#!/usr/bin/env python3
"""
Implements a Binary Tree as a list, where each each node of the tree
is given as a list:
    node = [ value, [left child], [right child]]
"""

__author__ = "Richard White"
__version__ = "2019-04-10"

def binary_tree(rootVal):
    """Creates a node with a root value and two empty lists
    as leaves.
    """
    return [rootVal,[],[]]

def get_root_val(root):
    return root[0]

def set_root_val(root, newValue):
    """Sets the root value of the identified tree to a 
    new value.
    """
    root[0] = newValue

def get_left_child(root):
    return root[1]

def get_right_child(root):
    return root[2]

def insert_left(root, new_branch):
    """Inserts a new branch at the left side of the root. If there
    is currently a tree there, that tree is moved down to become
    the left branch of the node inserted.
    """
    tmp = get_left_child(root)
    root[1] = [new_branch, [], []]
    root[1][1] = tmp

def insert_right(root, new_branch):
    """Inserts a new branch at the right side of the root. If there
    is currently a tree there, that tree is moved down to become
    the right branch of the node inserted.
    """
    tmp = get_right_child(root)
    root[2] = [new_branch, [], []]
    root[2][2] = tmp


def main():
    t = binary_tree(3)
    print("Instruction: t = binary_tree(3)")
    print("Result:", t)
    print("Expect: [3, [], []]")
    insert_left(t, 4)
    print("Instruction: insert_left(t, 4)")
    print("Result:", t)
    print("Expect: [3, [4, [], []], []]")
    insert_left(t, 5)
    print("Instruction: insert_left(t, 5)")
    print("Result:", t)
    print("Expect: [3, [5, [4, [], []], []], []]")
    insert_right(t, 6)
    print("Instruction: insert_right(t, 6)")
    print("Result:", t)
    print("Expect: [3, [5, [4, [], []], []], [6, [], []]]")
    insert_right(t, 7)
    print("Instruction: insert_right(t, 7)")
    print("Result:", t) 
    print("Expect: [3, [5, [4, [], []], []], [7, [], [6, [], []]]]")
    l = get_left_child(t)
    print("Instruction: l = get_left_child(t)")
    print("Result: l =", l)
    print("Expect: l = [5, [4, [], []], []]")
    set_root_val(l, 9)
    print("Instruction: set_root_val(l, 9)")
    print("Result: l =", l)
    print("Expect: l = [9, [4, [], []], []]")
    insert_left(l, 11)
    print("Instruction: insert_left(l, 11)")
    print("Result:", t)
    print("Expect: [3, [9, [11, [4, [], []], []], []], [7, [], [6, [], []]]]")
    print("Instruction: print(get_right_child(get_right_child(t)))")
    print("Result:", get_right_child(get_right_child(t)))
    print("Expect: [6, [], []]")    
    
if __name__ == "__main__":
    main()