; ***************************************************************************
; copyright   : (C) 2025 by Martin Preuss
; email       : martin@libchipcard.de
;
; ***************************************************************************
; * This file is part of the project "AqHome".                              *
; * Please see toplevel file COPYING of that project for license details.   *
; ***************************************************************************

#ifndef AQH_AVR_COMMON_LIST_H
#define AQH_AVR_COMMON_LIST_H


; ---------------------------------------------------------------------------
; This code implements a simple single-linked list.
; It assumes that the first 2 bytes of an object managed by this code contain
; a 2 byte pointer to the next object.
; ---------------------------------------------------------------------------




; ***************************************************************************
; defs

.equ LIST_OFFS_NEXT_LO = 0
.equ LIST_OFFS_NEXT_HI = 1
.equ LIST_SIZE         = 2





; ***************************************************************************
; code

.cseg



; ---------------------------------------------------------------------------
; @routine List_InitObject @global
;
; Reset list object fields.
; @param Y pointer to object
; @clobbers r16

List_InitObject:
  clr r16      ; set this->NEXT to NULL
  std Y+LIST_OFFS_NEXT_LO, r16
  std Y+LIST_OFFS_NEXT_HI, r16
  ret
; @end



; ---------------------------------------------------------------------------
; @routine List_GetNextObject @global

; @param  Y pointer to object
; @return X pointer to parent object
; @clobbers none

List_GetNextObject:
  ldd xl, Y+LIST_OFFS_NEXT_LO
  ldd xh, Y+LIST_OFFS_NEXT_HI
  ret
; @end



; ---------------------------------------------------------------------------
; @routine List_GetLastObject

; @param  X      pointer to one object in a list
; @return X      pointer to last object which has an empty NEXT pointer
; @clobbers r16, r17, X, Y

List_GetLastObject:
  clr yl
  clr yh
  rjmp List_GetPredecessorFor
; @end



; ---------------------------------------------------------------------------
; @routine List_GetPredecessorFor

; @param  Y      pointer to this object
; @param  X      pointer to first object in a list
; @return X      pointer to object whose NEXT pointer points to the given object (or NULL)
; @clobbers r16, r17, X

List_GetPredecessorFor:
    mov r16, xl
    or r16, xh
    breq List_GetPredecessorFor_ret
    ld r16, X+
    ld r17, X+
    cp r16, yl
    brne List_GetPredecessorFor_next
    cp r17, yh
    breq List_GetLastObject_haveIt
List_GetPredecessorFor_next:
    mov xl, r16
    mov xh, r17
  rjmp List_GetPredecessorFor
List_GetPredecessorFor_haveIt:
  sbiw xh:xl, 1
List_GetPredecessorFor_ret:
  ret
; @end



; ---------------------------------------------------------------------------
; @routine List_AddObject

; @param X      pointer to first object in a list
; @param Y      pointer to object to add
; @clobbers r16, r17, x

List_AddObject:
  push yl
    push yh
      rcall List_GetLastObject ; (r16, r17, X, Y)
    pop yh
  pop yl
  st X+, yl     ; WID_OFFS_WNEXT_LO
  st X+, yh     ; WID_OFFS_WNEXT_HI
  ret
; @end



; ---------------------------------------------------------------------------
; @routine List_UnlinkObject

; @param X      pointer to first object in a list
; @param Y      pointer to object to remove
; @clobbers r16, r17, x

List_UnlinkObject:
  push yl
    push yh
      rcall List_GetPredecessorFor ; (r16, r17, X)
    pop yh
  pop yl
  mov r16, xl
  or r16, xh
  breq List_UnlinkObject_ret
  ldd r16, Y+LIST_OFFS_NEXT_LO ; get this->NEXT
  ldd r17, Y+LIST_OFFS_NEXT_HI
  st X+, r16   ; store as NEXT in predecessor
  st X, r17
  clr r16      ; set this->NEXT to NULL
  std Y+LIST_OFFS_NEXT_LO, r16
  std Y+LIST_OFFS_NEXT_HI, r16
List_UnlinkObject_ret:
  ret
; @end



#endif ; AQH_AVR_COMMON_LIST_H