Decouple fetching metadata

spotdl/metadata/metadata_base.py

@@ -0,0 +1,69 @@
+from abc import ABC
+from abc import abstractmethod
+
+
+class StreamsBase(ABC):
+    @abstractmethod
+    def __init__(self, streams):
+        """
+        This method must parse audio streams into a list of
+        dictionaries with the keys:
+        "bitrate", "download_url", "encoding", "filesize".
+
+        The list should typically be sorted in descending order
+        based on the audio stream's bitrate.
+
+        This sorted list must be assigned to `self.all`.
+        """
+        self.all = streams
+
+    @abstractmethod
+    def getbest(self):
+        """
+        This method must return the audio stream with the
+        highest bitrate.
+        """
+        return self.all[0]
+
+    @abstractmethod
+    def getworst(self):
+        """
+        This method must return the audio stream with the
+        lowest bitrate.
+        """
+        return self.all[-1]
+
+
+class MetadataBase(ABC):
+    def set_credentials(self, client_id, client_secret):
+        """
+        This method may or not be used depending on
+        whether the metadata provider requires authentication
+        or not.
+        """
+        pass
+
+    @abstractmethod
+    def from_url(self, url):
+        """
+        This method must return track metadata from the
+        corresponding Spotify URL.
+        """
+        pass
+
+    @abstractmethod
+    def from_query(self, query):
+        """
+        This method must return track metadata from the
+        corresponding search query.
+        """
+        pass
+
+    @abstractmethod
+    def metadata_to_standard_form(self, metadata):
+        """
+        This method must transform the fetched metadata
+        into a format consistent with all other metadata
+        providers, for easy utilization.
+        """
+        pass