<?php

declare(strict_types=1);

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

echo "=== Reference RS Implementation ===\n\n";

// Known working Reed-Solomon implementation from qrcode.js
// Algorithm:
// 1. Generator polynomial: g(x) = (x - α^0)(x - α^1)...(x - α^(t-1))
// 2. Message polynomial: m(x) = data[0] + data[1]*x + ... + data[n-1]*x^(n-1)
// 3. Encoded: c(x) = m(x) * x^t + (m(x) * x^t) mod g(x)
// 4. EC codewords = remainder of (m(x) * x^t) / g(x)

// Initialize GF(256)
$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 gfMultiply(array $gfExp, array $gfLog, int $a, int $b): int
{
    if ($a === 0 || $b === 0) {
        return 0;
    }
    return $gfExp[$gfLog[$a] + $gfLog[$b]];
}

// Generate generator polynomial for degree t
function generateGenerator(array $gfExp, int $degree): array
{
    $poly = [1]; // Start with 1
    
    for ($i = 0; $i < $degree; $i++) {
        // Multiply by (x - α^i)
        $newPoly = array_fill(0, count($poly) + 1, 0);
        for ($j = 0; $j < count($poly); $j++) {
            $newPoly[$j] ^= $poly[$j];
            $newPoly[$j + 1] ^= gfMultiply($gfExp, $gfLog, $poly[$j], $gfExp[$i]);
        }
        $poly = $newPoly;
    }
    
    return $poly;
}

// RS Encode
function rsEncode(array $data, int $ecCodewords, array $gfExp, array $gfLog): array
{
    // Generate generator polynomial
    $generator = generateGenerator($gfExp, $ecCodewords);
    
    echo "Generator polynomial (monic): " . implode(', ', $generator) . "\n";
    echo "Length: " . count($generator) . " (expected: " . ($ecCodewords + 1) . ")\n\n";
    
    // Message polynomial: [data, 0, 0, ..., 0]
    $messagePoly = array_merge($data, array_fill(0, $ecCodewords, 0));
    
    // Polynomial division
    for ($i = 0; $i < count($data); $i++) {
        $coeff = $messagePoly[$i];
        
        if ($coeff !== 0) {
            // Leading coefficient is 1 (monic), so clear this position
            $messagePoly[$i] = 0;
            
            // Apply generator coefficients
            for ($j = 1; $j < count($generator); $j++) {
                $messagePoly[$i + $j - 1] ^= gfMultiply($gfExp, $gfLog, $generator[$j], $coeff);
            }
        }
    }
    
    return array_slice($messagePoly, count($data));
}

// Test
echo "Test with QR Code Data:\n";
$data = [64, 180, 132, 84, 196, 196, 242, 5, 116, 245, 36, 196, 64, 236, 17, 236];
$ecCodewords = 10;

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

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

// Verify with decoder
require_once __DIR__ . '/test-reed-solomon-decoder.php';
$fullCodeword = array_merge($data, $ec);
$decoder = new SimpleRSDecoder();
$syndromes = $decoder->calculateSyndromes($fullCodeword, $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 implementation. We need to update our code to match this.\n";
} else {
    echo "\n❌ Syndromes are not all zero - still wrong!\n";
}