export interface IndexEntry {
	name: string; // 原名 title，取自 frontmatter name
	topic: string; // 文件名
	hook: string; // 一行描述
	raw: string; // 原始行文本
}

export interface IndexFile {
	entries: IndexEntry[];
	raw: string;
}

// Matches: - [Name](topic.md) — hook
const LINE_RE = /^-\s+\[([^\]]+)\]\(([^)]+)\)\s*—\s*(.*)$/;

export function parseIndex(content: string): IndexFile {
	const entries: IndexEntry[] = [];
	for (const line of content.split("\n")) {
		const m = line.match(LINE_RE);
		if (m) {
			entries.push({
				name: m[1].trim(),
				topic: m[2].trim(),
				hook: m[3].trim(),
				raw: line,
			});
		}
	}
	return { entries, raw: content };
}

export function serializeIndex(entries: IndexEntry[]): string {
	return entries.map((e) => `- [${e.name}](${e.topic}) — ${e.hook}`).join("\n");
}

export function upsertEntryByTopic(entries: IndexEntry[], entry: IndexEntry): IndexEntry[] {
	const idx = entries.findIndex((e) => e.topic === entry.topic);
	if (idx === -1) return [...entries, entry];
	const next = [...entries];
	next[idx] = entry;
	return next;
}

export function removeEntryByTopic(entries: IndexEntry[], topic: string): IndexEntry[] {
	const idx = entries.findIndex((e) => e.topic === topic);
	if (idx === -1) throw new Error(`Topic "${topic}" not found in index`);
	const next = [...entries];
	next.splice(idx, 1);
	return next;
}

export function findEntryByTopic(entries: IndexEntry[], topic: string): IndexEntry | null {
	return entries.find((e) => e.topic === topic) ?? null;
}

export function updateHook(entries: IndexEntry[], topic: string, hook: string): IndexEntry[] {
	const idx = entries.findIndex((e) => e.topic === topic);
	if (idx === -1) throw new Error(`Topic "${topic}" not found in index`);
	const next = [...entries];
	next[idx] = { ...next[idx], hook, raw: "" };
	return next;
}

export function truncateForInjection(
	content: string,
	maxLines: number,
	maxBytes: number,
): { ok: boolean; content: string; truncated: boolean } {
	const lines = content.split("\n");
	let out = content;
	let truncated = false;
	if (lines.length > maxLines) {
		out = lines.slice(0, maxLines).join("\n");
		truncated = true;
	}
	if (Buffer.byteLength(out, "utf8") > maxBytes) {
		let cut = out;
		while (Buffer.byteLength(cut, "utf8") > maxBytes && cut.length > 0) cut = cut.slice(0, -1);
		out = cut;
		truncated = true;
	}
	if (truncated) out += `\n[truncated: memory index exceeds injection limit]`;
	return { ok: !truncated, content: out, truncated };
}

export function checkCapacity(entries: IndexEntry[], maxLines: number, maxBytes: number): boolean {
	const serialized = serializeIndex(entries);
	if (entries.length > maxLines) return false;
	if (Buffer.byteLength(serialized, "utf8") > maxBytes) return false;
	return true;
}