refactor(model): Extract vulnerability rating code to a function

This is a preparation for exclusively using the `getQualitativeRating()`
function going forward.

Signed-off-by: Sebastian Schuberth <sebastian@doubleopen.org>

model/src/main/kotlin/vulnerabilities/VulnerabilityReference.kt

@@ -54,16 +54,24 @@ data class VulnerabilityReference(
     companion object {
         private val CVSS3_SEVERITIES = Cvss3Rating.entries.map { it.name }
 
+        /**
+         * Return a qualitative rating that is determined based on the given [scoringSystem] and [score].
+         */
+        fun getQualitativeRating(scoringSystem: String?, score: Float?): Enum<*>? =
+            when (scoringSystem?.uppercase()) {
+                in Cvss2Rating.NAMES -> score?.let { Cvss2Rating.fromScore(it) }
+                in Cvss3Rating.NAMES -> score?.let { Cvss3Rating.fromScore(it) }
+                in Cvss4Rating.NAMES -> score?.let { Cvss4Rating.fromScore(it) }
+                else -> null
+            }
+
         /**
          * Return a human-readable string that is determined based on the given [scoringSystem] and [severity].
          */
         fun getSeverityString(scoringSystem: String?, severity: String?): String =
-            when (scoringSystem?.uppercase()) {
-                in Cvss2Rating.NAMES -> severity?.toFloatOrNull()?.let { Cvss2Rating.fromScore(it) }?.toString()
-                in Cvss3Rating.NAMES -> severity?.toFloatOrNull()?.let { Cvss3Rating.fromScore(it) }?.toString()
-                in Cvss4Rating.NAMES -> severity?.toFloatOrNull()?.let { Cvss4Rating.fromScore(it) }?.toString()
-                else -> severity?.uppercase()?.takeIf { it in CVSS3_SEVERITIES }
-            } ?: "UNKNOWN"
+            severity?.toFloatOrNull()?.let { getQualitativeRating(scoringSystem, it)?.name }
+                ?: severity?.uppercase()?.takeIf { it in CVSS3_SEVERITIES }
+                ?: "UNKNOWN"
     }
 
     /**