import type { MarkdownIt, Token } from "markdown-it";
import {
	blockAnchor,
	STANDALONE_BLOCK_ID_RE,
	TRAILING_BLOCK_ID_RE,
} from "../block-ids.ts";

// Tight list items hide their paragraph, so an id set there would never reach the HTML.
function anchorToken(tokens: Token[], inlineIndex: number): Token | null {
	let i = inlineIndex - 1;
	while (tokens[i]?.hidden && tokens[i - 1]?.nesting === 1) i--;
	return tokens[i] ?? null;
}

function isBlockStart(token: Token): boolean {
	return token.nesting !== -1 && token.type !== "inline";
}

// Obsidian block ids: "text ^id" ending a block, or "^id" alone on the line after one.
// Headings are excluded — Obsidian addresses those with "#Heading", and their id is
// already the heading anchor.
export function blockIdPlugin(mdi: MarkdownIt): void {
	mdi.core.ruler.after("block", "block_id", (state) => {
		const tokens = state.tokens;
		const standalone: number[] = [];
		let previousBlock: Token | null = null;
		let currentBlock: Token | null = null;

		for (let i = 0; i < tokens.length; i++) {
			const token = tokens[i];
			if (!token) continue;
			if (token.level === 0 && isBlockStart(token)) {
				previousBlock = currentBlock;
				currentBlock = token;
			}
			if (token.type !== "inline") continue;

			const content = token.content.trimEnd();

			const alone = STANDALONE_BLOCK_ID_RE.exec(content);
			if (alone?.[1] && token.level === 1 && previousBlock) {
				const anchor = blockAnchor(alone[1]);
				if (anchor) {
					previousBlock.attrSet("id", anchor);
					standalone.push(i - 1);
					currentBlock = previousBlock;
					continue;
				}
			}

			const trailing = TRAILING_BLOCK_ID_RE.exec(content);
			if (!trailing?.[1]) continue;
			const target = anchorToken(tokens, i);
			if (!target || target.type === "heading_open") continue;
			const anchor = blockAnchor(trailing[1]);
			if (!anchor) continue;
			target.attrSet("id", anchor);
			token.content = content.slice(0, trailing.index);
		}

		// Back to front: the marker paragraph itself leaves no output.
		for (let i = standalone.length - 1; i >= 0; i--) {
			tokens.splice(standalone[i] as number, 3);
		}
	});
}