''' Purpose: better experience functional development
'''

from PIL import Image

# helpful constants
SIMILARITY_THRESHOLD = 85                # minimum distance to be dissimilar
GREEN                = ( 0, 255, 0 )     # back screen color
# This is the green screen color we are detecting so we can use it
# to paint over

def distance( p1, p2 ) :
    ''' Returns the distance between p1 and p2 RGB values
    '''

    # Extract r,g,b values for p1 and p2
    r1, g1, b1 = p1
    r2, g2, b2 = p2
    distance_between_pixels = abs( r2-r1 ) + abs( g2-g1 ) + abs( b2-b1 )
    return distance_between_pixels

def similar( p1, p2 ) :
    ''' Returns whether the distance between pixels p1 and p2 is less than the
        similarity threshold
    '''

    # Use the distance() function defined earlier
    d = distance( p1, p2 ) # Pass in the parameters p1, p2 in this function as arguments to the function distance()
    if ( d < SIMILARITY_THRESHOLD ):
        return True
    else:
        return False

    # We will use the similar() function to see how close the colors in the image are
    # to the green screen color

def is_background( p, back_screen ) :
    ''' Returns whether p is similar to the back_screen color
    '''

    # Use the similar() function defined earlier
    similarity = similar( p, back_screen ) # This function returns True or False using the arguments p and back_screen
    if ( similarity == True ):
        return True
    else:
        return False

    # Or just return similarity since similar()'s return value is True / False

def inbounds( spot,  img ) :
    ''' Returns whether spot lies on img.
    '''

    # Determines if the spot is in the bounds of the image (0<=x<w and 0<=y<h)
    x, y = spot
    w, h = img.size
    if ( x < 0 or y < 0  ): # If either spot's x or y value is negative
        return False
    elif ( x >= w ):        # x coordinate is out of bounds
        return False
    elif ( y >= h ):        # y coordinate is out of bounds
        return False
    else:               # This means that x was positive and less than the width and y was positive and less than the height
        return True

def colorable( spot, img, p, back_screen ) :
    ''' Returns whether both
            spot is a location on img and
            color p is not similar to color back_screen
    '''

    # This function uses functions inbounds() and is_background()
    spot_on_image = inbounds( spot, img ) # Will be True if the spot is in bounds
    p_is_background_color = is_background( p, back_screen ) # Will be true if p is similar to backgorund
    if ( spot_on_image == False ): # Should be True to be colorable
        return False
    elif ( p_is_background_color == True ): # Should be False to be colorable
        return False
    else: # This means the spot was on the image and p was not the background color (so it's colorable!)
        return True


### DO NOT MODIFY THE BELOW CODE

def combine( bg, fg, sx, sy, back_screen ) :
    ''' Returns mash up of background image bg and foreground image fg, where
        the pixels in fg that are dissimilar to back_screen are copied on top
        of the background.
    
        The mash up uses location (sx, sy) as the spot in the background to
        start the lay over of fg.
    '''

    bw, bh = bg.size                      # size of background image
    fw, fh = fg.size                      # size of foreground image

    copy      = bg.copy()                 # get a copy of background image
    new_image = copy.convert( 'RGB' )     # to be the basis of new image

    for fx in range( 0, fw ) :            # consider every (fx, fy)
        for fy in range( 0, fh ):         # possibility of the new image

            fspot = ( fx, fy )            # name spot (fx, fy )

            fpixel = fg.getpixel( fspot ) # get the pixel at fspot

            nx = sx + fx                  # determine spot on new image
            ny = sy + fy                  # to paint fpixel
            nspot = ( nx, ny )

            # check whether fpixel should be painted on new image at nspot
            if ( colorable( nspot, new_image, fpixel, back_screen ) ) :
                new_image.putpixel( nspot, fpixel )

    return new_image                      # return the mash up

if ( __name__ == '__main__' ) :

    import smashing

    smashing.test_with_dino()
    smashing.test_with_beyonce()
    smashing.test_with_ww()