Add tagged template literal (#163)

templates.js

@@ -0,0 +1,175 @@
+'use strict';
+
+function data(parent) {
+	return {
+		styles: [],
+		parent,
+		contents: []
+	};
+}
+
+const zeroBound = n => n < 0 ? 0 : n;
+const lastIndex = a => zeroBound(a.length - 1);
+
+const last = a => a[lastIndex(a)];
+
+const takeWhileReverse = (array, predicate, start) => {
+	const out = [];
+
+	for (let i = start; i >= 0 && i <= start; i--) {
+		if (predicate(array[i])) {
+			out.unshift(array[i]);
+		} else {
+			break;
+		}
+	}
+
+	return out;
+};
+
+/**
+ * Checks if the character at position i in string is a normal character a.k.a a non control character.
+ * */
+const isNormalCharacter = (string, i) => {
+	const char = string[i];
+	const backslash = '\\';
+
+	if (!(char === backslash || char === '{' || char === '}')) {
+		return true;
+	}
+
+	const n = i === 0 ? 0 : takeWhileReverse(string, x => x === '\\', zeroBound(i - 1)).length;
+
+	return n % 2 === 1;
+};
+
+const collectStyles = data => data ? collectStyles(data.parent).concat(data.styles) : ['reset'];
+
+/**
+ * Computes the style for a given data based on it's style and the style of it's parent. Also accounts for !style styles
+ * which remove a style from the list if present.
+ * */
+const sumStyles = data => {
+	const negateRegex = /^~.+/;
+	let out = [];
+
+	for (const style of collectStyles(data)) {
+		if (negateRegex.test(style)) {
+			const exclude = style.slice(1);
+			out = out.filter(x => x !== exclude);
+		} else {
+			out.push(style);
+		}
+	}
+
+	return out;
+};
+
+/**
+ * Takes a string and parses it into a tree of data objects which inherit styles from their parent.
+ * */
+function parse(string) {
+	const root = data(null);
+	let pushingStyle = false;
+
+	let current = root;
+
+	for (let i = 0; i < string.length; i++) {
+		const char = string[i];
+
+		const addNormalCharacter = () => {
+			const lastChunk = last(current.contents);
+
+			if (typeof lastChunk === 'string') {
+				current.contents[lastIndex(current.contents)] = lastChunk + char;
+			} else {
+				current.contents.push(char);
+			}
+		};
+
+		if (pushingStyle) {
+			if (' \t'.indexOf(char) > -1) {
+				pushingStyle = false;
+			} else if (char === '\n') {
+				pushingStyle = false;
+				addNormalCharacter();
+			} else if (char === '.') {
+				current.styles.push('');
+			} else {
+				current.styles[lastIndex(current.styles)] = (last(current.styles) || '') + char;
+			}
+		} else if (isNormalCharacter(string, i)) {
+			addNormalCharacter();
+		} else if (char === '{') {
+			pushingStyle = true;
+			const nCurrent = data(current);
+			current.contents.push(nCurrent);
+			current = nCurrent;
+		} else if (char === '}') {
+			current = current.parent;
+		}
+	}
+
+	if (current !== root) {
+		throw new Error('literal template has an unclosed block');
+	}
+
+	return root;
+}
+
+/**
+ * Takes a tree of data objects and flattens it to a list of data objects with the inherited and negations styles
+ * accounted for.
+ * */
+function flatten(data) {
+	let flat = [];
+
+	for (const content of data.contents) {
+		if (typeof content === 'string') {
+			flat.push({
+				styles: sumStyles(data),
+				content
+			});
+		} else {
+			flat = flat.concat(flatten(content));
+		}
+	}
+
+	return flat;
+}
+
+function assertStyle(chalk, style) {
+	if (!chalk[style]) {
+		throw new Error(`invalid Chalk style: ${style}`);
+	}
+}
+
+/**
+ * Checks if a given style is valid and parses style functions.
+ * */
+function parseStyle(chalk, style) {
+	const fnMatch = style.match(/^\s*(\w+)\s*\(\s*([^)]*)\s*\)\s*/);
+	if (!fnMatch) {
+		assertStyle(chalk, style);
+		return chalk[style];
+	}
+
+	const name = fnMatch[1].trim();
+	const args = fnMatch[2].split(/,/g).map(s => s.trim());
+
+	assertStyle(chalk, name);
+
+	return chalk[name].apply(chalk, args);
+}
+
+/**
+ * Performs the actual styling of the string, essentially lifted from cli.js.
+ * */
+function style(chalk, flat) {
+	return flat.map(data => {
+		const fn = data.styles.reduce(parseStyle, chalk);
+		return fn(data.content.replace(/\n$/, ''));
+	}).join('');
+}
+
+module.exports = (chalk, string) => style(chalk, flatten(parse(string)));