extract.breakpoints <- function(rearr.ori,type=c("atfw","atrev","gcfw","gcrev"),nbreaks,gridsize=100,it.max=500){
  
  if(length(type)==0){
    stop("You must specify the type of skew: atfw, atrev, gcfw or gcrev. See ?extract.breakpoints for more details.")
  }
  if(sum(!type%in%c("atfw","atrev","gcfw","gcrev"))!=0){
    stop("The type of skew must be one of the following: atfw, atrev, gcfw or gcrev. See ?extract.breakpoints for more details.")
  }

  result=list()
  
  for(t in type){

    if(t=="gcfw"){
      print("Extracting breakpoints for GC-skew, forward-encoded genes")
      x.breaks=rearr.ori$meancoord.rear[rearr.ori$strand.rear=="forward"]
      y.breaks=cumsum(rearr.ori$gcskew.rear[rearr.ori$strand.rear=="forward"])
     }
     if(t=="gcrev"){
        print("Extracting breakpoints for GC-skew, reverse-encoded genes")
      x.breaks=rearr.ori$meancoord.rear[rearr.ori$strand.rear=="reverse"]
      y.breaks=cumsum(rearr.ori$gcskew.rear[rearr.ori$strand.rear=="reverse"])
     }
    if(t=="atfw"){
       print("Extracting breakpoints for AT-skew, forward-encoded genes")
      x.breaks=rearr.ori$meancoord.rear[rearr.ori$strand.rear=="forward"]
      y.breaks=cumsum(rearr.ori$atskew.rear[rearr.ori$strand.rear=="forward"])
     }
     if(t=="atrev"){
       print("Extracting breakpoints for AT-skew, reverse-encoded genes")
      x.breaks=rearr.ori$meancoord.rear[rearr.ori$strand.rear=="reverse"]
      y.breaks=cumsum(rearr.ori$atskew.rear[rearr.ori$strand.rear=="reverse"])
     }
    
    assign("x.breaks",x.breaks,envir=.seqinrEnv)
    assign("y.breaks",y.breaks,envir=.seqinrEnv)
    
    rss=numeric(0)
    starts=list()

    i=0
    while(i<gridsize){
     
      initpsi=runif(nbreaks[which(type==t)],min=min(x.breaks),max=max(x.breaks))
      if(exists("seg")){
        rm(seg)
      }

      try(seg <- segmented::segmented(lm(y.breaks~x.breaks),x.breaks,psi=initpsi,it.max=it.max), silent = TRUE)

      
      if(exists("seg")){
        starts[[length(starts)+1]]=initpsi
        rss=c(rss, sum(seg$residuals^2))
        i=i+1
      }
      
      gc()
    }

    wmin=which.min(rss)
   
    
    starts=starts[[wmin]]
    
    seg=seg <- segmented::segmented(lm(y.breaks~x.breaks),x.breaks,psi=starts,it.max=it.max)
    
    breaks=round(seg$psi[,2])
    
    breaks=breaks[order(breaks)]

    sl=c(x.breaks[1],breaks,x.breaks[length(x.breaks)])-x.breaks[1]+1

    
    slopes=numeric(length(sl)-1)
    
    for(i in seq_len(length(sl)-1)){
      u=(sl[i]:sl[i+1])+x.breaks[1]-1
      slopes[i]=summary(lm(y.breaks[sl[i]:sl[i+1]]~u))$coefficients[2,1]
    }
    
    slopes.left=slopes[-length(slopes)]
    slopes.right=slopes[-1]
    
    result[[t]]=list()

    result[[t]]$breaks=breaks
    result[[t]]$slopes.left=slopes.left
    result[[t]]$slopes.right=slopes.right

    real.coord=rearr.ori$meancoord.real[breaks]
    result[[t]]$real.coord=real.coord
    
    
  }

  return(result)

}
