From 2ba1330b38ae19f1e17197a2819fc59d458e8a8e Mon Sep 17 00:00:00 2001
From: Yichuan Shen <shen.yichuan@gmail.com>
Date: Thu, 23 Jan 2020 15:44:29 +0100
Subject: [PATCH] Use tab to cycle through edges #39

---
 src/components/App.js | 37 ++++++++++++++++++++++++++++++++++++-
 src/helper.js         | 14 ++++++++++++++
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/src/components/App.js b/src/components/App.js
index 316bd1c..07473fb 100644
--- a/src/components/App.js
+++ b/src/components/App.js
@@ -1,7 +1,7 @@
 import {h, render, Component} from 'preact'
 import copyText from 'copy-text-to-clipboard'
 import * as diagram from '../diagram'
-import {arrAdd} from '../helper'
+import {arrAdd, lexicalCompare} from '../helper'
 
 import Grid from './Grid'
 import Properties from './Properties'
@@ -60,6 +60,41 @@ export default class App extends Component {
             ? null
             : {selectedCell: arrAdd(state.selectedCell, arrowControl[evt.key])}
         )
+      } else if (evt.key === 'Tab' && this.state.selectedArrow != null) {
+        // Neutralize browser focus mechanism and instead cycle through arrows
+
+        evt.preventDefault()
+        evt.stopPropagation()
+
+        let diff = evt.shiftKey ? -1 : 1
+
+        this.setState(state => {
+          if (state.selectedArrow == null) return
+
+          let {nodes, edges} = state.diagram
+          let length = edges.length
+          let findNodePositionById = id =>
+            nodes.find(node => node.id === id).position
+
+          // Constructing a natural tab order for edges
+
+          let indices = [...Array(length)]
+            .map((_, i) => [
+              i,
+              [edges[i].from, edges[i].to]
+                .map(findNodePositionById)
+                .reduce((sum, x) => arrAdd(sum, x), [0, 0])
+            ])
+            .sort(([_, arr1], [__, arr2]) => lexicalCompare(arr1, arr2))
+            .map(([i, _]) => i)
+
+          let metaIndex = indices.indexOf(state.selectedArrow)
+
+          return {
+            selectedArrow:
+              indices[(((metaIndex + diff) % length) + length) % length]
+          }
+        })
       } else if (evt.key === 'Enter') {
         this.setState(state =>
           state.cellEditMode || state.selectedArrow != null
diff --git a/src/helper.js b/src/helper.js
index eca9c59..05168a5 100644
--- a/src/helper.js
+++ b/src/helper.js
@@ -8,6 +8,20 @@ export function clamp(min, max, x) {
   return Math.max(min, Math.min(max, x))
 }
 
+export function lexicalCompare(arr1, arr2) {
+  if (arr1.length != arr2.length) {
+    return arr1.length - arr2.length
+  } else if (arr1.length === 0) {
+    return 0
+  }
+
+  return arr1[0] < arr2[0]
+    ? -1
+    : arr1[0] > arr2[0]
+    ? 1
+    : lexicalCompare(arr1.slice(1), arr2.slice(1))
+}
+
 export function arrEquals(a, b) {
   return a.length === b.length && a.every((x, i) => x === b[i])
 }