"""
Classes to cache and read specific items from github issues in a uniform way
"""

from functools import partial as Partial
import datetime
import time
import shelve

# Requires PyGithub version >= 1.13 for access to raw_data attribute
import github

from six.moves import xrange


# Needed to not confuse cached 'None' objects
class Nothing(object):
    raw_data = None


# Needed to signal list cache, not github object
class SearchResults(object):

    def __init__(self, *stuff):
        self.raw_data = stuff


class GithubCache(object):

    """
    Auto-refreshing github.GithubObject.GithubObject from dict
    """

    cache_hits = 0
    cache_misses = 0

    cache_lifetimes = {
        'default': datetime.timedelta(hours=2),
        github.GitCommit.GitCommit: datetime.timedelta(days=30),
        github.NamedUser.NamedUser: datetime.timedelta(days=30),
        github.Commit.Commit: datetime.timedelta(days=30),
        github.Issue.Issue: datetime.timedelta(minutes=30),
        github.PullRequest.PullRequest: datetime.timedelta(hours=1),
        # Special case for github.Issue.Issue
        'closed': datetime.timedelta(days=30),
        SearchResults: datetime.timedelta(minutes=10),
        github.NamedUser.NamedUser: datetime.timedelta(hours=2),
        github.GitAuthor.GitAuthor: datetime.timedelta(days=9999),
        'total_issues': datetime.timedelta(days=9999)
    }

    def __init__(self, github_obj, cache_get_partial, cache_set_partial,
                 cache_del_partial, pre_fetch_partial, fetch_partial):
        self.github = github_obj
        self.cache_get = cache_get_partial  # Returns native dict
        self.cache_set = cache_set_partial  # called with value=dict
        self.cache_del = cache_del_partial
        self.pre_fetch = pre_fetch_partial  # called with nothing
        self.fetch = fetch_partial  # Returns github.GithubObject.GithubObject

    def __call__(self):
        """
        Retrieve instance from fresh or cached data
        """
        # microseconds aren't useful when fetch takes ~1 second
        now = datetime.datetime.utcnow()
        now = datetime.datetime(year=now.year, month=now.month,
                                day=now.day, hour=now.hour,
                                minute=now.minute, second=0, microsecond=0)
        try:
            data = self.cached_data()
            if data['expires'] < now:
                raise KeyError  # refresh cache
            self.cache_hits += 1
        except KeyError:
            data = self.fetched_data(now)
            self.cache_set(value=data)
            self.cache_misses += 1
        # Any exceptions thrown during conversion should purge cache entry
        try:
            # Format data for consumption
            if data['klass'] == github.PaginatedList.PaginatedList:
                inside_klass = data['inside_klass']
                result = []
                for item in data['raw_data']:
                    result.append(
                        self.github.create_from_raw_data(inside_klass,
                                                         item))
                return result
            elif data['klass'] == Nothing:
                return None  # it's a None object
            elif data['klass'] == SearchResults:
                return data['raw_data']  # just the contents
            else:
                return self.github.create_from_raw_data(data['klass'],
                                                        data['raw_data'])
        except Exception:
            try:
                self.cache_del()
            except KeyError:
                pass  # doesn't exist in cache, ignore
            raise  # original exception

    @staticmethod
    def format_data(klass, expires, raw_data, inside_klass=None):
        """
        Enforce uniform data format for fetched data
        """
        if inside_klass is None:
            return {'klass': klass,
                    'fetched': datetime.datetime.utcnow(),
                    'expires': expires,
                    'raw_data': raw_data}
        else:
            return {'klass': klass,
                    'inside_klass': inside_klass,
                    'fetched': datetime.datetime.utcnow(),
                    'expires': expires,
                    'raw_data': raw_data}

    def fetched_data(self, now):
        """
        Return dictionary containing freshly fetched values
        """
        try:
            if callable(self.pre_fetch):
                self.pre_fetch()
            fetched_obj = self.fetch()
        except github.GithubException as detail:
            if detail.status == 404:
                raise KeyError('Github item not-found error while calling %s '
                               'with args=%s and dargs=%s' % (self.fetch.func,
                                                              self.fetch.args,
                                                              self.fetch.keywords))
            else:
                raise
        if fetched_obj is None:
            fetched_obj = Nothing()
        klass = fetched_obj.__class__
        # github.PaginatedList.PaginatedList need special handling
        if isinstance(fetched_obj, github.PaginatedList.PaginatedList):
            raw_data = [item.raw_data for item in fetched_obj]
            inside_klass = fetched_obj[0].__class__
            expires = now + self.cache_lifetimes.get(inside_klass,
                                                     self.cache_lifetimes['default'])
            return self.__class__.format_data(klass,
                                              now + self.cache_lifetimes.get(
                                                  inside_klass,
                                                  self.cache_lifetimes[
                                                      'default']),
                                              raw_data, inside_klass)
        else:
            expires = now + self.cache_lifetimes.get(klass,
                                                     # else default
                                                     self.cache_lifetimes['default'])
            # closed issues/pull requests don't change much
            if hasattr(fetched_obj, 'closed_at'):
                if fetched_obj.closed_at is not None:
                    expires = now + self.cache_lifetimes['closed']
            return self.__class__.format_data(klass, expires,
                                              fetched_obj.raw_data)

    def cached_data(self):
        """
        Return dictionary containing cached values or raise KeyError
        """
        try:
            return self.cache_get()  # maybe raise KeyError or TypeError
        except KeyError:
            raise
        except Exception:
            # Try to delete the entry
            self.cache_del()
            raise


class GithubIssuesBase(list):

    """
    Base class for cached list of github issues
    """

    # Force static pickle protocol version
    protocol = 2

    # Class to use for cache management
    cache_class = GithubCache

    def __init__(self, github_obj, repo_full_name, cache_filename):
        """
        Initialize cache and reference github repository issues
        """

        self.github = github_obj
        self.repo_full_name = repo_full_name
        self.shelf = shelve.open(filename=cache_filename,
                                 protocol=self.protocol,
                                 writeback=True)

        # Avoid exceeding rate-limit per hour
        requests = self.github.rate_limiting[1]  # requests per hour
        period = 60.0 * 60.0  # one hour in seconds
        sleeptime = period / requests
        self.pre_fetch_partial = Partial(time.sleep, sleeptime)
        # self.pre_fetch_partial = None # cheat-mode enable (no delays)

        repo_cache_key = 'repo_%s' % self.repo_full_name
        # get_repo called same way throughout instance life
        cache_get_partial = Partial(self.shelf.__getitem__, repo_cache_key)
        cache_set_partial = Partial(self.shelf.__setitem__, repo_cache_key)
        cache_del_partial = Partial(self.shelf.__delitem__, repo_cache_key)
        fetch_partial = Partial(self.github.get_repo,
                                self.repo_full_name)
        # Callable instance retrieves cached or fetched value for key
        self.get_repo = self.cache_class(self.github,
                                         cache_get_partial,
                                         cache_set_partial,
                                         cache_del_partial,
                                         self.pre_fetch_partial,
                                         fetch_partial)
        super(GithubIssuesBase, self).__init__()

    def __del__(self):
        """
        Make sure cache is saved
        """
        try:
            self.shelf.close()
        except AttributeError:
            pass  # Open must have failed

    def __len__(self):
        """
        Binary search through issue numbers until largest identified
        """
        increment = 1000
        last_issue = 1
        if not self.__contains__(last_issue):
            return 0  # no issues
        while increment > 0:
            while self.__contains__(last_issue):
                last_issue += increment
            # Fall back to prior one
            last_issue -= increment
            # Chop increment in half
            increment /= 2
        return last_issue

    def __contains__(self, key):
        try:
            # Must call this classes method specifically
            GithubIssuesBase.__getitem__(self, key)
        except KeyError:
            return False
        return True

    def __iter__(self):
        for key in list(self.keys()):
            yield self[key]

    def __setitem__(self, key, value):
        raise KeyError("Read only mapping while trying to set %s to %s"
                       % (str(key), str(value)))

    def __delitem__(self, key):
        raise KeyError(
            "Read only mapping while trying to delete %s" % str(key))

    def __getitem__(self, key):
        """
        Return a standardized dict of github issue unless NoEnumerate=True
        """
        repo = self.get_repo()
        # Enforce uniform key string
        cache_key = self.get_issue_cache_key(key)
        fetch_partial = Partial(repo.get_issue, int(key))
        item = self.get_gh_obj(cache_key, fetch_partial)
        # No exception raised, update cache on disk
        self.shelf.sync()
        return item

    def get_issue_cache_key(self, number):
        return 'repo_%s_issue_%s' % (self.repo_full_name, str(int(number)))

    def has_key(self, key):
        return self.__contains__(key)

    def items(self):
        # Iterator comprehension
        return (self[key] for key in list(self.keys()))

    def keys(self):
        # Iterators are simply better
        return xrange(1, self.__len__() + 1)

    def values(self):
        # Iterator comprehension
        return (value for (key, value) in list(self.items()))


class GithubIssues(GithubIssuesBase, object):

    """
    Read-only List-like interface to cached github issues in standardized format
    """

    # Marshal callables for key to github.Issue.Issue value
    marshal_map = {
        'number': lambda gh_obj: getattr(gh_obj, 'number'),
        'summary': lambda gh_obj: getattr(gh_obj, 'title'),
        'description': lambda gh_obj: getattr(gh_obj, 'body'),
        'modified': lambda gh_obj: getattr(gh_obj, 'updated_at'),
        'commits': NotImplementedError,  # setup in __init__
        'opened': lambda gh_obj: getattr(gh_obj, 'created_at'),
        'closed': lambda gh_obj: getattr(gh_obj, 'closed_at'),
        'assigned': lambda gh_obj: getattr(gh_obj, 'assignee'),
        'author': lambda gh_obj: getattr(gh_obj, 'user').login,
        'commit_authors': NotImplementedError,  # setup in __init__
        'comments': lambda gh_obj: getattr(gh_obj, 'comments'),
        'comment_authors': NotImplementedError,  # setup in __init__
        'labels': lambda gh_obj: [label.name for label in gh_obj.labels],
        'url': lambda gh_obj: getattr(gh_obj, 'html_url'),
        'github_issue': lambda gh_obj: gh_obj
    }

    # Storage for property values
    _cache_hits = 0   # Tracks temporary cache instances
    _cache_misses = 0  # Tracks temporary cache instances

    def __init__(self, github_obj, repo_full_name):
        """
        Initialize cache and reference github repository issues
        """
        cache_filename = self.__class__.__name__ + '.cache'
        super(GithubIssues, self).__init__(github_obj,
                                           repo_full_name,
                                           cache_filename)
        # These marshal functions require state
        self.marshal_map['commits'] = self.gh_pr_commits
        self.marshal_map['commit_authors'] = self.gh_pr_commit_authors
        self.marshal_map['comment_authors'] = self.gh_issue_comment_authors

    def __del__(self):
        self.vacuum()
        super(GithubIssues, self).__del__()

    def vacuum(self):
        """Vacuum up all expired entries"""
        # Can't modify list while iterating
        keys_to_del = []
        now = datetime.datetime.utcnow()
        for key, value in list(self.shelf.items()):
            # no need to be precise
            if value['expires'] <= now:
                keys_to_del.append(key)
        for key in keys_to_del:
            del self.shelf[key]

    @property
    def cache_hits(self):
        return self.get_repo.cache_hits + self._cache_hits

    @property
    def cache_misses(self):
        return self.get_repo.cache_misses + self._cache_misses

    def __getitem__(self, key):
        """
        Return a standardized dict of github issue
        """
        item = self.marshal_gh_obj(super(GithubIssues, self).__getitem__(key))
        self.shelf.sync()
        return item

    def __len__(self):
        """
        Return cached number of issues
        """
        cache_key = 'repo_%s_total_issues' % self.repo_full_name
        # seconds aren't useful when fetch takes > 1 minute
        now = datetime.datetime.utcnow()
        now = datetime.datetime(year=now.year, month=now.month,
                                day=now.day, hour=now.hour,
                                minute=now.minute, second=0, microsecond=0)
        # Easier to do custom caching behavior here than fuss with GithubCache
        try:
            cache_data = self.shelf.__getitem__(cache_key)
            if cache_data['expires'] < now:
                raise KeyError
            # Bypass search_result caching used in self.search()
            searchresult = self.make_search_results(
                {'since': cache_data['since']})
            # about to change the number
            cache_data['since'] = now
            # total equal to old count plus new count since then
            cache_data['raw_data'] += len(searchresult.raw_data)
        except KeyError:
            cache_data = {}
            # doesn't expire ever
            cache_data['expires'] = now + GithubCache.cache_lifetimes[
                'total_issues']
            cache_data['since'] = now
            # This will take a while if issue cache is stale
            cache_data['raw_data'] = super(GithubIssues, self).__len__()
        self.shelf.__setitem__(cache_key, cache_data)
        return cache_data['raw_data']

    def get_gh_obj(self, cache_key, fetch_partial):
        """
        Helper to get object possibly from cache and update counters
        """
        cache_get_partial = Partial(self.shelf.__getitem__,
                                    cache_key)
        cache_set_partial = Partial(self.shelf.__setitem__,
                                    cache_key)
        cache_del_partial = Partial(self.shelf.__delitem__,
                                    cache_key)
        # Callable instance could change every time
        get_obj = GithubCache(self.github,
                              cache_get_partial,
                              cache_set_partial,
                              cache_del_partial,
                              self.pre_fetch_partial,
                              fetch_partial)
        result = get_obj()
        self._cache_hits += get_obj.cache_hits
        self._cache_misses += get_obj.cache_misses
        return result  # DOES NOT SYNC DATA!

    def search(self, criteria):
        """
        Return a list of issue-numbers that match a search criteria.

        :param criteria: Dictionary of search terms
            state - str - 'open', 'closed'
            assignee - list of str (login), "none" or "*"
            mentioned - str (login)
            labels - list of str (label name)
            sort - str - 'created', 'updated', 'comments'
            direction - str - 'asc', 'desc'
            since - datetime.datetime
        """
        valid_criteria = {}
        # use search dictionary to form hash for cached results
        search_cache_key = 'issue_search'
        # Validate & transform criteria
        if 'state' in criteria:
            state = str(criteria['state'])
            if state not in ('open', 'closed'):
                raise ValueError("'state' criteria must be 'open' or 'closed'")
            valid_criteria['state'] = state
            search_cache_key = '%s_%s' % (search_cache_key, state)

        if 'assignee' in criteria:
            assignee = str(criteria['assignee'])
            search_cache_key = '%s_%s' % (search_cache_key, assignee)
            if assignee in ('none', '*'):
                valid_criteria['assignee'] = assignee
            else:
                # returns github.NamedUser.NamedUser
                valid_criteria['assignee'] = self.get_gh_user(assignee)

        if 'mentioned' in criteria:
            mentioned = str(criteria['assignee'])
            search_cache_key = '%s_%s' % (search_cache_key, mentioned)
            if mentioned in ('none', '*'):
                valid_criteria['mentioned'] = mentioned
            else:
                # returns github.NamedUser.NamedUser
                valid_criteria['mentioned'] = self.get_gh_user(mentioned)

        if 'labels' in criteria:
            labels = criteria['labels']
            if not isinstance(labels, list):
                raise ValueError("'lables' criteria must be a list")
            valid_criteria['labels'] = []
            for name in labels:
                search_cache_key = '%s_%s' % (search_cache_key, labels)
                valid_criteria['labels'].append(self.get_gh_label(str(name)))

        if 'sort' in criteria:
            sort = str(criteria['sort'])
            if sort not in ('created', 'updated', 'comments'):
                raise ValueError("'sort' criteria must be 'created', 'updated'"
                                 ", 'comments'")
            valid_criteria['sort'] = sort
            search_cache_key = '%s_%s' % (search_cache_key, sort)

        if 'direction' in criteria:
            direction = str(criteria['direction'])
            if direction not in ('asc', 'desc'):
                raise ValueError("'direction' criteria must be 'asc', 'desc'")
            valid_criteria['direction'] = direction
            search_cache_key = '%s_%s' % (search_cache_key, direction)

        if 'since' in criteria:
            since = criteria['since']
            if not isinstance(since, datetime.datetime):
                raise ValueError("'since' criteria must be a "
                                 "datetime.datetime")
            # second and milisecond not useful to search or cache
            since = datetime.datetime(year=since.year,
                                      month=since.month,
                                      day=since.day,
                                      hour=since.hour,
                                      minute=since.minute,
                                      second=0,
                                      microsecond=0)
            search_cache_key = '%s_%s' % (search_cache_key, since.isoformat())
            valid_criteria['since'] = since

        # Do not perform search operation unless no cached results
        # or cached results have expired
        fetch_partial = Partial(self.make_search_results, valid_criteria)
        # This could take an arbitrarily LONG time
        return self.get_gh_obj(search_cache_key, fetch_partial)

    def make_search_results(self, valid_criteria):
        """
        Return a SearchResults instance from issue numbers found by search
        """
        repo = self.get_repo()
        result = repo.get_issues(**valid_criteria)
        return SearchResults(*[issue.number for issue in result])

    def clean_cache_entry(self, key):
        """
        Remove an entry from cache, ignoring any KeyErrors
        """
        try:
            del self.shelf[key]
        except KeyError:
            pass

    def get_gh_user(self, login):
        cache_key = 'github_user_%s' % login
        fetch_partial = Partial(self.github.get_user, login)
        try:
            return self.get_gh_obj(cache_key, fetch_partial)
        except KeyError:
            raise ValueError('login %s is not a valid github user' % login)

    def get_gh_label(self, name):
        repo = self.get_repo()
        cache_key = str('repo_%s_label_%s' % (self.repo_full_name, name))
        fetch_partial = Partial(repo.get_label, name)
        try:
            return self.get_gh_obj(cache_key, fetch_partial)
        except KeyError:
            raise ValueError('label %s is not valid for repo %s' % (name,
                                                                    self.repo_full_name))

    def marshal_gh_obj(self, gh_issue):
        """
        Translate a github issue object into dictionary w/ fixed keys
        """
        mkeys = list(self.marshal_map.keys())
        return dict([(key, self.marshal_map[key](gh_issue)) for key in mkeys])

    @staticmethod
    def gh_issue_is_pull(gh_issue):
        """
        Return True/False if gh_issue is a pull request or not
        """
        pullreq = gh_issue.pull_request
        if pullreq is not None:
            if (pullreq.diff_url is None and
                pullreq.html_url is None and
                    pullreq.patch_url is None):
                return False
        else:
            return False
        # pullreq not None but pullreq attributes are not None
        return True

    # marshal_map method
    def gh_issue_comment_authors(self, gh_issue):
        """
        Retrieve a list of comment author e-mail addresses
        """
        if gh_issue.comments > 0:
            num = gh_issue.number
            cache_key = ('repo_%s_issue_%s_comments'
                         % (self.repo_full_name, num))
            fetch_partial = Partial(gh_issue.get_comments)
            authors = set()
            for comment in self.get_gh_obj(cache_key, fetch_partial):
                # Referencing user attribute requires a request, so cache it
                user_cache_key = cache_key + '_%s_user' % comment.id
                user_fetch_partial = Partial(getattr, comment, 'user')
                try:
                    user = self.get_gh_obj(user_cache_key, user_fetch_partial)
                except Exception:
                    # Also clean up comments cache
                    self.clean_cache_entry(cache_key)
                    raise  # original exception
                authors.add(user.email)
            return authors
        else:
            return None

    # marshal_map method
    def gh_pr_commit_authors(self, gh_issue):
        """
        Return list of commit author e-mail addresses for a pull-request
        """

        if GithubIssues.gh_issue_is_pull(gh_issue):
            num = gh_issue.number
            repo = self.get_repo()
            cache_key = 'repo_%s_pull_%s' % (self.repo_full_name, str(num))
            fetch_partial = Partial(repo.get_pull, num)
            pull = self.get_gh_obj(cache_key, fetch_partial)
            if pull.commits is None or pull.commits < 1:
                return None  # No commits == no commit authors

            cache_key = 'repo_%s_pull_%s_commits' % (self.repo_full_name,
                                                     str(num))
            fetch_partial = Partial(pull.get_commits)
            authors = set()
            for commit in self.get_gh_obj(cache_key, fetch_partial):
                # Referencing commit author requires a request, cache it.
                author_cache_key = cache_key + '_%s_author' % str(commit.sha)
                author_fetch_partial = Partial(getattr, commit, 'author')
                try:
                    author_obj = self.get_gh_obj(author_cache_key,
                                                 author_fetch_partial)
                except Exception:
                    # clean up commit list cache entry also
                    self.clean_cache_entry(cache_key)
                    raise  # original exception
                # Retrieve e-mail from git commit object
                if author_obj is None:
                    # Referencing git commit requires a request, cache it
                    gitcommit_cache_key = (cache_key + '_%s_gitcommit'
                                                       % str(commit.sha))
                    gitcommit_fetch_partial = Partial(getattr, commit,
                                                      'commit')  # git commit
                    try:
                        gitcommit = self.get_gh_obj(gitcommit_cache_key,
                                                    gitcommit_fetch_partial)
                    except Exception:
                        # Need to clean commit and gitcommit entries
                        self.clean_cache_entry(cache_key)
                        self.clean_cache_entry(gitcommit_cache_key)
                        raise
                    authors.add(gitcommit.author.email)
                else:  # Author is a github user
                    authors.add(author_obj.login)
            return authors
        return None  # not a pull request

    # marshal_map method
    def gh_pr_commits(self, gh_issue):
        """
        Retrieves the number of commits on a pull-request, None if not a pull.
        """
        if GithubIssues.gh_issue_is_pull(gh_issue):
            num = gh_issue.number
            repo = self.get_repo()
            cache_key = 'repo_%s_pull_%s' % (self.repo_full_name, str(num))
            fetch_partial = Partial(repo.get_pull, num)
            pull = self.get_gh_obj(cache_key, fetch_partial)
            return pull.commits
        return None  # not a pull request


class MutateError(KeyError):

    def __init__(self, key, number):
        super(MutateError, self).__init__("Unable to modify %s on issue %d"
                                          % (str(key), number))


class MutableIssue(dict):

    """Allow modification of some issue values"""

    def __init__(self, github_issues, issue_number):
        if not isinstance(github_issues, GithubIssues):
            raise ValueError("github_issues %s is not a GithubIssues, it's a %s"
                             % (str(github_issues), str(type(github_issues))))
        # make sure issue_number is valid and cached
        junk = github_issues[issue_number]
        del junk
        # Private for private _github_issue property access
        self._github_issues = github_issues
        self._issue_number = issue_number
        super(MutableIssue, self).__init__()

    @property
    def _github_issue(self):
        return self._github_issues[self._issue_number]

    @property
    def _issue_cache_key(self):
        return self.get_issue_cache_key(self._issue_number)

    def _setdelitem(self, opr, key, value):
        if key not in list(self._github_issues.marshal_map.keys()):
            raise MutateError(key, self._issue_number)
        methodname = '%s_%s' % (opr, key)
        if callable(getattr(self, methodname)):
            method = getattr(self, methodname)
            if opr == 'set':
                method(value)
            else:
                method()
        else:
            raise MutateError(key, self._issue_number)

    def __getitem__(self, key):
        # Guarantees fresh/cached data for every call
        return self._github_issue[key]

    def __setitem__(self, key, value):
        self._setdelitem('set', key, value)

    def __delitem__(self, key):
        self._setdelitem('del', key, None)

    def set_labels(self, value):
        """
        Merge list of new lables into existing label set
        """
        new_labels = set(value)
        old_labels = set(self._github_issue['labels'])
        change_list = list(new_labels | old_labels)
        get_gh_label = self._github_issues.get_gh_label  # save typing
        # Raise exception if any label name is bad
        gh_labels = [get_gh_label(label) for label in change_list]
        # Access PyGithub object to change labels
        self._github_issue['github_issue'].set_labels(*gh_labels)
        # Force retrieval of changed item
        self._github_issues.clean_cache_entry(self._issue_cache_key)

    def del_labels(self):
        """
        Remove all lbels from an issue
        """
        self._github_issue['github_issue'].delete_labels()
        # Force retrieval of changed item
        self._github_issues.clean_cache_entry(self._issue_cache_key)

    # TODO: Write get_*(), set_*(), del_*() for other dictionary keys