.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


    # variables
    IMAGE_SIZE:     .long   0    # bitmap data size
	IMAGE_WIDTH:	.long	0	 # bitmap width
	IMAGE_HEIGHT:	.long	0 	 # bitmap height
	B_CHAR:			.byte	66	 # int value of letter B
	M_CHAR:			.byte	77	 # int value of letter M
	BITS_PER_PIXEL	.word	24	 # value of bits per pixel for our image
	COLOR_PALETTE	.long	0	 # color palette value for this assignment

	message_bytes: .quad 0   # the amount of bytes for the message

.section .bss
    .equ BUFFER_SIZE, 256
	.lcomm WRITE_DATA, BUFFER_SIZE
    .equ HEADER_SIZE, 54
	.lcomm HEADER_DATA, HEADER_SIZE


.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:
	###INITIALIZE PROGRAM###
	# r12 = file descriptor (INPUT)
	# r13 = file descriptor (OUTPUT)
    popq    %rdi         # load number of arguments into rdi
    popq    %rcx
    popq    %rcx         # Argument 0 - rcx = hidden message
    popq    %r8          # Argument 1 - r8 = filepath(input)
    popq    %r9          # Argument 2 - r9 = filepath(output)

    ### check for valid amount of arguments ###
    cmpq    $4, %rdi
    jne     error_arguments     # jump to errorhandling

    ### check if the bmp-input file exists ###
    movq    %r8, %rdi           # move filepath(input) into %rdi
    movq    $OPEN, %rax         # move open file number into %rax
    movq    $O_RDONLY, %rsi     # move read only number into %rsi
    syscall                     # call linux to open the file :)
    cmpq    $0, %rax            # check if file opening was successfull (return == 0)
    jl      error_open_file     # jump to errorhandling
    movq    %rax, %r12           # move file descriptor(input) from %rax to r12

    ### check the output file ###
    movq    %r9, %rdi                   # move filepath(output) into %rdi
    movq    $OPEN, %rax                 # move open file number into %rax
    movq    $O_PERMS, %rdx              # move permissions number into %rdx
    movq    $O_CREAT_WRONLY_TRUNC, %rsi # move write only number into %rsi
    syscall                             # create the file
    cmpq    $0, %rax                    # check if file creation was successful (return == 0)
    jl      error_output_file
    movq    %rax, %r13                  # move file descriptor(output) from %rax to r13

    ### read the header information ####
    movq    %r12, %rdi                  # move file descriptor(input) into %rdi
    movq    $READ, %rax                 # move read file number into %rax
    movq    $HEADER_DATA, %rsi          # move starting address into %rsi
    movq    $HEADER_SIZE, %rdx          # move buffer length into %rdx
    syscall                             # do it (read the file)
    cmpq    $0, %rax                    # check if file opening was successful
    jl      error_read_file
    cmpq    $HEADER_SIZE, %rax          # check if header size is valid
	jl		error_format

	### check the header information ###
	movq	$HEADER_DATA, %rbx
	movq	$HO_B, %rdi					# move offset for HO_B information into %rdi
	movb	(%rbx, %rdi, 1), %ah		# move the byte at offset into %ah
	movq	$HO_M, %rdi					# move offset for HO_M information into %rdi
	movb	(%rbx, %rdi, 1), %al		# move the bate at offset into %al
	cmpb	B_CHAR, %ah					# check if B is at the given position in the header
	jne		error_format
	cmpb	M_CHAR, %al					# check if M is at the given position in the header
	jne		error_format

	### check the color depth information ###
	movq	$HO_NUM_BITS_PIXEL, %rdi	# move offset for $HO_NUM_BITS_PIXEL information into %rdi
	movb	(%rbx, %rdi, 1), %al		# move the byte at offset into %al
	inc		%rbi						# increment %rbi to get the the second part of the value
    movb    (%rbx, %rdi, 1), %ah		# move the byte at offset into %ah
    cmpw    BITS_PER_PIXEL, %ax         # check if color depth is valid in our file
    jne     error_format

	### check the compression method information ###
	movq	$0, %rdi							# the compression imformation has to be 0, so move 0 into %rdi
	movq    $HO_COMPRESSION, %r14				# move the compression offset into %r14
	movl	HEADER_DATA(%r10, %rdi, 4), %eax	# move the compression information into %eax
	cmpl	$0, %eax							# check if the comperssion method is 0
	jne		error_format

	### check the color palette information ####
	movq	$0, %rdi							# move 0 into %rdi
	movq	$HO_NUM_COLORS_PALETTE, %r14		# move the collor palette offset innto %r14
	movl	HEADER_DATA(%r14, %rdi, 4), %eax 	# move the data into %eax
	cmpl	$COLOR_PALETTE, %eax				# the color palette information has to be 0
	jne		error_format

	### check the size of the image ###
	## get width and height ##
	movq    $0,%rdi										# move 0 into %rdi
    movq    $HO_WIDTH_PIXELS, %r14						# move offset for pixel width into %r14
    movl    HEADER_DATA(%r14, %rdi, 4), IMAGE_WIDTH		# move the value into variable width
    movq    $HO_HEIGHT_PIXELS, %r14						# move offset for picel height into %r14
    movl    HEADER_DATA(%r14, %rdi, 4), IMAGE_HEIGHT	# move the value into the variable height
	## actualy check the size ##
	movq    $0, %rdi								# move 0 into %rdi
    movq    $HO_IMAGE_SIZE, %r14					# move offset for image size into %r14
    movl    HEADER_DATA(%r14, %rdi, 4), IMAGE_SIZE  # move the size information into the variable IMAGE_SIZE
    cmpl    $0, IMAGE_HEIGHT						# check if the height is negative
    jl      negate_height
    jmp     get_size

negate_height:
	movl	IMAGE_HEIGHT, %esi		# move the image height into %esi
	neg     %edi                   	# negate the height value in %edi
    movl    %edi, IMAGE_HEIGHT      # move the postive height into the variable IMAGE_HEIGHT

get_size:
	### calculate the size of the image ###
	# esi = width
	# edi = height
    movl    IMAGE_WIDTH, %esi		# move image width into %esi
    movl    IMAGE_HEIGHT, %edi		# move image height into %edi
    imul    %esi, %edi              # multiply them to get the size of the image (pixels)
    imul    $3, %edi                # multiply the size by 3 to get the total bytes of the picture (1 pixel = 3 Byte (RGB))

    movq    %r8, %rcx               #
    call    count_bytes             #
                                    #
    add     $1, %rax                #
    imul    $8, %rax                #
    cmpl    %esi, %eax              #
    jle     encoded_message
    jmp		error_message_to_long

encode_message:
	### todo ... ###



#####ERROR LOOPS#####
# wrong amount of argumments #
error_arguments:
    movq    $RETURN_INVALID_NUM_ARGS, %rdi  # load return error message
    jmp     exit

# something went wrong while opening input file #
error_open_file:
    movq    %rax, %r10                  # preload file descriptor
    call    close_file                  # call close file function
    movq    $RETURN_ERR_INPUT, %rdi     # load return error message
    jmp     exit

# somthing went wrong while creating output file #
error_output_file:
    movq    %rax, %r10                  # preload file descriptor
    call    close_file                  # call close file function
    movq    $RETURN_ERR_OUTPUT, %rdi    # load return error message
    jmp     exit

# somthing went wrong with reading the file #
error_read_file:
    movq    $RETURN_READ_ERROR, %rdi    # load return message
    jmp exit

# somthing went wrong with the format while reading file #
error_format:
	movq	%rax, %r10						# preload file descriptor
	call	close_file						# call close file function
    movq	$RETURN_INVALID_FORMAT, %rdi	# load return message
	jmp		exit

# message is too long for the image #
error_message_to_long:
	movq	%rax, %r10					# preload file descriptor
	call 	close_file					# call close file function
    movq    $RETURN_MSG_TOO_LONG,%rdi   # load return error message
    jmp     exit


###EXIT###
exit:
	movq  $0, %rbx
	movq  $EXIT, %rax
	syscall

## close file function ##
# closes the file from file descriptor in %r10 #
    .type close_file, @function
close_file:
    ## save the registers ##
    pushq   %rbp
    movq    %rsp, %rbp
    pushq   %rdi
    ## close the file ##
    movq    $CLOSE, %rax        # move close file number into %rax
    movq    %r10, %rdi          # move dile descriptor into rdi
    syscall                     # close file
    ## restore the registers ##
    popq    %rdi
    movq    %rbp, %rsp
    popq    %rbp
ret