<?php
/*****************************************************************************
 * Download.php
 * Contains the code to download an album.
 *
 * Kabuki CMS (C) 2013-2019, Aaron van Geffen
 *****************************************************************************/

class Download
{
	public function __construct()
	{
		// Ensure we're logged in at this point.
		$user = Registry::get('user');
		if (!$user->isLoggedIn())
			throw new NotAllowedException();

		if (!isset($_GET['tag']))
			throw new UserFacingException('No album or tag has been specified for download.');

		$tag = (int)$_GET['tag'];
		$album = Tag::fromId($tag);

		if (isset($_SESSION['current_export']))
			throw new UserFacingException('An export of "' . $tag->tag . '" is ongoing. Please try again later.');

		// So far so good?
		$this->exportAlbum($album);
		exit;
	}

	private function exportAlbum(Tag $album)
	{
		$files = [];

		$album_ids = array_merge([$album->id_tag], $this->getChildAlbumIds($album->id_tag));
		foreach ($album_ids as $album_id)
		{
			$iterator = AssetIterator::getByOptions(['id_tag' => $album_id]);
			while ($asset = $iterator->next())
				$files[] = join(DIRECTORY_SEPARATOR, [$asset->getSubdir(), $asset->getFilename()]);
		}

		$descriptorspec = [
			0 => ['pipe', 'r'], // STDIN
			1 => ['pipe', 'w'], // STDOUT
		];

		$command = 'tar -cf - -C ' . escapeshellarg(ASSETSDIR) . ' --null -T -';

		$proc = proc_open($command, $descriptorspec, $pipes, ASSETSDIR);

		if(!$proc)
			throw new UnexpectedValueException('Could not execute TAR command');

		if(!$pipes[0])
			throw new UnexpectedValueException('Could not open pipe for STDIN');

		if(!$pipes[1])
			throw new UnexpectedValueException('Could not open pipe for STDOUT');

		// STDOUT should not block.
		stream_set_blocking($pipes[1], 0);

		header('Pragma: no-cache');
		header('Content-Description: File Download');
		header('Content-disposition: attachment; filename="' . $album->tag . '.tar"');
		header('Content-Type: application/octet-stream');
		header('Content-Transfer-Encoding: binary');

		// Write filenames to include to STDIN, separated by null bytes.
		foreach ($files as $file)
			fwrite($pipes[0], $file . "\0");

		// Close STDIN pipe to start archiving.
		fclose($pipes[0]);

		// At this point, end output buffering so we can enjoy more than ~62MB of photos.
		ob_end_flush();

		do
		{
			// Read STDOUT as `tar` is doing its work.
			echo stream_get_contents($pipes[1], 4096);

			// Are we still running?
			$status = proc_get_status($proc);
		}
		while (!empty($status) && $status['running']);

		// Close STDOUT pipe and clean up process.
		fclose($pipes[1]);

		proc_close($proc);
	}

	private function getChildAlbumIds($parent_id)
	{
		$ids = [];

		$albums = Tag::getAlbums($parent_id, 0, PHP_INT_MAX);
		foreach ($albums as $album)
		{
			$ids[] = $album['id_tag'];
			$ids = array_merge($ids, $this->getChildAlbumIds($album['id_tag']));
		}

		return $ids;
	}
}