First pass at preliminary thread support

This is missing a lot of functionality right now, such as two gateway
events and all the HTTP CRUD endpoints.

9 files changed, 504 insertions, 12 deletions

diff --git a/discord/__init__.py b/discord/__init__.py
index dcf421ff..b2c5a078 100644
--- a/discord/__init__.py
+++ b/discord/__init__.py
@@ -58,6 +58,7 @@ from .sticker import *
 from .stage_instance import *
 from .interactions import *
 from .components import *
+from .threads import *
 
 VersionInfo = namedtuple('VersionInfo', 'major minor micro releaselevel serial')
 
diff --git a/discord/channel.py b/discord/channel.py
index 743619f4..5179c8c4 100644
--- a/discord/channel.py
+++ b/discord/channel.py
@@ -173,6 +173,14 @@ class TextChannel(discord.abc.Messageable, discord.abc.GuildChannel, Hashable):
         """List[:class:`Member`]: Returns all members that can see this channel."""
         return [m for m in self.guild.members if self.permissions_for(m).read_messages]
 
+    @property
+    def threads(self):
+        """List[:class:`Thread`]: Returns all the threads that you can see.
+
+        .. versionadded:: 2.0
+        """
+        return [thread for thread in self.guild.threads if thread.parent_id == self.id]
+
     def is_nsfw(self):
         """:class:`bool`: Checks if the channel is NSFW."""
         return self.nsfw
diff --git a/discord/enums.py b/discord/enums.py
index d716fa6f..c145c829 100644
--- a/discord/enums.py
+++ b/discord/enums.py
@@ -155,14 +155,16 @@ else:
                 return value
 
 class ChannelType(Enum):
-    text     = 0
-    private  = 1
-    voice    = 2
-    group    = 3
-    category = 4
-    news     = 5
-    store    = 6
-    stage_voice = 13
+    text           = 0
+    private        = 1
+    voice          = 2
+    group          = 3
+    category       = 4
+    news           = 5
+    store          = 6
+    public_thread  = 11
+    private_thread = 12
+    stage_voice    = 13
 
     def __str__(self):
         return self.name
@@ -186,8 +188,10 @@ class MessageType(Enum):
     guild_discovery_requalified                  = 15
     guild_discovery_grace_period_initial_warning = 16
     guild_discovery_grace_period_final_warning   = 17
+    thread_created                               = 18
     reply                                        = 19
     application_command                          = 20
+    thread_starter_message                       = 21
     guild_invite_reminder                        = 22
 
 class VoiceRegion(Enum):
diff --git a/discord/flags.py b/discord/flags.py
index d6a892c8..0ca6e34d 100644
--- a/discord/flags.py
+++ b/discord/flags.py
@@ -279,6 +279,13 @@ class MessageFlags(BaseFlags):
         """
         return 16
 
+    @flag_value
+    def has_thread(self):
+        """:class:`bool`: Returns ``True`` if the source message is associated with a thread.
+
+        .. versionadded:: 2.0
+        """
+        return 32
 
 @fill_with_flags()
 class PublicUserFlags(BaseFlags):
diff --git a/discord/guild.py b/discord/guild.py
index e9756905..c373cb52 100644
--- a/discord/guild.py
+++ b/discord/guild.py
@@ -47,6 +47,7 @@ from .asset import Asset
 from .flags import SystemChannelFlags
 from .integrations import Integration, _integration_factory
 from .stage_instance import StageInstance
+from .threads import Thread
 
 __all__ = (
     'Guild',
@@ -182,7 +183,7 @@ class Guild(Hashable):
                  'description', 'max_presences', 'max_members', 'max_video_channel_users',
                  'premium_tier', 'premium_subscription_count', '_system_channel_flags',
                  'preferred_locale', '_discovery_splash', '_rules_channel_id',
-                 '_public_updates_channel_id', '_stage_instances', 'nsfw_level')
+                 '_public_updates_channel_id', '_stage_instances', 'nsfw_level', '_threads')
 
     _PREMIUM_GUILD_LIMITS = {
         None: _GuildLimit(emoji=50, bitrate=96e3, filesize=8388608),
@@ -196,6 +197,7 @@ class Guild(Hashable):
         self._channels = {}
         self._members = {}
         self._voice_states = {}
+        self._threads = {}
         self._state = state
         self._from_data(data)
 
@@ -214,6 +216,12 @@ class Guild(Hashable):
     def _remove_member(self, member):
         self._members.pop(member.id, None)
 
+    def _add_thread(self, thread):
+        self._threads[thread.id] = thread
+
+    def _remove_thread(self, thread):
+        self._threads.pop(thread.id, None)
+
     def __str__(self):
         return self.name or ''
 
@@ -360,12 +368,25 @@ class Guild(Hashable):
                 if factory:
                     self._add_channel(factory(guild=self, data=c, state=self._state))
 
+        if 'threads' in data:
+            threads = data['threads']
+            for thread in threads:
+                self._add_thread(Thread(guild=self, data=thread))
+
     @property
     def channels(self):
         """List[:class:`abc.GuildChannel`]: A list of channels that belongs to this guild."""
         return list(self._channels.values())
 
     @property
+    def threads(self):
+        """List[:class:`Thread`]: A list of threads that you have permission to view.
+
+        .. versionadded:: 2.0
+        """
+        return list(self._threads.values())
+
+    @property
     def large(self):
         """:class:`bool`: Indicates if the guild is a 'large' guild.
 
@@ -484,6 +505,23 @@ class Guild(Hashable):
         """
         return self._channels.get(channel_id)
 
+    def get_thread(self, thread_id):
+        """Returns a thread with the given ID.
+
+        .. versionadded:: 2.0
+
+        Parameters
+        -----------
+        thread_id: :class:`int`
+            The ID to search for.
+
+        Returns
+        --------
+        Optional[:class:`Thread`]
+            The returned thread or ``None`` if not found.
+        """
+        return self._threads.get(thread_id)
+
     @property
     def system_channel(self):
         """Optional[:class:`TextChannel`]: Returns the guild's channel used for system messages.
@@ -2377,7 +2415,7 @@ class Guild(Hashable):
         data = await self._state.http.get_widget(self.id)
 
         return Widget(state=self._state, data=data)
-    
+
     async def edit_widget(self, *, enabled: bool = utils.MISSING, channel: Optional[abc.Snowflake] = utils.MISSING) -> None:
         """|coro|
 
diff --git a/discord/http.py b/discord/http.py
index 3c4d8400..ee93d1a9 100644
--- a/discord/http.py
+++ b/discord/http.py
@@ -695,6 +695,8 @@ class HTTPClient:
             'type',
             'rtc_region',
             'video_quality_mode',
+            'archived',
+            'auto_archive_duration',
         )
         payload = {k: v for k, v in options.items() if k in valid_keys}
         return self.request(r, reason=reason, json=payload)
@@ -720,6 +722,7 @@ class HTTPClient:
             'rate_limit_per_user',
             'rtc_region',
             'video_quality_mode',
+            'auto_archive_duration',
         )
         payload.update({k: v for k, v in options.items() if k in valid_keys and v is not None})
 
@@ -728,6 +731,80 @@ class HTTPClient:
     def delete_channel(self, channel_id, *, reason=None):
         return self.request(Route('DELETE', '/channels/{channel_id}', channel_id=channel_id), reason=reason)
 
+    # Thread management
+
+    def start_public_thread(
+        self,
+        channel_id: int,
+        message_id: int,
+        *,
+        name: str,
+        auto_archive_duration: int,
+        type: int,
+    ):
+        payload = {
+            'name': name,
+            'auto_archive_duration': auto_archive_duration,
+            'type': type,
+        }
+
+        route = Route(
+            'POST', '/channels/{channel_id}/messages/{message_id}/threads', channel_id=channel_id, message_id=message_id
+        )
+        return self.request(route, json=payload)
+
+    def start_private_thread(
+        self,
+        channel_id: int,
+        *,
+        name: str,
+        auto_archive_duration: int,
+        type: int,
+    ):
+        payload = {
+            'name': name,
+            'auto_archive_duration': auto_archive_duration,
+            'type': type,
+        }
+
+        route = Route('POST', '/channels/{channel_id}/threads', channel_id=channel_id)
+        return self.request(route, json=payload)
+
+    def join_thread(self, channel_id: int):
+        return self.request(Route('POST', '/channels/{channel_id}/thread-members/@me', channel_id=channel_id))
+
+    def add_user_to_thread(self, channel_id: int, user_id: int):
+        return self.request(
+            Route('POST', '/channels/{channel_id}/thread-members/{user_id}', channel_id=channel_id, user_id=user_id)
+        )
+
+    def leave_thread(self, channel_id: int):
+        return self.request(Route('DELETE', '/channels/{channel_id}/thread-members/@me', channel_id=channel_id))
+
+    def remove_user_from_thread(self, channel_id: int, user_id: int):
+        route = Route('DELETE', '/channels/{channel_id}/thread-members/{user_id}', channel_id=channel_id, user_id=user_id)
+        return self.request(route)
+
+    def get_archived_threads(self, channel_id: int, before=None, limit: int = 50, public: bool = True):
+        if public:
+            route = Route('GET', '/channels/{channel_id}/threads/archived/public', channel_id=channel_id)
+        else:
+            route = Route('GET', '/channels/{channel_id}/threads/archived/private', channel_id=channel_id)
+
+        params = {}
+        if before:
+            params['before'] = before
+        params['limit'] = limit
+        return self.request(route, params=params)
+
+    def get_joined_private_archived_threads(self, channel_id, before=None, limit: int = 50):
+        route = Route('GET', '/channels/{channel_id}/users/@me/threads/archived/private', channel_id=channel_id)
+        params = {}
+        if before:
+            params['before'] = before
+        params['limit'] = limit
+        return self.request(route, params=params)
+
     # Webhook management
 
     def create_webhook(self, channel_id, *, name, avatar=None, reason=None):
diff --git a/discord/state.py b/discord/state.py
index f9c02856..7c1183d7 100644
--- a/discord/state.py
+++ b/discord/state.py
@@ -55,6 +55,7 @@ from .integrations import _integration_factory
 from .interactions import Interaction
 from .ui.view import ViewStore
 from .stage_instance import StageInstance
+from .threads import Thread, ThreadMember
 
 class ChunkRequest:
     def __init__(self, guild_id, loop, resolver, *, cache=True):
@@ -483,7 +484,7 @@ class ConnectionState:
         self.dispatch('message', message)
         if self._messages is not None:
             self._messages.append(message)
-        if channel and channel.__class__ is TextChannel:
+        if channel and channel.__class__ in (TextChannel, Thread):
             channel.last_message_id = message.id
 
     def parse_message_delete(self, data):
@@ -704,6 +705,44 @@ class ConnectionState:
         else:
             self.dispatch('guild_channel_pins_update', channel, last_pin)
 
+    def parse_thread_create(self, data):
+        guild_id = int(data['guild_id'])
+        guild = self._get_guild(guild_id)
+        if guild is None:
+            log.debug('THREAD_CREATE referencing an unknown guild ID: %s. Discarding', guild_id)
+            return
+
+        thread = Thread(guild=guild, data=data)
+        guild._add_thread(thread)
+        self.dispatch('thread_create', thread)
+
+    def parse_thread_update(self, data):
+        guild_id = int(data['guild_id'])
+        guild = self._get_guild(guild_id)
+        if guild is None:
+            log.debug('THREAD_UPDATE referencing an unknown guild ID: %s. Discarding', guild_id)
+            return
+
+        thread_id = int(data['id'])
+        thread = guild._get_thread(thread_id)
+        if thread is not None:
+            old = copy.copy(thread)
+            thread._update(data)
+            self.dispatch('thread_update', old, thread)
+
+    def parse_thread_delete(self, data):
+        guild_id = int(data['guild_id'])
+        guild = self._get_guild(guild_id)
+        if guild is None:
+            log.debug('THREAD_UPDATE referencing an unknown guild ID: %s. Discarding', guild_id)
+            return
+
+        thread_id = int(data['id'])
+        thread = guild._get_thread(thread_id)
+        if thread is not None:
+            guild._remove_thread(thread)
+            self.dispatch('thread_delete', thread)
+
     def parse_guild_member_add(self, data):
         guild = self._get_guild(int(data['guild_id']))
         if guild is None:
diff --git a/discord/threads.py b/discord/threads.py
new file mode 100644
index 00000000..cde4a329
--- /dev/null
+++ b/discord/threads.py
@@ -0,0 +1,244 @@
+"""
+The MIT License (MIT)
+
+Copyright (c) 2015-present Rapptz
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
+"""
+
+from __future__ import annotations
+from typing import Optional, TYPE_CHECKING
+
+from .mixins import Hashable
+from .abc import Messageable
+from .enums import ChannelType, try_enum
+from . import utils
+
+__all__ = (
+    'Thread',
+    'ThreadMember',
+)
+
+if TYPE_CHECKING:
+    from .types.threads import (
+        Thread as ThreadPayload,
+        ThreadMember as ThreadMemberPayload,
+        ThreadMetadata,
+    )
+    from .guild import Guild
+    from .channel import TextChannel
+    from .member import Member
+
+
+class Thread(Messageable, Hashable):
+    """Represents a Discord thread.
+
+    .. container:: operations
+
+        .. describe:: x == y
+
+            Checks if two threads are equal.
+
+        .. describe:: x != y
+
+            Checks if two threads are not equal.
+
+        .. describe:: hash(x)
+
+            Returns the thread's hash.
+
+        .. describe:: str(x)
+
+            Returns the thread's name.
+
+    .. versionadded:: 2.0
+
+    Attributes
+    -----------
+    name: :class:`str`
+        The thread name.
+    guild: :class:`Guild`
+        The guild the thread belongs to.
+    id: :class:`int`
+        The thread ID.
+    parent_id: :class:`int`
+        The parent :class:`TextChannel` ID this thread belongs to.
+    owner_id: :class:`int`
+        The user's ID that created this thread.
+    last_message_id: Optional[:class:`int`]
+        The last message ID of the message sent to this thread. It may
+        *not* point to an existing or valid message.
+    message_count: :class:`int`
+        An approximate number of messages in this thread. This caps at 50.
+    member_count: :class:`int`
+        An approximate number of members in this thread. This caps at 50.
+    me: Optional[:class:`ThreadMember`]
+        A thread member representing yourself, if you've joined the thread.
+        This could not be available.
+    archived: :class:`bool`
+        Whether the thread is archived.
+    archiver_id: Optional[:class:`int`]
+        The user's ID that archived this thread.
+    auto_archive_duration: :class:`int`
+        The duration in minutes until the thread is automatically archived due to inactivity.
+        Usually a value of 60, 1440, 4320 and 10080.
+    archive_timestamp: :class:`datetime.datetime`
+        An aware timestamp of when the thread's archived status was last updated in UTC.
+    """
+
+    __slots__ = (
+        'name',
+        'id',
+        'guild',
+        '_type',
+        '_state',
+        'owner_id',
+        'last_message_id',
+        'message_count',
+        'member_count',
+        'me',
+        'archived',
+        'archiver_id',
+        'auto_archive_duration',
+        'archive_timestamp',
+    )
+
+    def __init__(self, *, guild: Guild, data: ThreadPayload):
+        self._state = guild._state
+        self.guild = guild
+        self._from_data(data)
+
+    async def _get_channel(self):
+        return self
+
+    def _from_data(self, data: ThreadPayload):
+        self.id = int(data['id'])
+        self.parent_id = int(data['parent_id'])
+        self.owner_id = int(data['owner_id'])
+        self.name = data['name']
+        self.type = try_enum(ChannelType, data['type'])
+        self.last_message_id = utils._get_as_snowflake(data, 'last_message_id')
+        self._unroll_metadata(data['thread_metadata'])
+
+        try:
+            member = data['member']
+        except KeyError:
+            self.me = None
+        else:
+            self.me = ThreadMember(member, self._state)
+
+    def _unroll_metadata(self, data: ThreadMetadata):
+        self.archived = data['archived']
+        self.archiver_id = utils._get_as_snowflake(data, 'archiver_id')
+        self.auto_archive_duration = data['auto_archive_duration']
+        self.archive_timestamp = utils.parse_time(data['archive_timestamp'])
+
+    def _update(self, data):
+        try:
+            self.name = data['name']
+        except KeyError:
+            pass
+
+        try:
+            self._unroll_metadata(data['thread_metadata'])
+        except KeyError:
+            pass
+
+    @property
+    def parent(self) -> Optional[TextChannel]:
+        """Optional[:class:`TextChannel`]: The parent channel this thread belongs to."""
+        return self.guild.get_channel(self.parent_id)
+
+    @property
+    def owner(self) -> Optional[Member]:
+        """Optional[:class:`Member`]: The member this thread belongs to."""
+        return self.guild.get_member(self.owner_id)
+
+    @property
+    def last_message(self):
+        """Fetches the last message from this channel in cache.
+
+        The message might not be valid or point to an existing message.
+
+        .. admonition:: Reliable Fetching
+            :class: helpful
+
+            For a slightly more reliable method of fetching the
+            last message, consider using either :meth:`history`
+            or :meth:`fetch_message` with the :attr:`last_message_id`
+            attribute.
+
+        Returns
+        ---------
+        Optional[:class:`Message`]
+            The last message in this channel or ``None`` if not found.
+        """
+        return self._state._get_message(self.last_message_id) if self.last_message_id else None
+
+
+class ThreadMember(Hashable):
+    """Represents a Discord thread member.
+
+    .. container:: operations
+
+        .. describe:: x == y
+
+            Checks if two thread members are equal.
+
+        .. describe:: x != y
+
+            Checks if two thread members are not equal.
+
+        .. describe:: hash(x)
+
+            Returns the thread member's hash.
+
+        .. describe:: str(x)
+
+            Returns the thread member's name.
+
+    .. versionadded:: 2.0
+
+    Attributes
+    -----------
+    id: :class:`int`
+        The thread member's ID.
+    thread_id: :class:`int`
+        The thread's ID.
+    joined_at: :class:`datetime.datetime`
+        The time the member joined the thread in UTC.
+    """
+
+    __slots__ = (
+        'id',
+        'thread_id',
+        'joined_at',
+        'flags',
+        '_state',
+    )
+
+    def __init__(self, data: ThreadMemberPayload, state):
+        self._state = state
+        self._from_data(data)
+
+    def _from_data(self, data: ThreadMemberPayload):
+        self.id = int(data['user_id'])
+        self.thread_id = int(data['id'])
+        self.joined_at = utils.parse_time(data['join_timestamp'])
+        self.flags = data['flags']
diff --git a/docs/api.rst b/docs/api.rst
index 68b055f4..c0c60d8c 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -658,6 +658,33 @@ to handle it, which defaults to print a traceback and ignoring the exception.
     :param last_pin: The latest message that was pinned as an aware datetime in UTC. Could be ``None``.
     :type last_pin: Optional[:class:`datetime.datetime`]
 
+.. function:: on_thread_delete(thread)
+              on_thread_create(thread)
+
+    Called whenever a thread is deleted or created.
+
+    Note that you can get the guild from :attr:`Thread.guild`.
+
+    This requires :attr:`Intents.guilds` to be enabled.
+
+    .. versionadded:: 2.0
+
+    :param thread: The thread that got created or deleted.
+    :type thread: :class:`Thread`
+
+.. function:: on_thread_update(before, after)
+
+    Called whenever a thread is updated.
+
+    This requires :attr:`Intents.guilds` to be enabled.
+
+    .. versionadded:: 2.0
+
+    :param before: The updated thread's old info.
+    :type before: :class:`Thread`
+    :param after: The updated thread's new info.
+    :type after: :class:`Thread`
+
 .. function:: on_guild_integrations_update(guild)
 
     Called whenever an integration is created, modified, or removed from a guild.
@@ -1038,6 +1065,18 @@ of :class:`enum.Enum`.
 
         .. versionadded:: 1.7
 
+    .. attribute:: public_thread
+
+        A public thread
+
+        .. versionadded:: 2.0
+
+    .. attribute:: private_thread
+
+        A private thread
+
+        .. versionadded:: 1.8
+
 .. class:: MessageType
 
     Specifies the type of :class:`Message`. This is used to denote if a message
@@ -1129,9 +1168,14 @@ of :class:`enum.Enum`.
         Discovery requirements for 3 weeks in a row.
 
         .. versionadded:: 1.7
+    .. attribute:: thread_created
+
+        The system message denoting that a thread has been created
+
+        .. versionadded:: 2.0
     .. attribute:: reply
 
-        The message type denoting that the author is replying to a message.
+        The system message denoting that the author is replying to a message.
 
         .. versionadded:: 2.0
     .. attribute:: application_command
@@ -1144,6 +1188,12 @@ of :class:`enum.Enum`.
         The system message sent as a reminder to invite people to the guild.
 
         .. versionadded:: 2.0
+    .. attribute:: thread_starter_message
+
+        The system message denoting that this message is the one that started a thread's
+        conversation topic.
+
+        .. versionadded:: 2.0
 
 .. class:: UserFlags
 
@@ -3197,6 +3247,30 @@ TextChannel
     .. automethod:: typing
         :async-with:
 
+Thread
+~~~~~~~~
+
+.. attributetable:: Thread
+
+.. autoclass:: Thread()
+    :members:
+    :inherited-members:
+    :exclude-members: history, typing
+
+    .. automethod:: history
+        :async-for:
+
+    .. automethod:: typing
+        :async-with:
+
+ThreadMember
+~~~~~~~~~~~~~
+
+.. attributetable:: ThreadMember
+
+.. autoclass:: ThreadMember()
+    :members:
+
 StoreChannel
 ~~~~~~~~~~~~~