minimalistic blockchain in PHP

MiniBlockChain.php

#!/usr/bin/env php
<?php
declare (strict_types = 1);
/*
proof of concept of the inner workings of a Block Chain
 */
class BlockChain {
    public string $path;
    public array $data;
    public function __construct(string $path) {
        $this->path = $path;
        $this->read();
    }
    // loads the BC in memory
    public function read(): array{
        $file_path = $this->path;
        $is_present = file_exists($file_path);
        $this->data = [];
        if ($is_present) {
            $json_str = file_get_contents($file_path);
            try {
                $this->data = json_decode($json_str, $use_assoc = true, 512, JSON_THROW_ON_ERROR | JSON_OBJECT_AS_ARRAY);
            } catch (\JsonException $exception) { //php7.3
                echo 'JSON decode error:' . $exception->getMessage() . "\n";
            }
        }
        return $this->data;
    }
    // writes the in memory data serialized to file
    public function close(): void{
        $json = json_encode($this->data, JSON_PRETTY_PRINT | JSON_THROW_ON_ERROR);
        file_put_contents($this->path, $json); // default is overwriting file
    }
    /**
     * verifies the BlockChain
     * @return array{0: bool, 1: string, 2: string}
     */
    public function verify(): array{
        $_res = function (bool $ok, string $msg, string $hash): array{
            return [$ok, $msg, $hash];
        };
        if (!empty($this->data)) {
            foreach ($this->data as $key => $rec) {
                $prev_check = ($key > 0)
                ? $this->data[$key - 1]['check']
                : self::EMPTY_CHECK;
                $ok = self::hash($prev_check . $rec['content'] . $rec['time']) == $rec['check'];
                if (!$ok) {
                    return $_res(false, "rec {$rec['check']} is invalid.", $rec['check']);
                }
            }
        }
        return $_res(true, '', '');
    }
    // adds a block and signs it
    public function add(string $content): void{
        $last_rec = $this->getLastRercord();
        $rec = [
            'content' => $content,
            'time' => date('Y-m-d H:i:s'),
        ];
        $check = self::hash($last_rec['check'] . $rec['content'] . $rec['time']);
        $rec['check'] = $check;
        $this->data[] = $rec;
    }
    const EMPTY_CHECK = '';
    public function getLastRercord(): array{
        // if emty, return an emty data structure
        if (empty($this->data)) {
            return ['check' => self::EMPTY_CHECK];
        }
        $rec = $this->data[count($this->data) - 1];
        return $rec;
    }
    // calc the hash
    public static function hash(string $str): string{
        $hash = hash('sha256', $str);
        return $hash;
    }
}
//-- actions --------------------------------------
function action_verify(BlockChain $BC): void {
    list($ok, $msg, $k) = $BC->verify();
    echo ($ok ? "BlockChain is valid" : "invalid BlockChain: $msg") . "\n";
}
function action_add(BlockChain $BC): void {
    list($ok, $msg, $k) = $BC->verify();
    if ($ok) {
        $content = readline('Content to add: ');
        if (empty($content)) {
            die('specify a content to add');
        }
        $BC->add($content);
        echo "data added" . "\n";
    } else {
        echo "invalid BlockChain: $msg \n";
    }
}
function action_usage(): void {
    echo "{$_SERVER['argv'][0]} [verify|add] [content]
actions:
    verify = verify each block is consistent
    add = adds a block
\n";
}
function opt(int $k, string $def = ''): string{
    $argv = $_SERVER['argv'];
    return (string) isset($argv[$k]) ? $argv[$k] : $def;
}
function main(array $argv, int $argc): void{
    $file_path = opt(2, '');
    if (empty($file_path)) {
        die('invalid file path ' . $file_path);
    }
    $BC = new BlockChain($file_path);
    $action = opt(1);
    switch ($action) {
    case 'verify':
        action_verify($BC);
        break;
    case 'add':
        action_add($BC);
        break;
    default:
        action_usage();
        break;
    }
    $BC->close();
    exit(0);
}
main($argv = $_SERVER['argv'], $argc = $_SERVER['argc']);