Add security for follow

src/main/kotlin/fr/dcproject/security/voter/FollowVoter.kt

@@ -0,0 +1,53 @@
+package fr.dcproject.security.voter
+
+import io.ktor.application.ApplicationCall
+import fr.dcproject.entity.Follow as FollowEntity
+import fr.dcproject.entity.User as UserEntity
+
+class FollowVoter: Voter {
+    enum class Action: ActionI {
+        CREATE,
+        DELETE,
+        VIEW
+    }
+
+    override fun supports(action: ActionI, call: ApplicationCall, subject: Any?): Boolean {
+        return (action is Action) &&
+               (subject is List<*> || subject is FollowEntity<*>?)
+    }
+
+    override fun vote(action: ActionI, call: ApplicationCall, subject: Any?): Vote {
+        val user = call.user
+        if (action == Action.CREATE) {
+            return if (user != null) Vote.GRANTED
+            else Vote.DENIED
+        }
+
+        if (action == Action.DELETE) {
+            return if (user != null) Vote.GRANTED
+            else Vote.DENIED
+        }
+
+        if (action == Action.VIEW) {
+            if (subject is FollowEntity<*>) {
+                return voteView(user, subject)
+            }
+            if (subject is List<*>) {
+                subject.forEach {
+                    if (it !is FollowEntity<*> || voteView(user, it) == Vote.DENIED) {
+                        return Vote.DENIED
+                    }
+                }
+                return Vote.GRANTED
+            }
+            return Vote.DENIED
+        }
+
+        return Vote.ABSTAIN
+    }
+
+    private fun voteView(user: UserEntity?, subject: FollowEntity<*>): Vote {
+        return if ((user != null && subject.createdBy?.user?.id == user.id) || subject.createdBy?.followAnonymous == false) Vote.GRANTED
+        else Vote.DENIED
+    }
+}