XX Fingerprint: adjust the compare operation to produce the same order as sequoia-wot, for hex-shaped fingerprints

wot-dijkstra/src/main/kotlin/org/pgpainless/wot/network/Fingerprint.kt

@@ -13,7 +13,27 @@ class Fingerprint(fingerprint: String) : Comparable<Fingerprint> {
     }
 
     override fun compareTo(other: Fingerprint): Int {
-        return fingerprint.compareTo(other.fingerprint)
+        // The strings are equal
+        if (this == other) return 0
+
+        // Compare char by char.
+        // This ordering has the property that Hex-encoded Fingerprints are
+        // ordered in the same way as in sequoia-wot.
+        // (As they would be, if they were byte arrays).
+        //
+        // For other formats of "Fingerprint", the specific ordering doesn't matter to us.
+        //
+        // Following the sequoia-wot ordering means that we get the exact same output for the test suite.
+        val a = this.fingerprint.toCharArray()
+        val b = other.fingerprint.toCharArray()
+        a.zip(b).forEach { (x, y) ->
+            if (x != y) return x.compareTo(y)
+        }
+
+        // If prefix is the same, but one string is longer, we consider the longer one "bigger"
+        if (a.size != b.size) return a.size.compareTo(b.size)
+
+        throw RuntimeException("This should be unreachable")
     }
 
     override fun equals(other: Any?): Boolean {