######## user defined parameters ########

set file_to_save /home/RChen/Documents/data/mscs_d/pdb/posre_protein_backbone.itp;# position restraint file to be saved

set file_to_load /home/RChen/Documents/data/mscs_d/pdb/system.gro;  # the .gro/.pdb file to be used

set atoms_to_restrain "protein and backbone"; #test in VMD Graphics/Representations if unconfident

set fc_x 1000; #force constant for x axis

set fc_y 1000; #force constant for y axis

set fc_z 1000; #force constant for z axis

####### end of user defined parameters #####

proc make_bak {file_to_save} {
	set filelist [glob -nocomplain "${file_to_save}.bak.*"]
	if {[llength $filelist] == 0} {
		set i 1;
	} else {
		set numlist "";
		foreach filename $filelist {
			lappend numlist [lindex [split $filename "."] end]
		}
		set numlist [lsort -integer $numlist]
		set i [expr [lindex $numlist end] + 1]
	}
	exec mv ${file_to_save} ${file_to_save}.bak.${i}
	return "${file_to_save} is moved to ${file_to_save}.bak.${i}"
}

if {[file exists ${file_to_save}]} {
	set bakinfo [make_bak $file_to_save]
}

set fs [open ${file_to_save} a+]

set time_now [clock format [clock seconds] -format {%b. %d, %Y %I:%M:%S %p}];
puts $fs "; created by [exec whoami] on $time_now";
puts $fs "; Structure file is: $file_to_load";
puts $fs "; atomselection is: $atoms_to_restrain";
puts $fs "\[ position_restraints \]"
puts $fs "; atom  type      fx      fy      fz"

set filetype [string range $file_to_load end-2 end]

mol load ${filetype} ${file_to_load}

set sel [atomselect top "${atoms_to_restrain}"]

foreach index [$sel get index] {
	puts $fs "[format "%6s" [expr $index + 1]]   [format "%3s" 1]  ${fc_x}  ${fc_y}  ${fc_y}"
}

close $fs
if [info exists bakinfo] {puts "\n$bakinfo"}
puts "\nfile $file_to_save created\n"
exit;