From c9f89dc920088f367e53484b16e1e02c47325b2d Mon Sep 17 00:00:00 2001
From: Richard Schreiber <wiffbi@gmail.com>
Date: Fri, 19 Feb 2021 07:33:01 +0100
Subject: [PATCH] simplified selection algorithm

---
 src/pretix/static/pretixcontrol/js/ui/main.js | 34 +++++++------------
 1 file changed, 13 insertions(+), 21 deletions(-)

diff --git a/src/pretix/static/pretixcontrol/js/ui/main.js b/src/pretix/static/pretixcontrol/js/ui/main.js
index e672b9271a..7c9069c77b 100644
--- a/src/pretix/static/pretixcontrol/js/ui/main.js
+++ b/src/pretix/static/pretixcontrol/js/ui/main.js
@@ -676,7 +676,7 @@ $(function () {
         var $table = $toggle.closest("table");
         var $rows = $table.find("tbody tr");
         var $checkboxes = $rows.find("td:first-child input[type=checkbox]");
-        var firstIndex, lastIndex, currentIndex, selectionChecked, onChangeSelectionHappened = false;
+        var firstIndex, lastIndex, selectionChecked, onChangeSelectionHappened = false;
         var updateSelection = function(a, b, checked) {
             if (a > b) {
                 //[a, b] = [b, a];// ES6 not ready yet for pretix
@@ -695,29 +695,21 @@ $(function () {
             onChangeSelectionHappened = true;
 
             var row = ev.target.closest("tr");
-            currentIndex = 0;
+            var currentIndex = 0;
             while(row = row.previousSibling) {
                 if (row.tagName) currentIndex++;
             }
-
-            if (currentIndex > firstIndex && currentIndex > lastIndex) {
-                // special case: selection direction changed
-                if (lastIndex < firstIndex) {
-                    // reset all selected checkboxes before setting new lastIndex
-                    updateSelection(lastIndex, firstIndex);
-                }
-                lastIndex = currentIndex;
-
-            } else if (currentIndex < firstIndex && currentIndex < lastIndex) {
-                // special case: selection direction changed
-                if (lastIndex > firstIndex) {
-                    // reset all selected checkboxes before setting new lastIndex
-                    updateSelection(firstIndex, lastIndex);
-                }
-                lastIndex = currentIndex;
+            var dCurrent = currentIndex - firstIndex;
+            var dLast = lastIndex - firstIndex;
+            if (dCurrent*dLast < 0) {
+                // direction of selection changed => reset all previously selected
+                updateSelection(lastIndex, firstIndex);
             }
-
-            if (currentIndex != lastIndex) updateSelection(currentIndex, lastIndex);
+            else if (Math.abs(dCurrent) < Math.abs(dLast)) {
+                // selection distance decreased => reset unselected
+                updateSelection(currentIndex, lastIndex);
+            }
+            lastIndex = currentIndex;
             updateSelection(firstIndex, currentIndex, selectionChecked);
 
             ev.preventDefault();
@@ -731,7 +723,7 @@ $(function () {
             while(row = row.previousSibling) {
                 if (row.tagName) firstIndex++;
             }
-            lastIndex = currentIndex = firstIndex;
+            lastIndex = firstIndex;
 
             ev.preventDefault();
             $rows.on("pointerenter", onChangeSelection);