configure_ocean_tides Subroutine

   subroutine configure_ocean_tides(cfg, ocean_state, grid, compute_rank, ierr)
      !! Configure the equilibrium body-force tide slot (C1): parse the
      !! constituent list + reference dates, fill the astronomy catalog
      !! (phase0, nodal f/u), and build the (nx,ny,3) spatial-structure
      !! arrays from `metrics%geolatT/geolonT`.  Host-side setup — runs
      !! AFTER `configure_ocean_metrics` (lat/lon must be filled) and
      !! BEFORE `ocean_state_enter_data`.  `enable=.false.` => no-op,
      !! bit-identical.
      type(config_t), intent(in) :: cfg
      type(ocean_state_t), intent(inout) :: ocean_state
      type(hgrid_t), intent(in) :: grid
      integer, intent(in) :: compute_rank
      integer, intent(out), optional :: ierr
         !! Non-zero on a tides configuration conflict when present;
         !! absent behaves as today (`error stop`).
      integer :: cat_idx(TIDES_CATALOG_SIZE)
      integer :: nconst, y, m, d, nx, ny, local_ierr
      real(wp) :: dref, dnodal
      logical :: ok
      character(len=16) :: nodal_str

      associate (td => ocean_state%tides, tcfg => cfg%ocean%tides)
         td%enable = tcfg%enable
         if (.not. tcfg%enable) then
            if (present(ierr)) ierr = OCEAN_STATUS_OK
            return
         end if

         td%use_sal = tcfg%use_sal
         td%beta_sal = tcfg%beta_sal
         td%t_epoch = 0.0_wp

         if (td%use_sal .and. td%beta_sal <= 0.0_wp .and. compute_rank == 0) then
            call logger%warning("ocean_tides_nml: use_sal=.true. but "// &
                                "beta_sal<=0 => scalar SAL is inert "// &
                                "(typical beta ~0.085-0.12)")
         end if

         ! Parse the active constituent list -> catalog indices.
         if (present(ierr)) then
            call parse_constituent_list(tcfg%constituents, cat_idx, nconst, ierr=local_ierr)
            if (local_ierr /= 0) then
               ierr = local_ierr
               return
            end if
         else
            call parse_constituent_list(tcfg%constituents, cat_idx, nconst)
         end if
         if (nconst < 1) then
            call fail("ocean_tides_nml: constituents='"// &
                      trim(tcfg%constituents)//"' has no valid entries", ierr, OCEAN_STATUS_ERR_SETUP)
            return
         end if

         ! Reference date -> day number since 1900-01-01.
         call parse_date_string(tcfg%ref_date, y, m, d, ok)
         if (.not. ok) then
            call fail("ocean_tides_nml: bad ref_date '"// &
                      trim(tcfg%ref_date)//"' (want YYYY-MM-DD)", ierr, OCEAN_STATUS_ERR_SETUP)
            return
         end if
         dref = days_since_1900(y, m, d)

         nodal_str = tcfg%nodal_ref_date
         if (len_trim(nodal_str) == 0) nodal_str = tcfg%ref_date
         call parse_date_string(nodal_str, y, m, d, ok)
         if (.not. ok) then
            call fail("ocean_tides_nml: bad nodal_ref_date '"// &
                      trim(nodal_str)//"' (want YYYY-MM-DD)", ierr, OCEAN_STATUS_ERR_SETUP)
            return
         end if
         dnodal = days_since_1900(y, m, d)

         nx = grid%nx_total
         ny = grid%ny_total
         call tides_configure_astronomy(td, cat_idx(1:nconst), nconst, &
                                        dref, dnodal, tcfg%add_nodal, nx, ny)
         call tides_build_struct(td, ocean_state%metrics%geolatT, &
                                 ocean_state%metrics%geolonT, nx, ny)

         if (compute_rank == 0) then
            call logger%info("Equilibrium tide: C1 body force enabled ("// &
                             to_string(nconst)//" constituents, ref="// &
                             trim(tcfg%ref_date)//")")
         end if
      end associate
      if (present(ierr)) ierr = OCEAN_STATUS_OK
   end subroutine configure_ocean_tides