<?php
declare(strict_types=1);

/**
 * The accounts, as one JSON file: `data/users.json` holding `{username, password, role, createdAt}`
 * per user, where `password` is a hash from `password_hash` – the plain one is never stored.
 *
 * An entry without `role` is a `user` (#180): the weaker of the two is what a missing field means,
 * so a hand-written file never hands out rights by accident. `createdAt` is missing on the accounts
 * from before #179 and stays empty for them.
 *
 * Accounts are made from the command line (`tools/make-user.php`) or by an administrator through
 * the `users` routes (#179); nobody can sign up over the wire.
 */
final class UserStore
{
    /**
     * The shortest password an account may be given. The sign-in form knows the same number
     * (`loginRules.ts`) so it can say so without asking, but this is the one that decides: a
     * client is free to send anything.
     */
    public const MIN_PASSWORD_LENGTH = 8;

    public const ROLES = ['admin', 'user'];

    public function __construct(private readonly string $file) {}

    public static function isValidName(string $name): bool
    {
        return (bool) preg_match('/^[a-z0-9][a-z0-9._-]{1,31}$/i', $name);
    }

    public static function isValidPassword(string $password): bool
    {
        return strlen($password) >= self::MIN_PASSWORD_LENGTH;
    }

    public static function isValidRole(string $role): bool
    {
        return in_array($role, self::ROLES, true);
    }

    /** The name as stored, or null when the pair does not match an account. */
    public function verify(string $username, string $password): ?string
    {
        $user = $this->find($username);
        if ($user === null || !password_verify($password, $user['password'])) {
            return null;
        }
        return $user['username'];
    }

    public function exists(string $username): bool
    {
        return $this->find($username) !== null;
    }

    /** `user` for an account that does not exist, the same as for one without a role. */
    public function role(string $username): string
    {
        return $this->find($username)['role'] ?? 'user';
    }

    /**
     * Every account as the API may show it – never the hash.
     *
     * @return list<array{username:string,role:string,createdAt:string}>
     */
    public function accounts(): array
    {
        return array_map(
            static fn(array $u): array => [
                'username' => $u['username'],
                'role' => $u['role'],
                'createdAt' => $u['createdAt'],
            ],
            $this->all(),
        );
    }

    public function adminCount(): int
    {
        return count(array_filter($this->all(), static fn(array $u): bool => $u['role'] === 'admin'));
    }

    /**
     * Adds the account or replaces the password of one that is already there. Without `$role` a new
     * account is a `user` and an existing one keeps what it has, so resetting a password from the
     * command line never demotes an administrator.
     */
    public function put(string $username, string $password, ?string $role = null): void
    {
        if (!self::isValidName($username)) {
            throw new InvalidArgumentException("Invalid user name: {$username}");
        }
        if ($role !== null && !self::isValidRole($role)) {
            throw new InvalidArgumentException("Invalid role: {$role}");
        }
        $existing = $this->find($username);
        $users = $this->without($username);
        $users[] = [
            'username' => $existing['username'] ?? $username,
            'password' => password_hash($password, PASSWORD_DEFAULT),
            'role' => $role ?? $existing['role'] ?? 'user',
            'createdAt' => $existing !== null ? $existing['createdAt'] : gmdate('c'),
        ];
        $this->write($users);
    }

    /** @return bool False when there is no such account. */
    public function setRole(string $username, string $role): bool
    {
        if (!self::isValidRole($role)) {
            throw new InvalidArgumentException("Invalid role: {$role}");
        }
        return $this->change($username, static fn(array $u): array => ['role' => $role] + $u);
    }

    /**
     * Gives an account a new name. Only the name: the projects that carry the old one as `owner`
     * and the sessions that do are the caller's to move (see `Store::transfer`).
     *
     * @return bool False when there is no such account.
     * @throws InvalidArgumentException when the new name is invalid or taken by another account.
     */
    public function rename(string $from, string $to): bool
    {
        if (!self::isValidName($to)) {
            throw new InvalidArgumentException("Invalid user name: {$to}");
        }
        $other = $this->find($to);
        // Only a change of case is the same account; any other match is somebody else's name.
        if ($other !== null && strcasecmp($other['username'], $from) !== 0) {
            throw new InvalidArgumentException("The name {$to} is taken");
        }
        return $this->change($from, static fn(array $u): array => ['username' => $to] + $u);
    }

    /** @return bool False when there is no such account. */
    public function remove(string $username): bool
    {
        if ($this->find($username) === null) {
            return false;
        }
        $this->write($this->without($username));
        return true;
    }

    /** @param callable(array):array $edit */
    private function change(string $username, callable $edit): bool
    {
        $user = $this->find($username);
        if ($user === null) {
            return false;
        }
        $users = $this->without($username);
        $users[] = $edit($user);
        $this->write($users);
        return true;
    }

    /** @return list<array{username:string,password:string,role:string,createdAt:string}> */
    private function without(string $username): array
    {
        return array_values(
            array_filter($this->all(), static fn(array $u): bool => strcasecmp($u['username'], $username) !== 0),
        );
    }

    /** @return array{username:string,password:string,role:string,createdAt:string}|null */
    private function find(string $username): ?array
    {
        foreach ($this->all() as $user) {
            if (strcasecmp($user['username'], $username) === 0) {
                return $user;
            }
        }
        return null;
    }

    /** @return list<array{username:string,password:string,role:string,createdAt:string}> */
    private function all(): array
    {
        if (!is_file($this->file)) {
            return [];
        }
        $raw = file_get_contents($this->file);
        $data = $raw === false ? null : json_decode($raw, true);
        if (!is_array($data) || !is_array($data['users'] ?? null)) {
            return [];
        }
        $users = [];
        foreach ($data['users'] as $user) {
            if (is_array($user) && is_string($user['username'] ?? null) && is_string($user['password'] ?? null)) {
                $role = $user['role'] ?? null;
                $users[] = [
                    'username' => $user['username'],
                    'password' => $user['password'],
                    'role' => is_string($role) && self::isValidRole($role) ? $role : 'user',
                    'createdAt' => is_string($user['createdAt'] ?? null) ? $user['createdAt'] : '',
                ];
            }
        }
        return $users;
    }

    /** @param list<array{username:string,password:string,role:string,createdAt:string}> $users */
    private function write(array $users): void
    {
        usort($users, static fn(array $a, array $b): int => strcmp($a['username'], $b['username']));
        $dir = dirname($this->file);
        if (!is_dir($dir) && !mkdir($dir, 0775, true) && !is_dir($dir)) {
            throw new RuntimeException("Cannot create data directory {$dir}");
        }
        $json = json_encode(['users' => $users], JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES);
        if ($json === false) {
            throw new RuntimeException('Cannot encode users');
        }
        AtomicFile::write($this->file, $json, AtomicFile::HIDDEN, 'users file');
    }
}