import numpy as np
from itertools import product

class Camera(object):
    """
    Pinhole camera object.

    Args:
        - size: tuple, *optional*
            Pixel array shape.
        - film_size: tuple, *optional*
            Physical size of photographic film. Defaults to 35mm film size.
        - focal_length: float, *optional*
            Focal length of camera.
    """
    def __init__(self, size = (800, 600), film_size = (0.035, 0.024), \
                     focal_length=0.05):
        x = np.linspace(-film_size[0]/2, film_size[0]/2, size[0])
        z = np.linspace(-film_size[1]/2, film_size[1]/2, size[1])

        self.grid = np.array(tuple(product(x,[0],z)))

        self.grid += (0,focal_length,0)
        self.focal_point = np.zeros(3)

    def position(self, position):
        """Translate the camera to `position`."""
        self.grid += position
        self.focal_point += position

    def get_rays(self):
        """Return the position and direction for each pixel ray."""
        return self.grid, self.focal_point-self.grid