handle bad data

where by "handle" we mean that Track.parse now returns an Either
instead of making up data points that lie on the equator

lib/Track.hs

@@ -17,6 +17,7 @@ import Control.Exception
 import Data.List as List
 import Data.List qualified
 import Data.Map as Map
+import Data.Maybe
 import Data.Text qualified
 import Data.Text.Lazy as T
 import Data.Time
@@ -52,16 +53,12 @@ gpxNS localName =
 tpxNS localName =
   Name localName (Just "http://www.garmin.com/xmlschemas/TrackPointExtension/v2") Nothing
 
-mkPoint pos =
-  Point
-    pos
-    Nothing
-    (UTCTime (toEnum 60631) 43200)
-    Nothing
-    Nothing
-    Nothing
 
-elToPoint :: Cursor -> Point
+data BadFile = BadFile deriving (Show)
+
+instance Exception BadFile
+
+elToPoint :: Cursor -> Either SomeException Point
 elToPoint c =
   case node c of
     NodeElement (Element _ attrs _) ->
@@ -85,37 +82,27 @@ elToPoint c =
               >>= element (Name "PowerInWatts" (Just "http://www.garmin.com/xmlschemas/PowerExtension/v1") Nothing)
               >>= child
               >>= content
-       in Point
-            (Pos lat lon)
-            ( case ele of
-                [e] -> Just $ asFloat e
-                _ -> Nothing
-            )
-            ( case ts of
-                [e] -> case Data.Time.ISO8601.parseISO8601 (Data.Text.unpack e) of
-                  Just utime -> utime
-                  _ -> UTCTime (toEnum 0) 0
-                _ -> UTCTime (toEnum 0) 0
-            )
-            ( case cadence of
-                [e] -> Just (asInt e)
-                _ -> Nothing
-            )
-            ( case power of
-                [e] -> Just (asInt e)
-                _ -> Nothing
-            )
-            Nothing
+          parsedTime =
+            listToMaybe ts
+              >>= (Data.Time.ISO8601.parseISO8601 . Data.Text.unpack)
+       in case parsedTime of
+            Nothing -> Left (toException BadFile)
+            Just utime ->
+              Right $
+                Point
+                  (Pos lat lon)
+                  (listToMaybe ele >>= return . asFloat)
+                  utime
+                  (listToMaybe cadence >>= return . asInt)
+                  (listToMaybe power >>= return . asInt)
+                  Nothing
       where
         asFloat v = (read (Data.Text.unpack v) :: Float)
         asInt v = (read (Data.Text.unpack v) :: Int)
-        getAttr name =
-          case Map.lookup name attrs of
-            Just v -> asFloat v
-            _ -> 0
-    _ -> mkPoint (Pos 0 0)
+        getAttr name = maybe 0 asFloat (Map.lookup name attrs)
+    _ -> Left (toException BadFile)
 
-getPoints :: Cursor -> [Point]
+getPoints :: Cursor -> Either SomeException [Point]
 getPoints c =
   let trkpts =
         element (gpxNS "gpx") c
@@ -123,12 +110,12 @@ getPoints c =
           >>= element (gpxNS "trk")
           >>= descendant
           >>= element (gpxNS "trkpt")
-   in List.map elToPoint trkpts
+   in traverse elToPoint trkpts
 
 parse :: String -> Either SomeException [Point]
 parse str = do
   gpx <- parseText def (T.pack str)
-  return (getPoints (fromDocument gpx))
+  getPoints (fromDocument gpx)
 
 length :: Track -> Int
 length = Data.List.length

tests/UnitTest.hs

@@ -34,7 +34,9 @@ onepoint =
   wrap
     [r|
 <trk> <trkseg>
-<trkpt lat="51" lon="-0.1"> </trkpt>
+<trkpt lat="51" lon="-0.1">
+   <time>2024-10-23T08:34:59.779+01:00</time>
+</trkpt>
 </trkseg> </trk>
 |]