better error handling for convert.smart_convert

Returning None is pretty nondescript, so let's make it official that we
raise an exception there.

1 files changed, 17 insertions, 3 deletions

diff --git a/fietsboek/convert.py b/fietsboek/convert.py
index 9cd3297..de6314f 100644
--- a/fietsboek/convert.py
+++ b/fietsboek/convert.py
@@ -12,6 +12,17 @@ from .models import Track, Waypoint
 FIT_RECORD_FIELDS = ["position_lat", "position_long", "altitude", "timestamp"]
 
 
+class ConversionError(Exception):
+    """Error that occurred when loading a track from a file."""
+
+
+class UnknownFormat(ConversionError):
+    """The format of the source file could not be identified."""
+
+    def __str__(self):
+        return type(self).__doc__
+
+
 def semicircles_to_deg(circles: int) -> float:
     """Convert semicircles coordinate to degree coordinate.
 
@@ -30,6 +41,7 @@ def from_fit(data: bytes) -> Track:
 
     :param data: The input bytes.
     :return: The converted structure.
+    :raises ConversionError: If conversion failed.
     """
     fitfile = fitparse.FitFile(data)
     start_time = None
@@ -68,6 +80,7 @@ def from_gpx(data: bytes) -> Track:
 
     :param data: The input bytes.
     :return: The converted structure.
+    :raises ConversionError: If conversion failed.
     """
     # pylint: disable=too-many-locals
     gpx = gpxpy.parse(data)
@@ -132,7 +145,7 @@ def from_gpx(data: bytes) -> Track:
     return track
 
 
-def smart_convert(data: bytes) -> Optional[Track]:
+def smart_convert(data: bytes) -> Track:
     """Tries to be smart in converting the input bytes.
 
     This function automatically applies the correct conversion if possible.
@@ -142,12 +155,13 @@ def smart_convert(data: bytes) -> Optional[Track]:
 
     :param data: The input bytes.
     :return: The converted content.
+    :raises ConversionError: When conversion fails.
     """
     if len(data) > 11 and data[9:12] == b"FIT":
         return from_fit(data)
     if data.startswith(b"<?xml") and b"<gpx" in data[:200]:
         return from_gpx(data)
-    return None
+    raise UnknownFormat()
 
 
-__all__ = ["from_fit", "from_gpx", "smart_convert"]
+__all__ = ["ConversionError", "from_fit", "from_gpx", "smart_convert"]