; =============================================================================
; fs.asm - a small block-based filesystem (inodes + a root directory) on the
; persistent block device (blk.asm). Same syscall interface as before
; (open/close/getb/putb/list/remove) so the tools and libc are unchanged.
;
; Bitmaps (block 1) and the inode table (blocks 2-3) are cached in WRAMX; file
; and directory data stream through fs_datbuf / fs_dirbuf. Metadata bitmap
; writes are write-through; inode writes are flushed on close.
; =============================================================================
INCLUDE "include/gbos.inc"

SECTION "fs", ROM0

; -----------------------------------------------------------------------------
; small helpers
; -----------------------------------------------------------------------------
zero256:                        ; HL = buffer; zero 256 bytes
    ld b, 0
    xor a
.z
    ld [hl+], a
    dec b
    jr nz, .z
    ret

; inode_ptr - A = inode -> HL = &inode in fs_inobuf (= fs_inobuf + inode*16)
inode_ptr::
    ld c, a
    and $0F
    swap a
    ld l, a                     ; (inode & 15) << 4
    ld a, c
    swap a
    and $0F                     ; inode >> 4
    add HIGH(fs_inobuf)
    ld h, a
    ret

; write_inode - A = inode ; flush the inode's block (2 or 3) to disk
write_inode::
    cp 16
    jr nc, .hi
    ld hl, fs_inobuf
    ld a, BLK_INODE0
    jp write_block
.hi
    ld hl, fs_inobuf + 256
    ld a, BLK_INODE0 + 1
    jp write_block

; bit_addr - A = index, HL = bitmap base -> HL = &byte, E = mask(1<<bit)
bit_addr:
    ld c, a
    srl a
    srl a
    srl a                       ; index/8
    add l
    ld l, a
    ld a, h
    adc 0
    ld h, a
    ld a, c
    and 7
    ld e, 1
.sh
    or a
    jr z, .done
    sla e
    dec a
    jr .sh
.done
    ret

; -----------------------------------------------------------------------------
; block / inode allocators (bitmaps live in fs_bmbuf, write-through to block 1)
; -----------------------------------------------------------------------------
write_bitmap:
    ld hl, fs_bmbuf
    ld a, BLK_BITMAP
    jp write_block

; alloc_block -> A = block# (>=4) or 0 if the disk is full
alloc_block::
    ld c, BLK_DATA0
.l
    ld a, c
    ld hl, fs_bmbuf + BM_BLOCKS
    call bit_addr               ; HL=&byte, E=mask
    ld a, [hl]
    and e
    jr z, .found
    inc c
    ld a, c
    cp FS_NBLOCKS
    jr c, .l
    xor a
    ret
.found
    ld a, [hl]
    or e
    ld [hl], a
    ld a, c                     ; save block# (write_bitmap clobbers C)
    push af
    call write_bitmap
    pop af
    ret

; free_block - A = block#
free_block::
    ld hl, fs_bmbuf + BM_BLOCKS
    call bit_addr
    ld a, e
    cpl
    ld e, a
    ld a, [hl]
    and e
    ld [hl], a
    jp write_bitmap

; alloc_inode -> A = inode# (>=2) or 0
alloc_inode::
    ld c, 2
.l
    ld a, c
    ld hl, fs_bmbuf + BM_INODES
    call bit_addr
    ld a, [hl]
    and e
    jr z, .found
    inc c
    ld a, c
    cp NINODES
    jr c, .l
    xor a
    ret
.found
    ld a, [hl]
    or e
    ld [hl], a
    ld a, c                     ; save inode# (write_bitmap clobbers C)
    push af
    call write_bitmap
    pop af
    ret

; free_inode - A = inode#
free_inode::
    ld hl, fs_bmbuf + BM_INODES
    call bit_addr
    ld a, e
    cpl
    ld e, a
    ld a, [hl]
    and e
    ld [hl], a
    jp write_bitmap

; -----------------------------------------------------------------------------
; data-block cache (one block in fs_datbuf; wFsCurBlk / wFsDirty)
; -----------------------------------------------------------------------------
db_flush::
    ld a, [wFsDirty]
    or a
    ret z
    xor a
    ld [wFsDirty], a
    ld a, [wFsCurBlk]
    cp $FF
    ret z
    ld hl, fs_datbuf
    jp write_block

; db_use - A = block ; ensure that block is loaded in fs_datbuf
db_use::
    ld c, a
    ld a, [wFsCurBlk]
    cp c
    ret z
    push bc                     ; db_flush clobbers C (write_block does ld c,a)
    call db_flush
    pop bc
    ld a, c
    ld [wFsCurBlk], a
    ld hl, fs_datbuf
    jp read_block

; -----------------------------------------------------------------------------
; name compare: [HL] vs wFsNameBuf, <=15 bytes NUL-terminated -> Z if equal.
; preserves HL.
; -----------------------------------------------------------------------------
name_eq:
    push hl
    ld de, wFsNameBuf
    ld b, 15
.c
    ld a, [de]
    cp [hl]
    jr nz, .ne
    or a
    jr z, .eq
    inc hl
    inc de
    dec b
    jr nz, .c
.eq
    pop hl
    xor a
    ret
.ne
    pop hl
    ld a, 1
    and a
    ret

; entry_ptr - C = entry index -> HL = &fs_dirbuf[C*16]
entry_ptr:
    ld a, c
    swap a                      ; C*16 (C < 16)
    ld hl, fs_dirbuf
    add l
    ld l, a
    ret                         ; (fs_dirbuf is page-aligned, no carry)

; load_rootdir - read the root directory's data block into fs_dirbuf
load_rootdir:
    ld a, [fs_inobuf + 16 + I_BLOCKS]   ; root inode (1) blocks[0]
    ld hl, fs_dirbuf
    jp read_block

; write_rootdir - write fs_dirbuf back to the root directory's data block
write_rootdir:
    ld a, [fs_inobuf + 16 + I_BLOCKS]
    ld hl, fs_dirbuf
    jp write_block

; -----------------------------------------------------------------------------
; dir_find - name in wFsNameBuf -> A = inode (0 if not found)
; -----------------------------------------------------------------------------
dir_find::
    call load_rootdir
    ld c, 0
.l
    call entry_ptr              ; HL = &entry
    ld a, [hl]                  ; entry.inode
    or a
    jr z, .next
    inc hl                      ; &name
    call name_eq
    jr z, .found
.next
    inc c
    ld a, c
    cp DIRENTS
    jr c, .l
    xor a
    ret
.found
    dec hl                      ; back to entry base
    ld a, [hl]
    ret

; -----------------------------------------------------------------------------
; dir_add - A = inode to link (name in wFsNameBuf) -> A = 1 ok / 0 dir full
; -----------------------------------------------------------------------------
dir_add::
    ld [wFsInode], a
    call load_rootdir
    ld c, 0
.l
    call entry_ptr
    ld a, [hl]
    or a
    jr z, .free
    inc c
    ld a, c
    cp DIRENTS
    jr c, .l
    xor a
    ret
.free
    ld a, [wFsInode]
    ld [hl+], a                 ; entry.inode
    ld de, wFsNameBuf           ; copy the name
    ld b, 15
.cp
    ld a, [de]
    ld [hl+], a
    inc de
    dec b
    jr nz, .cp
    call write_rootdir
    ld a, 1
    ret

; -----------------------------------------------------------------------------
; dir_remove - name in wFsNameBuf -> A = inode removed (0 if not found)
; -----------------------------------------------------------------------------
dir_remove::
    call load_rootdir
    ld c, 0
.l
    call entry_ptr
    ld a, [hl]
    or a
    jr z, .next
    inc hl
    call name_eq
    jr z, .found
.next
    inc c
    ld a, c
    cp DIRENTS
    jr c, .l
    xor a
    ret
.found
    dec hl                      ; entry base
    ld a, [hl]
    ld [wFsInode], a
    xor a
    ld [hl], a                  ; clear entry.inode
    call write_rootdir
    ld a, [wFsInode]
    ret

; -----------------------------------------------------------------------------
; file_truncate - A = inode ; free all data blocks, size = 0 (cached inode)
; -----------------------------------------------------------------------------
file_truncate::
    ld [wFsInode], a
    call inode_ptr
    ld a, l
    add I_BLOCKS
    ld l, a                     ; HL = &blocks[0] (fs_inobuf, no page cross)
    ld b, NDIRECT
.fb
    ld a, [hl]
    or a
    jr z, .skip
    push bc
    push hl
    call free_block
    pop hl
    pop bc
    xor a
    ld [hl], a
.skip
    inc hl
    dec b
    jr nz, .fb
    ; size = 0
    ld a, [wFsInode]
    call inode_ptr
    ld a, l
    add I_SIZE
    ld l, a
    xor a
    ld [hl+], a
    ld [hl], a
    ld a, [wFsInode]
    jp write_inode

; -----------------------------------------------------------------------------
; format + mount
; -----------------------------------------------------------------------------
fs_format::
    ; superblock (block 0)
    ld hl, fs_datbuf
    call zero256
    ld hl, fs_datbuf
    ld a, SUPER_MAG0
    ld [hl+], a
    ld a, SUPER_MAG1
    ld [hl+], a
    ld a, SUPER_MAG2
    ld [hl+], a
    ld a, SUPER_MAG3
    ld [hl+], a
    ld a, FS_VERSION
    ld [hl], a
    ld a, BLK_SUPER
    ld hl, fs_datbuf
    call write_block
    ; bitmaps (block 1): blocks 0-4 used, inodes 0-1 used
    ld hl, fs_bmbuf
    call zero256
    ld a, $1F
    ld [fs_bmbuf + BM_BLOCKS], a
    ld a, $03
    ld [fs_bmbuf + BM_INODES], a
    call write_bitmap
    ; inode table (blocks 2-3): zero, then inode 1 = root dir
    ld hl, fs_inobuf
    call zero256
    ld hl, fs_inobuf + 256
    call zero256
    ld hl, fs_inobuf + 16       ; inode 1
    ld a, IT_DIR
    ld [hl], a                  ; I_TYPE
    ld a, 1
    ld [fs_inobuf + 16 + I_NLINK], a
    xor a
    ld [fs_inobuf + 16 + I_SIZE], a       ; size lo
    ld a, 1
    ld [fs_inobuf + 16 + I_SIZE + 1], a   ; size hi = 256 (one dir block)
    ld a, BLK_DATA0
    ld [fs_inobuf + 16 + I_BLOCKS], a     ; blocks[0] = block 4
    ld a, BLK_INODE0
    ld hl, fs_inobuf
    call write_block
    ld a, BLK_INODE0 + 1
    ld hl, fs_inobuf + 256
    call write_block
    ; root dir data block (block 4): empty
    ld hl, fs_dirbuf
    call zero256
    ld a, BLK_DATA0
    ld hl, fs_dirbuf
    jp write_block

; fs_init - mount: format on first boot (magic/version check), load caches.
fs_init::
    ld a, $FF
    ld [wFsCurBlk], a
    xor a
    ld [wFsDirty], a
    ; check superblock
    ld a, BLK_SUPER
    ld hl, fs_datbuf
    call read_block
    ld hl, fs_datbuf
    ld a, [hl+]
    cp SUPER_MAG0
    jr nz, .fmt
    ld a, [hl+]
    cp SUPER_MAG1
    jr nz, .fmt
    ld a, [hl+]
    cp SUPER_MAG2
    jr nz, .fmt
    ld a, [hl+]
    cp SUPER_MAG3
    jr nz, .fmt
    ld a, [hl]
    cp FS_VERSION
    jr z, .load
.fmt
    call fs_format
.load
    ld a, BLK_BITMAP
    ld hl, fs_bmbuf
    call read_block
    ld a, BLK_INODE0
    ld hl, fs_inobuf
    call read_block
    ld a, BLK_INODE0 + 1
    ld hl, fs_inobuf + 256
    call read_block
    ld a, $FF
    ld [wFsCurBlk], a
    ret

; -----------------------------------------------------------------------------
; OFPtr - A = fd -> HL = &open-file entry. preserves DE.
; -----------------------------------------------------------------------------
OFPtr::
    push de
    ld h, 0
    ld l, a
    ld d, h
    ld e, l
    add hl, hl
    add hl, hl
    add hl, de                  ; 5*fd
    ld de, wOFTable
    add hl, de
    pop de
    ret

; copy the NUL-terminated name at DE (process memory) into wFsNameBuf.
copy_name:
    ld hl, wFsNameBuf
    ld b, 15
.c
    ld a, [de]
    ld [hl+], a
    or a
    ret z
    inc de
    dec b
    jr nz, .c
    xor a
    ld [hl], a
    ret

; =============================================================================
; sys_open(DE = name, B = mode 0=read/1=write) -> A = fd or $FF
; =============================================================================
sys_open::
    ld a, b
    ld [wFsMode], a
    call copy_name              ; name -> wFsNameBuf (before any block I/O)
    call dir_find               ; A = inode or 0
    ld [wFsInode], a
    ld a, [wFsMode]
    or a
    jr nz, .write
    ; --- read ---
    ld a, [wFsInode]
    or a
    jr z, .fail
    jr .allocof
.write
    ld a, [wFsInode]
    or a
    jr nz, .trunc
    ; --- create ---
    call alloc_inode
    or a
    jr z, .fail
    ld [wFsInode], a
    call inode_ptr              ; HL = &inode
    push hl
    ld b, 16
    xor a
.zi
    ld [hl+], a
    dec b
    jr nz, .zi
    pop hl
    ld a, IT_FILE
    ld [hl], a
    inc hl
    ld a, 1
    ld [hl], a                  ; nlink
    ld a, [wFsInode]
    call write_inode
    ld a, [wFsInode]
    call dir_add
    or a
    jr z, .fail
    jr .allocof
.trunc
    ld a, [wFsInode]
    call file_truncate
.allocof
    ld c, 0
.ofl
    ld a, c
    call OFPtr
    ld a, [hl]
    or a
    jr z, .gotof
    inc c
    ld a, c
    cp OF_MAX
    jr c, .ofl
.fail
    ld a, $FF
    ret
.gotof
    ld a, 1
    ld [hl+], a                 ; inuse
    ld a, [wFsInode]
    ld [hl+], a                 ; inode
    ld a, [wFsMode]
    ld [hl+], a                 ; mode
    xor a
    ld [hl+], a                 ; pos lo
    ld [hl], a                  ; pos hi
    ld a, c
    ret

; =============================================================================
; sys_close(B = fd) - flush data + inode, free the descriptor
; =============================================================================
sys_close::
    ld a, b
    cp OF_MAX
    jr nc, .done
    ld [wFsSlot], a             ; save fd
    call OFPtr
    ld a, [hl]
    or a
    jr z, .done
    inc hl
    ld a, [hl]
    ld [wFsInode], a
    call db_flush
    ld a, [wFsInode]
    call write_inode
    ld a, [wFsSlot]
    call OFPtr
    xor a
    ld [hl], a                  ; inuse = 0
.done
    xor a
    ret

; =============================================================================
; sys_getb(B = fd) -> A = byte, CF set on EOF
; =============================================================================
sys_getb::
    ld a, b
    cp OF_MAX
    jr nc, .eof
    call OFPtr
    ld a, [hl]
    or a
    jr z, .eof
    ld a, l
    ld [wFsOFPtr], a
    ld a, h
    ld [wFsOFPtr+1], a
    inc hl
    ld a, [hl]
    ld [wFsInode], a
    inc hl
    inc hl                      ; OF_POS lo
    ld a, [hl+]
    ld e, a
    ld a, [hl]
    ld d, a                     ; DE = pos
    ; pos < size ?
    ld a, [wFsInode]
    call inode_ptr
    ld a, l
    add I_SIZE
    ld l, a
    ld a, [hl+]
    ld c, a
    ld a, [hl]
    ld b, a                     ; BC = size
    ld a, e
    sub c
    ld a, d
    sbc b
    jr nc, .eof                 ; pos >= size
    ; data block = inode.blocks[pos/256 = D]
    ld a, [wFsInode]
    call inode_ptr
    ld a, l
    add I_BLOCKS
    ld l, a
    ld a, d
    add l
    ld l, a                     ; &blocks[blkidx]
    ld a, [hl]
    push de
    call db_use
    pop de
    ; byte = fs_datbuf[E]
    ld hl, fs_datbuf
    ld a, e
    add l
    ld l, a
    ld a, h
    adc 0
    ld h, a
    ld a, [hl]
    ld [wFsByte], a
    inc de                      ; pos++
    ld a, [wFsOFPtr]
    add OF_POS
    ld l, a
    ld a, [wFsOFPtr+1]
    adc 0
    ld h, a
    ld a, e
    ld [hl+], a
    ld a, d
    ld [hl], a
    ld a, [wFsByte]
    and a                       ; CF = 0
    ret
.eof
    scf
    ret

; =============================================================================
; sys_putb(B = fd, E = byte)
; =============================================================================
sys_putb::
    ld a, e
    ld [wFsByte], a
    ld a, b
    cp OF_MAX
    jr nc, .done
    call OFPtr
    ld a, [hl]
    or a
    jr z, .done
    ld a, l
    ld [wFsOFPtr], a
    ld a, h
    ld [wFsOFPtr+1], a
    inc hl
    ld a, [hl]
    ld [wFsInode], a
    inc hl
    inc hl
    ld a, [hl+]
    ld e, a
    ld a, [hl]
    ld d, a                     ; DE = pos
    ; ensure inode.blocks[pos/256] is allocated
    ld a, [wFsInode]
    call inode_ptr
    ld a, l
    add I_BLOCKS
    ld l, a
    ld a, d
    add l
    ld l, a                     ; HL = &blocks[blkidx]
    ld a, [hl]
    or a
    jr nz, .haveblk
    push hl
    push de
    call alloc_block
    pop de
    pop hl
    or a
    jr z, .done                 ; disk full
    ld [hl], a
.haveblk
    ld a, [hl]                  ; data block#
    push de
    call db_use
    pop de
    ld hl, fs_datbuf
    ld a, e
    add l
    ld l, a
    ld a, h
    adc 0
    ld h, a
    ld a, [wFsByte]
    ld [hl], a
    ld a, 1
    ld [wFsDirty], a
    inc de                      ; pos++
    ld a, [wFsOFPtr]
    add OF_POS
    ld l, a
    ld a, [wFsOFPtr+1]
    adc 0
    ld h, a
    ld a, e
    ld [hl+], a
    ld a, d
    ld [hl], a
    ; size = max(size, pos) (cached inode; flushed on close)
    ld a, [wFsInode]
    call inode_ptr
    ld a, l
    add I_SIZE
    ld l, a
    ld a, [hl+]
    ld c, a
    ld a, [hl]
    ld b, a                     ; BC = size, HL at size+1
    ld a, c
    sub e
    ld a, b
    sbc d
    jr nc, .done                ; size >= pos
    dec hl                      ; size lo
    ld a, e
    ld [hl+], a
    ld a, d
    ld [hl], a
.done
    xor a
    ret

; =============================================================================
; sys_list(B = index, DE = namebuf) -> A = 1 (name copied) / 0 (no more)
; index selects the index-th *used* entry in the root directory.
; =============================================================================
sys_list::
    ld a, e
    ld [wFsOFPtr], a
    ld a, d
    ld [wFsOFPtr+1], a
    ld a, b
    ld [wFsSlot], a             ; wanted index
    call load_rootdir
    ld c, 0                     ; entry cursor
    ld b, 0                     ; used counter
.l
    call entry_ptr              ; HL = &entry
    ld a, [hl]
    or a
    jr z, .next
    ld a, [wFsSlot]
    cp b
    jr z, .found
    inc b
.next
    inc c
    ld a, c
    cp DIRENTS
    jr c, .l
    xor a
    ret
.found
    inc hl                      ; &name (fs_dirbuf)
    ld a, [wFsOFPtr]
    ld e, a
    ld a, [wFsOFPtr+1]
    ld d, a                     ; DE = namebuf (process memory)
    ld b, 15
.cp
    ld a, [hl+]
    ld [de], a
    inc de
    dec b
    jr nz, .cp
    ld a, 1
    ret

; =============================================================================
; sys_remove(DE = name) -> A = 0 ok / $FF not found
; =============================================================================
sys_remove::
    call copy_name
    call dir_remove             ; A = inode or 0
    or a
    jr z, .no
    ld [wFsInode], a
    call file_truncate          ; A = inode (frees data blocks)
    ld a, [wFsInode]
    call inode_ptr
    xor a
    ld [hl], a                  ; I_TYPE = free
    ld a, [wFsInode]
    call write_inode
    ld a, [wFsInode]
    call free_inode
    xor a
    ret
.no
    ld a, $FF
    ret