<?php

namespace App\Services\Qr;

class QrPdfExporter
{
    public function fromPng(string $pngBinary, string $title): string
    {
        if (! extension_loaded('gd')) {
            throw new \RuntimeException('PDF export requires the GD extension.');
        }

        $image = imagecreatefromstring($pngBinary);
        if ($image === false) {
            throw new \RuntimeException('Could not read QR image for PDF export.');
        }

        $width = imagesx($image);
        $height = imagesy($image);
        $canvas = imagecreatetruecolor($width, $height);
        $white = imagecolorallocate($canvas, 255, 255, 255);
        imagefilledrectangle($canvas, 0, 0, $width, $height, $white);
        imagecopy($canvas, $image, 0, 0, 0, 0, $width, $height);
        imagedestroy($image);

        ob_start();
        imagejpeg($canvas, null, 95);
        $jpeg = (string) ob_get_clean();
        imagedestroy($canvas);

        return $this->buildPdf($jpeg, $title, $width, $height);
    }

    private function buildPdf(string $jpeg, string $title, int $imgW, int $imgH): string
    {
        $pageW = 595.28;
        $pageH = 841.89;
        $margin = 48;
        $maxQr = min($pageW - ($margin * 2), 320);
        $scale = min($maxQr / max(1, $imgW), $maxQr / max(1, $imgH));
        $drawW = $imgW * $scale;
        $drawH = $imgH * $scale;
        $x = ($pageW - $drawW) / 2;
        $y = 120;
        $safeTitle = $this->pdfEscape(substr($title, 0, 80));

        $objects = [];
        $objects[] = "1 0 obj << /Type /Catalog /Pages 2 0 R >> endobj\n";
        $objects[] = "2 0 obj << /Type /Pages /Kids [3 0 R] /Count 1 >> endobj\n";
        $objects[] = sprintf(
            "3 0 obj << /Type /Page /Parent 2 0 R /MediaBox [0 0 %.2F %.2F] /Resources << /Font << /F1 4 0 R >> /XObject << /Im1 5 0 R >> >> /Contents 6 0 R >> endobj\n",
            $pageW,
            $pageH,
        );
        $objects[] = "4 0 obj << /Type /Font /Subtype /Type1 /BaseFont /Helvetica-Bold >> endobj\n";
        $objects[] = sprintf(
            "5 0 obj << /Type /XObject /Subtype /Image /Width %d /Height %d /ColorSpace /DeviceRGB /BitsPerComponent 8 /Filter /DCTDecode /Length %d >> stream\n%s\nendstream\nendobj\n",
            $imgW,
            $imgH,
            strlen($jpeg),
            $jpeg,
        );

        $content = "BT /F1 16 Tf 48 " . ($pageH - 72) . " Td ({$safeTitle}) Tj ET\n";
        $content .= sprintf("q %.4F 0 0 %.4F %.2F %.2F cm /Im1 Do Q\n", $drawW, $drawH, $x, $pageH - $y - $drawH);
        $content .= "BT /F1 10 Tf 48 48 Td (Generated by Ladill QR Codes) Tj ET\n";
        $objects[] = sprintf("6 0 obj << /Length %d >> stream\n%s\nendstream\nendobj\n", strlen($content), $content);

        $pdf = "%PDF-1.4\n";
        $offsets = [0];

        foreach ($objects as $object) {
            $offsets[] = strlen($pdf);
            $pdf .= $object;
        }

        $xrefPos = strlen($pdf);
        $pdf .= "xref\n0 " . count($offsets) . "\n";
        $pdf .= "0000000000 65535 f \n";
        for ($i = 1; $i < count($offsets); $i++) {
            $pdf .= sprintf("%010d 00000 n \n", $offsets[$i]);
        }
        $pdf .= "trailer << /Size " . count($offsets) . " /Root 1 0 R >>\n";
        $pdf .= "startxref\n{$xrefPos}\n%%EOF";

        return $pdf;
    }

    private function pdfEscape(string $text): string
    {
        return str_replace(['\\', '(', ')'], ['\\\\', '\\(', '\\)'], $text);
    }
}