import {Transaction} from 'kysely';
import {NachklangAdminDB} from '../Admin.db.js';
import {
	AdminDatabase,
	AppName,
	AppPermission,
	AppRole,
	ACCESS_ROLE,
	appsOf,
	isAppName,
	isAppRole
} from '../admin.schema.js';

const db = NachklangAdminDB.db;

/**
 * Everything that reads or writes permissions. Two callers with very different
 * hot-path requirements share this file: admin.middleware.ts runs
 * `loadAccess` on *every* admin-authenticated request (which is why it is one
 * query joining `user.disabled` and the permission rows - see the plan's
 * decision to run without better-auth's cookieCache), and the /admin/users
 * routes run the rest.
 */

export interface UserAccess {
	id: string;
	email: string;
	displayName: string;
	disabled: boolean;
	/** Every (app, role) grant this user holds. */
	permissions: AppPermission[];
	/** The distinct apps the above grants any access to. Derived, kept because
	 *  most callers only ever ask "may they open this app at all?". */
	apps: AppName[];
}

export type UserStatus = 'aktiv' | 'deaktiviert';

export interface UserListEntry {
	id: string;
	email: string;
	name: string;
	permissions: AppPermission[];
	apps: AppName[];
	status: UserStatus;
	createdAt: Date;
	lastSignInAt: Date | null;
}

export interface UserSessionEntry {
	id: string;
	createdAt: Date;
	expiresAt: Date;
	ipAddress: string | null;
	userAgent: string | null;
}

export interface UserDetail extends UserListEntry {
	sessions: UserSessionEntry[];
	passkeyCount: number;
}

/**
 * The single per-request lookup behind requireAppAccess. Returns null when the
 * user row is gone; `disabled` is returned rather than filtered so the
 * middleware can answer 403 (account deactivated) instead of a misleading 401.
 */
export const loadAccess = async (userId: string): Promise<UserAccess | null> => {
	const rows = await db
		.selectFrom('user')
		.leftJoin('user_app_permissions', 'user_app_permissions.user_id', 'user.id')
		.where('user.id', '=', userId)
		.select([
			'user.id as id',
			'user.email as email',
			'user.name as name',
			'user.disabled as disabled',
			'user_app_permissions.app as app',
			'user_app_permissions.role as role'
		])
		.execute();

	if (rows.length === 0) {
		return null;
	}

	const permissions = toPermissionRows(rows);

	return {
		id: rows[0].id,
		email: rows[0].email,
		displayName: rows[0].name,
		// MySQL TINYINT(1) comes back as 0/1 through mysql2.
		disabled: Boolean(rows[0].disabled),
		permissions,
		apps: appsOf(permissions)
	};
};

/**
 * Turns joined permission rows into AppPermission[]. The left join produces one
 * row with a null app for a user who holds nothing, and a role written directly
 * into the database that no longer appears in APP_ROLES is dropped rather than
 * trusted - the table is the store, APP_ROLES is the contract.
 */
const toPermissionRows = (rows: {app: AppName | null; role: string | null}[]): AppPermission[] => {
	return rows
		.filter((row): row is {app: AppName; role: string} =>
			isAppName(row.app) && isAppRole(row.app, row.role))
		.map(row => ({app: row.app, role: row.role}));
};

export const listUsers = async (): Promise<UserListEntry[]> => {
	const users = await db
		.selectFrom('user')
		.select(['id', 'email', 'name', 'disabled', 'createdAt'])
		.orderBy('name', 'asc')
		.execute();

	const permissions = await db
		.selectFrom('user_app_permissions')
		.select(['user_id', 'app', 'role'])
		.execute();

	// Last sign-in is derived from the newest session rather than stored: a
	// session row is created on every sign-in and we never update its
	// createdAt, so max(createdAt) is exactly that, with no extra column to
	// keep in sync.
	//
	// The expiry filter must match getUserDetail's. better-auth only deletes an
	// expired session when someone actually presents it, so expired rows linger
	// - without this, the list would report a last sign-in for someone the
	// detail view shows as never having signed in.
	const lastSessions = await db
		.selectFrom('session')
		.where('expiresAt', '>', new Date())
		.select(({fn}) => ['userId', fn.max('createdAt').as('lastSignInAt')])
		.groupBy('userId')
		.execute();

	const permissionsByUser = new Map<string, AppPermission[]>();
	for (const row of permissions) {
		if (!isAppRole(row.app, row.role)) {
			continue;
		}
		const held = permissionsByUser.get(row.user_id) || [];
		held.push({app: row.app, role: row.role});
		permissionsByUser.set(row.user_id, held);
	}

	const lastSignInByUser = new Map<string, Date | null>(
		lastSessions.map(row => [row.userId, row.lastSignInAt as Date | null])
	);

	return users.map(user => {
		const held = permissionsByUser.get(user.id) || [];
		return {
			id: user.id,
			email: user.email,
			name: user.name,
			permissions: held,
			apps: appsOf(held),
			status: user.disabled ? ('deaktiviert' as const) : ('aktiv' as const),
			createdAt: user.createdAt,
			lastSignInAt: lastSignInByUser.get(user.id) ?? null
		};
	});
};

export const getUserDetail = async (userId: string): Promise<UserDetail | null> => {
	const user = await db
		.selectFrom('user')
		.select(['id', 'email', 'name', 'disabled', 'createdAt'])
		.where('id', '=', userId)
		.executeTakeFirst();

	if (!user) {
		return null;
	}

	const [permissions, sessions, passkeys] = await Promise.all([
		db
			.selectFrom('user_app_permissions')
			.select(['app', 'role'])
			.where('user_id', '=', userId)
			.execute(),
		db
			.selectFrom('session')
			.select(['id', 'createdAt', 'expiresAt', 'ipAddress', 'userAgent'])
			.where('userId', '=', userId)
			.where('expiresAt', '>', new Date())
			.orderBy('createdAt', 'desc')
			.execute(),
		db
			.selectFrom('passkey')
			.select(({fn}) => fn.countAll<number>().as('count'))
			.where('userId', '=', userId)
			.executeTakeFirst()
	]);

	const held = toPermissionRows(permissions);

	return {
		id: user.id,
		email: user.email,
		name: user.name,
		permissions: held,
		apps: appsOf(held),
		status: user.disabled ? 'deaktiviert' : 'aktiv',
		createdAt: user.createdAt,
		lastSignInAt: sessions.length > 0 ? sessions[0].createdAt : null,
		sessions,
		passkeyCount: Number(passkeys?.count ?? 0)
	};
};

/**
 * Replaces a user's permission set. Written as delete-then-insert inside one
 * transaction rather than a diff: the set is at most four rows, and a diff
 * would only add branches for no measurable gain.
 */

/** The rows a permission list becomes. One row per (app, role). */
const permissionRows = (
	userId: string,
	permissions: AppPermission[],
	grantedBy: string | null
) => {
	return permissions.map(permission => ({
		user_id: userId,
		app: permission.app,
		role: permission.role,
		granted_by: grantedBy,
		granted_at: new Date()
	}));
};

/** Drops anything not in APP_ROLES and de-duplicates on (app, role). */
const validPermissions = (permissions: AppPermission[]): AppPermission[] => {
	const seen = new Set<string>();
	return permissions.filter(permission => {
		if (!isAppName(permission.app) || !isAppRole(permission.app, permission.role)) {
			return false;
		}
		const key = `${permission.app}:${permission.role}`;
		if (seen.has(key)) {
			return false;
		}
		seen.add(key);
		return true;
	});
};

export const setPermissions = async (
	userId: string,
	permissions: AppPermission[],
	grantedBy: string | null
): Promise<void> => {
	const valid = validPermissions(permissions);

	await db.transaction().execute(async trx => {
		await trx.deleteFrom('user_app_permissions').where('user_id', '=', userId).execute();
		if (valid.length > 0) {
			await trx
				.insertInto('user_app_permissions')
				.values(permissionRows(userId, valid, grantedBy))
				.execute();
		}
	});
};

/**
 * Why the guards live down here rather than in the router: they are
 * check-then-act, and the check has to happen inside the same transaction as
 * the write, over locked rows. Two admins each removing the other's `admin`
 * permission at the same moment would otherwise both read a count of 2, both
 * pass, and both commit - leaving nobody who can administer anything, with
 * ADMIN_BOOTSTRAP_EMAIL at the next restart as the only way back in.
 *
 * `SELECT ... FOR UPDATE` makes the second transaction wait and re-read the
 * count the first one just changed.
 */
export type LastAdminGuardResult = 'ok' | 'last-admin';

const countActiveAdminsForUpdate = async (trx: Transaction<AdminDatabase>): Promise<number> => {
	const row = await trx
		.selectFrom('user_app_permissions')
		.innerJoin('user', 'user.id', 'user_app_permissions.user_id')
		.where('user_app_permissions.app', '=', 'admin')
		.where('user.disabled', '=', false)
		// countDistinct, not countAll: with (user_id, app, role) as the key one
		// user can hold several roles on `admin`, and counting rows would make a
		// single admin with two roles look like two admins - defeating the guard
		// at exactly the moment it matters.
		.select(({fn}) => fn.count<number>('user_app_permissions.user_id').distinct().as('count'))
		.forUpdate()
		.executeTakeFirst();

	return Number(row?.count ?? 0);
};

/**
 * Replaces a user's permissions, refusing to remove the last active admin.
 * Returns 'last-admin' instead of throwing so the router can answer 409.
 */
export const setPermissionsGuarded = async (
	userId: string,
	permissions: AppPermission[],
	grantedBy: string | null
): Promise<LastAdminGuardResult> => {
	const valid = validPermissions(permissions);
	const keepsAdmin = valid.some(permission => permission.app === 'admin');

	return db.transaction().execute(async trx => {
		const target = await trx
			.selectFrom('user_app_permissions')
			.innerJoin('user', 'user.id', 'user_app_permissions.user_id')
			.where('user_app_permissions.user_id', '=', userId)
			.where('user_app_permissions.app', '=', 'admin')
			.select(['user.disabled as disabled'])
			.limit(1)
			.forUpdate()
			.executeTakeFirst();

		const losesAdmin = Boolean(target) && !keepsAdmin;
		if (losesAdmin && !target?.disabled && (await countActiveAdminsForUpdate(trx)) <= 1) {
			return 'last-admin';
		}

		await trx.deleteFrom('user_app_permissions').where('user_id', '=', userId).execute();
		if (valid.length > 0) {
			await trx
				.insertInto('user_app_permissions')
				.values(permissionRows(userId, valid, grantedBy))
				.execute();
		}

		return 'ok';
	});
};

/**
 * Disables a user and revokes every session, refusing to disable the last
 * active admin. Same locking rationale as setPermissionsGuarded.
 */
export const disableUserGuarded = async (userId: string): Promise<LastAdminGuardResult> => {
	return db.transaction().execute(async trx => {
		const isAdmin = await trx
			.selectFrom('user_app_permissions')
			.innerJoin('user', 'user.id', 'user_app_permissions.user_id')
			.where('user_app_permissions.user_id', '=', userId)
			.where('user_app_permissions.app', '=', 'admin')
			.where('user.disabled', '=', false)
			.select('user_app_permissions.user_id')
			.limit(1)
			.forUpdate()
			.executeTakeFirst();

		if (isAdmin && (await countActiveAdminsForUpdate(trx)) <= 1) {
			return 'last-admin';
		}

		await trx.updateTable('user').set({disabled: true}).where('id', '=', userId).execute();
		await trx.deleteFrom('session').where('userId', '=', userId).execute();

		return 'ok';
	});
};

export const grantPermission = async (
	userId: string,
	app: AppName,
	grantedBy: string | null,
	role: AppRole = ACCESS_ROLE
): Promise<void> => {
	await db
		.insertInto('user_app_permissions')
		.values({user_id: userId, app, role, granted_by: grantedBy, granted_at: new Date()})
		// The row already existing is the success case - this is "make sure they
		// hold it", not "re-grant it" - so nothing is overwritten and granted_by
		// keeps naming whoever granted it first.
		.onDuplicateKeyUpdate({role})
		.execute();
};

/** Disabling revokes every session: a disabled user must lose access now, not
 *  when their 30-day cookie happens to expire. */
export const disableUser = async (userId: string): Promise<void> => {
	await db.transaction().execute(async trx => {
		await trx.updateTable('user').set({disabled: true}).where('id', '=', userId).execute();
		await trx.deleteFrom('session').where('userId', '=', userId).execute();
	});
};

export const enableUser = async (userId: string): Promise<void> => {
	await db.updateTable('user').set({disabled: false}).where('id', '=', userId).execute();
};

export const revokeSession = async (userId: string, sessionId: string): Promise<boolean> => {
	const result = await db
		.deleteFrom('session')
		.where('id', '=', sessionId)
		.where('userId', '=', userId)
		.executeTakeFirst();

	return Number(result.numDeletedRows) > 0;
};

/**
 * Guard input for the self-lockout rules: how many enabled users still hold the
 * `admin` permission. Disabled admins do not count - they cannot sign in, so
 * leaving only disabled admins is the same lockout as leaving none.
 */
export const countActiveAdmins = async (): Promise<number> => {
	const row = await db
		.selectFrom('user_app_permissions')
		.innerJoin('user', 'user.id', 'user_app_permissions.user_id')
		.where('user_app_permissions.app', '=', 'admin')
		.where('user.disabled', '=', false)
		.select(({fn}) => fn.countAll<number>().as('count'))
		.executeTakeFirst();

	return Number(row?.count ?? 0);
};

export const userExists = async (userId: string): Promise<boolean> => {
	const row = await db.selectFrom('user').select('id').where('id', '=', userId).executeTakeFirst();
	return Boolean(row);
};

export const findUserByEmail = async (email: string): Promise<{id: string; email: string} | null> => {
	const row = await db
		.selectFrom('user')
		.select(['id', 'email'])
		.where('email', '=', email)
		.executeTakeFirst();

	return row ?? null;
};