<?php
/**
 * EWKB (Extended Well Known Binary) Adapter
 */
class EWKB extends WKB
{
  
  /**
   * Read WKB binary string into geometry objects
   *
   * @param string $wkb An Extended-WKB binary string
   *
   * @return Geometry
   */
  public function read($wkb, $is_hex_string = FALSE) {
    if ($is_hex_string) {
      $wkb = pack('H*',$wkb);
    }
    
    // Open the wkb up in memory so we can examine the SRID
    $mem = fopen('php://memory', 'r+');
    fwrite($mem, $wkb);
    fseek($mem, 0);
    $base_info = unpack("corder/ctype/cz/cm/cs", fread($mem, 5));
    if ($base_info['s']) {
      $srid = current(unpack("Lsrid", fread($mem, 4)));
    }
    else {
      $srid = NULL;
    }
    fclose($mem);
    
    // Run the wkb through the normal WKB reader to get the geometry
    $wkb_reader = new WKB();
    $geom = $wkb_reader->read($wkb);
    
    // If there is an SRID, add it to the geometry
    if ($srid) {
      $geom->setSRID($srid);
    }
    
    return $geom;
  }
  
  /**
   * Serialize geometries into an EWKB binary string.
   *
   * @param Geometry $geometry
   *
   * @return string The Extended-WKB binary string representation of the input geometries
   */
  public function write(Geometry $geometry, $write_as_hex = FALSE) {
    // We always write into NDR (little endian)
    $wkb = pack('c',1);
    
    switch ($geometry->getGeomType()) {
      case 'Point';
        $wkb .= pack('L',1);
        $wkb .= $this->writePoint($geometry);
        break;
      case 'LineString';
        $wkb .= pack('L',2);
        $wkb .= $this->writeLineString($geometry);
        break;
      case 'Polygon';
        $wkb .= pack('L',3);
        $wkb .= $this->writePolygon($geometry);
        break;
      case 'MultiPoint';
        $wkb .= pack('L',4);
        $wkb .= $this->writeMulti($geometry);
        break;
      case 'MultiLineString';
        $wkb .= pack('L',5);
        $wkb .= $this->writeMulti($geometry);
        break;
      case 'MultiPolygon';
        $wkb .= pack('L',6);
        $wkb .= $this->writeMulti($geometry);
        break;
      case 'GeometryCollection';
        $wkb .= pack('L',7);
        $wkb .= $this->writeMulti($geometry);
        break;
    }
    
    if ($write_as_hex) {
      $unpacked = unpack('H*',$wkb);
      return $unpacked[1];
    }
    else {
      return $wkb;
    }
  }

}