import sys
from typing import NamedTuple

# Folding function.
def fold(f, z, l):
    # This is a simple for loop that accumulates a value and then returns it.
    for x in l:
        z = f(z, x)
    return z

# This is what the algorithm uses to tell whether a page was used or not.
class Bits(NamedTuple):
    read: bool
    write: bool

# This class manages the state of physical/virtual memory.
class State(NamedTuple):
    faults: int
    hits: int
    order: list[int]
    page_table: dict[int, Bits]
    physical_capacity: int

    # Increase hits by 1.
    def hit(s):
        return State(s.faults, s.hits + 1, s.order, s.page_table, s.physical_capacity)

    # Increase faults by 1.
    def fault(s):
        return State(s.faults + 1, s.hits, s.order, s.page_table, s.physical_capacity)

    # Change the mode on a page.
    def modify(s, page, mode):
        return State(s.faults, s.hits, s.order, s.page_table | {page: Bits(mode, False)}, s.physical_capacity)

    # Make space in physical memory depending on the order.
    def evict(s):
        def rec(page_table, order, page):
            # if the page table says that the page's R bit was set:
            if page_table[page].read == True:
                # rotate the queue: s_.order[1:] + [page]
                # change the current page's R bit to False: s_.page_table | {page: Bits(False, False)}
                # the next page to check for is: s_.order[0]
                return rec(page_table | {page: Bits(False, False)}, order[1:] + [order[0]], order[0])
            else:
                return page, order
        last_page, new_order = rec(s.page_table, s.order[1:] + [s.order[0]], s.order[0])
        # Finally, return the new state, without that page.
        return State(s.faults, s.hits, new_order[:-1], {k: v for k, v in s.page_table.items() if k != last_page}, s.physical_capacity)

    # This function simply inserts a page into the page table.
    def insert(s, page):
        return State(s.faults, s.hits, s.order + [page], s.page_table | {page: Bits(False, False)}, s.physical_capacity)

# This is the algorithm for second chance page replacement.
def second(state, access) -> State:
    page = access[1]
    # If the page is in the page table, that is a page hit.
    if page in state.page_table:
        # Also, the page's R bit must be set to 1.
        return state.modify(page, True).hit()
    else:
        # If there isn't any space in the page table, call make_space()
        if len(state.page_table) == state.physical_capacity:
            return state.evict().insert(page).fault()
        else:
            # If there is space in the page table, we can simply insert the page.
            return state.insert(page).fault()

def main():
    # The user must provide the physical capacity and the file path to the
    # access sequence.
    if len(sys.argv) != 3:
        print("USAGE:", sys.argv[0], "number_of_pages", "file_path")
        print("\twhere:\n\t\tnumber_of_pages : int\n\t\tfile_path : string")

    # The second argument is the file path.
    file_path = sys.argv[2]

    # This simply parses the access sequence file.
    accesses = []
    with open(file_path) as f:
        accesses = [(x.split(":")[0], int(x.split(":")[1])) for x in f.read().split()]

    # The physical capacity is the first argument.
    limit = int(sys.argv[1])
    # The result is simply the evaluation of the second algorithm on the access
    # sequence.
    res = fold(second, State(0, 0, [], dict(), limit), accesses)

    # Print the result.
    print("Faults:", res.faults, "\nHits:", res.hits)

main()