import { createReadStream } from 'node:fs';
import { stat } from 'node:fs/promises';
import { Readable } from 'node:stream';
import express, { type Request, type Response, type Router } from 'express';
import { SchulcloudApiError } from '../core/client.ts';
import {
	compareNames,
	FileManagerMarkupError,
	FsError,
	nameMatcher,
	type FmFile,
	type FsErrorCode,
	type WalkEntry,
} from '../core/legacy-files.ts';
import { dayLessons, dayNoteSkeleton, dayNoteTitle, missingHeadings } from '../core/day-note.ts';
import { isCalendarDate, schoolToday } from '../core/dates.ts';
import {
	dayNotePath,
	NoteConflict,
	NoteNotFound,
	filterNotes,
	readNoteAt,
	readNotes,
	replaceNote,
	writeNote,
} from '../core/notes.ts';
import { resolveWithin } from '../core/paths.ts';
import { TokenRejected } from '../core/session-token.ts';
import type { Services } from '../services.ts';

/**
 * The CLI's backend: file bytes, the sync manifest, and on-demand re-crawls.
 *
 * These sit behind the same bearer check as `/mcp`, on the same host. Bytes go
 * over plain HTTP rather than through MCP because base64 inside JSON-RPC costs
 * a third more bandwidth and buffers whole files in memory; ranged streaming
 * from the mirror does neither, which matters for the video files.
 *
 * Nothing here can write to Schulcloud. `/refresh` writes only to the Pi's own
 * index and mirror, `/token` only to the server's own token, and every upstream
 * call either triggers is a GET.
 */
const NO_NOTES_DIR =
	'This server keeps no notes: NOTES_DIR is not set on it. See docs/NOTES.md.';

export function createApiRouter(services: Services): Router {
	const router = express.Router();

	router.get('/manifest', async (req: Request, res: Response) => {
		if (!services.store) return res.status(503).json({ error: 'no_index' });
		try {
			const sinceParam = typeof req.query.since === 'string' ? req.query.since : undefined;
			const since = sinceParam ? await services.store.resolveCursor(sinceParam) : undefined;
			if (sinceParam && since === undefined) {
				// An unresolvable cursor must not silently mean "everything is new":
				// say so, so the client can decide to do a full sync deliberately.
				return res.status(409).json({
					error: 'cursor_unknown',
					message: `No crawl at or before "${sinceParam}". Sync without a cursor for a full manifest.`,
				});
			}
			const { crawlId, entries } = await services.store.manifest(since);
			const stats = await services.store.stats();
			return res.json({ crawlId, cursor: String(crawlId), crawledAt: stats.crawledAt, count: entries.length, entries });
		} catch (error) {
			return fail(res, error, 'manifest');
		}
	});

	router.get('/status', async (_req: Request, res: Response) => {
		if (!services.store) return res.status(503).json({ error: 'no_index' });
		try {
			const stats = await services.store.stats();
			return res.json({ ...stats, indexer: services.indexer?.status() ?? null });
		} catch (error) {
			return fail(res, error, 'status');
		}
	});

	router.post('/refresh', express.json({ limit: '16kb' }), async (req: Request, res: Response) => {
		if (!services.indexer) return res.status(503).json({ error: 'no_index' });
		const body = (req.body ?? {}) as { courseId?: string; force?: boolean; wait?: boolean };
		try {
			const scope = body.courseId ?? 'full';
			// `wait: false` answers at once and leaves the caller to poll /status.
			// Waiting for the result in this request is kept for older clients, but
			// it cannot outlast a long crawl: Node's fetch abandons a response whose
			// headers have not arrived within five minutes.
			if (body.wait === false) {
				const { run, joined } = services.indexer.start(scope, { force: body.force === true });
				// The outcome is recorded by the indexer (status().lastResult/lastError);
				// this only keeps an unawaited failure from becoming an unhandled one.
				run.catch(() => {});
				const status = services.indexer.status();
				return res.status(202).json({ started: !joined, joined, scope, startedAt: status.startedAt ?? null });
			}
			const result = await services.indexer.refresh(scope, { force: body.force === true });
			return res.json(result);
		} catch (error) {
			// A rate-limit refusal is the caller's problem to act on, not a fault.
			const message = error instanceof Error ? error.message : String(error);
			if (/Wait \d+s/.test(message)) return res.status(429).json({ error: 'too_soon', message });
			return fail(res, error, 'refresh');
		}
	});

	// --- the file manager ("Dateien"), as a filesystem ----------------------
	//
	// Live, not from the index: these answer what the file manager holds now, and
	// need no database. Paths are the same ones the MCP fs_* tools print.

	router.get('/fs/list', async (req: Request, res: Response) => {
		try {
			const node = await services.files.resolve(stringParam(req.query.path) ?? '/');
			if (node.kind === 'file') return res.json({ path: node.path, kind: 'file', file: node.file });
			const listing = await services.files.list(node.ref);
			return res.json({
				path: node.path,
				kind: 'directory',
				area: node.ref.area ?? null,
				directories: listing.directories.map((entry) => ({ ...entry, path: childPath(node.path, entry.name) })),
				files: listing.files.map((entry) => ({ ...entry, path: childPath(node.path, entry.name) })),
			});
		} catch (error) {
			return fsFail(res, error, 'fs list');
		}
	});

	router.get('/fs/tree', async (req: Request, res: Response) => {
		try {
			const node = await services.files.resolve(stringParam(req.query.path) ?? '/');
			if (node.kind === 'file') return res.json({ path: node.path, kind: 'file', file: node.file });
			const result = await services.files.walk(node, {
				maxDepth: boundedInt(req.query.depth, 3, 1, 12),
				maxDirectories: boundedInt(req.query.maxFolders, 200, 1, 1000),
			});
			return res.json({
				path: node.path,
				kind: 'directory',
				entries: result.entries.map(treeEntry),
				visited: result.visited,
				truncated: result.truncated,
				failures: result.failures,
			});
		} catch (error) {
			return fsFail(res, error, 'fs tree');
		}
	});

	router.get('/fs/find', async (req: Request, res: Response) => {
		const name = stringParam(req.query.name);
		if (!name) return res.status(400).json({ error: 'bad_request', message: 'Give name.' });
		try {
			const node = await services.files.resolve(stringParam(req.query.path) ?? '/');
			if (node.kind === 'file') return res.json({ path: node.path, kind: 'file', matches: [] });
			const type = stringParam(req.query.type) ?? 'any';
			const matches = nameMatcher(name);
			const result = await services.files.walk(node, {
				maxDepth: 12,
				maxDirectories: boundedInt(req.query.maxFolders, 400, 1, 1000),
			});
			return res.json({
				path: node.path,
				kind: 'directory',
				matches: result.entries
					.filter((entry) => (type === 'file' ? entry.file : type === 'folder' ? entry.directory : true))
					.filter((entry) => matches((entry.file ?? entry.directory)?.name ?? ''))
					.sort((a, b) => compareNames(a.path, b.path))
					.map(treeEntry),
				visited: result.visited,
				truncated: result.truncated,
				failures: result.failures,
			});
		} catch (error) {
			return fsFail(res, error, 'fs find');
		}
	});

	router.get('/fs/file', async (req: Request, res: Response) => {
		try {
			const path = stringParam(req.query.path);
			const id = stringParam(req.query.id);
			let file: Pick<FmFile, 'id' | 'name'> & Partial<FmFile>;
			if (path) {
				const node = await services.files.resolve(path);
				if (node.kind !== 'file') return res.status(400).json({ error: 'not_a_file', message: `${node.path} is a folder.` });
				file = node.file;
			} else if (id && /^[0-9a-f]{24}$/i.test(id)) {
				file = { id, name: stringParam(req.query.name) ?? id };
			} else {
				return res.status(400).json({ error: 'bad_request', message: 'Give path, or id (and name).' });
			}
			if (file.blocked) {
				return res.status(403).json({ error: 'blocked', message: 'The instance virus scanner blocked this file.' });
			}

			// Streamed straight through rather than buffered: the CLI uses this for
			// whole folders, and videos routinely exceed any sensible in-memory cap.
			const signed = await services.client.getFileManagerSignedUrl(file.id, file.name);
			const upstream = await services.client.openSignedUrl(signed);
			if (!upstream.body) return res.status(502).json({ error: 'upstream_failed', message: 'empty response' });

			res.setHeader('Content-Type', file.mimeType || upstream.headers.get('content-type') || 'application/octet-stream');
			res.setHeader('Content-Disposition', contentDisposition(file.name));
			const length = upstream.headers.get('content-length');
			if (length) res.setHeader('Content-Length', length);
			res.setHeader('X-Schulcloud-Source', 'file-manager');
			Readable.fromWeb(upstream.body as never).pipe(res);
		} catch (error) {
			return fsFail(res, error, 'fs file');
		}
	});

	/**
	 * Streams one file. Served from the local mirror when present; otherwise
	 * proxied live, which is what keeps files too large to mirror reachable.
	 */
	router.get('/files/:fileId', async (req: Request, res: Response) => {
		const raw = req.params.fileId;
		const fileId = Array.isArray(raw) ? raw[0] : raw;
		// Mongo ObjectId shape. Validated before it reaches the store or a path.
		if (typeof fileId !== 'string' || !/^[0-9a-f]{24}$/i.test(fileId)) {
			return res.status(400).json({ error: 'bad_file_id' });
		}
		if (!services.store) return res.status(503).json({ error: 'no_index' });

		try {
			const entry = await services.store.mirrorEntry(fileId);
			if (entry) {
				const absolute = resolveWithin(services.config.mirrorDir, entry.path);
				const info = await stat(absolute).catch(() => undefined);
				if (info?.isFile()) {
					res.setHeader('Content-Type', entry.mimeType);
					res.setHeader('Content-Disposition', contentDisposition(entry.name));
					// sendFile handles Range, ETag and conditional requests for us.
					return res.sendFile(absolute, { dotfiles: 'deny', acceptRanges: true }, (error) => {
						if (error && !res.headersSent) res.status(500).end();
					});
				}
			}
			const known = await services.store.fileSource(fileId);
			if (known?.source === 'file-manager') return await proxyFileManager(services, fileId, known, res);
			return await proxyLive(services, fileId, res);
		} catch (error) {
			return fail(res, error, 'file');
		}
	});

	// --- the Schulcloud session token -------------------------------------------
	//
	// A write, but to this server's own state: the token it reads Schulcloud with.
	// The only upstream call is the GET /me a replacement must pass first. Works
	// without an index, since a server without one still needs a token.

	// --- the user's own lesson notes ----------------------------------------
	//
	// Read off disk, like the fs_* routes read Schulcloud: no index involved, so
	// these answer before the first crawl and while Postgres is down. The POST is
	// the only write in this server that is not the index or its own token, and
	// it can reach nothing but the notes directory — `writeNote` builds every
	// path component with `safeComponent` and checks the result with
	// `resolveWithin`.

	router.get('/notes', async (req: Request, res: Response) => {
		const root = services.config.notesDir;
		if (!root) return res.status(503).json({ error: 'no_notes_dir', message: NO_NOTES_DIR });
		try {
			const path = stringParam(req.query.path);
			if (path) return res.json(await readNoteAt(root, path));
			const notes = filterNotes(await readNotes(root), {
				...pickParam('subject', req.query.subject),
				...pickParam('since', req.query.since),
				...pickParam('until', req.query.until),
				...pickParam('courseId', req.query.courseId),
			});
			const limit = Math.min(Number.parseInt(stringParam(req.query.limit) ?? '', 10) || 500, 2000);
			return res.json({
				root,
				writable: services.config.notesWritable,
				count: notes.length,
				// The body is dropped from a listing: a term of notes is megabytes,
				// and the CLI asks for the ones it wants by path.
				notes: notes.slice(0, limit).map(({ text, ...rest }) => rest),
			});
		} catch (error) {
			if (error instanceof NoteNotFound) return res.status(404).json({ error: 'not_found', message: error.message });
			return fail(res, error, 'notes');
		}
	});

	router.post('/notes', express.json({ limit: '1mb' }), async (req: Request, res: Response) => {
		const root = services.config.notesDir;
		if (!root) return res.status(503).json({ error: 'no_notes_dir', message: NO_NOTES_DIR });
		if (!services.config.notesWritable) {
			return res.status(403).json({ error: 'notes_readonly', message: 'This server was started with NOTES_READONLY.' });
		}
		const body = (req.body ?? {}) as Record<string, unknown>;
		const title = typeof body.title === 'string' ? body.title.trim() : '';
		const noteText = typeof body.text === 'string' ? body.text : '';
		if (!title || !noteText.trim()) {
			return res.status(400).json({ error: 'invalid', message: 'A note needs a title and some text.' });
		}
		try {
			const { note, appended } = await writeNote(root, {
				title,
				text: noteText,
				...pickParam('date', body.date),
				...pickParam('subject', body.subject),
				...pickParam('courseId', body.courseId),
				...pickParam('path', body.path),
				...pickParam('source', body.source),
				...(Array.isArray(body.tags) ? { tags: body.tags.filter((tag): tag is string => typeof tag === 'string') } : {}),
				append: body.append === true,
			});
			return res.status(appended ? 200 : 201).json({ ...note, appended });
		} catch (error) {
			return fail(res, error, 'save a note');
		}
	});

	// --- one school day, as the notes page edits it -------------------------
	//
	// The page is a Markdown editor for a single file, so these two are `GET the
	// day` and `PUT the day`. What makes them worth their own routes rather than
	// the generic ones above is the skeleton: WebUntis is the only thing that
	// knows which lessons a day held, and handing someone their day already laid
	// out is the difference between a note per day and an empty box.

	router.get('/notes/day', async (req: Request, res: Response) => {
		const root = services.config.notesDir;
		if (!root) return res.status(503).json({ error: 'no_notes_dir', message: NO_NOTES_DIR });
		const date = stringParam(req.query.date) ?? schoolToday();
		if (!isCalendarDate(date)) {
			return res.status(400).json({ error: 'invalid', message: `Not a date in the calendar: ${date}.` });
		}
		try {
			const path = dayNotePath(date);
			const note = await readNoteAt(root, path).catch((error: unknown) => {
				if (error instanceof NoteNotFound) return undefined;
				throw error;
			});

			// Never fatal, and reported rather than hidden: without a key, or with
			// WebUntis down, the page still has to open — it just cannot offer the
			// lessons, and saying so beats an empty skeleton that looks like a day
			// with no school.
			let lessons: ReturnType<typeof dayLessons> = [];
			let timetable: 'ok' | 'off' | 'unavailable' = services.untis ? 'ok' : 'off';
			if (services.untis) {
				try {
					lessons = dayLessons(await services.untis.timetable(date, date), date);
				} catch {
					timetable = 'unavailable';
				}
			}

			return res.json({
				date,
				path,
				title: dayNoteTitle(date),
				exists: Boolean(note),
				text: note?.text ?? '',
				modifiedAt: note?.modifiedAt ?? null,
				timetable,
				lessons,
				skeleton: dayNoteSkeleton(lessons),
				// What the page would add to a note already started, so "top up the
				// day" never rewrites what is there.
				missing: note ? dayNoteSkeleton(missingHeadings(note.text, lessons)) : '',
			});
		} catch (error) {
			return fail(res, error, 'read a day note');
		}
	});

	router.put('/notes/day', express.json({ limit: '2mb' }), async (req: Request, res: Response) => {
		const root = services.config.notesDir;
		if (!root) return res.status(503).json({ error: 'no_notes_dir', message: NO_NOTES_DIR });
		if (!services.config.notesWritable) {
			return res.status(403).json({ error: 'notes_readonly', message: 'This server was started with NOTES_READONLY.' });
		}
		const body = (req.body ?? {}) as { date?: unknown; text?: unknown; expectedModifiedAt?: unknown };
		const date = typeof body.date === 'string' ? body.date : '';
		if (!isCalendarDate(date)) {
			return res.status(400).json({ error: 'invalid', message: `Not a date in the calendar: ${date || '(none)'}.` });
		}
		if (typeof body.text !== 'string') {
			return res.status(400).json({ error: 'invalid', message: 'A day note needs its text.' });
		}
		try {
			const note = await replaceNote(
				root,
				dayNotePath(date),
				{ title: dayNoteTitle(date), text: body.text, date, source: 'notes-page' },
				typeof body.expectedModifiedAt === 'string' ? { expectedModifiedAt: body.expectedModifiedAt } : {},
			);
			return res.json({ path: note.path, modifiedAt: note.modifiedAt, bytes: note.bytes });
		} catch (error) {
			// A clash is the caller's to resolve, not a fault: the page shows both
			// and lets the person decide, which is the only safe answer when the
			// notes folder is synced and open in two places.
			if (error instanceof NoteConflict) {
				return res.status(409).json({ error: 'conflict', message: error.message, modifiedAt: error.modifiedAt });
			}
			return fail(res, error, 'save a day note');
		}
	});

	router.get('/token', (_req: Request, res: Response) => {
		res.json(tokenStatus(services));
	});

	router.put('/token', express.json({ limit: '16kb' }), async (req: Request, res: Response) => {
		const jwt = (req.body as { jwt?: unknown } | undefined)?.jwt;
		if (typeof jwt !== 'string' || !jwt.trim()) {
			return res.status(400).json({ error: 'missing_jwt', message: 'Send {"jwt": "<the value of the jwt cookie>"}.' });
		}
		try {
			const { changed, persisted } = await services.session.replace(jwt);
			if (changed) console.log('[schulcloud-mcp] session token replaced at runtime');
			return res.json({ changed, persisted, ...tokenStatus(services) });
		} catch (error) {
			if (error instanceof TokenRejected) return res.status(422).json({ error: error.problem, message: error.message });
			// Anything else is the instance failing to answer the check. The error
			// cannot contain the token — SchulcloudApiError carries only a path — but
			// the response still says no more than that.
			const detail = error instanceof SchulcloudApiError ? `HTTP ${error.status}` : error instanceof Error ? error.name : 'error';
			console.error(`[schulcloud-mcp] token check failed: ${detail}`);
			return res.status(502).json({
				error: 'check_failed',
				message: `Schulcloud did not answer the check (${detail}); the token in use is unchanged. Try again shortly.`,
			});
		}
	});

	// A body that is not JSON would otherwise reach Express's default handler,
	// which logs it — and here the body is a credential.
	router.use((error: unknown, _req: Request, res: Response, next: (error?: unknown) => void) => {
		const type = (error as { type?: string } | undefined)?.type;
		if (type === 'entity.parse.failed' || type === 'entity.too.large') {
			res.status(400).json({ error: 'bad_request' });
			return;
		}
		next(error);
	});

	return router;
}

function tokenStatus(services: Services) {
	return { ...services.session.status(), keepalive: services.keepalive?.state() ?? null };
}

/** Falls back to Schulcloud for anything not in the mirror, streaming through. */
/** Streams a file-manager file live, via its pre-signed URL; no credentials leave for the storage host. */
async function proxyFileManager(
	services: Services,
	fileId: string,
	known: { name: string; mimeType: string; size: number },
	res: Response,
): Promise<void> {
	const signed = await services.client.getFileManagerSignedUrl(fileId, known.name);
	const upstream = await services.client.openSignedUrl(signed);
	if (!upstream.body) {
		res.status(502).json({ error: 'upstream_failed', message: 'empty response' });
		return;
	}
	res.setHeader('Content-Type', known.mimeType || 'application/octet-stream');
	res.setHeader('Content-Disposition', contentDisposition(known.name));
	const length = upstream.headers.get('content-length');
	if (length) res.setHeader('Content-Length', length);
	res.setHeader('X-Schulcloud-Source', 'live');
	Readable.fromWeb(upstream.body as never).pipe(res);
}

async function proxyLive(services: Services, fileId: string, res: Response): Promise<void> {
	const record = await services.client.getFileRecord(fileId);
	if (record.securityCheckStatus === 'blocked') {
		res.status(403).json({ error: 'blocked', message: 'The instance virus scanner blocked this file.' });
		return;
	}

	const url =
		`${services.config.baseUrl}/api/v3/file/download/${encodeURIComponent(record.id)}` +
		`/${encodeURIComponent(record.name)}`;
	const upstream = await fetch(url, { headers: { Authorization: `Bearer ${services.config.jwt}` } });
	if (!upstream.ok || !upstream.body) {
		res.status(upstream.status === 401 ? 502 : upstream.status).json({
			error: 'upstream_failed',
			message: upstream.status === 401 ? 'The Schulcloud session has expired on the server.' : `HTTP ${upstream.status}`,
		});
		return;
	}

	res.setHeader('Content-Type', record.mimeType || 'application/octet-stream');
	res.setHeader('Content-Disposition', contentDisposition(record.name));
	if (record.size) res.setHeader('Content-Length', String(record.size));
	res.setHeader('X-Schulcloud-Source', 'live');
	Readable.fromWeb(upstream.body as never).pipe(res);
}

/**
 * RFC 5987 Content-Disposition.
 *
 * Built by hand because the instance's own header is malformed — it emits
 * `attachment;; filename="…"` with the name percent-encoded inside the quotes —
 * and we should not pass that on to clients.
 */
function contentDisposition(name: string): string {
	const ascii = name.replace(/[^\x20-\x7e]/g, '_').replace(/["\\]/g, '_');
	return `attachment; filename="${ascii}"; filename*=UTF-8''${encodeURIComponent(name)}`;
}

function fail(res: Response, error: unknown, what: string): void {
	console.error(`[schulcloud-mcp] ${what} failed:`, error);
	if (!res.headersSent) res.status(500).json({ error: 'internal_error' });
}

function stringParam(value: unknown): string | undefined {
	const first = Array.isArray(value) ? value[0] : value;
	return typeof first === 'string' && first.length > 0 ? first : undefined;
}

/**
 * A query or body value as an optional field, so callers can spread it into an
 * options object without turning "not given" into `undefined` the way an
 * exactOptionalPropertyTypes build rejects.
 */
function pickParam<K extends string>(key: K, value: unknown): Partial<Record<K, string>> {
	const text = stringParam(value);
	return text ? ({ [key]: text } as Record<K, string>) : {};
}

function boundedInt(value: unknown, fallback: number, min: number, max: number): number {
	const parsed = Number.parseInt(stringParam(value) ?? '', 10);
	return Number.isFinite(parsed) ? Math.min(max, Math.max(min, parsed)) : fallback;
}

function childPath(parent: string, name: string): string {
	return `${parent === '/' ? '' : parent}/${name}`;
}

/** A walk entry as JSON; `name` travels separately because names may contain "/". */
function treeEntry(entry: WalkEntry) {
	if (entry.directory) {
		return { type: 'directory', path: entry.path, parentPath: entry.parentPath, depth: entry.depth, id: entry.directory.id, name: entry.directory.name };
	}
	const file = entry.file as FmFile;
	return {
		type: 'file',
		path: entry.path,
		parentPath: entry.parentPath,
		depth: entry.depth,
		id: file.id,
		name: file.name,
		size: file.size,
		mimeType: file.mimeType ?? null,
		blocked: file.blocked,
	};
}

const FS_STATUS: Record<FsErrorCode, number> = {
	not_found: 404,
	ambiguous: 409,
	not_a_directory: 400,
	not_a_file: 400,
	not_navigable: 422,
};

function fsFail(res: Response, error: unknown, what: string): void {
	if (res.headersSent) return;
	if (error instanceof FsError) {
		res.status(FS_STATUS[error.code]).json({ error: error.code, message: error.message });
		return;
	}
	if (error instanceof FileManagerMarkupError) {
		res.status(502).json({ error: 'markup_changed', message: error.message });
		return;
	}
	if (error instanceof SchulcloudApiError) {
		// 401 upstream is the Pi's session, not the caller's token: say which.
		const status = error.status === 401 ? 502 : error.status === 403 || error.status === 404 ? error.status : 502;
		const message = error.status === 401 ? 'The Schulcloud session has expired on the server.' : error.message;
		res.status(status).json({ error: 'upstream_failed', message });
		return;
	}
	fail(res, error, what);
}