[BITS 16]
align 4
section .text

        org 7C00h

        mov bx,000Fh   ;Page 0, colour attribute 15 (white) for the int 10 calls below
        mov cx,1       ;We will want to write 1 character
        xor dx,dx      ;Start at top left corner
        mov ds,dx      ;Ensure ds = 0 (to let us load the message)
        cld            ;Ensure direction flag is cleared (for LODSB)
	
	STACKSIZE equ 0x4000

	mov ax,stack+STACKSIZE
	mov ss,ax
	mov sp,ax

	call kernel_main
	jmp the_end



back_space: db 8
end_back_space:

message: db ">>>SimpleOS 1.0.0a",13,10,0
end_message:

prompt: db "SimpleOS> ",0
end_prompt:

crlf: db 13,10,0
end_crlf:

exit_str: db "exit",0

date_str: db "date",0

dir_str: db "dir",0

exit_message: db "System shutdown...",13,10,0
end_exit_message:

date_message: db "Current date and time...",13,10,0
end_date_message:

dir_message: db "Directory listing...",13,10,0
end_dir_message:

crt_write_const:
	push bp
	mov bp,sp
	mov si,word [bp+6]
	mov di,word [bp+4]
Char:	mov ah,0xE
	int 10h
	lodsb
	inc dl
	cmp dl,80
	jne Skip
        xor dl,dl
        inc dh
        cmp dh,25
	jne Skip
	xor dl,dl
Skip:   cmp si,di
	jne Char
	leave
	ret

crt_write:
	push bp
	mov bp,sp
	push back_space
	push end_back_space
	call crt_write_const
	add sp,4
	push word [bp+6]
	push word [bp+4]
	call crt_write_const
	add sp,4
	leave
	ret


crt_read:
	push bp
	mov bp,sp
	mov bx,dx
	lea di,[buffer]
	mov al,0
.L4:	mov [di],byte 0
	inc di
	inc al
	cmp al,127
	jne .L4
	lea di,[buffer]
	;inc di
	mov dx,0
.L3:	mov ah,0
	int 16h
	inc dx
	cmp dx,126
	je .L2
	mov [di],byte al
	cmp al,byte 13
	je .L2
	inc di
	mov ah,0xE
	int 10h
	lodsb
	jmp .L3
.L2:	push crlf
	push end_crlf
        call crt_write
	add sp,4
	leave
	ret


streq:
	push bp
	mov bp,sp
	mov ax,1
	mov si,[bp+4]
	mov di,[bp+6]
.L9:	mov cl,byte [di]
	mov ch,byte [si]
	inc si
	inc di
	mov al,cl
	cmp al,byte 0
	je .L11
	mov dl,ch
	cmp dl,byte 0
	je .L11
	mov dl,ch
	mov al,cl
	cmp byte dl,byte al
	je .L9
	mov ax,0
.L11:	
	leave
	ret


exit_command:
	push bp
	mov bp,sp
	push exit_message
	push end_exit_message
	call crt_write
	add sp,4
.hang:
	mov ax,0
	int 19h
	jmp .hang
	leave
	ret


date_command:
	push bp
	mov bp,sp
	push date_message
	push end_date_message
	call crt_write
	add sp,4
	leave
	ret

dir_command:
        push bp
        mov bp,sp
        push dir_message
        push end_dir_message
        call crt_write
        add sp,4
        leave
        ret

cmd:
	push bp
	mov bp,sp

        push word buffer
        push word exit_str
        call streq
        add sp,4
        cmp ax,0
        je .L21
        call exit_command
	jmp .L23

.L21:	
	;push word buffer
	;push word date_str
	;call streq
	;add sp,4
	;cmp ax,0
	;je .L22
	;call date_command
	;jmp .L23

.L22:	
	push word buffer
	push word dir_str
	call streq
	add sp,4
	cmp ax,0
	je .L23
	call dir_command

.L23:
	leave
	ret


kernel_main:
	push bp
	mov bp,sp
        xor eax,eax
        xor ax,ax
	push message
	push end_message
	call crt_write
	add sp,4
.L1:	push prompt
	push end_prompt
        call crt_write
	add sp,4
	call crt_read
	lea di,[buffer]
.L5:	mov al,byte [di]
	cmp al,byte 13
	je .L10
	push word di
	push word di
	inc di
	push word di
	call crt_write_const
	add sp,4
	pop word di
	inc di
	mov al,byte [di]
	;cmp al,byte 0dh
	cmp al,byte 13
	jne .L5
.L10:	push crlf
	push end_crlf
	call crt_write_const
	add sp,4
	call cmd
	jmp .L1
	leave
	ret

section .bss
buffer:
stack:
   resb STACKSIZE

section .text
	times 1474560 - 2 - ($ - $$) db 0
	;times 1474560 - 527 db 0

the_end:

        ENDSTAMP dw 0AA55h
stack_start: