feat: Custom copyItem to clone model objects

BREAKING CHANGE:

If you are using `copy` with `[dragulaModel]`, you must now provide your
own `copyItem` function. The old one was `JSON.parse(JSON.stringify(x))`,
which was terrible.

modules/ng2-dragula/src/DragulaOptions.ts

@@ -3,7 +3,12 @@
 // the copy prop in @types/dragula are just booleans, which is severely limiting.
 // and it doesn't have copySortSource.
 // TODO: PR this against @types/dragula
-export interface DragulaOptions {
+export interface DragulaOptions<T = any> {
+
+  // note: it's possible you could wrap DragulaOptions such that
+  // the important functions would get model data included.
+  // that wouldn't be a breaking change if you appended the args to the callbacks.
+
   /* from @types/dragula */
   containers?: Element[];
   isContainer?: (el?: Element) => boolean;
@@ -19,4 +24,6 @@ export interface DragulaOptions {
   /* modifications */
   copy?: boolean | ((el: Element, source: Element) => boolean);
   copySortSource?: boolean | ((el: Element, source: Element) => boolean);
+
+  copyItem?: (item: T) => T;
 }

modules/ng2-dragula/src/components/dragula.service.ts

@@ -210,21 +210,28 @@ export class DragulaService {
         // but targetModel still has the old value
         targetModel = sourceModel;
       } else {
-        let notCopy = dragElm === dropElm;
-        let dropElmModel = notCopy
-          ? sourceModel[dragIndex]
-          // TODO: BURN WITH FIRE
-          : JSON.parse(JSON.stringify(sourceModel[dragIndex]));
-        item = dropElmModel;
-
-        if (notCopy) {
+        let isCopying = dragElm !== dropElm;
+        item = sourceModel[dragIndex];
+        if (isCopying) {
+          if (!options.copyItem) {
+            throw new Error("If you have enabled `copy` on a group, you must provide a `copyItem` function.")
+          }
+          item = options.copyItem(item);
+        }
+
+        if (!isCopying) {
           sourceModel = sourceModel.slice(0)
           sourceModel.splice(dragIndex, 1);
         }
         targetModel = targetModel.slice(0)
-        targetModel.splice(dropIndex, 0, dropElmModel);
+        targetModel.splice(dropIndex, 0, item);
         drake.models[drake.containers.indexOf(source)] = sourceModel;
         drake.models[drake.containers.indexOf(target)] = targetModel;
+        if (isCopying) {
+          try {
+            target.removeChild(dropElm);
+          } catch (e) {}
+        }
       }
       this.dispatch$.next({
         event: EventTypes.DropModel,

modules/ng2-dragula/src/public_api.ts

@@ -5,6 +5,7 @@ export { DragulaModule } from './components/dragula.module';
 export { dragula, DrakeFactory } from './DrakeFactory';
 export { Group } from './Group';
 export { DrakeWithModels } from './DrakeWithModels';
+export { DragulaOptions } from './DragulaOptions';
 
 export { EventTypes } from './EventTypes';
 export { MockDrake, MockDrakeFactory } from './spec/MockDrake';