%include "src/constants.asm"

extern	__INTERNAL_fmt

extern	strlen
extern	umask_get

section .text
	global	stat
	global	lstat
	global	fgettype
	global	fgetmod
	global	fopen
	global	fclose
	global	fexist
	global	fwrite

;----- stat(*file[], *statBuffer[]) -----;
; Gets information from a file, stores it into statBuffer[]
; Return value: 0 if stats received, -errno otherwise
; Used registers:
;	rax*	(ret)
;	rdi*	(arg) Pointer to file
;	rsi*	arg for syscall NR_newfstatat
;	rdx*	arg for syscall NR_newfstatat
;	r10*	arg(flag) for syscall NR_newfstatat
stat:
	sub	rsp, SIZE_QWORD
	mov	rax, NR_newfstatat
	mov	rdx, rsi
	mov	rsi, rdi
	mov	rdi, AT_FDCWD
	xor	r10, r10
	syscall
	add	rsp, SIZE_QWORD
	ret

;----- lstat(*file[], *statBuffer[]) -----;
; Same as stat, except do not follow links
lstat:
	sub	rsp, SIZE_QWORD
	mov	rax, NR_newfstatat
	mov	rdx, rsi
	mov	rsi, rdi
	mov	rdi, AT_FDCWD
	mov	r10, AT_SYMLINK_NOFOLLOW
	syscall
	add	rsp, SIZE_QWORD
	ret

;----- fgettype(*statBuffer[]) -----;
; Gets file type from stat buffer
; Return value: File type or -EINVAL if statBuffer is invalid (first bit is 0)
;		See src/constants/file.asm for file types (S_IFxxx, eg S_IFREG for regular files)
; Used registers:
;	rax*	(ret)
;	rdi	(arg) Pointer to statBuffer[]
fgettype:
	cmp	byte [rdi], 0
	jne	.buffok
	mov	rax, -EINVAL
	ret
	.buffok:
	mov	eax, [rdi + ST_MODE]
	and	eax, 0xF000
	ret

;----- fgetmod(*statBuffer[]) -----;
; Gets file mode bits (file permissions) from stat buffer
; Return value: Permissions of given file or -EINVAL if statBuffer is invalid (first bit is 0)
; Used registers:
;	rax*	(ret)
;	rdi	(arg) Pointer to stat buffer
fgetmod:
	cmp	byte [rdi], 0
	jne	.buffok
	mov	rax, -EINVAL
	ret
	.buffok:
	mov	eax, [rdi + ST_MODE]
	and	eax, 0x0FFF
	ret

;----- fopen(*file[], char mode) -----;
; Opens a file
; Return value: Pointer to opened file pointer, -errno otherwise
; Possible modes:
;	'r'	Read-only, file must exist
;	'w'	Write-only. Creates empty file or truncates an existing file
;	'a'	Append. Creates file if it does not exist
;	'R'	Read+write, file must exist
;	'W'	Read+write. Creates empty file or truncates an existing file
;	'A'	Read+append. Creates file if it does not exist
;	<!>	Invalid mode will also return 0 (EOS)
; Used registers:
;	rax*	(ret)
;	rdi	(arg) Pointer to string holding (path+)file name
;	rsi	Mode to open the file with (see description above)
fopen:
	%macro createFile 0
	push	rdi
	push	rsi
	call	fexist
	pop	rsi
	pop	rdi
	test	rax, 1
	jz	%%createFile
	jmp	%%cnt
	%%createFile:
	push	rsi
	push	rdi
	call	umask_get
	pop	rdi
	push	rdi
	not	rax
	mov	rsi, DEF_MODE_FILE
	and	rsi, rax
	mov	rax, NR_creat
	syscall
	pop	rdi
	pop	rsi
	%%cnt:
	%endmacro
	;;;
	;;; ENTRY
	;;;
	sub	rsp, SIZE_QWORD

	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, -EINVAL
	jmp	.quit

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

	.open:
	mov	rax, NR_open
	syscall

	.quit:
	add	rsp, SIZE_QWORD
	ret

;----- fclose(*filePointer) -----;
; Closes an opened file
; Return value: 0 if file closed. Negative error number if an error occured
; Used registers:
;	rax*	(ret)
;	rdi	(arg) Pointer to opened file
fclose:
	sub	rsp, SIZE_QWORD
	cmp	rdi, 3
	jl	.invalid_fd ;disallow closing stdin,stdout,stderr
	mov	rax, NR_close
	syscall
	jmp	.quit

	.invalid_fd:
	mov	rax, -EINVAL

	.quit:
	add	rsp, SIZE_QWORD
	ret

;----- fexist(*file[]) -----;
; Checks if given file exists (attempts to open the file)
; Return value: 1- File exists. 0- File does not exist or is a directory
; Used registers:
;	rax*	(ret)
;	rdi	(arg) Pointer to string holding (path+)file name
fexist:
	sub	rsp, SIZE_QWORD
	mov	rsi, 'r'
	call	fopen
	test	rax, rax
	js	.not_exist
	mov	rdi, rax
	call	fclose
	mov	rax, 1
	jmp	.quit
	.not_exist:
	xor	rax, rax
	.quit:
	add	rsp, SIZE_QWORD
	ret

;--- fwrite(*filePointer, *data[], ...) -----;
; Writes data to given file. Allows format specifiers and variable arguments (see `__INTERNAL_fmt` for supported specifiers)
; Return value: Length of given string(data[]), 0 if nothing was written (eg invalid file or file not writable, or data[] is empty)
; Used registers:
;	rax*	(ret)
;	rdi	(arg) Pointer to file
;	rsi	(arg) Data to write
fwrite:
	push	rbp
	mov	rbp, rsp
	cmp	rdi, 2
	jg	.cnt
	xor	rax, rax
	leave
	ret
	.cnt:
	mov	rax, rdi
	mov	rdi, rsi
	mov	rsi, rdx
	mov	rdx, rcx
	mov	rcx, r8
	mov	r8, r9
	mov	r9, [rbp + RBP_OFFSET_CALLER]
	call	__INTERNAL_fmt
	leave
	ret