Added Cooldowns and the ability to use Multiple cooldowns.

**NOTE:** This is very alpha and needs serious testing.

twitchio/ext/commands/cooldowns.py

@@ -0,0 +1,133 @@
+# -*- coding: utf-8 -*-
+
+"""
+The MIT License (MIT)
+
+Copyright (c) 2017-2019 TwitchIO
+
+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.
+"""
+
+import enum
+import time
+from .errors import *
+
+
+__all__ = ('Bucket', 'Cooldown', )
+
+
+class Bucket(enum.Enum):
+
+    default    = 0
+    channel    = 1
+    member     = 2
+    user       = 3
+    subscriber = 4
+    mod        = 5
+
+
+class Cooldown:
+
+    __slots__ = ('_rate', '_per', 'bucket', '_window', '_tokens', '_cache')
+
+    def __init__(self, rate: int, per: float, bucket: Bucket):
+        self._rate = rate
+        self._per = per
+        self.bucket = bucket
+
+        self._window = time.time() + self._per
+        self._tokens = 0
+
+        self._cache = {}
+
+    def get_tokens(self, now=None):
+        now = now or time.time()
+        tokens = self._tokens
+
+        if now > self._window + self._per:
+            tokens = 0
+
+        return tokens
+
+    def update_bucket(self, ctx):
+        now = time.time()
+
+        self._tokens = self.get_tokens(now)
+
+        if self._tokens == 0:
+            self._window = now
+
+        if self._tokens == self._rate:
+            retry = self._per - (now - self._window)
+            return CommandOnCooldown(command=ctx.command, retry_after=retry)
+
+        self._tokens += 1
+
+        if self._tokens == self._rate:
+            self._window = now
+
+    def reset(self):
+        self._tokens = 0
+        self._window = time.time()
+
+    def _bucket_keys(self, ctx):
+        buckets = []
+
+        for bucket in ctx.command._cooldowns:
+            if bucket.bucket == Bucket.default:
+                buckets.append('default')
+
+            if bucket.bucket == Bucket.channel:
+                buckets.append(ctx.channel.name)
+
+            if bucket.bucket == Bucket.member:
+                buckets.append((ctx.channel.name, ctx.author.id))
+            if bucket.bucket == Bucket.user:
+                buckets.append(ctx.author.id)
+
+            if bucket.bucket == Bucket.subscriber:
+                buckets.append((ctx.channel.name, ctx.author.id, 0))
+            if bucket.bucket == Bucket.mod:
+                buckets.append((ctx.channel.name, ctx.author.id, 1))
+
+        return buckets
+
+    def _update_cache(self, now=None):
+        now = now or time.time()
+        dead = [key for key, cooldown in self._cache.items() if now > cooldown._window + cooldown._per]
+
+        for bucket in dead:
+            del self._cache[bucket]
+
+    def get_buckets(self, ctx):
+        now = time.time()
+
+        self._update_cache(now)
+
+        bucket_keys = self._bucket_keys(ctx)
+        buckets = []
+
+        for index, bucket in enumerate(bucket_keys):
+            if bucket not in self._cache:
+                buckets.append(ctx.command._cooldowns[index])
+                self._cache[bucket] = ctx.command._cooldowns[index]
+            else:
+                buckets.append(self._cache[bucket])
+
+        return buckets