library(filelock)

init.remember <- function(){

    if(exists("r") == FALSE){
        if(file.exists(remember.file)){
            if(!exists("remember.file.lock"))
                init.file.lock()
            lck  <- lock(remember.file.lock, exclusive = FALSE)
            r <<- readRDS(remember.file)
            unlock(lck)
        } else {
            r <<- list()
        }
    }

}

remember.file <<- "remembr.RDS"
init.file.lock <- function(){
    remember.file.lock <<- paste0(remember.file,"_LOCK")
}

remember.prefix  <<- ""


change.remember.file <- function(file,clear=FALSE){
    if(!clear){
        remember.file <<- file
        init.file.lock()
        save.remember()
    } else {
        remember.file <<- file
        rm(r,pos=globalenv())
        init.remember()
    }
}
set.remember.prefix <- function(prefix){
    remember.prefix <<- prefix
}

load.if.exists <- function(){
    if(file.exists(remember.file)){
        if(!exists("remember.file.lock"))
            init.file.lock()
        lck  <- lock(remember.file.lock, exclusive = FALSE)
        r <<- readRDS(remember.file)
        unlock(lck)
    } else {
        r <<- list()
    }
}

remember <- function(var,name,lock=T){

    init.remember()

    load.if.exists()

    if(remember.prefix == ""){
        r[[name]] <<- var
    } else {
        if(is.null(r[[remember.prefix]])){
            r[[remember.prefix]]  <<- list()
        }
        r[[remember.prefix]][[name]]  <<- var
    }

    save.remember()
}

save.remember <- function(lock=T){
    if(!exists("remember.file.lock"))
        init.file.lock()
    
    lck  <- lock(remember.file.lock, exclusive=TRUE)
    saveRDS(r,file=remember.file)
    unlock(lck)
}
init.remember()