Port safe client access and tooltip key from tinkers

src/main/java/slimeknights/mantle/client/SafeClientAccess.java

@@ -0,0 +1,68 @@
+package slimeknights.mantle.client;
+
+import net.minecraft.client.Minecraft;
+import net.minecraft.client.gui.screens.Screen;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.level.Level;
+import net.minecraftforge.api.distmarker.Dist;
+import net.minecraftforge.fml.loading.FMLEnvironment;
+
+import javax.annotation.Nullable;
+
+/** Class to add one level of static indirection to client only lookups */
+public class SafeClientAccess {
+  /** Gets the currently pressed key for tooltips, returns UNKNOWN on a server */
+  public static TooltipKey getTooltipKey() {
+    if (FMLEnvironment.dist == Dist.CLIENT) {
+      return ClientOnly.getPressedKey();
+    }
+    return TooltipKey.UNKNOWN;
+  }
+
+  /** Gets the client player entity, or null on a server */
+  @Nullable
+  public static Player getPlayer() {
+    if (FMLEnvironment.dist == Dist.CLIENT) {
+      return ClientOnly.getClientPlayer();
+    }
+    return null;
+  }
+
+  /** Gets the client player entity, or null on a server */
+  @Nullable
+  public static Level getLevel() {
+    if (FMLEnvironment.dist == Dist.CLIENT) {
+      return ClientOnly.getClientLevel();
+    }
+    return null;
+  }
+
+  /** This class is only loaded on the client, so is safe to reference client only methods */
+  private static class ClientOnly {
+    /** Gets the currently pressed key modifier for tooltips */
+    public static TooltipKey getPressedKey() {
+      if (Screen.hasShiftDown()) {
+        return TooltipKey.SHIFT;
+      }
+      if (Screen.hasControlDown()) {
+        return TooltipKey.CONTROL;
+      }
+      if (Screen.hasAltDown()) {
+        return TooltipKey.ALT;
+      }
+      return TooltipKey.NORMAL;
+    }
+
+    /** Gets the client player instance */
+    @Nullable
+    public static Player getClientPlayer() {
+      return Minecraft.getInstance().player;
+    }
+
+    /** Gets the client level instance */
+    @Nullable
+    public static Level getClientLevel() {
+      return Minecraft.getInstance().level;
+    }
+  }
+}

src/main/java/slimeknights/mantle/client/TooltipKey.java

@@ -0,0 +1,20 @@
+package slimeknights.mantle.client;
+
+/** Options for which tooltip is being used on an item */
+public enum TooltipKey {
+  /** Tooltip with neither shift nor control */
+  NORMAL,
+  /** Tooltip with shift held */
+  SHIFT,
+  /** Tooltip with control held */
+  CONTROL,
+  /** Tooltip with alt held */
+  ALT,
+  /** Tooltip key cannot be determined, typically caused by being on a server */
+  UNKNOWN;
+
+  /** Common operation is wanting to cancel when shift or unknown */
+  public boolean isShiftOrUnknown() {
+    return this == SHIFT || this == UNKNOWN;
+  }
+}