plugin.api: Add StreamMapper, a helper to map data to stream objects.

src/livestreamer/plugin/api/__init__.py

@@ -3,9 +3,10 @@
 from types import ModuleType as module
 
 from .http_session import HTTPSession
+from .mapper import StreamMapper
 from .support_plugin import load_support_plugin
 
-__all__ = ["HTTPSession", "load_support_plugin", "http"]
+__all__ = ["HTTPSession", "StreamMapper", "load_support_plugin", "http"]
 
 
 class SupportPlugin(module):

src/livestreamer/plugin/api/mapper.py

@@ -0,0 +1,49 @@
+from functools import partial
+from itertools import product
+from operator import eq
+
+
+class StreamMapper(object):
+    """The stream mapper can be used to simplify the process of creating
+       stream objects from data.
+
+    :param cmp: This callable is used to compare each mapping's key
+                with a value.
+    """
+    def __init__(self, cmp=eq):
+        self._map = []
+        self._cmp = cmp
+
+    def map(self, key, func, *args, **kwargs):
+        """Creates a key-function mapping.
+
+        The return value from the function should be either
+          - A tuple containing a name and stream
+          - A iterator of tuples containing a name and stream
+
+        Any extra arguments will be passed to the function.
+        """
+        self._map.append((key, partial(func, *args, **kwargs)))
+
+    def _cmp_filter(self, args):
+        value, (key, func) = args
+        return self._cmp(key, value)
+
+    def _mapped_func(self, args):
+        value, (key, func) = args
+        return func(value)
+
+    def __call__(self, values):
+        """Runs through each value and transform it with a mapped function."""
+        values = product(values, self._map)
+        for value in map(self._mapped_func, filter(self._cmp_filter, values)):
+            if isinstance(value, tuple) and len(value) == 2:
+                yield value
+            else:
+                try:
+                    # TODO: Replace with "yield from" when dropping Python 2.
+                    for __ in value:
+                        yield __
+                except TypeError:
+                    # Non-iterable returned
+                    continue