<?php

declare(strict_types=1);

/** 
 * @author Robert Strutts <Bob_586@Yahoo.com>
 * @copyright (c) 2024, Robert Strutts
 * @license MIT
 */

namespace CodeHydrater;

class String_fns {
    public static function isUTF8(string $string) {
        // Empty string is valid UTF-8
        if ($string === '') {
            return true;
        }

        // Convert string to array of bytes
        $bytes = unpack('C*', $string);

        // Pattern matching state
        $state = 0;
        $expectedBytes = 0;

        foreach ($bytes as $byte) {
            // Single byte character (0xxxxxxx)
            if ($byte <= 0x7F) {
                $state = 0;
                continue;
            }

            // Start of multibyte sequence
            if ($state === 0) {
                // 2 bytes (110xxxxx)
                if (($byte & 0xE0) === 0xC0) {
                    $expectedBytes = 1;
                }
                // 3 bytes (1110xxxx)
                elseif (($byte & 0xF0) === 0xE0) {
                    $expectedBytes = 2;
                }
                // 4 bytes (11110xxx)
                elseif (($byte & 0xF8) === 0xF0) {
                    $expectedBytes = 3;
                }
                // Invalid UTF-8 start byte
                else {
                    return false;
                }
                $state = $expectedBytes;
                continue;
            }

            // Continuation byte (10xxxxxx)
            if (($byte & 0xC0) !== 0x80) {
                return false;
            }

            $state--;
        }

        // Check if we finished the last multibyte sequence
        return $state === 0;
    }
    
    // Check if string contains multibyte characters
    public static function has_multibyte_chars(string $string) {
        return (bool) preg_match('/[\xC2-\xDF][\x80-\xBF]|\xE0[\xA0-\xBF][\x80-\xBF]|[\xE1-\xEC\xEE\xEF][\x80-\xBF]{2}|\xED[\x80-\x9F][\x80-\xBF]|\xF0[\x90-\xBF][\x80-\xBF]{2}|[\xF1-\xF3][\x80-\xBF]{3}|\xF4[\x80-\x8F][\x80-\xBF]{2}/', $string);
    }  
    
    // Get the length of a string
    public function strlen($string) {
        return strlen($string);
    }

    // Convert a string to lowercase
    public function strtolower($string)  {
        return strtolower($string);
    }

    // Convert a string to uppercase
    public function strtoupper($string)  {
        return strtoupper($string);
    }

    // Get a substring from a string
    public function substr($string, $start, $length = null) {
        return ($length !== null) ? substr($string, $start, $length) : substr($string, $start);
    }

    // Reverse a string
    public function strrev($string) {
        return strrev($string);
    }
}