ChartStackedBar: implement, but make it a simple unlabelled bar.

We can put the legend elsewhere, and manage multiple bars with a CSS 
grid or something.

src/static/js/ui/charts/ChartStackedBar.mjs

@@ -1,37 +1,79 @@
 "use strict";
 
+import { SVG } from 'svg.js';
+
 class ChartStackedBar {
+	get weight_total() {
+		return this.categories.reduce((cat, acc) => cat.weight + acc, 0);
+	}
+	
 	constructor(el) {
 		this.el = el;
 		
 		/**
-		 * The category names and their properties.
+		 * The categories of this bar.
 		 * @type {Object[]}
 		 */
 		this.categories = [
-			// { name: "Some category name", colour: "hsl(46, 80%, 50%)" }
-			// ....
-		]
-		/**
-		 * Whether to normalise all bars to be the same height or not.
-		 * @type {Boolean}
-		 */
-		this.percentage = false;
-		/**
-		 * The bars to render.
-		 * Additional properties can be specified on the objects passed and
-		 * this class will ignore them. It's strongly recommended though that
-		 * any additional properties start with an underscore.
-		 * @type {Object[]}
-		 */
-		this.bars = [
-			// { name: "bar name 1", values: [ { value: 3, cat: 1 }, .... ] }
+			// { colour: "hsl(46, 80%, 50%)", weight: 4 }
 			// ....
 		];
+		
+		this.auto_render = true;
+		
+		
+		this.#svg = SVG().size("100%", "100%");
+		
+		this.sym_bar = Symbol();
+		
+	}
+	
+	/**
+	 * Adds a new category to the bar.
+	 * @param {string} colour	The colour to assign to the category.
+	 * @param {number} weight	The weighting value to assign to the category.
+	 */
+	category_add(colour, weight) {
+		const id = Symbol();
+		this.categories.push({
+			id,
+			colour,
+			weight,
+			[this.sym_bar]: null
+		});
+		if(this.auto_render) this.render();
+		return id;
+	}
+	
+	category_remove(id) {
+		for(const i in this.categories) {
+			if(this.categories[i].id === id) {
+				this.categories.splice(i, 1);
+				if(this.auto_render) this.render();
+				return true;
+			}
+		}
+		return false;
 	}
 	
 	render() {
+		let percent_so_far = 0;
+		for(const cat of this.categories) {
+			const percent_this = this.#weight_percent(cat.weight);
+			if(cat[this.sym_bar] === null) {
+				cat[this.sym_bar] = this.#svg.rect("100%", "10%")
+					.fill(cat.colour)
+			}
+			cat[this.sym_bar].height = `${percent_this}%`;
+			cat[this.sym_bar] = cat[this.sym_bar].fill(cat.colour)
+				.move("0%", `${percent_so_far}%`);
 			
+			percent_so_far += percent_this;
+		}
+	}
+	
+	#weight_percent(weight) {
+		return (weight / this.weight_total) * 100
 	}
 }