############################################################
#
#  Frame stack handling		
#	Jari-Matti Auttila / 2002-12-13
#
############################################################
#
# Function list:
#
# * stack_append(form)
#		- Append a form object to the end of the stack
#	
# * stack_first as object;
#		- returns the first object in the stack
#
# * stack_previous
#		- returns the last added form from the stack
#
# * stack_pop_previous;
#		- same as above, but deletes the returned form from the stack
#
# * stack_del_previous;
#		- only deletes the last added form from the stack
#
# * stack_pop_first as object;
#		- returns and deletes the first item in the stack.
#		- all stack items are dropped down one bit.
#
# * stack_del_first;
#		- deletes the first item, but does not return anything
#
# * stack_reset;
#		- clears the whole stack
#
# * fReturnToPreviousScreen;
#		- this function always displays the last added frame
#
# * fOpenScreen(nextform);
#		- displays the form "nextform"
#		- automatically appends "nextform" to the stack
#
############################################################

# Variable stack

variables;
	numeric nStackMax = -1;
	object oStack[50];
end;

function stack_append(object form);
	nStackMax = nStackMax + 1;
	oStack[nStackMax] = form;
end;

function stack_first as object;
	stack_first = oStack[0];
end;

function stack_previous as object;
	stack_previous = oStack[nStackMax - 1];
end;

function stack_pop_previous as object;
	stack_pop_previous = stack_previous;
	nStackMax = nStackMax - 1;
end;

function stack_del_previous;
	nStackMax = nStackMax - 1;
end;

function stack_pop_first as object;
	variables;
		numeric ind;
	end;

	stack_pop_first = stack_first;

	for ind = 0, ind < nStackMax - 1;
		oStack[ind] = oStack[ind + 1];
	next ind + 1;

	nStackMax = nStackMax - 1;
end;

function stack_del_first;
	variables;
		numeric ind;
	end;

	for ind = 0, ind < nStackMax - 1;
		oStack[ind] = oStack[ind + 1];
	next ind + 1;

	nStackMax = nStackMax - 1;
end;

function stack_reset;
	nStackMax = -1;
end;

# Return to the previous screen

function fReturnToPreviousScreen;
	variables;
		object previous;
	end;

	previous = stack_pop_previous;
	previous.hidden = 0;
end;


# Open the next screen

function fOpenScreen(object nextform);
	stack_append(nextform);
	nextform.hidden = 0;
end;