// client-side comment threading, ported from NewCommentList in appview/models/comment.go.
// bobbin returns comments flat; we group replies under the top-level comment their
// replyTo strongRef points at, and sort everything oldest-first.

export interface CommentView {
	uri: string;
	// content hash, needed to strongRef this comment when replying to it
	cid?: string;
	rkey: string;
	authorDid: string;
	authorHandle: string;
	createdAt: string;
	body: string;
	bodyHtml: string | null;
}

export interface CommentThread {
	self: CommentView;
	replies: CommentView[];
}

// pairs a rendered view with the parent uri it replies to (null for top-level).
export interface ThreadInput {
	comment: CommentView;
	replyTo: string | null;
}

const byCreatedAt = (a: CommentView, b: CommentView) => a.createdAt.localeCompare(b.createdAt);

export function buildCommentThreads(inputs: ThreadInput[]): CommentThread[] {
	const threads = new Map<string, CommentThread>();
	const orphanReplies: ThreadInput[] = [];

	for (const input of inputs) {
		if (input.replyTo === null) {
			threads.set(input.comment.uri, { self: input.comment, replies: [] });
		}
	}

	for (const input of inputs) {
		if (input.replyTo === null) continue;
		const parent = threads.get(input.replyTo);
		if (parent) {
			parent.replies.push(input.comment);
		} else {
			// parent not found (e.g. legacy/cross-collection ref): surface as top-level
			// so nothing is dropped.
			orphanReplies.push(input);
		}
	}

	for (const orphan of orphanReplies) {
		threads.set(orphan.comment.uri, { self: orphan.comment, replies: [] });
	}

	const list = [...threads.values()];
	list.sort((a, b) => byCreatedAt(a.self, b.self));
	for (const thread of list) thread.replies.sort(byCreatedAt);
	return list;
}