/**
 * THE SESSION MARKDOWN EXPORT (owner, release polish 2026-10-06): the
 * user-facing export the session-markdown engine was built for — the
 * same document the extractor reads, minted anchorless (anchors are
 * extraction provenance; a learner's export carries no message ids).
 *
 * GET /api/chats/:id/markdown → the whole session as one markdown file
 * (Content-Disposition attachment; filename from the slugified title).
 * 404 unknown chat. Both session kinds export — practice sessions ride
 * the same engine (problem/conclude results render as tool blocks,
 * markers are invisible by the engine's law).
 */
import { sessionMarkdown } from "@/src/core";
import { getChat, applicationLanguage } from "@/src/server";

/** Filename-safe title (own module scope on purpose: tiny + pure). */
function slugify(title: string): string {
	const slug = title
		.toLowerCase()
		.normalize("NFKD")
		.replace(/[^\p{L}\p{N}]+/gu, "-")
		.replace(/^-+|-+$/g, "");
	return slug.length > 0 ? slug : "session";
}

export async function GET(_req: Request, ctx: { params: Promise<{ id: string }> }): Promise<Response> {
	const { id } = await ctx.params;
	const record = getChat(id);
	if (!record) return Response.json({ error: "Unknown chat" }, { status: 404 });
	const markdown = sessionMarkdown(record.messages, { title: record.title, anchors: false, language: applicationLanguage(_req.headers.get("accept-language")) });
	return new Response(markdown, {
		headers: {
			"content-type": "text/markdown; charset=utf-8",
			"content-disposition": `attachment; filename="${/^[a-z0-9-]+$/.test(slugify(record.title)) ? slugify(record.title) : "session"}.md"; filename*=UTF-8''${encodeURIComponent(slugify(record.title))}.md`,
		},
	});
}