* Offering ability - Fixed use in available mana calculation (related to #6698).

Mage.Tests/src/test/java/org/mage/test/cards/abilities/keywords/OfferingTest.java

@@ -46,6 +46,33 @@ public class OfferingTest extends CardTestPlayerBase {
 
         assertPermanentCount(playerA, kurosTaken, 1);
         assertPermanentCount(playerA, nezumiPatron, 1);
-        assertTappedCount("Swamp", true, 7); // {5}{B}{B} - {1}{B} = {4}{B} = 7 swamps tapped
+        assertTappedCount("Swamp", true, 7); // {5}{B}{B} - {1}{B} = {4}{B} = 7 swamps tapped              
     }
+    
+    @Test
+    public void testCastWithMinimalMana() {
+        setStrictChooseMode(true);
+        
+        // Goblin offering (You may cast this card any time you could cast an instant by sacrificing a Goblin and paying the difference in mana costs between this and the sacrificed Goblin. Mana cost includes color.)
+        // Whenever Patron of the Akki attacks, creatures you control get +2/+0 until end of turn.        
+        String patron = "Patron of the Akki"; // Creature {4}{R}{R} (5/5)
+
+        addCard(Zone.HAND, playerA, patron, 1);
+        
+        addCard(Zone.BATTLEFIELD, playerA, "Mountain", 3);
+        addCard(Zone.BATTLEFIELD, playerA, "Akki Drillmaster"); // Creature Goblin {2}{R}  (2/2)
+
+        castSpell(1, PhaseStep.PRECOMBAT_MAIN, playerA, patron);                
+        setChoice(playerA, "Yes");
+        addTarget(playerA, "Akki Drillmaster");
+        
+        setStopAt(1, PhaseStep.POSTCOMBAT_MAIN);
+        execute();
+
+        assertAllCommandsUsed();
+        assertPermanentCount(playerA, patron, 1);
+        
+        assertGraveyardCount(playerA, "Akki Drillmaster", 1);
+
+    }    
 }

Mage/src/main/java/mage/abilities/keyword/OfferingAbility.java

@@ -1,14 +1,26 @@
 package mage.abilities.keyword;
 
+import java.util.ArrayList;
+import java.util.List;
 import java.util.UUID;
+import mage.Mana;
+import mage.ObjectColor;
 import mage.abilities.Ability;
+import mage.abilities.SpecialAction;
 import mage.abilities.SpellAbility;
 import mage.abilities.StaticAbility;
+import mage.abilities.costs.mana.ActivationManaAbilityStep;
+import mage.abilities.costs.mana.AlternateManaPaymentAbility;
+import mage.abilities.costs.mana.ManaCost;
 import mage.abilities.effects.AsThoughEffectImpl;
 import mage.abilities.effects.common.cost.CostModificationEffectImpl;
+import mage.abilities.mana.ManaOptions;
 import mage.cards.Card;
 import mage.constants.*;
 import mage.filter.common.FilterControlledCreaturePermanent;
+import mage.filter.predicate.Predicates;
+import mage.filter.predicate.mageobject.ColorPredicate;
+import mage.filter.predicate.permanent.TappedPredicate;
 import mage.game.Game;
 import mage.game.permanent.Permanent;
 import mage.players.Player;
@@ -39,7 +51,7 @@ import mage.util.GameLog;
  *
  * @author LevelX2
  */
-public class OfferingAbility extends StaticAbility {
+public class OfferingAbility extends StaticAbility implements AlternateManaPaymentAbility {
 
     private FilterControlledCreaturePermanent filter = new FilterControlledCreaturePermanent();
 
@@ -72,6 +84,31 @@ public class OfferingAbility extends StaticAbility {
         String subtype = filter.getMessage();
         return subtype + " offering <i>(You may cast this card any time you could cast an instant by sacrificing a " + subtype + " and paying the difference in mana costs between this and the sacrificed " + subtype + ". Mana cost includes color.)</i>";
     }
+
+    @Override
+    public ActivationManaAbilityStep useOnActivationManaAbilityStep() {
+        return ActivationManaAbilityStep.NORMAL;
+    }
+
+    @Override
+    public void addSpecialAction(Ability source, Game game, ManaCost unpaid) {
+        // No special Action
+    }
+
+    @Override
+    public ManaOptions getManaOptions(Ability source, Game game, ManaCost unpaid) {        
+        ManaOptions options = new ManaOptions();
+
+        // Creatures from the offerd type
+        game.getBattlefield().getActivePermanents(filter, source.getControllerId(), source.getSourceId(), game)
+                .stream()
+                .forEach(permanent -> {
+                    options.addMana(permanent.getSpellAbility().getManaCosts().getMana());
+                });
+
+        options.removeDuplicated();
+        return options;
+    }
 }
 
 class OfferingAsThoughEffect extends AsThoughEffectImpl {
@@ -145,8 +182,8 @@ class OfferingAsThoughEffect extends AsThoughEffectImpl {
                         game.addEffect(effect, source);
                         game.getState().setValue("offering_ok_" + card.getId(), true);
                         game.getState().setValue("offering_Id_" + card.getId(), activationId);
-                        game.informPlayers(player.getLogName() + " announces to offer " 
-                                + offer.getLogName() + " to cast " 
+                        game.informPlayers(player.getLogName() + " announces to offer "
+                                + offer.getLogName() + " to cast "
                                 + GameLog.getColoredObjectName(spellToCast));// No id name to prevent to offer hand card knowledge after cancel casting
                         return true;
                     }
@@ -192,7 +229,7 @@ class OfferingCostReductionEffect extends CostModificationEffectImpl {
         if (game.inCheckPlayableState()) { // Cost modifaction does not work correctly for checking available spells
             return false;
         }
-        if (abilityToModify.getSourceId().equals(source.getSourceId()) 
+        if (abilityToModify.getSourceId().equals(source.getSourceId())
                 && abilityToModify instanceof SpellAbility) {
             Card card = game.getCard(source.getSourceId());
             if (card != null) {