<?php

abstract class Entity
{
   /**
    * Different visibility types for entities
    */
   const VSB_INVISIBLE = 0;
   const VSB_VISIBLE = 1;
   const VSB_SEETHROUGH = 2;

   protected $place;
   protected $seenCells = array();


   public function __toString()
   {
      return static::CHAR;
   }

   static public function getChar()
   {
      return static::CHAR;
   }

   public function getVisibility()
   {
      return static::VISIBILITY;
   }

   public function setPlace(Place $place)
   {
      // Remove from old place if exists
      if ($this->place !== null)
         $this->place->getLevel()->removeEntity($this->place->getCoord());

      $this->place = $place;

      if ($this->place !== null)
         $this->place->getLevel()->insertEntity($this->place->getCoord(), $this);
   }

   public function getPlace()
   {
      return $this->place;
   }

   public function drawPath(Entity $target, $callback)
   {
      $targetX = $target->getPlace()->getCoord()->x;
      $targetY = $target->getPlace()->getCoord()->y;
      $startX = $this->getPlace()->getCoord()->x;
      $startY = $this->getPlace()->getCoord()->y;

      if ($startX == $targetX && $startY == $targetY)
         return;

      $diffX = $targetX - $startX;
      $diffY = $targetY - $startY;

      $step = max(abs($diffX), abs($diffY));
      $stepX = $diffX / $step;
      $stepY = $diffY / $step;
      if ($stepX != 0)
         $steps = floor($diffX / $stepX);
      else
         $steps = floor($diffY / $stepY);

      $x = $startX;
      $y = $startY;
      $i = 0;
      do
      {
         $x += $stepX;
         $y += $stepY;
         ++$i;
         if (!$callback(new Coord(floor($x), floor($y))))
            return;
            
      } while ((floor($x) != $targetX || floor($y) != $targetY)
               && $i < $steps);
   }

   public function canSee(Entity $target)
   {
      // Check if already marked as seen
      if (isset($this->seenCells[$target->getPlace()->getCoord()->x][$target->getPlace()->getCoord()->y]))
         return true;

      // Check distance
      if ($this->getSight() < $this->getPlace()->getCoord()->getDistance($target->getPlace()->getCoord()))
         return false;

      // Check each cell on the way for opaque objects
      $level = $this->getPlace()->getLevel();
      $return = true;
      $seenCells =& $this->seenCells;
      $this->drawPath($target, function(Coord $coord) use (&$return, $level, $target,
                                                            &$seenCells)
      {
         $obj = $level->whatsAt($coord);
         if ($obj !== null && $obj != $target && $obj->getVisibility() == Entity::VSB_VISIBLE)
         {
            $return = false;
            return false;
         }
         $seenCells[$coord->x][$coord->y] = true;
         return true;
      });

      return $return;
   }
}