Complete(?) AppBar state management

packages/gallery/src/interface/components/appbar.js

@@ -1,13 +1,27 @@
-import { prop, computed, bundle } from 'frptools';
+import { prop, computed, container } from 'frptools';
 
+import { Icon } from './icon.js';
 import { defineElement as el, subscribeToRender } from '../../utils/domvm.js';
 import { injectStyle, styled } from '../../services/style.js';
+import { pick } from '../../utils/conversion.js';
+
+let seq = 0;
+const getSeq = pick('_seq');
 
 export function AppBarView(vm, params, key, opts) {
-	const title = prop(params.title);
-	const renderButtons = prop(params.renderButtons || (() => []));
-	const hasBackButton = prop(false);
+	const stateStack = container([], arr => arr.length);
 	const companionScrollTop = prop(0);
+	const previousState = prop({ _seq: seq }, getSeq);
+
+	const currentState = computed(stack => stack[0] || {}, [stateStack]);
+	const title = computed(state => state.title || '', [currentState]);
+	const renderButtons = computed(state => state.buttons, [currentState]);
+	const hasBackButton = computed(stack => stack.length > 1, [stateStack]);
+	const stateChange = computed((c, p) => ({ newState: c, oldState: p }), [
+		currentState,
+		previousState
+	]);
+
 	const boxShadowStyle = computed(
 		t => (t === 0 ? 'none' : `0px ${Math.min(t / 10, 3)}px 3px rgba(0, 0, 0, .2)`),
 		[companionScrollTop]
@@ -17,22 +31,49 @@ export function AppBarView(vm, params, key, opts) {
 		throw new Error('Cannot have more than one AppBar.');
 	}
 
+	function pushState(newState) {
+		const oldState = currentState() || {};
+		stateStack.unshift(Object.assign({ _seq: seq++ }, newState));
+		previousState(oldState);
+	}
+
+	function popState() {
+		const oldState = currentState();
+		stateStack.shift();
+		previousState(oldState);
+	}
+
 	opts.appbar = {
-		title,
-		renderButtons,
-		hasBackButton,
-		companionScrollTop
+		pushState,
+		popState,
+		companionScrollTop,
+		subscribe: stateChange.subscribe
 	};
 
-	subscribeToRender(vm, [boxShadowStyle, renderButtons]);
+	subscribeToRender(vm, [boxShadowStyle, renderButtons, hasBackButton, title]);
 
 	return (vm, params) => {
-		const { title } = params;
+		const _buttons = renderButtons() || (() => {});
+
 		return header(
 			{
 				css: { boxShadow: boxShadowStyle() }
 			},
-			[titleContainer(title), headerRight(renderButtons()())]
+			[
+				hasBackButton()
+					? backButtonContainer([
+							Icon({
+								name: 'arrow_left',
+								size: 0.75,
+								attrs: {
+									onclick: popState
+								}
+							})
+					  ])
+					: null,
+				titleContainer(title()),
+				headerRight(_buttons())
+			]
 		);
 	};
 }
@@ -45,11 +86,16 @@ const header = styled({
 	alignItems: 'center'
 });
 
+const backButtonContainer = styled({
+	marginRight: '1em'
+});
+
 const headerRight = styled({
 	display: 'flex',
 	alignItems: 'center'
 });
 
 const titleContainer = styled({
-	fontSize: '20pt'
+	fontSize: '20pt',
+	flex: 1
 });

packages/gallery/src/interface/gallery.js

@@ -16,14 +16,12 @@ export function GalleryView(vm) {
 	let data = null;
 	let laCleanup = null;
 	const context = {};
-	const title = prop('');
 	const hasData = prop(null);
 
 	subscribeToRender(vm, [hasData]);
 
 	routeChanged.subscribe(function onRouteChange(name, params) {
 		if (name == 'photos') {
-			title('Photos');
 			ImageType.find({
 				['sizes.thumbnail']: { $exists: true }
 			}).then(results => {
@@ -56,14 +54,7 @@ export function GalleryView(vm) {
 
 	function renderMain() {
 		return [
-			vw(
-				AppBarView,
-				{
-					title: 'Photos'
-				},
-				'appbar',
-				context
-			),
+			vw(AppBarView, {}, 'appbar', context),
 			content(
 				{
 					onscroll: handleContentScroll

packages/gallery/src/utils/conversion.js

@@ -45,7 +45,7 @@ export function deepAssign(to, ...rest) {
 	return to;
 }
 
-export const pick = id => doc => doc[id];
+export const pick = id => doc => doc && doc[id];
 
 export const extractID = pick('_id');
 export const extractREV = pick('_rev');