extern	NR_read
extern	NR_write
extern	NR_open
extern	NR_close

extern	strlen

section .rodata
	O_RDONLY	equ	00000000
	O_WRONLY	equ	00000001
	O_RDWR		equ	00000002
	O_CREAT		equ	00000100
	O_TRUNC		equ	00001000
	O_APPEND	equ	00002000
	
section .text
	global	fopen
	global	fclose
	global	fwrite

;----- fopen(const char *filename, const char mode) -----;
; return value: pointer to file or value < 0 (neg errno) if file failed to open
fopen:
	cmp	sil, 'r'
	je	.setMode_r
	cmp	sil, 'w'
	je	.setMode_w
	cmp	sil, 'a'
	je	.setMode_a
	cmp	sil, 'R'
	je	.setMode_R
	cmp	sil, 'W'
	je	.setMode_W
	cmp	sil, 'A'
	je	.setMode_A
	mov	rax, -22
	jmp	.quit

	.setMode_r:
		mov	rsi, O_RDONLY
		jmp	.open
	.setMode_w:
		mov	rsi, O_WRONLY | O_CREAT | O_TRUNC
		jmp	.open
	.setMode_a:
		mov	rsi, O_WRONLY | O_CREAT | O_APPEND
		jmp	.open
	.setMode_R:
		mov	rsi, O_RDWR
		jmp	.open
	.setMode_W:
		mov	rsi, O_RDWR | O_CREAT | O_TRUNC
		jmp	.open
	.setMode_A:
		mov	rsi, O_RDWR | O_CREAT | O_APPEND
		jmp	.open

	.open:
	mov	rax, NR_open
	syscall

	.quit:
	ret
;----- fclose(FILE* fp) -----;
; return value: 0 on success, below 0 otherwise (neg errno)
fclose:
	cmp	rdi, 3
	jl	.ebadf

	mov	rax, NR_close
	syscall
	jmp	.quit

	.ebadf:
	mov	rax, -9

	.quit:
	ret
;----- fwrite(FILE* fp, char* str) -----;
; writes a string to opened file
; return value: amount of written characters on success, below 0 otherwise (neg errno)
fwrite:
	cmp	rdi, 3
	jl	.ebadf

	mov	r9, rdi
	mov	rdi, rsi
	call	strlen
	mov	rdx, rax
	mov	rax, NR_write
	mov	rdi, r9
	syscall
	jmp	.quit

	.ebadf:
	mov	rax, -9

	.quit:
	ret