Remove unused salsify images after a pull

[mak001]

Would help with keeping the files section clean and keeping the number of assets down

[mak001]

possibly a good example: https://github.com/xddesigners/silverstripe-shopify/blob/master/src/Task/Import.php

[mak001]

could be done like the following. The only issue doing it this way is if the image is related to a non-salsify object.

    /**
     * @param $file
     * @param bool $multiple
     */
    public function onAfterMap($file, $multiple)
    {
        if ($multiple == Mapper::$SINGLE) {
            return;
        }

        // Images and Files
        $this->owner->resetAssetStream();
        $assetStream = $this->owner->getAssetStream();
        $this->archiveUnused($assetStream, File::class, 'assets', true);
    }

    /**
     * @param JsonMachine $stream
     * @param string|DataObject $class
     * @param string $typeName
     * @param bool $excludeNull If things with a null salsify ID should be archived
     */
    private function archiveUnused($stream, $class, $typeName, $excludeNull = false)
    {
        $codes = [];
        if ($excludeNull) {
            $codes[] = null;
        }

        foreach ($this->owner->yieldKeyVal($stream) as $name => $data) {
            $codes[] = $data['salsify:id'];
        }

        $invalidObjects = $class::get()->exclude([
            'SalsifyID' => $codes,
        ]);

        $count = 0;
        foreach ($this->owner->yieldSingle($invalidObjects) as $invalid) {
            /** @var File $invalidProduct */
            $invalid->doArchive();
            $count++;
        }
        ImportTask::output("Archived {$count} {$typeName}.");
    }