<?php

declare(strict_types=1);

require_once __DIR__ . '/../../vendor/autoload.php';

echo "=== Correct RS Algorithm Test ===\n\n";

// Initialize GF(256) - same as in ReedSolomonEncoder
$gfLog = array_fill(0, 256, 0);
$gfExp = array_fill(0, 512, 0);

$x = 1;
for ($i = 0; $i < 255; $i++) {
    $gfExp[$i] = $x;
    $gfLog[$x] = $i;
    $x <<= 1;
    if ($x & 0x100) {
        $x ^= 0x11d;
    }
}

for ($i = 255; $i < 512; $i++) {
    $gfExp[$i] = $gfExp[$i - 255];
}

function gfMult(array $gfExp, array $gfLog, int $a, int $b): int
{
    if ($a === 0 || $b === 0) return 0;
    return $gfExp[$gfLog[$a] + $gfLog[$b]];
}

// Correct RS encoding algorithm
function rsEncodeCorrect(array $data, int $ecCodewords, array $gfExp, array $gfLog): array
{
    // Generator polynomial from specification
    // Format: [0, 251, 67, 46, 61, 118, 70, 64, 94, 32, 45] for 10 EC codewords
    // This represents: g(x) = x^10 + 251*x^9 + 67*x^8 + ... + 45
    $generators = [
        10 => [0, 251, 67, 46, 61, 118, 70, 64, 94, 32, 45],
    ];
    
    if (!isset($generators[$ecCodewords])) {
        throw new Exception("No generator for {$ecCodewords} EC codewords");
    }
    
    $generator = $generators[$ecCodewords];
    
    // Message polynomial: [data, 0, 0, ..., 0]
    $msg = array_merge($data, array_fill(0, $ecCodewords, 0));
    
    // Polynomial division
    // Generator format [0, a1, a2, ...] means leading coefficient is 1
    for ($i = 0; $i < count($data); $i++) {
        $lead = $msg[$i];
        
        if ($lead !== 0) {
            // Clear leading position (division by monic polynomial)
            $msg[$i] = 0;
            
            // Apply generator coefficients
            // generator[0] = 0 means leading coeff = 1, so we start at j=1
            for ($j = 1; $j < count($generator); $j++) {
                if ($i + $j < count($msg)) {
                    $msg[$i + $j] ^= gfMult($gfExp, $gfLog, $generator[$j], $lead);
                }
            }
        }
    }
    
    return array_slice($msg, count($data));
}

// Test
$data = [64, 180, 132, 84, 196, 196, 242, 5, 116, 245, 36, 196, 64, 236, 17, 236];
$ecCodewords = 10;

echo "Data: " . implode(', ', $data) . "\n\n";

$ec = rsEncodeCorrect($data, $ecCodewords, $gfExp, $gfLog);

echo "EC codewords: " . implode(', ', $ec) . "\n\n";

// Verify
require_once __DIR__ . '/test-reed-solomon-decoder.php';
$full = array_merge($data, $ec);
$decoder = new SimpleRSDecoder();
$syndromes = $decoder->calculateSyndromes($full, $ecCodewords);

echo "Syndromes: " . implode(', ', $syndromes) . "\n";
$allZero = true;
foreach ($syndromes as $s) {
    if ($s !== 0) {
        $allZero = false;
        break;
    }
}

if ($allZero) {
    echo "\n✅ ALL SYNDROMES ARE ZERO - Reed-Solomon is CORRECT!\n";
    echo "\nThis is the correct algorithm. We need to update our implementation.\n";
} else {
    echo "\n❌ Still wrong!\n";
}