Basic Discover AI based on modified PlayAi logic (#4271)

* - Basic Discover AI.

* - Remove some unused code.

* - Remove some more unused code.

* - Fix imports

* - Return false for LandAbility to avoid a potential CTD

* - Minor comment tweak.

forge-ai/src/main/java/forge/ai/SpellApiToAi.java

@@ -75,6 +75,7 @@ public enum SpellApiToAi {
             .put(ApiType.DigMultiple, DigMultipleAi.class)
             .put(ApiType.DigUntil, DigUntilAi.class)
             .put(ApiType.Discard, DiscardAi.class)
+            .put(ApiType.Discover, DiscoverAi.class)
             .put(ApiType.Draft, ChooseCardNameAi.class)
             .put(ApiType.DrainMana, DrainManaAi.class)
             .put(ApiType.Draw, DrawAi.class)

forge-ai/src/main/java/forge/ai/ability/DiscoverAi.java

@@ -0,0 +1,67 @@
+package forge.ai.ability;
+
+import forge.ai.AiPlayDecision;
+import forge.ai.ComputerUtil;
+import forge.ai.PlayerControllerAi;
+import forge.ai.SpellAbilityAi;
+import forge.card.CardStateName;
+import forge.game.ability.AbilityUtils;
+import forge.game.card.Card;
+import forge.game.player.Player;
+import forge.game.player.PlayerActionConfirmMode;
+import forge.game.spellability.LandAbility;
+import forge.game.spellability.Spell;
+import forge.game.spellability.SpellAbility;
+
+import java.util.Map;
+
+public class DiscoverAi extends SpellAbilityAi {
+
+    @Override
+    protected boolean checkApiLogic(final Player ai, final SpellAbility sa) {
+        if (ComputerUtil.preventRunAwayActivations(sa)) {
+            return false; // prevent infinite loop
+        }
+
+        return true;
+    }
+
+    /**
+     * <p>
+     * doTriggerAINoCost
+     * </p>
+     * @param sa
+     *            a {@link forge.game.spellability.SpellAbility} object.
+     * @param mandatory
+     *            a boolean.
+     *
+     * @return a boolean.
+     */
+    @Override
+    protected boolean doTriggerAINoCost(final Player ai, final SpellAbility sa, final boolean mandatory) {
+        return mandatory || checkApiLogic(ai, sa);
+    }
+
+    @Override
+    public boolean confirmAction(Player ai, SpellAbility sa, PlayerActionConfirmMode mode, String message, Map<String, Object> params) {
+        Card c = (Card)params.get("Card");
+        for (SpellAbility s : AbilityUtils.getBasicSpellsFromPlayEffect(c, ai, CardStateName.Original)) { // TODO: other states for split cards and MDFC?
+            if (s instanceof LandAbility) {
+                // return false or we get a ClassCastException later if the AI encounters MDFC with land backside
+                return false;
+            }
+            Spell spell = (Spell) s;
+            if (AiPlayDecision.WillPlay == ((PlayerControllerAi)ai.getController()).getAi().canPlayFromEffectAI(spell, false, true)) {
+                // Before accepting, see if the spell has a valid number of targets (it should at this point).
+                // Proceeding past this point if the spell is not correctly targeted will result
+                // in "Failed to add to stack" error and the card disappearing from the game completely.
+                if (!spell.isTargetNumberValid()) {
+                    // if we won't be able to pay the cost, don't choose the card
+                    return false;
+                }
+                return true;
+            }
+        }
+        return false;
+    }
+}