the 'mastermind' function of https://github.com/lucablackwell/heroica, loosely based on the 1972 board game for 2.

mastermind-heroica.php

<?php

function cyan($text) {
    return "\e[1;36m$text\e[0m";
}

function red($text) {
    return "\e[1;31m$text\e[0m";
}

function green($text) {
    return "\e[1;32m$text\e[0m";
}

function yellow($text) {
    return "\e[1;33m$text\e[0m";
}

function mastermind($limit, $attempt_max, $hard) {
    echo cyan("You come across a door with an ancient mechanism.\nYou'll need to input the correct combination of 4 numbers to proceed.\n");
    sleep(2);
    echo cyan("You can only use the numbers from 0-" . $limit . ", including 0 itself.\n");
    sleep(2);
    echo cyan("Studying the mechanism, you see that you'll have " . $attempt_max . " attempts before the combination resets.\n");
    sleep(2);
    echo "Enter 4 numbers to input them into the mechanism.\n";

    $beaten = false;

    while (!$beaten) {
        // For the remaining, add a random one to the combo
        $combo = [];
        $remaining = [];
        for ($i = 0; $i <= $limit; $i++) {
            $remaining[] = $i;
        }
        for ($i = 0; $i < 4; $i++) {
            $rand = array_rand($remaining);
            $combo[] = $rand;
            unset($remaining[array_search($rand, $remaining)]);
        }

        $attempt_total = 0;
        $input_arr = [];
        $correct = 0;
        while (($correct != 4 || implode($input_arr) != implode($combo)) && $attempt_total < $attempt_max) {
            $attempt_total += 1;
            echo '>';
            $input = readline();
            $sanitised = false;
            while (!$sanitised) {
                // If there are more or less than 4 characters
                if (strlen($input) != 4) {
                    echo "The ancient mechanism only has 4 spaces.\n";
                    $input = readline();
                    // If there are letters
                } elseif (preg_match('/[a-z]/', $input)) {
                    echo "Only numbers are usable to unlock this mechanism.\n";
                    $input = readline();
                    // If there are symbols
                } elseif (preg_match('/[^\p{L}\d\s@]/u', $input)) {
                    echo "Only numbers are usable to unlock this mechanism.\n";
                    $input = readline();
                    // If there are only numbers
                } elseif (preg_match('/[0-9]/', $input)) {
                    $low_enough = true;
                    foreach (str_split($input) as $num) {
                        if ($num > $limit) {
                            $low_enough = false;
                        }
                    }
                    // If any of the numbers are too high
                    if (!$low_enough) {
                        echo "The given numbers only go up to " . ($limit) . "!\n";
                        $input = readline();
                    }
                    // If there are duplicates
                    if (strlen(count_chars($input, 3)) != 4) {
                        echo "You are only given one of each number.\n";
                        $input = readline();
                    }
                    if ($low_enough && strlen(count_chars($input, 3)) == 4) {
                        $sanitised = true;
                    }
                }
            }

            $input_arr = str_split($input);

            $correct = 0;
            $half = 0;
            $wrong = 0;
            if ($hard) {
                for ($i = 0; $i < count($input_arr); $i++) {
                    // If at least right number in any place
                    if (in_array($input_arr[$i], $combo)) {
                        // If right place
                        if ($input_arr[$i] == $combo[$i]) {
                            $correct += 1;
                        } else {
                            $half += 1;
                        }
                    } else {
                        $wrong += 1;
                    }
                }
                echo "      " . green($correct) . " " . yellow($half) . " " . red($wrong);
            } else {
                for ($i = 0; $i < count($input_arr); $i++) {
                    // If at least right number in any place
                    if (in_array($input_arr[$i], $combo)) {
                        // If right place
                        if ($input_arr[$i] == $combo[$i]) {
                            $correct += 1;
                            echo green($input_arr[$i]);
                        } else {
                            echo yellow($input_arr[$i]);
                        }
                    } else {
                        echo red($input_arr[$i]);
                    }
                }
            }
            echo "  Attempt $attempt_total";
            // If all correct
            if ($correct == 4 || implode($input_arr) == implode($combo)) {
                echo cyan("\nDust falls as the ancient lock opens.");
                sleep(2);
                $beaten = true;
            }
            echo "\n";
        }
        if ($attempt_total == $attempt_max && ($correct != 4 || implode($input_arr) != implode($combo))) {
            echo cyan("You took too many attempts, and the ancient lock reconfigured itself!\nTry again...\n");
        }
    }

}

// run mastermind with numbers 0-9 inclusive and 6 attempts
mastermind(9, 6, false);