Question

Ok i’ve to admin i’m not a master in recursion. This could be kinda a newbie problem.

What i’m trying to do is to compute the section number. As you can see as you go in depth the section number changes in a predictable way:

multipart/mixed
 -- (part 0, sec. "1") multipart/related
    -- (part 0, sec. "1.1") multipart/alternative
       -- (part 0, sec. "1.1.1") text/plain
       -- (part 1, sec. "1.1.2") text/html
    -- (part 1, sec. "1.2") image/gif
 -- (part 1, sec. "2") image/png

That is, section number is simply the part number (plus 1) followed by a dot and again by the part number (plus 1), how many times depends on nesting level.

A simple $struct to pass to parse() function is like:

object(stdClass)
   public 'type' => int // if 1 it's multipart
   public 'parts' => array // Inner parts

While my function is quite like this:

public function parse($struct, $depth = '')
{
   if(!isset($struct->parts)) return; // Base case of recursion: no parts inside

   // $struct->parts is array: index starting from 0.
   for($i = 0, $j = count($struct->parts); $i < $j; $i++)
   {
      $part = $struct->parts[$i]; // Current part
      $ptno = $i + 1; // This is the part number, will be used to build $secno

      // Multipart? Go further in recursion passing the new level of nesting
      if($part->type == 1) $this->parse($part, $depth .= "$partno" . ".");

      // Compute the section number with the given $depth (if any)
      // ACTUALLY NOT WORKING
      $secno = !empty($depth) ? "$depth$ptno" : "$ptno";

      // Where am i?
      echo self::$TYPES[$part->type] . '/' . $part->subtype . ": $secno<br/>";
   }
}

Output (wrong):

text/PLAIN: 1.1.1
text/HTML: 1.1.2
multipart/ALTERNATIVE: 1.1.1
image/GIF: 1.1.2
multipart/RELATED: 1.1
image/PNG: 1.2

This is how it should be:

text/PLAIN: 1.1.1
text/HTML: 1.1.2
multipart/ALTERNATIVE: 1.1
image/GIF: 1.2
multipart/RELATED: 1
image/PNG: 2

EDIT: copy & paste test data:

$test = (object) array(
    'type' => 1, // multipart
    'subtype' => 'MIXED',
    'parts' => array(
        (object) array(
            'type'    => 1, // multipart
            'subtype' => 'RELATED',
            'parts'   => array(
                (object) array(
                    'type'    => 1, // multipart
                    'subtype' => 'ALTERNATIVE',
                    'parts'   => array(
                        (object) array('type' => 0, 'subtype' => 'PLAIN'),
                        (object) array('type' => 0, 'subtype' => 'HTML'),
                    )
                ),
                (object) array(
                    'type'    => 5, // image
                    'subtype' => 'GIF'
                )
            )
        ),
        (object) array(
            'type'    => 5, // image
            'subtype' => 'PNG'
        )
    )
);

Answer 1

The problem is you are .= appending $partno when you should just be . appending here:

$this->parse($part, $depth .= "$partno" . ".");

So fixing that in the context of your code, you get:

public function parse($struct, $depth = '')
{
   if(!isset($struct->parts)) return; // Base case of recursion: no parts inside

   // $struct->parts is array: index starting from 0.
   for($i = 0, $j = count($struct->parts); $i < $j; $i++)
   {
      $part = $struct->parts[$i]; // Current part
      $ptno = $i + 1; // This is the part number, will be used to build $secno

      // Multipart? Go further in recursion passing the new level of nesting
      if($part->type == 1) $this->parse($part, $depth . "$partno" . ".");

      // Compute the section number with the given $depth (if any)
      $secno = !empty($depth) ? "$depth$ptno" : "$ptno";

      // Where am i?
      echo self::$TYPES[$part->type] . '/' . $part->subtype . ": $secno<br/>";
   }
}

And you can restructure your code like this to avoid code duplication more:

public function parse($struct, $depth = '')
{
   if(!isset($struct->parts)) return; // Base case of recursion: no parts inside

   // $struct->parts is array: index starting from 0.
   for($i = 0, $j = count($struct->parts); $i < $j; $i++)
   {
      $part = $struct->parts[$i]; // Current part
      $ptno = $i + 1; // This is the part number, will be used to build $secno

      // Compute the section number with the given $depth (if any)
      $secno = $depth . $ptno

      // Multipart? Go further in recursion passing the new level of nesting
      if($part->type == 1) $this->parse($part, $secno . '.');

      // Where am i?
      echo self::$TYPES[$part->type] . '/' . $part->subtype . ": $secno<br/>";
   }
}