/**
 * Runtime configuration, read once from the environment — except `jwt`, which
 * can be replaced while the server runs.
 *
 * The two Schulcloud values are named after the browser artefacts they come
 * from (`TSC_URL`, `TSC_JWT_COOKIE`) so that copying a fresh token out of
 * DevTools stays an obvious, mechanical step — see docs/AUTH.md.
 */

import { resolve } from 'node:path';
import type { UntisConfig } from './core/untis.ts';

export interface Config {
	/** Instance base URL, no trailing slash, e.g. `https://schulcloud-thueringen.de`. */
	baseUrl: string;
	/**
	 * Raw JWT from the instance's `jwt` cookie. Sent as `Authorization: Bearer`.
	 * Replaced at runtime by core/session-token.ts, so read it at the moment of
	 * use and never keep a copy.
	 */
	jwt: string;
	/** Shared secret callers must present to this MCP server. Unused in stdio mode. */
	authToken: string | undefined;
	/**
	 * A second token, accepted on `/mcp` only: the one claude.ai's connector
	 * sends as a request header. It is stored by a third party, so it opens the
	 * read-only MCP tools and not `/api`, which can replace the session token
	 * and stream the file mirror — and it can be revoked on its own.
	 */
	connectorToken: string | undefined;
	/**
	 * Serves MCP at `/<secret>/mcp` without a bearer token, for clients that can
	 * send none — claude.ai's connector dialog takes only a URL. The path is then
	 * the credential, so it must never be logged.
	 */
	mcpPathSecret: string | undefined;
	/** Where state that must survive a restart is kept: a replaced session token. Unset = memory only. */
	stateDir: string | undefined;
	port: number;
	bindHost: string;
	/** Hard ceiling on how many bytes `download_file` will pull from the instance. */
	maxDownloadBytes: number;
	/** Characters of extracted text returned before truncation kicks in. */
	maxExtractedChars: number;
	requestTimeoutMs: number;
	/**
	 * How often to ping the instance to hold the session open. Must stay well
	 * under the instance's `JWT_TIMEOUT_SECONDS` (7200s here) — see
	 * src/core/keepalive.ts. Zero disables the keepalive.
	 */
	keepaliveIntervalMs: number;

	/** Postgres for the search index and file mirror. Unset = live-only mode. */
	databaseUrl: string | undefined;
	/** Where mirrored file bytes live on disk. */
	mirrorDir: string;
	/** Files larger than this are indexed as metadata but not mirrored. */
	mirrorMaxBytes: number;
	/** Index personal files and submitted/returned work as well as course content. */
	indexPersonalFiles: boolean;
	/** Walk the file manager (Kurs-, Persönliche, Team- and Geteilte Dateien) when crawling. */
	indexFileManager: boolean;
	/** How often to re-crawl on a timer. Zero = only on demand. */
	crawlIntervalMs: number;

	/**
	 * Password for the web app at `/app` — the notes editor and the settings
	 * page. Unset = the app is not served at all, by the same rule the untis_*
	 * tools follow: a login screen no password can open is worse than no page.
	 *
	 * A credential, and the only one here a person types: it is hashed at
	 * startup and the plain value is never compared, stored or logged.
	 */
	webPassword: string | undefined;
	/**
	 * Where the user's own lesson notes live, as Markdown files. Unset = the
	 * note tools are not offered, the same rule the untis_* tools follow.
	 */
	notesDir: string | undefined;
	/**
	 * Whether add_note may write. The notes directory is the only thing in this
	 * server anything can write to, so turning it off is a real setting and not
	 * a theoretical one — a deployment that syncs its notes in from elsewhere
	 * wants the files left alone.
	 */
	notesWritable: boolean;
	/**
	 * How far back to read the WebUntis class register into the index. Zero =
	 * not at all. Costs one timetable call per 90 days plus one per lesson
	 * series, so a school year is a few dozen requests on a background crawl.
	 */
	untisHistoryDays: number;

	/**
	 * WebUntis, where the school keeps the timetable. Unset = the untis_* tools
	 * are not offered at all, which is the right answer for a school that does
	 * not use it — Schulcloud alone cannot say what happens when.
	 */
	untis: UntisConfig | undefined;
}

function required(name: string): string {
	const value = process.env[name]?.trim();
	if (!value) throw new Error(`Missing required environment variable ${name}`);
	return value;
}

/** `1`, `true`, `yes` and `on` are all true; anything else falls back. */
function bool(name: string, fallback: boolean): boolean {
	const raw = process.env[name]?.trim().toLowerCase();
	if (!raw) return fallback;
	return ['1', 'true', 'yes', 'on'].includes(raw);
}

function int(name: string, fallback: number): number {
	const raw = process.env[name]?.trim();
	if (!raw) return fallback;
	const parsed = Number.parseInt(raw, 10);
	if (!Number.isFinite(parsed) || parsed <= 0) {
		throw new Error(`Environment variable ${name} must be a positive integer, got ${raw}`);
	}
	return parsed;
}

/** A URL-safe secret of at least 32 characters, or undefined when unset. */
function pathSecret(name: string): string | undefined {
	const value = process.env[name]?.trim();
	if (!value) return undefined;
	// The value is a credential: the error states the rule and never echoes it.
	if (!/^[A-Za-z0-9_-]{32,}$/.test(value)) {
		throw new Error(
			`Environment variable ${name} must be at least 32 characters of A-Z, a-z, 0-9, "-" or "_". ` +
				'Generate one with: openssl rand -hex 32',
		);
	}
	return value;
}

/** A token of at least 32 characters without whitespace, or undefined when unset. */
function secretToken(name: string): string | undefined {
	const value = process.env[name]?.trim();
	if (!value) return undefined;
	// A credential: the error states the rule and never echoes the value.
	if (value.length < 32 || /\s/.test(value)) {
		throw new Error(
			`Environment variable ${name} must be at least 32 characters without spaces. ` +
				'Generate one with: openssl rand -hex 32',
		);
	}
	return value;
}

/**
 * The four WebUntis values, or undefined when none is set.
 *
 * All four or nothing: three of them are harmless identifiers and the fourth is
 * a credential, so a half-filled block is a copy-paste that went wrong, not a
 * configuration to guess at. They come from one dialog — WebUntis → Profil →
 * Freigaben → Untis Mobile → QR-Code — and the error says so, because that is
 * the only place to find them.
 */
function untisConfig(): UntisConfig | undefined {
	const server = process.env.UNTIS_SERVER?.trim();
	const school = process.env.UNTIS_SCHOOL?.trim();
	const user = process.env.UNTIS_USER?.trim();
	const secret = process.env.UNTIS_SECRET?.trim();
	const missing = Object.entries({ UNTIS_SERVER: server, UNTIS_SCHOOL: school, UNTIS_USER: user, UNTIS_SECRET: secret })
		.filter(([, value]) => !value)
		.map(([name]) => name);
	if (missing.length === 4) return undefined;
	if (!server || !school || !user || !secret) {
		throw new Error(
			`WebUntis needs all four of UNTIS_SERVER, UNTIS_SCHOOL, UNTIS_USER and UNTIS_SECRET — missing: ` +
				`${missing.join(', ')}. All four are in WebUntis → Profil → Freigaben → Untis Mobile → QR-Code.`,
		);
	}
	if (!/^[a-z0-9][a-z0-9.-]*\.[a-z]{2,}$/i.test(server)) {
		throw new Error(
			`UNTIS_SERVER must be the bare host from the QR dialog's "Url" field, e.g. "ags-erfurt.webuntis.com" — ` +
				`no scheme and no path, got "${server}".`,
		);
	}
	// A credential: the error states the rule and never echoes the value.
	if (!/^[A-Za-z2-7]{8,}$/.test(secret)) {
		throw new Error(
			'UNTIS_SECRET must be the key from the Untis Mobile QR dialog: at least 8 characters of A-Z and 2-7 ' +
				'(base32), no spaces.',
		);
	}
	return { server, school, user, secret };
}

/**
 * The app password, or undefined when the app is switched off.
 *
 * A length floor and nothing else: this one is typed by a person on a phone,
 * so demanding punctuation would buy little and cost the thing that actually
 * matters, which is that they pick something long. The error states the rule
 * and never echoes the value.
 */
function webPassword(): string | undefined {
	const value = process.env.WEB_PASSWORD;
	if (!value) return undefined;
	if (value.length < 12) {
		throw new Error(
			'WEB_PASSWORD must be at least 12 characters — it is the only thing between the internet and the ' +
				'notes app. A passphrase of three or four words is ideal.',
		);
	}
	return value;
}

/** Like `int`, but 0 is meaningful (it disables the feature) rather than invalid. */
function intAllowingZero(name: string, fallback: number): number {
	const raw = process.env[name]?.trim();
	if (!raw) return fallback;
	const parsed = Number.parseInt(raw, 10);
	if (!Number.isFinite(parsed) || parsed < 0) {
		throw new Error(`Environment variable ${name} must be a non-negative integer, got ${raw}`);
	}
	return parsed;
}

export function loadConfig(): Config {
	const authToken = process.env.MCP_AUTH_TOKEN?.trim() || undefined;
	const connectorToken = secretToken('MCP_CONNECTOR_TOKEN');
	if (connectorToken && !authToken) {
		// Without the main token /api would be open while /mcp is not.
		throw new Error('MCP_CONNECTOR_TOKEN needs MCP_AUTH_TOKEN as well, or /api would be left unauthenticated.');
	}
	if (connectorToken && connectorToken === authToken) {
		throw new Error('MCP_CONNECTOR_TOKEN must differ from MCP_AUTH_TOKEN, or it cannot be limited to /mcp or revoked on its own.');
	}

	return {
		baseUrl: required('TSC_URL').replace(/\/+$/, ''),
		jwt: required('TSC_JWT_COOKIE'),
		authToken,
		connectorToken,
		mcpPathSecret: pathSecret('MCP_PATH_SECRET'),
		stateDir: process.env.STATE_DIR?.trim() ? resolve(process.env.STATE_DIR.trim()) : undefined,
		port: int('PORT', 8080),
		bindHost: process.env.BIND_HOST?.trim() || '0.0.0.0',
		maxDownloadBytes: int('MAX_DOWNLOAD_BYTES', 25 * 1024 * 1024),
		maxExtractedChars: int('MAX_EXTRACTED_CHARS', 120_000),
		requestTimeoutMs: int('REQUEST_TIMEOUT_MS', 30_000),
		keepaliveIntervalMs: intAllowingZero('KEEPALIVE_INTERVAL_MS', 30 * 60_000),
		databaseUrl: process.env.DATABASE_URL?.trim() || undefined,
		// Absolute: res.sendFile rejects a relative path, and resolveWithin only
		// returns an absolute path if the root it is given is one.
		mirrorDir: resolve(process.env.MIRROR_DIR?.trim() || '/var/lib/schulcloud-mcp/mirror'),
		mirrorMaxBytes: int('MIRROR_MAX_BYTES', 64 * 1024 * 1024),
		// Off by default: submissions are per task, so this roughly doubles the
		// cost of a full crawl. Worth turning on to make your own handed-in work
		// searchable, which no other route offers.
		indexPersonalFiles: bool('INDEX_PERSONAL_FILES', false),
		// On by default: many teachers keep their material only in Kurs-Dateien,
		// so an index without it misses whole courses. One page load per folder.
		indexFileManager: bool('INDEX_FILE_MANAGER', true),
		crawlIntervalMs: intAllowingZero('CRAWL_INTERVAL_MS', 6 * 60 * 60_000),
		// Absolute for the same reason as the mirror: resolveWithin only returns
		// an absolute path when the root it is given is one.
		webPassword: webPassword(),
		notesDir: process.env.NOTES_DIR?.trim() ? resolve(process.env.NOTES_DIR.trim()) : undefined,
		notesWritable: !bool('NOTES_READONLY', false),
		untisHistoryDays: intAllowingZero('UNTIS_HISTORY_DAYS', 180),
		untis: untisConfig(),
	};
}