runelite-api: Add Grand Exchange offer support

This includes a new event: GrandExchangeOfferChanged which is fired
whenever a grand exchange offer is updated, either manually by the
player, or as a result of the offer being fufilled (partially or
otherwise)

runelite-mixins/src/main/java/net/runelite/mixins/RSClientMixin.java

@@ -29,6 +29,7 @@ import java.util.List;
 import net.runelite.api.ChatMessageType;
 import net.runelite.api.ClanMember;
 import net.runelite.api.GameState;
+import net.runelite.api.GrandExchangeOffer;
 import net.runelite.api.IndexedSprite;
 import net.runelite.api.InventoryID;
 import net.runelite.api.MenuAction;
@@ -44,6 +45,7 @@ import net.runelite.api.Skill;
 import net.runelite.api.Varbits;
 import net.runelite.api.events.ExperienceChanged;
 import net.runelite.api.events.GameStateChanged;
+import net.runelite.api.events.GrandExchangeOfferChanged;
 import net.runelite.api.events.MapRegionChanged;
 import net.runelite.api.events.PlayerMenuOptionsChanged;
 import net.runelite.api.events.ResizeableChanged;
@@ -483,6 +485,28 @@ public abstract class RSClientMixin implements RSClient
 		eventBus.post(gameStateChange);
 	}
 
+	@Inject
+	@FieldHook("grandExchangeOffers")
+	public static void onGrandExchangeOffersChanged(int idx)
+	{
+		if (idx == -1)
+		{
+			return;
+		}
+
+		GrandExchangeOffer internalOffer = client.getGrandExchangeOffers()[idx];
+
+		if (internalOffer == null)
+		{
+			return;
+		}
+
+		GrandExchangeOfferChanged offerChangedEvent = new GrandExchangeOfferChanged();
+		offerChangedEvent.setOffer(internalOffer);
+		offerChangedEvent.setSlot(idx);
+		eventBus.post(offerChangedEvent);
+	}
+
 	@FieldHook("settings")
 	@Inject
 	public static void settingsChanged(int idx)

runelite-mixins/src/main/java/net/runelite/mixins/RSGrandExchangeOfferMixin.java

@@ -0,0 +1,107 @@
+/*
+ * Copyright (c) 2018, SomeoneWithAnInternetConnection
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package net.runelite.mixins;
+
+import net.runelite.api.GrandExchangeOfferState;
+import static net.runelite.api.GrandExchangeOfferState.BOUGHT;
+import static net.runelite.api.GrandExchangeOfferState.BUYING;
+import static net.runelite.api.GrandExchangeOfferState.CANCELLED;
+import static net.runelite.api.GrandExchangeOfferState.EMPTY;
+import static net.runelite.api.GrandExchangeOfferState.SELLING;
+import static net.runelite.api.GrandExchangeOfferState.SOLD;
+import net.runelite.api.mixins.Inject;
+import net.runelite.api.mixins.Mixin;
+import net.runelite.rs.api.RSGrandExchangeOffer;
+
+@Mixin(RSGrandExchangeOffer.class)
+public abstract class RSGrandExchangeOfferMixin implements RSGrandExchangeOffer
+{
+
+	/*
+		 Internally a GrandExchangeOffer's state is represented as 4 flags
+		 packed into the lower half of a byte. They are:
+	*/
+
+	//Set for sell offers, unset for buy offers
+	private static final int IS_SELLING = 1 << 3; // 0b1000
+
+
+	/*
+	Set for offers that have finished, either because they've
+	been filled, or because they were cancelled
+	*/
+	private static final int COMPLETED = 1 << 2; // 0b0100
+
+	/*
+	Set for offers that are actually live
+	NB: Insta-buy/sell offers will be simultaneously LIVE and LOCAL
+	*/
+	private static final int LIVE = 1 << 1; // 0b0010
+
+	//True for just-made, just-cancelled, completely cancelled, and completed offers
+	private static final int LOCAL = 1;
+
+	@Inject
+	@Override
+	public GrandExchangeOfferState getState()
+	{
+		byte code = getRSState();
+		boolean isSelling = (code & IS_SELLING) == IS_SELLING;
+		boolean isFinished = (code & COMPLETED) == COMPLETED;
+
+
+		if (code == 0)
+		{
+			return EMPTY;
+		}
+		else if (isFinished && getQuantitySold() < getTotalQuantity())
+		{
+			return CANCELLED;
+		}
+		else if (isSelling)
+		{
+			if (isFinished)
+			{
+				return SOLD;
+			}
+			else // if isUnfinished
+			{
+				return SELLING;
+			}
+		}
+		else // if isBuying
+		{
+			if (isFinished)
+			{
+				return BOUGHT;
+			}
+			else // if isUnfinished
+			{
+				return BUYING;
+			}
+		}
+	}
+}