From 045cf17deea53267d5a15d94d8da2fdc096f38b0 Mon Sep 17 00:00:00 2001
From: Peter Stuifzand <peter@stuifzand.eu>
Date: Sat, 14 Nov 2020 15:42:03 +0100
Subject: [PATCH] Add new function 'deleteCharacterBackward'

---
 list-editor/index.js | 61 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/list-editor/index.js b/list-editor/index.js
index 86db1d0..b0fb3de 100644
--- a/list-editor/index.js
+++ b/list-editor/index.js
@@ -43,6 +43,7 @@ function editor(root, inputData, options) {
     editorKeymap.mapKey('C-S-ArrowUp', 'blockMoveBackward')
     editorKeymap.mapKey('C-S-ArrowDown', 'blockMoveForward')
     editorKeymap.mapKey('C-.', 'toggleBlock')
+    editorKeymap.mapKey('Backspace', 'deleteCharacterBackward')
     // keymap.mapKey('C-]', 'zoomIn')
     // keymap.mapKey('C-[', 'zoomOut')
 
@@ -179,6 +180,8 @@ function editor(root, inputData, options) {
         blockMoveBackward,
         blockMoveForward,
 
+        deleteCharacterBackward,
+
         expandBlock,
         collapseBlock,
         toggleBlock
@@ -658,6 +661,64 @@ function editor(root, inputData, options) {
         return toggleBlock(event, false)
     }
 
+    function countBraces(sset, as) {
+        let set = _(sset).chain().split('').value()
+        let defaults = {}
+        defaults[set[0]] = 0
+        defaults[set[1]] = 0
+        return _(as)
+            .chain()
+            .takeWhile(c => _.includes(set, c))
+            .countBy()
+            .defaults(defaults)
+            .thru(x => x[set[0]] - x[set[1]])
+            .value()
+    }
+
+    function deleteCharacterBackward(event) {
+        let input = event.target
+        let value = input.value
+
+        // There is text selected, so we skip
+        if (input.selectionStart !== input.selectionEnd) return true
+
+        let prefix = value.slice(0, input.selectionStart)
+        let suffix = value.slice(input.selectionStart)
+
+        let braces = {
+            '[': '[]',
+            '(': '()',
+            '{': '{}',
+        }
+
+        let c = prefix[prefix.length-1]
+        let braceSet = braces[c]
+
+        let prefixCount = _(prefix)
+            .split('').reverse()
+            .thru(_.partial(countBraces, braceSet))
+            .value()
+
+        let suffixCount = _(suffix)
+            .split('')
+            .thru(_.partial(countBraces, braceSet))
+            .value()
+
+        if (prefixCount > 0 && suffixCount < 0 && prefixCount + suffixCount === 0) {
+            event.preventDefault()
+
+            input.value = prefix.slice(0, prefix.length - 1) + suffix.slice(1)
+            _.defer(() => {
+                input.selectionStart = prefix.length - 1
+                input.selectionEnd = input.selectionStart
+            })
+
+            return false
+        }
+
+        return true
+    }
+
     $(root).on('keydown', function (event) {
         if (editing) {
             return editorKeymap.handleKey(EDITOR, event)