; =============================================================================
; proc.asm - process table management, task creation, fork/exec (stubs)
; =============================================================================
INCLUDE "include/gbos.inc"

SECTION "proc", ROM0

; -----------------------------------------------------------------------------
; ProcInit - table already zeroed by ClearKernelRAM (PS_FREE=0). Seed pids.
; -----------------------------------------------------------------------------
ProcInit::
    ld a, 1
    ld [wNextPid], a
    ret

; -----------------------------------------------------------------------------
; PcbPtr - slot -> PCB pointer.  in: A=slot  out: DE=&PCB.  preserves BC.
; -----------------------------------------------------------------------------
PcbPtr::
    push bc
    ld hl, wProcTable
    ld bc, PROC_SIZE
    and a
    jr z, .done
.mul
    add hl, bc
    dec a
    jr nz, .mul
.done
    ld d, h
    ld e, l
    pop bc
    ret

; -----------------------------------------------------------------------------
; ProcCreate - allocate a PCB and build an initial (runnable) task.
;   in:  HL = task entry, B = cart-RAM bank, C = SVBK u-area bank
;   out: A  = pid, or 0 if the table is full
; -----------------------------------------------------------------------------
ProcCreate::
    ; stash params
    ld a, l
    ld [wTmpEntry], a
    ld a, h
    ld [wTmpEntry+1], a
    ld a, b
    ld [wTmpRamB], a
    ld a, c
    ld [wTmpWramB], a

    ; find a free slot
    ld c, 0
.find
    ld a, c
    call PcbPtr                 ; DE = &PCB[c]
    ld a, [de]
    cp PS_FREE
    jr z, .found
    inc c
    ld a, c
    cp MAX_PROCS
    jr c, .find
    xor a                       ; table full
    ret

.found
    ld a, c
    ld [wTmpSlot], a

    ; fill fields; HL walks the PCB
    ld h, d
    ld l, e
    ld a, PS_READY
    ld [hl+], a                 ; PROC_STATE
    ld a, [wNextPid]
    ld [hl+], a                 ; PROC_PID
    ld [wTmpPid], a
    inc a
    ld [wNextPid], a
    inc hl                      ; skip PROC_SP (filled below)
    inc hl
    ld a, 1
    ld [hl+], a                 ; PROC_ROMB lo (placeholder text bank)
    xor a
    ld [hl+], a                 ; PROC_ROMB hi
    ld a, [wTmpRamB]
    ld [hl+], a                 ; PROC_RAMB
    ld a, [wTmpWramB]
    ld [hl+], a                 ; PROC_WRAMB
    xor a
    ld [hl+], a                 ; PROC_PARENT
    ld [hl], a                  ; PROC_EXIT

    ; build the initial stack frame in the task's RAM bank
    ld a, [wTmpEntry]
    ld l, a
    ld a, [wTmpEntry+1]
    ld h, a                     ; HL = entry
    ld a, [wTmpRamB]
    ld b, a                     ; B = RAM bank
    call ProcSetupStack         ; out: HL = initial SP
    ld a, l
    ld [wTmpSP], a
    ld a, h
    ld [wTmpSP+1], a

    ; store SP into PCB.PROC_SP
    ld a, [wTmpSlot]
    call PcbPtr                 ; DE = &PCB
    ld a, e
    add PROC_SP
    ld l, a
    ld a, d
    adc 0
    ld h, a                     ; HL = &PROC_SP
    ld a, [wTmpSP]
    ld [hl+], a
    ld a, [wTmpSP+1]
    ld [hl], a

    ld a, [wTmpPid]
    ret

; -----------------------------------------------------------------------------
; ProcSetupStack - lay a fresh switch-in frame at the top of a task RAM bank.
;   in:  HL = entry, B = cart-RAM bank
;   out: HL = initial SP (points at the saved-HL slot)
; The frame matches hSwitchTo's restore sequence:
;   [SP+0..1]=hl [+2..3]=de [+4..5]=bc [+6]=f [+7]=a [+8..9]=entry (ret target)
; -----------------------------------------------------------------------------
ProcSetupStack::
    ld a, b
    ld [MBC5_RAMB], a           ; map task's RAM bank into $A000-$BFFF
    push hl                     ; save entry
    ld hl, TASK_STACK_TOP - 9   ; frame base = $BFF6
    xor a
    ld [hl+], a                 ; hl_lo
    ld [hl+], a                 ; hl_hi
    ld [hl+], a                 ; de_lo
    ld [hl+], a                 ; de_hi
    ld [hl+], a                 ; bc_lo
    ld [hl+], a                 ; bc_hi
    ld [hl+], a                 ; f
    ld [hl+], a                 ; a
    pop de                      ; DE = entry
    ld a, e
    ld [hl+], a                 ; entry lo (ret target)
    ld a, d
    ld [hl], a                  ; entry hi
    ld hl, TASK_STACK_TOP - 9   ; initial SP
    ret

; -----------------------------------------------------------------------------
; sys_fork / sys_exec - TODO. Plan:
;   fork: alloc slot, copy parent's 8 KiB RAM bank -> child bank, dup u-area,
;         patch child's saved-A to 0 (child return), parent gets child pid.
;   exec: point PROC_ROMB at a flashed program image, reset RAM-bank layout
;         (copy .data from ROM, zero .bss, fresh heap/stack), longjmp in.
; -----------------------------------------------------------------------------