#' function to generate input singals (rgs/rbs/prbs/sine)
#' 
#' \code{idinput} is a function for generating input signals (rgs/rbs/prbs/sine) for identification purposes
#' 
#' @param n integer length of the input singal to be generated
#' @param type the type of input signal to be generated. 
#' 'rgs' - generates random gaussian signal
#' 'rbs' - generates random binary signal
#' 'prbs' - generates pseudorandom binary signal
#' 'sine' - generates a signal that is a sum of sinusoids
#' 
#' Default value is type='rgs'
#' @param band determines the frequency content of the signal. 
#' For type='rbs'/'sine'/,  band = [wlow,whigh]
#' which specifies the lower and the upper bound of the passband frequencies(expressed as fractions of Nyquist frequency). Default is c(0,1)
#' For type='prbs', band=[0,B]
#' where B is such that the singal is constant over 1/B (clock period). Default is c(0,1)
#' @param levels row vector defining the input level. It is of the form 
#' levels=c(minu, maxu)
#' For 'rbs','prbs', 'sine', the generated signal always between minu and maxu.
#' For 'rgs', minu=mean value of signal minus one standard deviation and maxu=mean value of signal plus one standard deviation
#' 
#' Default value is levels=c(-1,1)
#' @export
idinput<-function(n,type='rgs',band=c(0,1),levels=c(-1,1)){
  if(type=="rbs"){
    v1<-gen.rbs(n,band,levels)
  } 
  else if(type=="rgs"){
    v1<-gen.rgs(n,band,levels)
  }
  return(v1)
}

gen.rgs<-function(n,band,levels){
  require(signal)
  mu<-(levels[1]+levels[2])/2
  sigma<-(levels[2]-levels[1])/2
  v<-rnorm(n,mu,sigma)
  v<-sapply(v, function(x) {if(x==0) rnorm(1) else x})
  gfilt<-butter(8,band,type ='pass',plane ='z')
  v1<-filter(gfilt,v)
  return(v1)
}

gen.rbs<-function(n,band,levels){
  require(signal)
  v<-rnorm(n)
  
  v<-sapply(v, function(x) {if(x==0) rnorm(1) else x}, simplify = 'vector')
  #if we do not specify else case, it assigns it as NULL
  bfilt<-butter(8,band,type = 'pass',plane = 'z')
  v1<-filter(bfilt,v)
  v1<-sapply(v1, function(x) {ifelse(x>0 , levels[2] , levels[1]) })
  return(v1)
}