program day8b
    implicit none
    integer, parameter :: max_chars = 400
    integer, parameter :: max_nodes = 1000
    integer, parameter :: max_iter = 100000
    character(200) :: fname
    character(max_chars) :: fline
    integer :: n_arguments
    integer :: istat
    character(max_chars) :: dir_ins
    integer :: n_dir_ins
    integer :: n_nodes
    character(len=3) :: node
    character(len=1) :: dir
    character(len=3) :: nodes(1:max_nodes), lnodes(1:max_nodes), rnodes(1:max_nodes)
    integer :: periods(max_nodes)
    integer :: cursors(max_nodes)
    integer :: n_cursors
    integer :: i, ic, i2, LRcur, i3
    logical :: found_z
    integer, parameter :: b_kind = selected_int_kind(20)
    integer(kind=b_kind) :: p_sum

    n_arguments = command_argument_count()
    if (n_arguments .eq. 1) then
        call get_command_argument(1, fname)
        print *, "File: ", trim(fname)
        print *
    else
        print *, "Wrong number of arguments: ", n_arguments
        stop
    end if

    open(10, file=fname)
    read(10, "(a)") dir_ins
    n_dir_ins = len_trim(dir_ins)
    read(10, "(a)") fline
    n_nodes = 0
    do i=1,max_nodes
        read(10, "(a)", iostat=istat) fline
        if ((len_trim(fline) .eq. 0) .or. (is_iostat_end(istat))) then
            exit
        end if
        read(fline(1:3), "(a)") nodes(i)
        read(fline(8:10), "(a)") lnodes(i)
        read(fline(13:15), "(a)") rnodes(i)
        n_nodes = n_nodes + 1
    end do
    close(10)
    cursors = -1
    n_cursors = 0
    do i=1, n_nodes
        if (nodes(i)(3:3) .eq. "A") then
            n_cursors = n_cursors + 1
            cursors(n_cursors) = i
        end if
    end do
    print *, "Number of cursors: ", n_cursors
    periods = 0
    do i=1,max_iter
        LRcur = mod(i-1, n_dir_ins) + 1
        dir = dir_ins(LRcur:LRcur)
        do ic=1,n_cursors
            if (dir .eq. "L") then
                node = lnodes(cursors(ic))
            else
                node = rnodes(cursors(ic))
            end if
            do i2=1, n_nodes
                if (nodes(i2) .eq. node) then
                    cursors(ic) = i2
                    exit
                end if
            end do
        end do
        found_z = .true.
        do ic=1,n_cursors
            if (nodes(cursors(ic))(3:3) .ne. "Z") then
                found_z = .false.
            else if (periods(ic) .eq. 0) then
                periods(ic) = i
            end if
        end do
        if (found_z) then
            exit
        end if
    end do
    if (found_z) then
        print *, "Found nodes ending in Z after ", i, " iterations"
    else
        print *, "Did not find nodes ending in Z after ", max_iter, " iterations"
        print *, "Periods:"
        print "(1i9)", periods(1:n_cursors)
        p_sum = 1
        print *
        do ic=1,n_cursors
            p_sum = p_sum * periods(ic)
        end do
        print *, "Potential answer: ", p_sum
        do i=1,n_cursors-1
            do i2 = i+1,n_cursors
                do i3=2,periods(i2)
                    if (mod(periods(i), i3) .eq. 0 .and. mod(periods(i2), i3) .eq. 0) then
                        do
                            periods(i) = periods(i) / i3
                            if (mod(periods(i), i3) .ne. 0) then
                                exit
                            end if
                        end do
                    end if
                end do
            end do
        end do
        print *, "Factors: "
        print "(1i9)", periods(1:n_cursors)
        p_sum = 1
        print *
        do ic=1,n_cursors
            p_sum = p_sum * periods(ic)
        end do
        print *, "Potential answer: ", p_sum
    end if

end program day8b