Initial work to reorder zoom fields.

src/components/fields/FunctionSpecField.jsx

@@ -17,6 +17,9 @@ import MdInsertChart from 'react-icons/lib/md/insert-chart'
 import PropTypes from 'prop-types'
 import capitalize from 'lodash.capitalize'
 
+import docUid from '../../libs/document-uid'
+import sortNumerically from '../../libs/sort-numerically'
+
 function isZoomField(value) {
   return typeof value === 'object' && value.stops && typeof value.property === 'undefined'
 }
@@ -43,6 +46,70 @@ export default class FunctionSpecProperty  extends React.Component {
     ]),
   }
 
+	constructor() {
+		super()
+		this.state = {
+			refs: {}
+		}
+	}
+
+	/**
+	 * We cache a reference for each stop by its index.
+   *
+   * When the stops are reordered the references are also updated (see this.orderStops) this allows React to use the same key for the element and keep keyboard focus.
+	 */
+	setStopRefs(props) {
+		// This is initialsed below only if required to improved performance.
+		let newRefs;
+
+		if(props.value && props.value.stops) {
+			props.value.stops.forEach((val, idx) => {
+				if(!this.state.refs.hasOwnProperty(idx)) {
+					if(!newRefs) {
+						newRefs = {...this.state.refs};
+					}
+					newRefs[idx] = docUid("stop-");
+				}
+			})
+		}
+
+		if(newRefs) {
+			this.setState({
+				refs: newRefs
+			})
+		}
+	}
+
+	componentWillReceiveProps(nextProps) {
+		this.setStopRefs(nextProps);
+	}
+
+  // Order the stops altering the refs to reflect their new position.
+  orderStopsByZoom(stops) {
+    const mappedWithRef = stops
+      .map((stop, idx) => {
+        return {
+          ref: this.state.refs[idx],
+          data: stop
+        }
+      })
+      // Sort by zoom
+      .sort((a, b) => sortNumerically(a.data[0], b.data[0]));
+
+    // Fetch the new position of the stops
+    const newRefs = {};
+    mappedWithRef
+      .forEach((stop, idx) =>{
+        newRefs[idx] = stop.ref;
+      })
+
+    this.setState({
+      refs: newRefs
+    });
+
+    return mappedWithRef.map((item) => item.data);
+  }
+
   addStop() {
     const stops = this.props.value.stops.slice(0)
     const lastStop = stops[stops.length - 1]
@@ -122,11 +189,14 @@ export default class FunctionSpecProperty  extends React.Component {
   }
 
   changeStop(changeIdx, stopData, value) {
-    const stops = this.props.value.stops.slice(0)
-    stops[changeIdx] = [stopData, value]
+    const stops = this.props.value.stops.slice(0);
+    stops[changeIdx] = [stopData, value];
+
+    const orderedStops = this.orderStopsByZoom(stops);
+
     const changedValue = {
       ...this.props.value,
-      stops: stops,
+      stops: orderedStops
     }
     this.props.onChange(this.props.fieldName, changedValue)
   }
@@ -241,11 +311,12 @@ export default class FunctionSpecProperty  extends React.Component {
   renderZoomProperty() {
     const zoomFields = this.props.value.stops.map((stop, idx) => {
       const zoomLevel = stop[0]
+      const key  = this.state.refs[idx];
       const value = stop[1]
       const deleteStopBtn= <DeleteStopButton onClick={this.deleteStop.bind(this, idx)} />
 
       return <InputBlock
-        key={zoomLevel}
+        key={key}
         doc={this.props.fieldSpec.doc}
         label={labelFromFieldName(this.props.fieldName)}
         action={deleteStopBtn}

src/libs/document-uid.js

@@ -0,0 +1,9 @@
+/**
+ * A unique id for the current document.
+ */
+let REF = 0;
+
+export default function(prefix="") {
+  REF++;
+  return prefix+REF;
+}

src/libs/sort-numerically.js

@@ -0,0 +1,14 @@
+export default function(a, b) {
+  a = parseFloat(a, 10);
+  b = parseFloat(b, 10);
+
+  if(a < b) {
+    return -1
+  }
+  else if(a > b) {
+    return 1
+  }
+  else {
+    return 0;
+  }
+}