import type { KkastContent, Root } from "@rshirohara/kkast";
import type { Options } from "./options.js";

type KkastNode = KkastContent | Root;
type Postprocessor<T extends KkastNode> = (node: T, option: Options) => T;

export const postprocess: Postprocessor<Root> = (node, options) => {
	const processors: Postprocessor<Root>[] = [
		removeEmptyNode,
		insertParagraphMargin,
	];
	let result: Root = { ...node };
	for (const processor of processors) {
		result = processor(result, options);
	}
	return result;
};

function removeEmptyNode<T extends Root>(node: T, _: Options): T {
	function removeNode<T extends KkastContent>(node: T): T | undefined {
		if (node.type === "paragraph" && node.children.length === 0) {
			return undefined;
		}
		return node;
	}

	return {
		...node,
		children: [...node.children]
			.map((node) => removeNode(node))
			.filter((node) => node !== undefined),
	};
}

function insertParagraphMargin<T extends Root>(node: T, _: Options): T {
	return {
		...node,
		children: [...node.children].flatMap((value, index) =>
			index + 1 < node.children.length
				? [value, { type: "paragraphMargin", size: 1 }]
				: [value],
		),
	};
}