from __future__ import absolute_import
try:
    from collections.abc import Mapping, MutableMapping
except ImportError:
    from collections import Mapping, MutableMapping
try:
    from threading import RLock
except ImportError:  # Platform-specific: No threads available
    class RLock:
        def __enter__(self):
            pass

        def __exit__(self, exc_type, exc_value, traceback):
            pass


from collections import OrderedDict
from .exceptions import InvalidHeader
from six import iterkeys, itervalues, PY3


__all__ = ['RecentlyUsedContainer', 'HTTPHeaderDict']


_Null = object()


class RecentlyUsedContainer(MutableMapping):
    """
    Provides a thread-safe dict-like container which maintains up to
    ``maxsize`` keys while throwing away the least-recently-used keys beyond
    ``maxsize``.

    :param maxsize:
        Maximum number of recent elements to retain.

    :param dispose_func:
        Every time an item is evicted from the container,
        ``dispose_func(value)`` is called.  Callback which will get called
    """

    ContainerCls = OrderedDict

    def __init__(self, maxsize=10, dispose_func=None):
        self._maxsize = maxsize
        self.dispose_func = dispose_func

        self._container = self.ContainerCls()
        self.lock = RLock()

    def __getitem__(self, key):
        # Re-insert the item, moving it to the end of the eviction line.
        with self.lock:
            item = self._container.pop(key)
            self._container[key] = item
            return item

    def __setitem__(self, key, value):
        evicted_value = _Null
        with self.lock:
            # Possibly evict the existing value of 'key'
            evicted_value = self._container.get(key, _Null)
            self._container[key] = value

            # If we didn't evict an existing value, we might have to evict the
            # least recently used item from the beginning of the container.
            if len(self._container) > self._maxsize:
                _key, evicted_value = self._container.popitem(last=False)

        if self.dispose_func and evicted_value is not _Null:
            self.dispose_func(evicted_value)

    def __delitem__(self, key):
        with self.lock:
            value = self._container.pop(key)

        if self.dispose_func:
            self.dispose_func(value)

    def __len__(self):
        with self.lock:
            return len(self._container)

    def __iter__(self):
        raise NotImplementedError('Iteration over this class is unlikely to be threadsafe.')

    def clear(self):
        with self.lock:
            # Copy pointers to all values, then wipe the mapping
            values = list(itervalues(self._container))
            self._container.clear()

        if self.dispose_func:
            for value in values:
                self.dispose_func(value)

    def keys(self):
        with self.lock:
            return list(iterkeys(self._container))


class HTTPHeaderDict(MutableMapping):
    """
    :param headers:
        An iterable of field-value pairs. Must not contain multiple field names
        when compared case-insensitively.

    :param kwargs:
        Additional field-value pairs to pass in to ``dict.update``.

    A ``dict`` like container for storing HTTP Headers.

    Field names are stored and compared case-insensitively in compliance with
    RFC 7230. Iteration provides the first case-sensitive key seen for each
    case-insensitive pair.

    Using ``__setitem__`` syntax overwrites fields that compare equal
    case-insensitively in order to maintain ``dict``'s api. For fields that
    compare equal, instead create a new ``HTTPHeaderDict`` and use ``.add``
    in a loop.

    If multiple fields that are equal case-insensitively are passed to the
    constructor or ``.update``, the behavior is undefined and some will be
    lost.

    >>> headers = HTTPHeaderDict()
    >>> headers.add('Set-Cookie', 'foo=bar')
    >>> headers.add('set-cookie', 'baz=quxx')
    >>> headers['content-length'] = '7'
    >>> headers['SET-cookie']
    'foo=bar, baz=quxx'
    >>> headers['Content-Length']
    '7'
    """

    def __init__(self, headers=None, **kwargs):
        super(HTTPHeaderDict, self).__init__()
        self._container = OrderedDict()
        if headers is not None:
            if isinstance(headers, HTTPHeaderDict):
                self._copy_from(headers)
            else:
                self.extend(headers)
        if kwargs:
            self.extend(kwargs)

    def __setitem__(self, key, val):
        self._container[key.lower()] = [key, val]
        return self._container[key.lower()]

    def __getitem__(self, key):
        val = self._container[key.lower()]
        return ', '.join(val[1:])

    def __delitem__(self, key):
        del self._container[key.lower()]

    def __contains__(self, key):
        return key.lower() in self._container

    def __eq__(self, other):
        if not isinstance(other, Mapping) and not hasattr(other, 'keys'):
            return False
        if not isinstance(other, type(self)):
            other = type(self)(other)
        return (dict((k.lower(), v) for k, v in self.itermerged()) ==
                dict((k.lower(), v) for k, v in other.itermerged()))

    def __ne__(self, other):
        return not self.__eq__(other)

    if not PY3:  # Python 2
        iterkeys = MutableMapping.iterkeys
        itervalues = MutableMapping.itervalues

    __marker = object()

    def __len__(self):
        return len(self._container)

    def __iter__(self):
        # Only provide the originally cased names
        for vals in self._container.values():
            yield vals[0]

    def pop(self, key, default=__marker):
        '''D.pop(k[,d]) -> v, remove specified key and return the corresponding value.
          If key is not found, d is returned if given, otherwise KeyError is raised.
        '''
        # Using the MutableMapping function directly fails due to the private marker.
        # Using ordinary dict.pop would expose the internal structures.
        # So let's reinvent the wheel.
        try:
            value = self[key]
        except KeyError:
            if default is self.__marker:
                raise
            return default
        else:
            del self[key]
            return value

    def discard(self, key):
        try:
            del self[key]
        except KeyError:
            pass

    def add(self, key, val):
        """Adds a (name, value) pair, doesn't overwrite the value if it already
        exists.

        >>> headers = HTTPHeaderDict(foo='bar')
        >>> headers.add('Foo', 'baz')
        >>> headers['foo']
        'bar, baz'
        """
        key_lower = key.lower()
        new_vals = [key, val]
        # Keep the common case aka no item present as fast as possible
        vals = self._container.setdefault(key_lower, new_vals)
        if new_vals is not vals:
            vals.append(val)

    def extend(self, *args, **kwargs):
        """Generic import function for any type of header-like object.
        Adapted version of MutableMapping.update in order to insert items
        with self.add instead of self.__setitem__
        """
        if len(args) > 1:
            raise TypeError("extend() takes at most 1 positional "
                            "arguments ({0} given)".format(len(args)))
        other = args[0] if len(args) >= 1 else ()

        if isinstance(other, HTTPHeaderDict):
            for key, val in other.iteritems():
                self.add(key, val)
        elif isinstance(other, Mapping):
            for key in other:
                self.add(key, other[key])
        elif hasattr(other, "keys"):
            for key in other.keys():
                self.add(key, other[key])
        else:
            for key, value in other:
                self.add(key, value)

        for key, value in kwargs.items():
            self.add(key, value)

    def getlist(self, key, default=__marker):
        """Returns a list of all the values for the named field. Returns an
        empty list if the key doesn't exist."""
        try:
            vals = self._container[key.lower()]
        except KeyError:
            if default is self.__marker:
                return []
            return default
        else:
            return vals[1:]

    def _prepare_for_method_change(self):
        """
        Remove content-specific header fields before changing the request
        method to GET or HEAD according to RFC 9110, Section 15.4.
        """
        content_specific_headers = [
            "Content-Encoding",
            "Content-Language",
            "Content-Location",
            "Content-Type",
            "Content-Length",
            "Digest",
            "Last-Modified",
        ]
        for header in content_specific_headers:
            self.discard(header)
        return self

    # Backwards compatibility for httplib
    getheaders = getlist
    getallmatchingheaders = getlist
    iget = getlist

    # Backwards compatibility for http.cookiejar
    get_all = getlist

    def __repr__(self):
        return "%s(%s)" % (type(self).__name__, dict(self.itermerged()))

    def _copy_from(self, other):
        for key in other:
            val = other.getlist(key)
            if isinstance(val, list):
                # Don't need to convert tuples
                val = list(val)
            self._container[key.lower()] = [key] + val

    def copy(self):
        clone = type(self)()
        clone._copy_from(self)
        return clone

    def iteritems(self):
        """Iterate over all header lines, including duplicate ones."""
        for key in self:
            vals = self._container[key.lower()]
            for val in vals[1:]:
                yield vals[0], val

    def itermerged(self):
        """Iterate over all headers, merging duplicate ones together."""
        for key in self:
            val = self._container[key.lower()]
            yield val[0], ', '.join(val[1:])

    def items(self):
        return list(self.iteritems())

    @classmethod
    def from_httplib(cls, message):  # Python 2
        """Read headers from a Python 2 httplib message object."""
        # python2.7 does not expose a proper API for exporting multiheaders
        # efficiently. This function re-reads raw lines from the message
        # object and extracts the multiheaders properly.
        obs_fold_continued_leaders = (' ', '\t')
        headers = []

        for line in message.headers:
            if line.startswith(obs_fold_continued_leaders):
                if not headers:
                    # We received a header line that starts with OWS as described
                    # in RFC-7230 S3.2.4. This indicates a multiline header, but
                    # there exists no previous header to which we can attach it.
                    raise InvalidHeader(
                        'Header continuation with no previous header: %s' % line
                    )
                else:
                    key, value = headers[-1]
                    headers[-1] = (key, value + ' ' + line.strip())
                    continue

            key, value = line.split(':', 1)
            headers.append((key, value.strip()))

        return cls(headers)
