Implement version handling in check

.gitignore

@@ -1 +1,5 @@
 /.idea/
+/check
+/debian-dsa
+/in
+/out

README.md

@@ -65,11 +65,11 @@ shortened and pretty-printed example output looks like this:
   [
     {
       "date": "2023-01-18",
-      "title": "DSA-5322"
+      "dsa": "DSA-5322"
     },
     {
       "date": "2023-01-19",
-      "title": "DSA-5323"
+      "dsa": "DSA-5323"
     }
   ]
   ```
@@ -87,7 +87,7 @@ metadata. If the version exists. The following input example returns the output
     "params": {},
     "version": {
       "date": "2023-01-18",
-      "title": "DSA-5322"
+      "dsa": "DSA-5322"
     }
   }
   ```

internal/resource/dsa/dsa.go

@@ -147,8 +147,10 @@ func (r *Resource) Check() error {
 		return fmt.Errorf("could not parse input from Concourse: %w", err)
 	}
 
+	var inputDate time.Time
+
 	if len(input.Version.Date) > 0 {
-		_, err = parseISODate(input.Version.Date)
+		inputDate, err = parseISODate(input.Version.Date)
 		if err != nil {
 			return fmt.Errorf("could not interpret version from Concourse as date: %w", err)
 		}
@@ -164,7 +166,14 @@ func (r *Resource) Check() error {
 	for _, item := range dsaData.Items {
 		parts := strings.SplitN(item.Title, " ", 2)
 
-		dates.addVersion(Version{Date: item.Date, DSANumber: parts[0]})
+		versionDate, err := parseISODate(item.Date)
+		if err != nil {
+			return fmt.Errorf("could not interpret date from RDF feed as date: %w", err)
+		}
+
+		if inputDate.IsZero() || inputDate.Before(versionDate) {
+			dates.addVersion(Version{Date: item.Date, DSANumber: parts[0]})
+		}
 	}
 
 	sort.Sort(dates)