import { slugify } from "./slug.ts";

interface Heading {
	text: string;
	level: number;
	anchor: string;
}

/**
 * Allocate an anchor for `text`, disambiguating repeats by suffixing -1, -2, ...
 * `seen` tracks how many times each base slug has been used so far in the doc.
 */
export function makeAnchor(text: string, seen: Map<string, number>): string {
	const base = slugify(text);
	if (!base) return base;
	const n = seen.get(base) ?? 0;
	seen.set(base, n + 1);
	return n === 0 ? base : `${base}-${n}`;
}

const HEADING_RE = /^(#{1,6})\s+(.+?)\s*#*\s*$/;
const FENCE_RE = /^(`{3,}|~{3,})/;

/** Extract ATX headings from markdown, skipping fenced code blocks. */
export function extractHeadings(md: string): Heading[] {
	const out: Heading[] = [];
	const seen = new Map<string, number>();
	let fence: string | null = null;
	for (const line of md.split("\n")) {
		const fenceMatch = line.match(FENCE_RE);
		if (fenceMatch) {
			const marker = fenceMatch[1]?.[0];
			if (fence === null) {
				fence = marker ?? null;
			} else if (marker === fence) {
				fence = null;
			}
			continue;
		}
		if (fence !== null) continue;
		const m = line.match(HEADING_RE);
		if (!m) continue;
		const level = m[1]?.length ?? 0;
		const text = m[2]?.trim() ?? "";
		if (!text) continue;
		const anchor = makeAnchor(text, seen);
		if (!anchor) continue;
		out.push({ text, level, anchor });
	}
	return out;
}