html.js

import { createElement } from './src/core.js';

const MODE_SLASH = 0;
const MODE_TEXT = 1;
const MODE_WHITESPACE = 2;
const MODE_TAGNAME = 3;
const MODE_COMMENT = 4;
const MODE_PROP_SET = 5;
const MODE_PROP_APPEND = 6;

const CHILD_APPEND = 0;
const CHILD_RECURSE = 2;
const TAG_SET = 3;
const PROPS_ASSIGN = 4;
const PROP_SET = MODE_PROP_SET;
const PROP_APPEND = MODE_PROP_APPEND;

const evaluate = (h, built, fields, args) => {
	let tmp;

	// `build()` used the first element of the operation list as
	// temporary workspace. Now that `build()` is done we can use
	// that space to track whether the current element is "dynamic"
	// (i.e. it or any of its descendants depend on dynamic values).
	built[0] = 0;

	for (let i = 1; i < built.length; i++) {
		const type = built[i++];

		// Set `built[0]`'s appropriate bits if this element depends on a dynamic value.
		const value = built[i] ? ((built[0] |= type ? 1 : 2), fields[built[i++]]) : built[++i];

		if (type === TAG_SET) {
			args[0] = value;
		}
		else if (type === PROPS_ASSIGN) {
			args[1] = Object.assign(args[1] || {}, value);
		}
		else if (type === PROP_SET) {
			(args[1] = args[1] || {})[built[++i]] = value;
		}
		else if (type === PROP_APPEND) {
			args[1][built[++i]] += (value + '');
		}
		else if (type) { // type === CHILD_RECURSE
			// Set the operation list (including the staticness bits) as
			// `this` for the `h` call.
			tmp = h.apply(value, evaluate(h, value, fields, ['', null]));
			args.push(tmp);

			if (value[0]) {
				// Set the 2nd lowest bit it the child element is dynamic.
				built[0] |= 2;
			}
			else {
				// Rewrite the operation list in-place if the child element is static.
				// The currently evaluated piece `CHILD_RECURSE, 0, [...]` becomes
				// `CHILD_APPEND, 0, tmp`.
				// Essentially the operation list gets optimized for potential future
				// re-evaluations.
				built[i-2] = CHILD_APPEND;
				built[i] = tmp;
			}
		}
		else { // type === CHILD_APPEND
			args.push(value);
		}
	}

	return args;
};

const build = function(statics) {

	let mode = MODE_TEXT;
	let buffer = '';
	let quote = '';
	let current = [0];
	let char, propName;

	const commit = field => {
		if (mode === MODE_TEXT && (field || (buffer = buffer.replace(/^\s*\n\s*|\s*\n\s*$/g,'')))) {
			{
				current.push(CHILD_APPEND, field, buffer);
			}
		}
		else if (mode === MODE_TAGNAME && (field || buffer)) {
			{
				current.push(TAG_SET, field, buffer);
			}
			mode = MODE_WHITESPACE;
		}
		else if (mode === MODE_WHITESPACE && buffer === '...' && field) {
			{
				current.push(PROPS_ASSIGN, field, 0);
			}
		}
		else if (mode === MODE_WHITESPACE && buffer && !field) {
			{
				current.push(PROP_SET, 0, true, buffer);
			}
		}
		else if (mode >= MODE_PROP_SET) {
			{
				if (buffer || (!field && mode === MODE_PROP_SET)) {
					current.push(mode, 0, buffer, propName);
					mode = MODE_PROP_APPEND;
				}
				if (field) {
					current.push(mode, field, 0, propName);
					mode = MODE_PROP_APPEND;
				}
			}
		}

		buffer = '';
	};

	for (let i=0; i<statics.length; i++) {
		if (i) {
			if (mode === MODE_TEXT) {
				commit();
			}
			commit(i);
		}

		for (let j=0; j<statics[i].length;j++) {
			char = statics[i][j];

			if (mode === MODE_TEXT) {
				if (char === '<') {
					// commit buffer
					commit();
					{
						current = [current];
					}
					mode = MODE_TAGNAME;
				}
				else {
					buffer += char;
				}
			}
			else if (mode === MODE_COMMENT) {
				// Ignore everything until the last three characters are '-', '-' and '>'
				if (buffer === '--' && char === '>') {
					mode = MODE_TEXT;
					buffer = '';
				}
				else {
					buffer = char + buffer[0];
				}
			}
			else if (quote) {
				if (char === quote) {
					quote = '';
				}
				else {
					buffer += char;
				}
			}
			else if (char === '"' || char === "'") {
				quote = char;
			}
			else if (char === '>') {
				commit();
				mode = MODE_TEXT;
			}
			else if (!mode) ;
			else if (char === '=') {
				mode = MODE_PROP_SET;
				propName = buffer;
				buffer = '';
			}
			else if (char === '/' && (mode < MODE_PROP_SET || statics[i][j+1] === '>')) {
				commit();
				if (mode === MODE_TAGNAME) {
					current = current[0];
				}
				mode = current;
				{
					(current = current[0]).push(CHILD_RECURSE, 0, mode);
				}
				mode = MODE_SLASH;
			}
			else if (char === ' ' || char === '\t' || char === '\n' || char === '\r') {
				// <a disabled>
				commit();
				mode = MODE_WHITESPACE;
			}
			else {
				buffer += char;
			}

			if (mode === MODE_TAGNAME && buffer === '!--') {
				mode = MODE_COMMENT;
				current = current[0];
			}
		}
	}
	commit();
	return current;
};

const CACHE = new Map();

function html(statics) {
    let tmp = CACHE;

    tmp = evaluate(
        createElement,
        tmp.get(statics) || (tmp.set(statics, (tmp = build(statics))), tmp),
        arguments,
        []
    );

    return tmp.length > 1 ? tmp : tmp[0];
}

export { html };