"use strict";

const assert = require("assert");

const acceptableFirstCharacters = /^[a-zA-Z_]$/;
const acceptableSubsequentCharacters = /^[0-9a-zA-Z_]$/;

const reservedWords = new Set([
	"import",
	"const",
	"let",
	"var"
]);

// This function deterministically and statelessly translates a name such that it is guaranteed to be valid in all identifier positions in JS.
// TODO: This can probably be made more performant...

function mangleCharacter(character) {
	return (character === "$")
		? "$$"
		: `$${character.codePointAt(0)}`;
}

module.exports = function mangleName(name) {
	assert(name.length > 0);
	
	if (reservedWords.has(name)) {
		return "$" + name;
	} else if (name.startsWith("$")) {
		// FIXME: Tag an identifier of this type with an internal property instead
		return name;
	} else {
		let completedFirstCharacter = false;

		return Array.from(name)
			.map((character) => {
				if (!completedFirstCharacter) {
					completedFirstCharacter = true;
					
					return (acceptableFirstCharacters.test(character))
						? character
						: mangleCharacter(character);
				} else {
					return (acceptableSubsequentCharacters.test(character))
						? character
						: mangleCharacter(character);
				}
			})
			.join("");
	}
};