export class LocalIdent {
	readonly name: string | undefined;

	constructor(name: string | undefined) {
		this.name = name;
	}
}

export class CodeFragment {
	readonly strings: readonly string[];
	readonly values: readonly unknown[];

	constructor(strings: readonly string[], values: readonly unknown[]) {
		this.strings = strings;
		this.values = values;
	}

	/** evaluate the fragment via `new Function`, returning the result */
	eval(): unknown {
		const seen = new Map<unknown, string>();
		const interpolations: unknown[] = [];

		let uid = 0;
		let params = '';

		const resolve = ({ strings, values }: CodeFragment): string => {
			let source = strings[0]!;

			for (let idx = 0, len = values.length; idx < len; idx++) {
				const val = values[idx];

				if (val instanceof CodeFragment) {
					source += resolve(val);
				} else if (val instanceof LocalIdent) {
					let name = seen.get(val);
					if (name === undefined) {
						if (val.name !== undefined) {
							name = `_$${uid++}_${val.name}`;
						} else {
							name = `_$${uid++}`;
						}

						seen.set(val, name);
					}

					source += name;
				} else {
					let name = seen.get(val);
					if (name === undefined) {
						name = `_$${uid++}`;
						params = params ? params + ',' + name : name;

						seen.set(val, name);
						interpolations.push(val);
					}

					source += name;
				}

				source += strings[idx + 1]!;
			}

			return source;
		};

		const source = resolve(this);

		const fn = new Function(`[${params}]`, source);

		return fn(interpolations);
	}
}

const EMPTY: readonly unknown[] = [];
const NONIDENT_RE = /[^A-Za-z0-9_$]/g;

// #__NO_SIDE_EFFECTS__
export const raw = (source: string): CodeFragment => {
	return new CodeFragment([source], EMPTY);
};

// #__NO_SIDE_EFFECTS__
export const x = (strings: TemplateStringsArray, ...values: unknown[]): CodeFragment => {
	return new CodeFragment(strings, values);
};

// #__NO_SIDE_EFFECTS__
export const local = (name?: string): LocalIdent => {
	return new LocalIdent(name?.replace(NONIDENT_RE, '_'));
};