# Students: 
#

from samples import *
import turtle

def draw(tree, xScale, yScale):
    """Draw the tree centered to the right of the current position,
    such that leaves end up separated vertically by yScale,
    and levels separated horizontally by xScale.
    """
    # name the three pieces of the tuple
    label,first,second = tree
    isInternal  = (first != ())  # by convention

    # advance to node and draw label
    advance(xScale)
    drawLabel(yScale, label)

    if isInternal:
        # if there are subtrees, draw those
        a = leafCount(first)
        b = leafCount(second)
        n = a + b

        lateral(-b/2 * yScale)
        draw(first, xScale, yScale)   # recurse
        lateral(n/2 * yScale)
        draw(second, xScale, yScale)  # recurse
        lateral(-a/2 * yScale)

    # remember to retreat from the node
    advance(-xScale)

#==============================================================

def advance(distance):
    """Move forward given distance in current direction."""
    turtle.forward(distance)

def lateral(distance):
    """Assuming turtle starts (and ends) with rightward orientation,
    implement a vertical move of given distance.

    Positive value should be upward.
    """
    turtle.right(90)
    turtle.forward(distance)
    turtle.left(90)


#=========== some utility functions we've written =============
def drawLabel(yScale,label):
    fontSize = round(0.7*yScale)
    turtle.penup()
    turtle.right(90)
    turtle.forward(fontSize/2)
    turtle.left(90)
    turtle.write( ' '+str(label), font=("Arial", fontSize, "normal"))
    turtle.right(90)
    turtle.backward(fontSize/2)
    turtle.left(90)
    turtle.pendown()
    
def leafCount(tree):
    """Return number of leaves of the tree."""
    root,first,second = tree    # unpack the tuple
    if first == second == ():
        return 1              # tree with one node
    else:
        return leafCount(first) + leafCount(second)

def reset():
    """Reset the state of the turtle canvas and position."""
    turtle.clear()
    turtle.up()
    turtle.goto(-0.5*turtle.window_width(), 0)
    turtle.down()
    turtle.setheading(0)

reset()  # reset on startup

def savePostscript(filename):
    turtle.getscreen().getcanvas().postscript(file=filename)
#==============================================================