# PROGRAM Stacks as Linked Lists:

####### DECLARE LINKED LIST #######

class ListNode:
    def __init__(self, value, pointer):
        self.value = value
        self.pointer = pointer
# END ListNode.

nodeD = ListNode(31, None)
nodeC = ListNode(37, nodeD)
nodeB = ListNode(62, nodeC)
nodeA = ListNode(23, nodeB)

HeadNode = nodeA

##################################


########## SIMPLE PRINT ##########
def PrintNodes():
    print("[", nodeA.value, "] -> [",nodeB.value, "] -> [",nodeC.value, "] -> [",nodeD.value, "] -> NULL")
# END PrintNodes.

# PrintNodes()

##################################

def CreateEmptyList():
    global HeadNode
    HeadNode = None
# END CreateEmptyList.

##################################

def DeleteAList():
    global HeadNode
    HeadNode = None
# END DeleteAList.

##################################

def ListIsEmpty():
    global HeadNode
    return HeadNode == None
# END ListIsEmpty.

##################################

########## PRINT WITH LOOP ##########

def PrintNodesWithLoop():
    global HeadNode
    Current = HeadNode
    if (Current != None):
    # THEN
        while (Current.pointer != None):
        # DO
            print(Current.value)
            Current = Current.pointer
        # ENDWHILE;
        print(Current.value)
    else:
        print("Empty list")
    # ENDIF;
# END PrintNodesWithLoop.

# PrintNodesWithLoop()

########## PRINT AND COUNT ##########

def PrintNodesWithLoopAndCount():
    global HeadNode
    Current = HeadNode
    CountNodes = 0
    if (Current != None):
    # THEN
        while (Current.pointer != None):
            # DO
            print(Current.value)
            Current = Current.pointer
            CountNodes = CountNodes + 1
        # ENDWHILE;

        # Print out and count for last node
        CountNodes = CountNodes + 1
        print(Current.value)
    
        print("Count:", CountNodes)
    else:
        print("Empty list")
    # ENDIF;
# END PrintNodesWithLoopAndCount.

# PrintNodesWithLoopAndCount()

##################################

def FindANode(N):
    global HeadNode
    Current = HeadNode
    while ((Current.pointer != None) and (Current.value != N)):
    # DO
        Current = Current.pointer
    # ENDWHILE;

    # Print out and count for last node
    if (Current.pointer == None):
    # THEN
        print(N, "is not in the list")
    else:
        print("Found value:", Current.value)
    # ENDIF; 
# END FindANode.
# FindANode(33337)

##################################

def InsertANode(Pos, N):
    global HeadNode
    Current = HeadNode

    nodeX = ListNode(N, None)

    PositionCounter = 1
    CountNodes = 0
    if Pos == 0:
    # THEN
        HeadNode = nodeX
        nodeX.pointer = Current
    else:
        while (Pos > PositionCounter):
            # DO
            Current = Current.pointer
            PositionCounter = PositionCounter + 1
        # ENDWHILE;

        nodeX.pointer = Current.pointer
        Current.pointer = nodeX
    # ENDIF;
# END InsertANode.
# InsertANode(2, 12345)       
# PrintNodesWithLoopAndCount()

##################################

def DeleteANode(N):
    global HeadNode
    Previous = None
    Current = HeadNode
    if Current.value == N:
    # THEN
        HeadNode = Current.pointer
    else:
        while ((Current.pointer != None) and (Current.value != N)):
        # DO
            Previous = Current
            Current = Current.pointer
        # ENDWHILE;
        Previous.pointer = Current.pointer
    # ENDIF;
# END DeleteANode.

# DeleteANode(12345)
# PrintNodesWithLoopAndCount()
    
#################################
########## S T A C K S ##########
#################################

# PrintNodesWithLoopAndCount()
StackTop = HeadNode;
# PrintNodesWithLoopAndCount()

##################################

def CreateEmptyStack():
    global StackTop
    StackTop = None
# END CreateEmptyStack.

# CreateEmptyStack()

##################################

def StackIsEmpty():
    global StackTop
    return StackTop == None
# END StackIsEmpty.

##################################

def PrintStack():
    global StackTop
    SPrint = StackTop
    print("Printing Stack...")
    while(SPrint != None):
    # DO
        print(SPrint.value)
        SPrint = SPrint.pointer
    # ENDWHILE;
    print("* End of Stack *")
# END QueueIsEmpty.

##################################

def StackPush(N):
    global StackTop
    nodeX = ListNode(N, None)
    if StackIsEmpty():
    # THEN
        StackTop = nodeX
    else:
        nodeX.pointer = StackTop
        StackTop = nodeX
    # ENDIF;
# END StackPush.

# StackPush(35)
# StackPush(34)
# StackPush(33)
# StackPush(32)
# PrintStack()

##################################

def StackPop():
    global StackTop
    if StackIsEmpty():
    # THEN
        print("Stack is empty")
        N = 0
    else:
        N = StackTop.value
        StackTop = StackTop.pointer
    # ENDIF;
    return N
# END StackPop.

# PopValue = StackPop()
# print("Pop value:", PopValue)
# PrintStack()
##################################

def ShowStackTop():
    global StackTop
    if StackIsEmpty():
    # THEN
        print("Stack is empty")
        N = 0
    else:
        N = StackTop.value
        print("Top value:", StackTop.value)
    # ENDIF;
    return N
# END ShowStackTop.

# TopValue = ShowStackTop()
# PrintStack()

############

# Program Stack Menu

print("1) Create a stack")
print("2) Check if the stack is full")
print("3) Check if the stack is empty")
print("4) Push an element onto the stack")
print("5) Pop an element off the stack")
print("6) Inspect the top of the stack")
print("7) Clear stack")
print("99) Exit")

John = int(input("Please select an option: "))

while (John != 99):
	if (John == 1):
		CreateEmptyStack()
		print("This stack is now created")
	elif (John == 2):
		print("Stack is implemented as a linked list, cannot be full")
	elif (John == 3):
		if (StackIsEmpty() == True):
			print("It's Empty")
		else:
			print("It ain't Empty")
		# endif;
	elif (John == 4):
		NewValue = int(input("What value should I add to the stack: "))
		StackPush(NewValue)
	elif (John == 5):
		print("The Popped value is: ", StackPop())
	elif (John == 6):
		print("The Top value is: ", ShowStackTop())
	elif (John == 7):
		CreateEmptyStack()
		print("This stack is now empty")
	elif (John == 99):
   		None
	else:
  		print("Invalid Option")
	#endif
	John = int(input("Please select an option: "))

#endwhile

#END.