Convert InfiniteScrollListener to Kotlin.

The Runnable was just too much boilerplate!

app/src/main/java/io/plaidapp/ui/recyclerview/InfiniteScrollListener.kt

@@ -0,0 +1,52 @@
+/*
+ *  Copyright 2017 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package io.plaidapp.ui.recyclerview
+
+import android.support.v7.widget.LinearLayoutManager
+import android.support.v7.widget.RecyclerView
+
+import io.plaidapp.data.DataLoadingSubject
+
+/**
+ * A scroll listener for RecyclerView to load more items as you approach the end.
+ *
+ * Adapted from https://gist.github.com/ssinss/e06f12ef66c51252563e
+ */
+abstract class InfiniteScrollListener(
+        private val layoutManager: LinearLayoutManager,
+        private val dataLoading: DataLoadingSubject
+) : RecyclerView.OnScrollListener() {
+    private val loadMoreRunnable = Runnable { onLoadMore() }
+
+    override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
+        // bail out if scrolling upward or already loading data
+        if (dy < 0 || dataLoading.isDataLoading) return
+
+        val visibleItemCount = recyclerView.childCount
+        val totalItemCount = layoutManager.itemCount
+        val firstVisibleItem = layoutManager.findFirstVisibleItemPosition()
+
+        if (totalItemCount - visibleItemCount <= firstVisibleItem + VISIBLE_THRESHOLD) {
+            recyclerView.post(loadMoreRunnable)
+        }
+    }
+
+    abstract fun onLoadMore()
+
+    companion object {
+        // The minimum number of items remaining before we should loading more.
+        private const val VISIBLE_THRESHOLD = 5
+    }
+}