proc parse_mmcif_atoms {filename} {
    # Open and read the mmCIF file
    if {[catch {open $filename r} filehandle]} {
        puts "Error: Cannot open file $filename"
        return [list]
    }

	set extracting 0
	
	set header_dict {}
	set atom_data {}

	while {[gets $filehandle line] >= 0} {
		# Check for start marker
		if {[string first "_atom_site.group_PDB" $line] != -1} {
			set i 0
			dict set header_dict [string trim $line] $i
			set extracting 1
			continue
		}
		
		# Check for end marker
		if {$extracting && [string first "#" $line] != -1} {
			break
		}
		
		# Collect lines while extracting
		if {$extracting} {
			if {[string first "_atom_site" $line] != -1 } {
				dict set header_dict [string trim $line] [incr i]
			} else {
				lappend atom_data $line
			}
			
		}
	}

	close $filehandle

# TEST
#~ # Create a temporary molecule and fill it with dummy atoms
	#~ set n [llength $atom_data]
	#~ set tmpmolid [ mol new atoms $n]
	#~ set atomslist [list]
	#~ for {set i 1} {$i<=$n} {incr i} {
		#~ ## list format {radius resname resid chain x y z occupancy element segname}
		#~ lappend atomslist [list 0 DUM 9999 X 0.00 0.00 0.00 0 DUM MOLF]
	#~ }

	#~ # Initialize the dummy atoms pool
	#~ set sel [atomselect $tmpmolid "all"]

	# Select molecule (top)
	set mol_id [molinfo top]
	set sel [atomselect $mol_id all] 
	
	# Create an empty frame.
	animate dup $mol_id

	# Build coordinate and property lists
	set coords_x [list]
	set coords_y [list]
	set coords_z [list]
	set elements [list]
	set names [list]
	set resnames [list]
	set chains [list]
	set resids [list]
	set betas [list]
	set occupancies [list]
	set serials [list]

	# Populate the lists
	foreach atom $atom_data {
		lappend coords_x    [lindex $atom [dict get $header_dict "_atom_site.Cartn_x"]]
		lappend coords_y    [lindex $atom [dict get $header_dict "_atom_site.Cartn_y"]]
		lappend coords_z    [lindex $atom [dict get $header_dict "_atom_site.Cartn_z"]]
		lappend elements    [lindex $atom [dict get $header_dict "_atom_site.type_symbol"]]
		lappend names       [lindex $atom [dict get $header_dict "_atom_site.label_atom_id"]]
		lappend resnames    [lindex $atom [dict get $header_dict "_atom_site.label_comp_id"]]
		lappend chains      [lindex $atom [dict get $header_dict "_atom_site.label_asym_id"]]
		lappend molecule    [lindex $atom [dict get $header_dict "_atom_site.label_entity_id"]]
		lappend resids      [lindex $atom [dict get $header_dict "_atom_site.auth_seq_id"]]
		lappend betas       [lindex $atom [dict get $header_dict "_atom_site.B_iso_or_equiv"]]
		lappend occupancies [lindex $atom [dict get $header_dict "_atom_site.occupancy"]]
	}

	
	# Set all atomic properties at once
	$sel set x $coords_x
	$sel set y $coords_y  
	$sel set z $coords_z
	$sel set element $elements
	$sel set name $names
	$sel set resname $resnames
	$sel set chain $chains
	$sel set resid $resids
	$sel set beta $betas
	$sel set occupancy $occupancies

	# Housekeeping: Delete selection
	$sel delete

	# Update VMD
	mol reanalyze $mol_id
	display resetview

	puts "Successfully created molecule $mol_id with [llength $atom_data] atoms"
}