diff --git a/index.php b/index.php
new file mode 100644
index 0000000..3698e82
--- /dev/null
+++ b/index.php
@@ -0,0 +1,248 @@
+<?php
+// Simple URL shortener in a single PHP file
+// by bagaag.com
+
+// Configuration
+$last_file = 'last.txt'; // file to store the last incremented key
+$urls_file = 'urls.txt'; // file to store the URLs with their keys
+$charset = 'acr8mqbs7di4tuh6e9fjv2gwx0nlk5poy1z3'; // unique set of characters for generating keys
+$max_url_length = 100; // urls longer than this are considered nefarious
+$allowed_domains = []; // list of allowed domains for URL shortening
+$password = 'change me!'; // password to shorten a URL, leave empty to disable password protection
+$enable_test = false; // enable the test function to output a series of incremented keys
+
+// Returns the contents of $last_file, or empty string if the file does not exist
+function get_last() {
+    global $last_file;
+    if (file_exists($last_file)) {
+        return trim(file_get_contents($last_file));
+    }
+    return '';
+}
+
+// Writes to $last_file
+function set_last($s) {
+    global $last_file;
+    file_put_contents($last_file, $s);
+}
+
+// Provides the next key by incrementing the previous key.
+// Start with empty string and then feed the return value 
+// back into this function to get the next key, and repeat.
+function increment_string($s) {
+    global $charset;
+    // convert the charset to an array of characters
+    $chars = str_to_chars($charset);
+    // if the string is empty, return the first character
+    if ($s === '') {
+        return $chars[0];
+    }
+    // convert the input string to an array of characters
+    $string = str_to_chars($s);
+    // iterate over the input string characters from end to beginning
+    for ($index = count($string) - 1; $index >= 0; $index--) {
+        // find and validate the position of the character in the charset
+        $char = $string[$index];
+        $pos = array_search($char, $chars);
+        if ($pos === false) {
+            return "Character not in set: $char";
+        }
+        // if the character is not the last in the charset, increment it and break
+        if ($pos < count($chars) - 1) {
+            $string[$index] = $chars[$pos + 1];
+            break;
+        } 
+        // character is the last in the charset; wrap around to the first character
+        $string[$index] = $chars[0];
+        // if we are at the beginning of the string, prepend the first character and break
+        if ($index === 0) {
+            array_unshift($string, $chars[0]);
+            break;
+        }
+    }
+    return join('', $string);
+}
+
+// Splits a string into an array of characters
+function str_to_chars($str, $l = 0) {
+    if ($l > 0) {
+        $ret = array();
+        $len = mb_strlen($str, "UTF-8");
+        for ($i = 0; $i < $len; $i += $l) {
+            $ret[] = mb_substr($str, $i, $l, "UTF-8");
+        }
+        return $ret;
+    }
+    return preg_split("//u", $str, -1, PREG_SPLIT_NO_EMPTY);
+}
+
+// Reads the last key, increments it, saves it, and returns it
+function next_key() {
+    $last = get_last();
+    $next = increment_string($last);
+    set_last($next);
+    return $next;
+}
+
+// Adds a URL to urls.txt and returns the generated key
+function add_url($url) {
+    global $urls_file;
+    $key = next_key();
+    // append the key and url to urls.txt
+    file_put_contents($urls_file, $key . ' ' . $url . "\n", FILE_APPEND);
+    return $key;
+}
+
+// Looks up a key in urls.txt and returns the corresponding URL, or null if not found
+function get_url($key) {
+    global $urls_file;
+    $lines = file($urls_file, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
+    foreach ($lines as $line) {
+        list($k, $url) = explode(' ', $line, 2);
+        if ($k === $key) {
+            return $url;
+        }
+    }
+    return null;
+}
+
+// Test function to print a series of incremented keys
+// Usage: output_keys('', 100);
+function output_keys($key, $count) {
+    header('Content-Type: text/plain');
+    for ($i = 0; $i < $count; $i++) {
+        $key = increment_string($key);
+        // set content type to plain text
+        print($key . "\n");
+    }
+}
+
+// Get input either from a GET or POST request
+function get_input($name) {
+    if (isset($_POST[$name])) {
+        return $_POST[$name];
+    } elseif (isset($_GET[$name])) {
+        return $_GET[$name];
+    }
+    return null;
+}
+
+// Test if a host is in the allowed domains list
+function test_host($host) {
+    global $allowed_domains;
+    if (empty($allowed_domains)) {
+        return true; // if the list is empty, allow all domains
+    }
+    return in_array($host, $allowed_domains);
+}
+
+
+/* HTTP Request Handling */
+
+// read input parameters
+$url = get_input('url');
+$input_password = get_input('password');
+$key = get_input('key');
+$test_start = get_input('test_start');
+$test_count = get_input('test_count');
+
+// If a URL is provided, attempt to shorten it
+if ($url) {
+    // if a password is set, check it
+    if ($password !== '' && $input_password !== $password) {
+        http_response_code(401); // Unauthorized
+        echo "Unauthorized: Incorrect password.\n";
+        exit;
+    }
+    // return 422 if the URL is longer than max_url_length
+    if (strlen($url) > $max_url_length) {
+        http_response_code(422); // Unprocessable Entity
+        echo "Invalid URL.\n";
+	    exit;
+    }
+    // return 403 if the URL's domain is not in the allowed list
+    $parsed_url = parse_url($url);
+    if ($parsed_url === false || !isset($parsed_url['host']) || !test_host($parsed_url['host'])) {
+        http_response_code(403);
+        echo "Forbidden: This URL is not within the list of allowed domains.\n";
+        exit;
+    }
+    // validate the URL and shorten it
+    if (filter_var($url, FILTER_VALIDATE_URL)) {
+        $key = add_url($url);
+        $shortened_url = "https://$_SERVER[HTTP_HOST]/$key";
+        echo "$shortened_url\n";
+    } else {
+        http_response_code(422); // Unprocessable Entity
+        echo "Invalid URL.\n";
+    }
+    exit;
+}
+
+// If test parameters are provided, output a series of incremented keys
+if ($enabed_test && $test_start !== null && $test_count !== null) {
+    // validate password
+    if ($password !== '' && $input_password !== $password) {
+        http_response_code(401); // Unauthorized
+        echo "Unauthorized: Incorrect password.\n";
+        exit;
+    }
+    output_keys($test_start, (int)$test_count);
+    exit;
+}
+
+// Otherwise, assume the request URI is a key to look up
+$path = parse_url($_SERVER['REQUEST_URI'], PHP_URL_PATH);
+$key = trim($path, '/');
+
+// If the key is valid, look up the URL and redirect
+if ($key !== '') {
+    $url = get_url($key);
+    if ($url !== null) {
+        header("Location: $url", true, 301);
+        exit;
+    } else {
+        http_response_code(404);
+        echo "Not Found.\n";
+        exit;
+    }
+}
+// If no key or url is provided, show a simple HTML form to submit a URL
+?>
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>Bagaag.com Micro URL Shortener</title>
+</head>
+<body>
+    <h1>Bagaag.com Micro URL Shortener</h1>
+
+    <form method="post" action="">
+        <label for="url">Enter URL to shorten:</label><br>
+        <input type="text" id="url" name="url" size="50" required><br><br>
+        <?php if ($password !== ''): ?>
+            <label for="password">Enter the password:</label><br>
+            <input type="password" id="password" name="password" size="20" required><br><br>
+        <?php endif; ?>
+        <input type="submit" value="Shorten">
+    </form>
+
+    <?php if ($enable_test): ?>
+        <h2>Test Key Generation</h2>
+        <form method="post" action="">
+            <label for="test_start">Generate keys from:</label><br>
+            <input type="text" id="test_start" name="test_start" size="50" placeholder="Leave blank to start from beginning"><br><br>
+            <label for="test_count">How many keys to generate:</label><br>
+            <input type="text" id="test_count" name="test_count" size="10" required><br><br>
+            <?php if ($password !== ''): ?>
+                <label for="password">Enter the password:</label><br>
+                <input type="password" id="password" name="password" size="20" required><br><br>
+            <?php endif; ?>
+            <input type="submit" value="Generate">
+        </form>
+    <?php endif; ?>
+
+</body>
+</html>