check_keys Subroutine

    subroutine check_keys(table, valid_keys, error)

        !> Instance of the TOML data structure
        type(toml_table), intent(inout) :: table

        !> List of keys to check.
        character(len=*), intent(in) :: valid_keys(:)

        !> Error handling
        type(error_t), allocatable, intent(out) :: error

        type(toml_key), allocatable :: keys(:)
        type(toml_table), pointer :: child
        character(:), allocatable :: name, value, valid_keys_string
        integer :: ikey, ivalid

        call table%get_key(name)
        call table%get_keys(keys)

        do ikey = 1, size(keys)
            if (.not. any(keys(ikey)%key == valid_keys)) then
                ! Generate error message
                valid_keys_string = new_line('a')//new_line('a')
                do ivalid = 1, size(valid_keys)
                    valid_keys_string = valid_keys_string//trim(valid_keys(ivalid))//new_line('a')
                end do
                allocate (error)
                error%message = "Key '"//keys(ikey)%key//"' not allowed in the '"// &
                & name//"' table."//new_line('a')//new_line('a')//'Valid keys: '//valid_keys_string
                return
            end if

            ! Check if value can be mapped or else (wrong type) show error message with the error location.
            ! Right now, it can only be mapped to a string or to a child node, but this can be extended in the future.
            call get_value(table, keys(ikey)%key, value)
            if (.not. allocated(value)) then

                ! If value is not a string, check if it is a child node
                call get_value(table, keys(ikey)%key, child)

                if (.not.associated(child)) then
                    allocate (error)
                    error%message = "'"//name//"' has an invalid '"//keys(ikey)%key//"' entry."
                    return
                endif
            end if
        end do

    end subroutine check_keys