"""
Loader mechanism for caching data, with data expiration, etc.

.. versionadded:: 2016.11.0
"""

import datetime
import logging
import time
from collections import OrderedDict

import salt.config
import salt.loader
import salt.syspaths
from salt.exceptions import SaltCacheError
from salt.utils.decorators import cached_property

log = logging.getLogger(__name__)


def factory(opts, **kwargs):
    """
    Creates and returns the cache class.
    If memory caching is enabled by opts MemCache class will be instantiated.
    If not Cache class will be returned.
    """
    if opts.get("memcache_expire_seconds", 0):
        cls = MemCache
    else:
        cls = Cache
    return cls(opts, **kwargs)


class Cache:
    """
    Base caching object providing access to the modular cache subsystem.

    Related configuration options:

    :param cache:
        The name of the cache driver to use. This is the name of the python
        module of the `salt.cache` package. Default is `localfs`.

    Terminology:

    Salt cache subsystem is organized as a tree with nodes and leafs like a
    filesystem. Cache consists of banks. Each bank can contain a number of
    keys. Each key can contain a dict or any other object serializable with
    `salt.payload`. I.e. any data object in the cache can be
    addressed by the path to the bank and the key name:
        bank: 'minions/alpha'
        key:  'data'

    Bank names should be formatted in a way that can be used as a
    directory structure. If slashes are included in the name, then they
    refer to a nested structure.

    Key name is a string identifier of a data container (like a file inside a
    directory) which will hold the data.
    """

    def __init__(self, opts, cachedir=None, **kwargs):
        self.opts = opts

        if kwargs.get("driver"):
            self.driver = kwargs["driver"]
        else:
            self.driver = opts.get("cache", salt.config.DEFAULT_MASTER_OPTS["cache"])

        self.cachedir = kwargs["cachedir"] = cachedir or opts.get(
            "cachedir", salt.syspaths.CACHE_DIR
        )
        self._modules = None
        self._kwargs = kwargs

    @cached_property
    def modules(self):
        return salt.loader.cache(self.opts)

    @cached_property
    def kwargs(self):
        try:
            return self.modules[f"{self.driver}.init_kwargs"](self._kwargs)
        except KeyError:
            return {}

    def cache(self, bank, key, fun, loop_fun=None, **kwargs):
        """
        Check cache for the data. If it is there, check to see if it needs to
        be refreshed.

        If the data is not there, or it needs to be refreshed, then call the
        callback function (``fun``) with any given ``**kwargs``.

        In some cases, the callback function returns a list of objects which
        need to be processed by a second function. If that is the case, then
        the second function is passed in as ``loop_fun``. Each item in the
        return list from the first function will be the only argument for the
        second function.
        """
        expire_seconds = kwargs.get("expire", 86400)  # 1 day

        updated = self.updated(bank, key)
        update_cache = False
        if updated is None:
            update_cache = True
        else:
            if int(time.time()) - updated > expire_seconds:
                update_cache = True

        data = self.fetch(bank, key)

        if not data or update_cache is True:
            if loop_fun is not None:
                data = []
                items = fun(**kwargs)
                for item in items:
                    data.append(loop_fun(item))
            else:
                data = fun(**kwargs)
            self.store(bank, key, data)

        return data

    def store(self, bank, key, data, expires=None):
        """
        Store data using the specified module

        :param bank:
            The name of the location inside the cache which will hold the key
            and its associated data.

        :param key:
            The name of the key (or file inside a directory) which will hold
            the data. File extensions should not be provided, as they will be
            added by the driver itself.

        :param data:
            The data which will be stored in the cache. This data should be
            in a format which can be serialized by msgpack.

        :param expires:
            how many seconds from now the data should be considered stale.

         :raises SaltCacheError:
            Raises an exception if cache driver detected an error accessing data
            in the cache backend (auth, permissions, etc).
        """
        fun = f"{self.driver}.store"
        try:
            return self.modules[fun](bank, key, data, expires=expires, **self.kwargs)
        except TypeError:
            # if the backing store doesnt natively support expiry, we handle it as a fallback
            if expires:
                expires_at = datetime.datetime.now().astimezone() + datetime.timedelta(
                    seconds=expires
                )
                expires_at = int(expires_at.timestamp())
                return self.modules[fun](
                    bank, key, {"data": data, "_expires": expires_at}, **self.kwargs
                )
            else:
                return self.modules[fun](bank, key, data, **self.kwargs)

    def fetch(self, bank, key):
        """
        Fetch data using the specified module

        :param bank:
            The name of the location inside the cache which will hold the key
            and its associated data.

        :param key:
            The name of the key (or file inside a directory) which will hold
            the data. File extensions should not be provided, as they will be
            added by the driver itself.

        :return:
            Return a python object fetched from the cache or an empty dict if
            the given path or key not found.

        :raises SaltCacheError:
            Raises an exception if cache driver detected an error accessing data
            in the cache backend (auth, permissions, etc).
        """
        fun = f"{self.driver}.fetch"
        ret = self.modules[fun](bank, key, **self.kwargs)

        # handle fallback if necessary
        if isinstance(ret, dict) and set(ret.keys()) == {"data", "_expires"}:
            now = datetime.datetime.now().astimezone().timestamp()
            if ret["_expires"] > now:
                return ret["data"]
            else:
                return {}
        else:
            return ret

    def updated(self, bank, key):
        """
        Get the last updated epoch for the specified key

        :param bank:
            The name of the location inside the cache which will hold the key
            and its associated data.

        :param key:
            The name of the key (or file inside a directory) which will hold
            the data. File extensions should not be provided, as they will be
            added by the driver itself.

        :return:
            Return an int epoch time in seconds or None if the object wasn't
            found in cache.

        :raises SaltCacheError:
            Raises an exception if cache driver detected an error accessing data
            in the cache backend (auth, permissions, etc).
        """
        fun = f"{self.driver}.updated"
        return self.modules[fun](bank, key, **self.kwargs)

    def flush(self, bank, key=None):
        """
        Remove the key from the cache bank with all the key content. If no key is specified remove
        the entire bank with all keys and sub-banks inside.

        :param bank:
            The name of the location inside the cache which will hold the key
            and its associated data.

        :param key:
            The name of the key (or file inside a directory) which will hold
            the data. File extensions should not be provided, as they will be
            added by the driver itself.

        :raises SaltCacheError:
            Raises an exception if cache driver detected an error accessing data
            in the cache backend (auth, permissions, etc).
        """
        fun = f"{self.driver}.flush"
        return self.modules[fun](bank, key=key, **self.kwargs)

    def list(self, bank):
        """
        Lists entries stored in the specified bank.

        :param bank:
            The name of the location inside the cache which will hold the key
            and its associated data.

        :return:
            An iterable object containing all bank entries. Returns an empty
            iterator if the bank doesn't exists.

        :raises SaltCacheError:
            Raises an exception if cache driver detected an error accessing data
            in the cache backend (auth, permissions, etc).
        """
        fun = f"{self.driver}.list"
        return self.modules[fun](bank, **self.kwargs)

    def list_all(self, bank, include_data=False):
        """
        Lists all entries with their data from the specified bank.
        This is more efficient than calling list() + fetch() for each entry.

        :param bank:
            The name of the location inside the cache which will hold the key
            and its associated data.

        :param include_data:
            Whether to include the full data for each entry. For some drivers
            (like localfs_key), setting this to False avoids expensive disk reads.

        :return:
            A dict of {key: data} for all entries in the bank. Returns an empty
            dict if the bank doesn't exist or the driver doesn't support list_all.

        :raises SaltCacheError:
            Raises an exception if cache driver detected an error accessing data
            in the cache backend (auth, permissions, etc).
        """
        fun = f"{self.driver}.list_all"
        if fun in self.modules:
            return self.modules[fun](bank, include_data=include_data, **self.kwargs)
        else:
            # Fallback for drivers that don't implement list_all
            raise AttributeError(
                f"Cache driver '{self.driver}' does not implement list_all"
            )

    def contains(self, bank, key=None):
        """
        Checks if the specified bank contains the specified key.

        :param bank:
            The name of the location inside the cache which will hold the key
            and its associated data.

        :param key:
            The name of the key (or file inside a directory) which will hold
            the data. File extensions should not be provided, as they will be
            added by the driver itself.

        :return:
            Returns True if the specified key exists in the given bank and False
            if not.
            If key is None checks for the bank existense.

        :raises SaltCacheError:
            Raises an exception if cache driver detected an error accessing data
            in the cache backend (auth, permissions, etc).
        """
        fun = f"{self.driver}.contains"
        return self.modules[fun](bank, key, **self.kwargs)

    def clean_expired(self, bank, *args, **kwargs):
        """
        Clean expired keys

        :param bank:
            The name of the location inside the cache which will hold the key
            and its associated data.

        :raises SaltCacheError:
            Raises an exception if cache driver detected an error accessing data
            in the cache backend (auth, permissions, etc).
        """
        # If the cache driver has a clean_expired() func, call it to clean up
        # expired keys.
        clean_expired = f"{self.driver}.clean_expired"
        if clean_expired in self.modules:
            self.modules[clean_expired](bank, *args, **{**self.kwargs, **kwargs})
        else:
            list_ = f"{self.driver}.list"
            updated = f"{self.driver}.updated"
            flush = f"{self.driver}.flush"
            for key in self.modules[list_](bank, **self.kwargs):
                ts = self.modules[updated](bank, key, **self.kwargs)
                if ts is not None and ts <= time.time():
                    self.modules[flush](bank, key, **self.kwargs)


class MemCache(Cache):
    """
    Short-lived in-memory cache store keeping values on time and/or size (count)
    basis.
    """

    # {<storage_id>: odict({<key>: [atime, data], ...}), ...}
    data = {}

    def __init__(self, opts, **kwargs):
        super().__init__(opts, **kwargs)
        self.expire = opts.get("memcache_expire_seconds", 10)
        self.max = opts.get("memcache_max_items", 1024)
        self.cleanup = opts.get("memcache_full_cleanup", False)
        self.debug = opts.get("memcache_debug", False)
        if self.debug:
            self.call = 0
            self.hit = 0
        self._storage = None

    @classmethod
    def __cleanup(cls, expire):
        now = time.time()
        for storage in cls.data.values():
            for key, data in list(storage.items()):
                if data[0] + expire < now:
                    del storage[key]
                else:
                    break

    def _get_storage_id(self):
        fun = f"{self.driver}.storage_id"
        if fun in self.modules:
            return self.modules[fun](self.kwargs)
        else:
            return self.driver

    @property
    def storage(self):
        if self._storage is None:
            storage_id = self._get_storage_id()
            if storage_id not in MemCache.data:
                MemCache.data[storage_id] = OrderedDict()
            self._storage = MemCache.data[storage_id]
        return self._storage

    def fetch(self, bank, key):
        if self.debug:
            self.call += 1
        now = time.time()
        expires = None
        record = self.storage.pop((bank, key), None)
        # Have a cached value for the key
        if record is not None:
            if len(record) == 2:
                (created_at, data) = record
            elif len(record) == 3:
                (created_at, expires, data) = record
            else:
                raise SaltCacheError("Unexpected record structure")

            if (created_at + (expires or self.expire)) >= now:
                if self.debug:
                    self.hit += 1
                    log.debug(
                        "MemCache stats (call/hit/rate): %s/%s/%s",
                        self.call,
                        self.hit,
                        float(self.hit) / self.call,
                    )
                # update atime and return
                record[0] = now
                self.storage[(bank, key)] = record
                return data

        # Have no value for the key or value is expired
        data = super().fetch(bank, key)
        if len(self.storage) >= self.max:
            if self.cleanup:
                MemCache.__cleanup(self.expire)
            if len(self.storage) >= self.max:
                self.storage.popitem(last=False)
        self.storage[(bank, key)] = [now, self.expire, data]
        return data

    def store(self, bank, key, data, expires=None):
        self.storage.pop((bank, key), None)
        super().store(bank, key, data, expires=expires)
        if len(self.storage) >= self.max:
            if self.cleanup:
                MemCache.__cleanup(self.expire)
            if len(self.storage) >= self.max:
                self.storage.popitem(last=False)
        self.storage[(bank, key)] = [time.time(), expires, data]

    def flush(self, bank, key=None):
        if key is None:
            for bank_, key_ in tuple(self.storage):
                if bank == bank_:
                    self.storage.pop((bank_, key_))
        else:
            self.storage.pop((bank, key), None)
        super().flush(bank, key)
