.section .data

    # System call numbers
    .equ OPEN, 2
    .equ WRITE, 1
    .equ READ, 0
    .equ CLOSE, 3
    .equ EXIT, 60

    # File modes
    .equ O_RDONLY, 0
    .equ O_CREAT_WRONLY_TRUNC, 03101
    .equ O_PERMS, 0666

    .equ END_OF_FILE, 0     # End of file

.section .bss
#... Define buffer(s) here ...
.equ BUFFER_SIZE, 500
.lcomm BUFFER_DATA, BUFFER_SIZE

#Stack Postions

.equ ST_SIZE_RESERVE, 24
.equ ST_FD_IN, 0
.equ ST_FD_OUT, 8
.equ ST_ARGC, ST_SIZE_RESERVE
.equ ST_ARGV_0, ST_SIZE_RESERVE+8
.equ ST_ARGV_1, ST_SIZE_RESERVE+16
.equ ST_ARGV_2, ST_SIZE_RESERVE+24
.equ ST_ARGV_3, ST_SIZE_RESERVE+32


.section .text

    # RETURN VALUES
    .equ RETURN_SUCCESS, 0
    .equ RETURN_INVALID_NUM_ARGS, 1
    .equ RETURN_ERR_INPUT, 2
    .equ RETURN_ERR_OUTPUT, 3
    .equ RETURN_INVALID_FORMAT, 4
    .equ RETURN_MSG_TOO_LONG, 5

    # BMP HEADER OFFSETS
    .equ HO_B, 0
    .equ HO_M, 1
    .equ HO_SIZE_V3, 14
    .equ HO_WIDTH_PIXELS, 18
    .equ HO_HEIGHT_PIXELS, 22
    .equ HO_NUM_BITS_PIXEL, 28
    .equ HO_COMPRESSION, 30
    .equ HO_NUM_COLORS_PALETTE, 46

    .globl _start

_start:
subq $ST_SIZE_RESERVE, %rsp
movq %rsp, %rbp
movq    ST_ARGC(%rbp), %rdi             #check for 4 args
cmpq $4, %rdi
jne exit_invalid_num_args

open_input:
movq ST_ARGV_2, %rdi
movq $O_RDONLY, %rsi
movq $O_PERMS, %rdx
movq $OPEN, %rax
syscall
cmpq $0, %rax
jl exit_err_input
movq %rax, ST_FD_IN(%rbp)

open_output:
movq ST_ARGV_3(%rbp), %rdi
movq $O_CREAT_WRONLY_TRUNC, %rsi
movq $O_PERMS, %rdx
movq $OPEN, %rax
syscall
cmpq $0, %rax
jl exit_err_output
movq %rax, ST_FD_OUT(%rbp)



read_loop_begin:
movq ST_FD_IN(%rbp), %rdi
movq $BUFFER_DATA, %rsi
movq BUFFER_SIZE, %rdx
movq $OPEN, %rax
syscall
#check if end of file
cmpq $END_OF_FILE, %rax
jle end_loop
continiue_read_loop:
movq $BUFFER_DATA, %rdi
movq %rax, %rsi
#call method
movq ST_FD_OUT(%rbp), %rdi
movq $BUFFER_DATA, %rsi
movq %rax, %rdx
movq $WRITE, %rax
syscall
jmp read_loop_begin






end_loop:
movq ST_FD_OUT(%rbp), %rdi
movq $CLOSE, %rax
syscall
jmp exit_success





exit_success:
movq $RETURN_SUCCESS, %rdi
jmp exit



exit_invalid_num_args:                  #invalid number of args
movq $RETURN_INVALID_NUM_ARGS, %rdi
jmp exit

exit_err_input:
movq $RETURN_ERR_INPUT, %rdi
jmp exit

exit_err_output:
movq $RETURN_ERR_OUTPUT, %rdi
jmp exit

exit_invalid_format:
movq $RETURN_INVALID_FORMAT, %rdi
jmp exit

exit_msg_too_long:
movq $RETURN_MSG_TOO_LONG, %rdi
jmp exit

exit:
movq $EXIT, %rax
syscall