    def _get_commit_from_timestamp(self, date):
        return self._get_stdout((
            'git', 'rev-list',
            '--date=iso',
            '-n', '1',
            f'--before="{date.isoformat()}"',
            self._last_valid_branch
        ))

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

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

    @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._branch

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

    @property
    def _last_valid_branch(self):
        self._update_last_valid_branch()
        return self.__last_valid_branch

    def _update_last_valid_branch(self):
        if not self._head_detached:
            self.__last_valid_branch = self._branch

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

    @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': datetime.fromisoformat(timestamp)
            })

        return commits