From 02fd1057bb157032a98d619396c587485715dab5 Mon Sep 17 00:00:00 2001
From: Stephen <stephband@cruncher.ch>
Date: Fri, 26 Jul 2024 18:50:49 +0200
Subject: [PATCH] Adds data property type to element()

---
 element/README.md   | 13 ++++++++++++
 element/element.js  |  2 +-
 element/property.js |  5 +++++
 modules/template.js | 50 +++++++++++++++++++++++++++++++++------------
 4 files changed, 56 insertions(+), 14 deletions(-)

diff --git a/element/README.md b/element/README.md
index f1bb9bf..ac60484 100644
--- a/element/README.md
+++ b/element/README.md
@@ -53,6 +53,19 @@ definitions.
 - `"tokens"` - defines a tokens attribute (think `class`) and a string setter / TokenList getter property
 - `"src"`    - defines a URL attribute that links to a data property (TODO)
 - `"module"` - defines a URL attribute that ... (TODO)
+- `"data"` - defines a property that exposes Literal's `data` object. This is
+useful if you are building a closed system where literal custom elements are
+authored inside literal templates, as data can be passed efficiently from
+template to custom element.
+
+```html
+<template is="literal-html">
+    <p>The light is <toggle-button data="${ data }"></toggle-button></p>
+</template>
+```
+
+It is probably less useful for publishing custom elements intended for general
+consumption.
 
 Changes to properties defined in this way are signalled to Literal's renderer.
 Literal updates the shadow DOM (not the whole thing, just the parts that need
diff --git a/element/element.js b/element/element.js
index 8f2652e..cd9f966 100644
--- a/element/element.js
+++ b/element/element.js
@@ -113,7 +113,7 @@ export default function LiteralElement(tag, lifecycle = {}, properties = {}, par
     // Create templates. This is a crude way to do it, and we should probably
     // isolate templates in the shadow from those outside with a separate
     // template cache (based around shadow.getElementById()?)... but... it'll
-    // do for now
+    // do for now... ?
     if (window.DEBUG) document.head.appendChild(create('comment', ' Templates for ' + name));
     document.head.append.apply(document.head, templates);
 
diff --git a/element/property.js b/element/property.js
index 73c3c50..4518bd7 100644
--- a/element/property.js
+++ b/element/property.js
@@ -110,6 +110,11 @@ const types = {
             .then((object) => this[symbol].value = object)
             .catch((error) => console.error(error));
         }
+    }),
+
+    data: (name, symbol) => ({
+        get: function() { return getInternals(this).renderer.data; },
+        set: function(data) { getInternals(this).renderer.push(data); }
     })
 };
 
diff --git a/modules/template.js b/modules/template.js
index f1a0628..357d970 100644
--- a/modules/template.js
+++ b/modules/template.js
@@ -92,7 +92,7 @@ export class LiteralDOM {
         const children  = content.childNodes;
 
         // The first node may change. The last node is always the last node.
-        this.#data      = Signal.of(Data.of(data));
+        this.#data      = Signal.of(Data.objectOf(data));
         this.#first     = children[0];
         this.#last      = children[children.length - 1];
 
@@ -131,8 +131,8 @@ export class LiteralDOM {
     }
 
     /*
-    template.firstNode
-    template.lastNode
+    .firstNode
+    .lastNode
     */
 
     get firstNode() {
@@ -148,24 +148,40 @@ export class LiteralDOM {
         return this.#last;
     }
 
-    /*
-    .push()
-    */
+    /**
+    .data
+    Read-only property exposing (literal's `data` proxy of) the currently
+    rendered object. This is the same object available as `data` inside a
+    literal template. Setting properties on this object causes the DOM to update.
+    **/
+
+    get data() {
+        const data = this.#data.value;
+        return Data.of(data) || data;
+    }
+
+    /**
+    .push(object)
+    Rerenders and binds the DOM to (literal's `data` proxy of) `object`. This is
+    the same object available as `data` inside the template.
+    **/
 
     push(object) {
         if (this.status === 'done') throw new Error('Renderer is done, cannot .push() data');
 
+        // Make sure we have the raw object
+        object = Data.objectOf(object);
+
         // Dedup
-        if (this.#data === object) return;
+        if (this.#data.value === object) return;
 
         // If we are coming out of sleep put content back in the DOM
-        if (this.#data === null && object !== null) {
+        if (this.#data.value === null && object !== null) {
             this.lastNode.before(this.content);
         }
 
-        // Causes renderers to .invalidate() because they are dependent on
-        // this.#data signal
-        this.#data.value = Data.of(object);
+        // Causes renderers dependent on this signal to .invalidate()
+        this.#data.value = object;
 
         // If object is null put template to sleep: remove all but the last node
         // to the content fragment and blank out the last text node, which we
@@ -246,8 +262,16 @@ export default class LiteralRenderer extends LiteralDOM {
     }
 
     static of(html) {
-        const template = create('template', html);
-        return new LiteralRenderer(template);
+        return LiteralRenderer.from(create('template', html));
+    }
+
+    static from(template, parent) {
+        const id       = identify(template, 'literal-');
+        const fragment = template.content;
+        const compiled = cache[id]
+            || (cache[id] = LiteralRenderer.compile(fragment, options, '#' + id));
+
+        return new LiteralDOM(compiled, fragment.cloneNode(true), parent = template.parentElement);
     }
 
     static compile(fragment, options, src) {