MODULE lmdz_regr_lint

  USE lmdz_assert_eq, ONLY: assert_eq
  USE lmdz_assert, ONLY: assert
  USE lmdz_interpolation, ONLY: hunt

  IMPLICIT NONE

  ! Purpose: Each procedure regrids by linear interpolation along dimension "ix"
  !          the input field "vs" to the output field "vt".
  ! Remark:
  !   * "vs" and "vt" have the same dimensions except Nr. ix (ns for vs, nt for vt)

  ! Argument                         Type         Description
  !-------------------------------------------------------------------------------
  !  INTEGER, INTENT(IN)  :: ix      Scalar       dimension regridded <=rank(vs)
  !  REAL,    INTENT(IN)  :: vs(*)   Rank>=1      source grid field values
  !  REAL,    INTENT(IN)  :: xs(:)   Vector(ns)   centers of source grid, asc. order
  !  REAL,    INTENT(IN)  :: xt(:)   Vector(nt)   centers of target grid, asc. order
  !  REAL,    INTENT(OUT) :: vt(*)   Rank>=1      regridded field

  INTERFACE regr_lint
    ! The procedures differ only from the rank of the input/output fields.
    MODULE PROCEDURE regr1_lint, regr2_lint, regr3_lint, &
            regr4_lint, regr5_lint
  END INTERFACE

  PRIVATE
  PUBLIC :: regr_lint

CONTAINS


  !-------------------------------------------------------------------------------

  SUBROUTINE regr1_lint(ix, vs, xs, xt, vt)

    !-------------------------------------------------------------------------------
    ! Arguments:
    INTEGER, INTENT(IN) :: ix
    REAL, INTENT(IN) :: vs(:)
    REAL, INTENT(IN) :: xs(:)
    REAL, INTENT(IN) :: xt(:)
    REAL, INTENT(OUT) :: vt(:)
    !-------------------------------------------------------------------------------
    ! Local variables:
    INTEGER :: is, it, ns, nt, isb ! "is" bound between 1 and "ns - 1"
    REAL :: r
    !-------------------------------------------------------------------------------
    CALL check_size(ix, SHAPE(vs), SHAPE(vt), SIZE(xs), SIZE(xt), ns, nt)
    is = -1 ! go immediately to bisection on first CALL to "hunt"
    DO it = 1, SIZE(xt)
      CALL hunt(xs, xt(it), is); isb = MIN(MAX(is, 1), ns - 1)
      r = (xs(isb + 1) - xt(it)) / (xs(isb + 1) - xs(isb))
      vt(it) = r * vs(isb) + (1. - r) * vs(isb + 1)
    END DO

  END SUBROUTINE regr1_lint

  !-------------------------------------------------------------------------------


  !-------------------------------------------------------------------------------

  SUBROUTINE regr2_lint(ix, vs, xs, xt, vt)

    !-------------------------------------------------------------------------------
    ! Arguments:
    INTEGER, INTENT(IN) :: ix
    REAL, INTENT(IN) :: vs(:, :)
    REAL, INTENT(IN) :: xs(:)
    REAL, INTENT(IN) :: xt(:)
    REAL, INTENT(OUT) :: vt(:, :)
    !-------------------------------------------------------------------------------
    ! Local variables:
    INTEGER :: is, it, ns, nt, isb ! "is" bound between 1 and "ns - 1"
    REAL :: r
    !-------------------------------------------------------------------------------
    CALL check_size(ix, SHAPE(vs), SHAPE(vt), SIZE(xs), SIZE(xt), ns, nt)
    is = -1 ! go immediately to bisection on first CALL to "hunt"
    DO it = 1, SIZE(xt)
      CALL hunt(xs, xt(it), is); isb = MIN(MAX(is, 1), ns - 1)
      r = (xs(isb + 1) - xt(it)) / (xs(isb + 1) - xs(isb))
      IF(ix==1) vt(it, :) = r * vs(isb, :) + (1. - r) * vs(isb + 1, :)
      IF(ix==2) vt(:, it) = r * vs(:, isb) + (1. - r) * vs(:, isb + 1)
    END DO

  END SUBROUTINE regr2_lint

  !-------------------------------------------------------------------------------


  !-------------------------------------------------------------------------------

  SUBROUTINE regr3_lint(ix, vs, xs, xt, vt)

    !-------------------------------------------------------------------------------
    ! Arguments:
    INTEGER, INTENT(IN) :: ix
    REAL, INTENT(IN) :: vs(:, :, :)
    REAL, INTENT(IN) :: xs(:)
    REAL, INTENT(IN) :: xt(:)
    REAL, INTENT(OUT) :: vt(:, :, :)
    !-------------------------------------------------------------------------------
    ! Local variables:
    INTEGER :: is, it, ns, nt, isb ! "is" bound between 1 and "ns - 1"
    REAL :: r
    !-------------------------------------------------------------------------------
    CALL check_size(ix, SHAPE(vs), SHAPE(vt), SIZE(xs), SIZE(xt), ns, nt)
    is = -1 ! go immediately to bisection on first CALL to "hunt"
    DO it = 1, SIZE(xt)
      CALL hunt(xs, xt(it), is); isb = MIN(MAX(is, 1), ns - 1)
      r = (xs(isb + 1) - xt(it)) / (xs(isb + 1) - xs(isb))
      IF(ix==1) vt(it, :, :) = r * vs(isb, :, :) + (1. - r) * vs(isb + 1, :, :)
      IF(ix==2) vt(:, it, :) = r * vs(:, isb, :) + (1. - r) * vs(:, isb + 1, :)
      IF(ix==3) vt(:, :, it) = r * vs(:, :, isb) + (1. - r) * vs(:, :, isb + 1)
    END DO

  END SUBROUTINE regr3_lint

  !-------------------------------------------------------------------------------


  !-------------------------------------------------------------------------------

  SUBROUTINE regr4_lint(ix, vs, xs, xt, vt)

    !-------------------------------------------------------------------------------
    ! Arguments:
    INTEGER, INTENT(IN) :: ix
    REAL, INTENT(IN) :: vs(:, :, :, :)
    REAL, INTENT(IN) :: xs(:)
    REAL, INTENT(IN) :: xt(:)
    REAL, INTENT(OUT) :: vt(:, :, :, :)
    !-------------------------------------------------------------------------------
    ! Local variables:
    INTEGER :: is, it, ns, nt, isb ! "is" bound between 1 and "ns - 1"
    REAL :: r
    !-------------------------------------------------------------------------------
    CALL check_size(ix, SHAPE(vs), SHAPE(vt), SIZE(xs), SIZE(xt), ns, nt)
    is = -1 ! go immediately to bisection on first CALL to "hunt"
    DO it = 1, SIZE(xt)
      CALL hunt(xs, xt(it), is); isb = MIN(MAX(is, 1), ns - 1)
      r = (xs(isb + 1) - xt(it)) / (xs(isb + 1) - xs(isb))
      IF(ix==1) vt(it, :, :, :) = r * vs(isb, :, :, :) + (1. - r) * vs(isb + 1, :, :, :)
      IF(ix==2) vt(:, it, :, :) = r * vs(:, isb, :, :) + (1. - r) * vs(:, isb + 1, :, :)
      IF(ix==3) vt(:, :, it, :) = r * vs(:, :, isb, :) + (1. - r) * vs(:, :, isb + 1, :)
      IF(ix==4) vt(:, :, :, it) = r * vs(:, :, :, isb) + (1. - r) * vs(:, :, :, isb + 1)
    END DO

  END SUBROUTINE regr4_lint

  !-------------------------------------------------------------------------------


  !-------------------------------------------------------------------------------

  SUBROUTINE regr5_lint(ix, vs, xs, xt, vt)

    !-------------------------------------------------------------------------------
    ! Arguments:
    INTEGER, INTENT(IN) :: ix
    REAL, INTENT(IN) :: vs(:, :, :, :, :)
    REAL, INTENT(IN) :: xs(:)
    REAL, INTENT(IN) :: xt(:)
    REAL, INTENT(OUT) :: vt(:, :, :, :, :)
    !-------------------------------------------------------------------------------
    ! Local variables:
    INTEGER :: is, it, ns, nt, isb ! "is" bound between 1 and "ns - 1"
    REAL :: r
    !-------------------------------------------------------------------------------
    CALL check_size(ix, SHAPE(vs), SHAPE(vt), SIZE(xs), SIZE(xt), ns, nt)
    is = -1 ! go immediately to bisection on first CALL to "hunt"
    DO it = 1, SIZE(xt)
      CALL hunt(xs, xt(it), is); isb = MIN(MAX(is, 1), ns - 1)
      r = (xs(isb + 1) - xt(it)) / (xs(isb + 1) - xs(isb))
      IF(ix==1) vt(it, :, :, :, :) = r * vs(isb, :, :, :, :) + (1. - r) * vs(isb + 1, :, :, :, :)
      IF(ix==2) vt(:, it, :, :, :) = r * vs(:, isb, :, :, :) + (1. - r) * vs(:, isb + 1, :, :, :)
      IF(ix==3) vt(:, :, it, :, :) = r * vs(:, :, isb, :, :) + (1. - r) * vs(:, :, isb + 1, :, :)
      IF(ix==4) vt(:, :, :, it, :) = r * vs(:, :, :, isb, :) + (1. - r) * vs(:, :, :, isb + 1, :)
      IF(ix==5) vt(:, :, :, :, it) = r * vs(:, :, :, :, isb) + (1. - r) * vs(:, :, :, :, isb + 1)
    END DO

  END SUBROUTINE regr5_lint

  !-------------------------------------------------------------------------------


  !-------------------------------------------------------------------------------

  SUBROUTINE check_size(ix, svs, svt, nxs, nxt, ns, nt)

    !-------------------------------------------------------------------------------
    ! Arguments:
    INTEGER, INTENT(IN) :: ix, svs(:), svt(:), nxs, nxt
    INTEGER, INTENT(OUT) :: ns, nt
    !-------------------------------------------------------------------------------
    ! Local variables:
    INTEGER :: rk, is
    CHARACTER(LEN = 80) :: sub, msg
    !-------------------------------------------------------------------------------
    rk = SIZE(svs)
    WRITE(sub, '(a,2i0,a)')"regr", rk, ix, "_lint"
    CALL assert(ix>=1.AND.ix<=rk, TRIM(sub) // ": ix exceeds fields rank")
    DO is = 1, rk; IF(is==ix) CYCLE
    WRITE(msg, '(a,i1)')TRIM(sub) // " n", is
    CALL assert(svs(is)==svt(is), msg)
    END DO
    ns = assert_eq(svs(ix), nxs, TRIM(sub) // " ns")
    nt = assert_eq(svt(ix), nxt, TRIM(sub) // " nt")

  END SUBROUTINE check_size

  !-------------------------------------------------------------------------------

END MODULE lmdz_regr_lint

!-------------------------------------------------------------------------------