!--------------------------------------------------------------------------------------------------
!> @author Martin Diehl, Max-Planck-Institut für Eisenforschung GmbH
!> @author Pratheek Shanthraj, Max-Planck-Institut für Eisenforschung GmbH
!> @author Philip Eisenlohr, Michigan State University
!> @brief material subroutine for variable heat source
!--------------------------------------------------------------------------------------------------
submodule(constitutive:constitutive_thermal) source_thermal_externalheat


  integer,           dimension(:),   allocatable :: &
    source_thermal_externalheat_offset, &                                                           !< which source is my current thermal dissipation mechanism?
    source_thermal_externalheat_instance                                                            !< instance of thermal dissipation source mechanism

  type :: tParameters                                                                               !< container type for internal constitutive parameters
    real(pReal), dimension(:), allocatable :: &
      time, & 
      heat_rate
    integer :: &
     nIntervals
  end type tParameters

  type(tParameters), dimension(:), allocatable  :: param                                            !< containers of constitutive parameters (len Ninstance)


contains


!--------------------------------------------------------------------------------------------------
!> @brief module initialization
!> @details reads in material parameters, allocates arrays, and does sanity checks
!--------------------------------------------------------------------------------------------------
module function source_thermal_externalheat_init(source_length) result(mySources)

  integer, intent(in)                  :: source_length  
  logical, dimension(:,:), allocatable :: mySources

  class(tNode), pointer :: &
    phases, &
    phase, &
    sources, &
    src 
  integer :: Ninstance,sourceOffset,NipcMyPhase,p

  write(6,'(/,a)') ' <<<+-  source_thermal_externalHeat init  -+>>>'

  mySources = source_active('thermal_externalheat',source_length)
  
  Ninstance = count(mySources)
  write(6,'(a16,1x,i5,/)') '# instances:',Ninstance; flush(6)
  if(Ninstance == 0) return

  phases => material_root%get('phase')
  allocate(param(Ninstance))
  allocate(source_thermal_externalheat_offset  (phases%length), source=0)
  allocate(source_thermal_externalheat_instance(phases%length), source=0)

  do p = 1, phases%length
    phase => phases%get(p) 
    if(any(mySources(:,p))) source_thermal_externalheat_instance(p) = count(mySources(:,1:p))
    if(count(mySources(:,p)) == 0) cycle
    sources => phase%get('source')
    do sourceOffset = 1, sources%length
      if(mySources(sourceOffset,p)) then
        source_thermal_externalheat_offset(p) = sourceOffset
        associate(prm  => param(source_thermal_externalheat_instance(p)))
        src => sources%get(sourceOffset) 

        prm%time       = src%get_asFloats('t_n')
        prm%nIntervals = size(prm%time) - 1

        prm%heat_rate = src%get_asFloats('f_T',requiredSize = size(prm%time))

        NipcMyPhase = count(material_phaseAt==p) * discretization_nIP
        call constitutive_allocateState(sourceState(p)%p(sourceOffset),NipcMyPhase,1,1,0)
        end associate

      endif
    enddo
  enddo

end function source_thermal_externalheat_init


!--------------------------------------------------------------------------------------------------
!> @brief rate of change of state
!> @details state only contains current time to linearly interpolate given heat powers
!--------------------------------------------------------------------------------------------------
module subroutine source_thermal_externalheat_dotState(phase, of)

  integer, intent(in) :: &
    phase, &
    of

  integer :: &
    sourceOffset

  sourceOffset = source_thermal_externalheat_offset(phase)

  sourceState(phase)%p(sourceOffset)%dotState(1,of) = 1.0_pReal                                     ! state is current time

end subroutine source_thermal_externalheat_dotState


!--------------------------------------------------------------------------------------------------
!> @brief returns local heat generation rate
!--------------------------------------------------------------------------------------------------
module subroutine source_thermal_externalheat_getRateAndItsTangent(TDot, dTDot_dT, phase, of)

  integer, intent(in) :: &
    phase, &
    of
  real(pReal),  intent(out) :: &
    TDot, &
    dTDot_dT

  integer :: &
    sourceOffset, interval
  real(pReal) :: &
    frac_time

  sourceOffset = source_thermal_externalheat_offset(phase)

  associate(prm => param(source_thermal_externalheat_instance(phase)))
  do interval = 1, prm%nIntervals                                                                   ! scan through all rate segments
    frac_time = (sourceState(phase)%p(sourceOffset)%state(1,of) - prm%time(interval)) &
              / (prm%time(interval+1) - prm%time(interval))                                         ! fractional time within segment
    if (     (frac_time <  0.0_pReal .and. interval == 1) &
        .or. (frac_time >= 1.0_pReal .and. interval == prm%nIntervals) &
        .or. (frac_time >= 0.0_pReal .and. frac_time < 1.0_pReal) ) &
      TDot = prm%heat_rate(interval  ) * (1.0_pReal - frac_time) + &
             prm%heat_rate(interval+1) * frac_time                                                  ! interpolate heat rate between segment boundaries...
                                                                                                    ! ...or extrapolate if outside of bounds
  enddo
  dTDot_dT = 0.0
  end associate

end subroutine source_thermal_externalheat_getRateAndItsTangent

end submodule source_thermal_externalheat