base64-encoded-import.ts

import type { Condition } from './conditions';
import { formatImportPrelude } from './format-import-prelude';

// Base64 encode an import with conditions
// The order of conditions is important and is interleaved with cascade layer declarations
// Each group of conditions and cascade layers needs to be interpreted in order
// To achieve this we create a list of base64 encoded imports, where each import contains a stylesheet with another import.
// Each import can define a single group of conditions and a single cascade layer.
export function base64EncodedConditionalImport(prelude: string, conditions: Array<Condition>): string {
	conditions.reverse();
	const first = conditions.pop();
	if (!first) {
		return prelude;
	}

	let params = `${prelude} ${formatImportPrelude(
		first.layer,
		first.media,
		first.supports,
		first.scope,
	)}`;

	for (const condition of conditions) {
		params = `"data:text/css;base64,${Buffer.from(
			`@import ${params}`,
		).toString('base64')}" ${formatImportPrelude(
			condition.layer,
			condition.media,
			condition.supports,
			condition.scope,
		)}`;
	}

	return params;
}