implemented un-subscribe

src/main/java/de/srsoftware/widerhall/data/ListMember.java

@@ -3,6 +3,7 @@ package de.srsoftware.widerhall.data;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import javax.xml.crypto.Data;
 import java.sql.SQLException;
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -90,4 +91,27 @@ public class ListMember {
                 .run();
         return this;
     }
+
+    public static void unsubscribe(String listEmail, User user) throws SQLException {
+        var db = Database.open();
+        var rs = db.query("SELECT * FROM "+TABLE_NAME)
+                .where(LIST_EMAIL,listEmail)
+                .where(USER_EMAIL,user.email())
+                .exec();
+        while (rs.next()){
+            int state = rs.getInt(STATE) ^ STATE_SUBSCRIBER;
+            if (state < 1) { // drop entry
+                db.query("DELETE FROM "+TABLE_NAME)
+                        .where(LIST_EMAIL,listEmail)
+                        .where(USER_EMAIL,user.email())
+                        .run();
+            } else { // update entry: whitdraw subscription
+                db.query("UPDATE "+TABLE_NAME)
+                        .set(STATE,state)
+                        .where(LIST_EMAIL,listEmail)
+                        .where(USER_EMAIL,user.email())
+                        .run();
+            }
+        }
+    }
 }