import { USERNAME_RE, UsersFileSchema } from '../../domain/schemas';
import type { User } from '../../domain/types';
import { ulid } from '../../domain/ulid';
import { hashPassword, MIN_PASSWORD_LENGTH, verifyPassword } from '../auth/password';
import { decodeText, encodeText, type BucketStore } from '../storage/store';

export const USERS_PATH = 'users.json';
export const BOOTSTRAP_ADMIN_PASSWORD = '1234';

export class UserValidationError extends Error {
	constructor(
		message: string,
		public readonly field: string
	) {
		super(message);
		this.name = 'UserValidationError';
	}
}

export interface CreateUserInput {
	username: string;
	displayName: string;
	password: string;
}

export interface UsersRepoOptions {
	clock?: () => Date;
	newId?: () => string;
}

/** Owns users.json. Every mutation rewrites the whole file, then swaps memory. */
export class UsersRepo {
	private queue: Promise<unknown> = Promise.resolve();

	private constructor(
		private readonly store: BucketStore,
		private users: User[],
		private readonly clock: () => Date,
		private readonly newId: () => string
	) {}

	static async load(store: BucketStore, opts: UsersRepoOptions = {}): Promise<UsersRepo> {
		const clock = opts.clock ?? (() => new Date());
		const newId = opts.newId ?? ulid;
		const bytes = await store.get(USERS_PATH);
		const existing = bytes ? UsersFileSchema.parse(JSON.parse(decodeText(bytes))).users : [];
		if (bytes && existing.some((u) => u.role === 'admin')) {
			return new UsersRepo(store, existing, clock, newId);
		}
		// users.json is missing, or present but has no admin: bootstrap/re-bootstrap one.
		const now = clock().toISOString();
		const admin: User = {
			id: 'u_admin',
			username: 'admin',
			displayName: 'Admin',
			passwordHash: await hashPassword(BOOTSTRAP_ADMIN_PASSWORD),
			role: 'admin',
			active: true,
			mustChangePassword: true,
			sessionVersion: 1,
			createdAt: now,
			updatedAt: now
		};
		const repo = new UsersRepo(store, existing, clock, newId);
		await repo.persist([...existing, admin]);
		return repo;
	}

	// ---- reads -------------------------------------------------------------

	all(): User[] {
		return [...this.users];
	}
	byId(id: string): User | undefined {
		return this.users.find((u) => u.id === id);
	}
	byUsername(username: string): User | undefined {
		const key = username.trim().toLowerCase();
		return this.users.find((u) => u.username === key);
	}
	/** Active non-admin users, sorted by display name. */
	activeMembers(): User[] {
		return this.members().filter((u) => u.active);
	}
	/** All non-admin users, sorted by display name. */
	members(): User[] {
		return this.users
			.filter((u) => u.role === 'member')
			.sort((a, b) => a.displayName.localeCompare(b.displayName) || a.id.localeCompare(b.id));
	}
	isActiveMember(id: string): boolean {
		const u = this.byId(id);
		return !!u && u.role === 'member' && u.active;
	}

	async authenticate(username: string, password: string): Promise<User | null> {
		const user = this.byUsername(username);
		// Always run a hash comparison so timing does not reveal whether the username exists.
		// A ScryptOverloadError from a login flood propagates: the guarded action turns it into a 503.
		const ok = await verifyPassword(password, user?.passwordHash ?? 'scrypt$32768$8$1$AAAAAAAAAAAAAAAAAAAAAA==$AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=');
		return ok && user && user.active ? user : null;
	}

	// ---- writes ------------------------------------------------------------

	create(input: CreateUserInput): Promise<User> {
		return this.run(async () => {
			const username = input.username.trim().toLowerCase();
			const displayName = input.displayName.trim();
			if (!USERNAME_RE.test(username)) throw new UserValidationError('Username must be 3–32 characters: a–z, 0–9, _ . -', 'username');
			if (username === 'admin' || this.byUsername(username)) throw new UserValidationError('Username is taken', 'username');
			if (displayName.length === 0 || displayName.length > 120) throw new UserValidationError('Display name is required', 'displayName');
			validatePassword(input.password);
			const now = this.clock().toISOString();
			const user: User = {
				id: `u_${this.newId()}`,
				username,
				displayName,
				passwordHash: await hashPassword(input.password),
				role: 'member',
				active: true,
				mustChangePassword: true,
				sessionVersion: 1,
				createdAt: now,
				updatedAt: now
			};
			await this.persist([...this.users, user]);
			return user;
		});
	}

	setPassword(id: string, password: string, opts: { mustChange: boolean }): Promise<User> {
		return this.run(async () => {
			validatePassword(password);
			const passwordHash = await hashPassword(password);
			return this.patch(id, (u) => ({ ...u, passwordHash, mustChangePassword: opts.mustChange, sessionVersion: u.sessionVersion + 1 }));
		});
	}

	setActive(id: string, active: boolean): Promise<User> {
		return this.run(async () => {
			const u = this.require(id);
			if (u.role === 'admin') throw new UserValidationError('The admin account cannot be deactivated', 'active');
			return this.patch(id, (cur) => ({ ...cur, active, sessionVersion: active ? cur.sessionVersion : cur.sessionVersion + 1 }));
		});
	}

	rename(id: string, displayName: string): Promise<User> {
		return this.run(async () => {
			const name = displayName.trim();
			if (name.length === 0 || name.length > 120) throw new UserValidationError('Display name is required', 'displayName');
			return this.patch(id, (u) => ({ ...u, displayName: name }));
		});
	}

	// ---- internals ---------------------------------------------------------

	private run<T>(fn: () => Promise<T>): Promise<T> {
		const next = this.queue.then(fn, fn);
		this.queue = next.catch(() => undefined);
		return next;
	}

	private require(id: string): User {
		const u = this.byId(id);
		if (!u) throw new UserValidationError('User not found', 'id');
		return u;
	}

	private async patch(id: string, fn: (u: User) => User): Promise<User> {
		const current = this.require(id);
		const updated = { ...fn(current), updatedAt: this.clock().toISOString() };
		await this.persist(this.users.map((u) => (u.id === id ? updated : u)));
		return updated;
	}

	private async persist(users: User[]): Promise<void> {
		const file = UsersFileSchema.parse({ version: 1, users });
		await this.store.put(USERS_PATH, encodeText(JSON.stringify(file, null, 2)), 'application/json');
		this.users = users;
	}
}

export function validatePassword(password: string): void {
	if (password.length < MIN_PASSWORD_LENGTH) throw new UserValidationError(`Password must be at least ${MIN_PASSWORD_LENGTH} characters`, 'password');
	if (password.length > 256) throw new UserValidationError('Password is too long', 'password');
}