# rotrw -- a func to read from a file, rot, and write to 
# a new file
# file: name of source file
# rot:  number to rot by
# field: ascii or alpha, selects what characters to rot thru
#		 If select alpha, only alphas are rotted.
#		 If select ascii, all ascii chars are rotted
# 		Set field to either 'ascii' or 'alpha' for charset
#
# Oct08: embedded all flavors of "rot" into one source file.
# Future upgrade: allow an arb. vector to be passed as FIELD,
# and in the ELSE clause set "old" to FIELD and do same rot
#

rotrw<-function(file,rot=13,field=ascii)
{
	readLines(file)->fin
	if(field=='alpha')
		{
		source('rot13.R')
		rot13(fin,rot)->tempf	
		}
	else if(field=='ascii')
		{
		source('rotit.R')
		rotit(fin,rot)->tempf
		}
	else 
		{
		stop("Error: ",field,' is unknown type.\n')
		}
#	strip the .extension so can get  file name and build
#	output name 'file'[rot].ext
	strsplit(file,split='\\.')->splitfil# to get file name alone
	unlist(splitfil)->unfil # makes it a char vector,
	# so unlist[1] is name, unlist[2] is ext
	paste(unfil[1],rot,field,'.',unfil[2],sep="")->outname
	writeLines(tempf,con=outname)
	}
	
rot13 <- function(string,rot=13){
  #  Just coerce it. I will only shift alpha chars anyway
  cstr<-as.character(string)
  #get fancy: force ROT into 0-25, by shifting negative values and
  # taking a modulus:    
  rtm<-(rot+(rot<0)*26)%%26
  old<-paste(c(letters,LETTERS),collapse="")
  # this is legal:  letters[c(20:26,1:3)], so just fix start and end
  shift<-c(rtm+1,26,1,rtm)
  
  new<-paste(c(letters[shift[1]:shift[2]],letters[shift[3]:shift[4]],LETTERS[shift[1]:shift[2]],LETTERS[shift[3]:shift[4]]),collapse="")
  rotted<-chartr(old = old, new = new, x = string)
  return(rotted)
}

#modified from the seqinr package, allows user to set any rot value
rotit <- function(string,rot=13){
	library(sfsmisc) #needed for chars8bit()
  #  Just coerce it. 
  cstr<-as.character(string)
  #get fancy: force ROT into 0-95, by shifting negative values and
  # taking a modulus:    
  rtm<-(rot+(rot<0)*95)%%95
  # OLD is full baseline ASCII char set. Note that it's a vector
  old<-c(chars8bit(seq(32,126)))
  # this is legal:  x[c(20:26,1:3)], so just fix start and end indices
  shift<-c(rtm+1,95,1,rtm)
  new<-paste(c(old[shift[1]:shift[2]],old[shift[3]:shift[4]]),collapse="")
  rotted<-chartr(old = paste(old,collapse=""), new = new, x = string)
  return(rotted)
}