; Reset the disk system using int 13h / AH = 00h
disk_reset:
   pusha
   stc
   mov ah, 00h
   int 13h
   popa
   ret

; ------------------------------------

; Load the root directory into memory (into disk_buffer which is 24000h)
disk_load_root:
   pusha
   mov ax, 19 ; First sector of root entry
   call math_lba_to_chs ; Assigns ch, cl and dh the correct values
   xor ax,ax
   mov dl, [ebr_drive_number]  ; Drive number
   mov ah, 02h  ; BIOS ah code for read disk sectors to memory
   mov al, 0Ch  ; Root directory has 12 sectors

   mov si, root_buffer		; ES:BX should point to our buffer
   mov bx, si

   ; repeat drive read 3 times (incase of random error)
   mov di, 3 ; counter
   ; This is basically
   ; for di in range(3,1,1):
   ; We test to see if we can read the disk 3 times
.try_read_disk: ; Try read the floppy three times
   ; When the disk is tried to be read, the CF flag will be
   ; set if there's an error, so we just clear it to return it to
   ; the default state
   stc ; sets the cf flag
   int 13h
   jnc .done_read ; jump if cf = 0

   call disk_reset ; Reset drivers of disk

   dec di       ; di -= 1
   test di, di   ; if di = 0
   jnz .try_read_disk
   jmp .disk_error
.disk_error:
   mov si, disk_read_fail
   call os_print_string
   popa
   ret
.done_read:
   popa
   ret

; ---------------------------------------------

; Reads a certain number of sectors into memory
; int 13h/ah = 02h read disk sectors into memory
; al = number of sectors to read
; ch = cylinder number
; cl = sector number
; dh = head number
; dl = drive number
; es:bx = points to data buffer
disk_read:
   push ax
   push bx
   push cx
   push dx
   push di


   ; cl = sector
   ; ch = cylinder
   ; dh = head
   ; dl = drive
   call math_lba_to_chs  ; Get the chs address

   mov ah, 02h  ; BIOS ah code for read disk sectors to memory

   ; repeat drive read 3 times (incase of random error)
   mov di, 3 ; counter

; This is basically
; for di in range(3,1,1):
; We test to see if we can read the disk 3 times
.retry:
   ; When the disk is tried to be read, the CF flag will be
   ; set if there's an error, so we just clear it to return it to
   ; the default state
   stc ; sets the cf flag
   int 13h
   jnc .done_read ; jump if cf = 0

   call .disk_reset ; Reset drivers of disk

   dec di       ; di -= 1
   test di, di   ; if di = 0
   jnz .retry

.fail_disk_read:
   pop di
   pop dx
   pop cx
   pop bx
   pop ax
   ret

; int 13h / ah = 00h reset disk system
.disk_reset:
   pusha
   mov ah, 0 ; Reset drive
   stc
   int 13h
   jc .fail_disk_read
   popa
   ret

.done_read:
   pop di
   pop dx
   pop cx
   pop bx
   pop ax
   ret

; -------------------------------------

disk_load_file:
   pusha
   mov di, fat12_file_name
   call os_format_fat_filename

   ; Prepare values
   mov si, root_buffer
   xor bx,bx
.search_root:
   mov di, fat12_file_name ; Move the name of the kernel into di
   mov cx, 11 ; length of 'KERNEL  BIN'
   push si ; Preserve si
   repe cmpsb ; Repeat a comparison of bytes between file name and current bytes until it finds a match
   pop si ; Retrieve si
   je .found_file

   add si, 32 ; increment di to the next directory entry
   inc bx
   cmp bx, [bdb_dir_entries_count] ; Have we reached the number of directories that exist
   jl .search_root ; Repeat search

   jmp .file_not_found ; If the last dir has been searched, then there is no kernel
.found_file:
   mov ax, [si+26]   ; ax is now a pointer to the pointer to the file relative to the data segments :D
   add ax, 20h
   mov [file_cluster], ax
   ; Setup registers for disk read
   mov bx, data_buffer
   mov dl, [ebr_drive_number]

   call disk_read ; Load file from disk into memory
   jmp .done
.file_not_found:
   mov si, file_not_found
   call os_print_string
   jmp .done
.done:
   popa
   ret



section .data:
   disk_read_fail: db 'Error: Could not read disk\n', 0
   file_not_found: db 'File not found\n', 0
   file_found: db 'File found\n', 0
   loading_root: db 'Loading root diretory\n', 0
   file_cluster: dw 0
   fat12_file_name: db '           '