Implement utilities for AsyncIterator.

Closes #473.

discord/iterators.py

@@ -35,7 +35,108 @@ from .object import Object
 
 PY35 = sys.version_info >= (3, 5)
 
-class ReactionIterator:
+@asyncio.coroutine
+def _probably_coroutine(f, e):
+    if asyncio.iscoroutinefunction(f):
+        return (yield from f(e))
+    else:
+        return f(e)
+
+class _AsyncIterator:
+    __slots__ = ()
+
+    def get(self, **attrs):
+        def predicate(elem):
+            for attr, val in attrs.items():
+                nested = attr.split('__')
+                obj = elem
+                for attribute in nested:
+                    obj = getattr(obj, attribute)
+
+                if obj != val:
+                    return False
+            return True
+
+        return self.find(predicate)
+
+    @asyncio.coroutine
+    def find(self, predicate):
+        while True:
+            try:
+                elem = yield from self.get()
+            except NoMoreItems:
+                return None
+
+            ret = yield from _probably_coroutine(predicate, elem)
+            if ret:
+                return elem
+
+    def map(self, func):
+        return _MappedAsyncIterator(self, func)
+
+    def filter(self, predicate):
+        return _FilteredAsyncIterator(self, predicate)
+
+    @asyncio.coroutine
+    def flatten(self):
+        ret = []
+        while True:
+            try:
+                item = yield from self.get()
+            except NoMoreItems:
+                return ret
+            else:
+                ret.append(item)
+
+    if PY35:
+        @asyncio.coroutine
+        def __aiter__(self):
+            return self
+
+        @asyncio.coroutine
+        def __anext__(self):
+            try:
+                msg = yield from self.get()
+            except NoMoreItems:
+                raise StopAsyncIteration()
+            else:
+                return msg
+
+def _identity(x):
+    return x
+
+class _MappedAsyncIterator(_AsyncIterator):
+    def __init__(self, iterator, func):
+        self.iterator = iterator
+        self.func = func
+
+    @asyncio.coroutine
+    def get(self):
+        # this raises NoMoreItems and will propagate appropriately
+        item = yield from self.iterator.get()
+        return (yield from _probably_coroutine(self.func, item))
+
+class _FilteredAsyncIterator(_AsyncIterator):
+    def __init__(self, iterator, predicate):
+        self.iterator = iterator
+
+        if predicate is None:
+            predicate = _identity
+
+        self.predicate = predicate
+
+    @asyncio.coroutine
+    def get(self):
+        getter = self.iterator.get
+        pred = self.predicate
+        while True:
+            # propagate NoMoreItems similar to _MappedAsyncIterator
+            item = yield from getter()
+            ret = yield from _probably_coroutine(pred, item)
+            if ret:
+                return item
+
+class ReactionIterator(_AsyncIterator):
     def __init__(self, message, emoji, limit=100, after=None):
         self.message = message
         self.limit = limit
@@ -85,32 +186,7 @@ class ReactionIterator:
                     else:
                         yield from self.users.put(User(state=self.state, data=element))
 
-    @asyncio.coroutine
-    def flatten(self):
-        ret = []
-        while True:
-            try:
-                user = yield from self.get()
-            except NoMoreItems:
-                return ret
-            else:
-                ret.append(user)
-
-    if PY35:
-        @asyncio.coroutine
-        def __aiter__(self):
-            return self
-
-        @asyncio.coroutine
-        def __anext__(self):
-            try:
-                msg = yield from self.get()
-            except NoMoreItems:
-                raise StopAsyncIteration()
-            else:
-                return msg
-
-class HistoryIterator:
+class HistoryIterator(_AsyncIterator):
     """Iterator for receiving a channel's message history.
 
     The messages endpoint has two behaviours we care about here:
@@ -281,18 +357,3 @@ class HistoryIterator:
             self.around = None
             return data
         return []
-
-    if PY35:
-        @asyncio.coroutine
-        def __aiter__(self):
-            return self
-
-        @asyncio.coroutine
-        def __anext__(self):
-            try:
-                msg = yield from self.get()
-                return msg
-            except NoMoreItems:
-                # if we're still empty at this point...
-                # we didn't get any new messages so stop looping
-                raise StopAsyncIteration()