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module intqueue
implicit none

    type :: queue
    integer :: n, ipop, ipush
    integer, allocatable :: a(:)

    contains
    procedure :: push
    procedure :: pop
    procedure :: empty
    final :: free
    end type queue

    interface queue
        module procedure newQueue
    end interface queue

    contains

!########################################################
!######################CONSTRUCTORS######################
!########################################################

    function newQueue(n) result(res)
        implicit none

        type(queue) :: res
        integer, intent(IN) :: n

        res%n = n
        res%ipop = 1
        res%ipush = 1
        allocate(res%a(n))

    end function newQueue

!########################################################
!########################METHODS#########################
!########################################################

    subroutine push(o, element)
        implicit none

        integer, intent(IN) :: element
        class(queue), intent(INOUT) :: o

        o%a(o%ipush) = element
        o%ipush = o%ipush + 1

    end subroutine push

    function pop(o) result(element)
        implicit none

        integer :: element
        class(queue), intent(INOUT) :: o

        element = o%a(o%ipop)
        o%ipop = o%ipop + 1
        o%ipush = o%ipush - 1

    end function pop

    function empty(o) result(r)
        implicit none

        class(queue), intent(INOUT) :: o
        logical :: r

        r = o%ipop-o%ipush .eq. 0

    end function empty

    subroutine free(o)
        implicit none

        type(queue), intent(INOUT) :: o

        if (allocated(o%a)) deallocate(o%a)

    end subroutine free

end module intqueue