require(knitr)
# Figure out which version of Stata is available
if (file.exists("C:/Program Files (x86)/Stata14/StataMP-64.exe")) {
  statapath <- "C:/Program Files (x86)/Stata14/StataMP-64.exe"
} else if (file.exists("C:/Program Files (x86)/Stata15/StataSE-64.exe")) {
  statapath <- "C:/Program Files (x86)/Stata15/StataSE-64.exe"
}

# Set universal chunk options
opts_chunk$set(engine="stata", engine.path=statapath, comment=NA)

# Define a "collectcode" chunk option
knit_hooks$set(collectcode = function(before, options, envir) {
  if (!before) {
    if (options$engine == "stata") {
      profile <- file("profile.do", open="at")
      writeLines(options$code, profile)
      close(profile)
    }
  }
})

# Always hide SOME Stata commands in the echoed source,
#   e.g. "graph export"
hook_source <- knit_hooks$get("source")
knit_hooks$set(source = function(x, options) {
  if (options$engine == "stata") {
    y <- strsplit(x, "\n")[[1]]
    # Find and remove graph export in Stata source
    graphexport <- grep("^graph export.*", y)
    if (length(graphexport)>0) {y <- y[-(graphexport)]}
    # Now treat the result as regular source code
    hook_source(y, options)
  } else {
    hook_source(x, options)
  }
})

# Always clean Stata commands from the output
hook_output <- knit_hooks$get("output")
knit_hooks$set(output = function(x, options) {
  if (options$engine == "stata") {
    y <- strsplit(x, "\n")[[1]]
    # Find output lines that are commands
    commandlines <- grep("^\\.", y)
    if (length(commandlines)>0) {y <- y[-(grep("^\\.", y))]}
    # Some commands have a leading space?
    if (length(grep("^[[:space:]*]\\.", y))>0) {
      y <- y[-(grep("^[[:space:]*]\\.", y))]
    }
    # Ensure a trailing blank line
    if (length(y)>0 && y[length(y)] != "") { y <- c(y, "") }
    # Remove blank lines at the top of the Stata log
    firsttext <- min(grep("[[:alnum:]]", y))
    if (firsttext != Inf) {y <- y[-(1:(firsttext-1))]}
    # Now treat the result as regular output
    hook_output(y, options)
  } else {
    hook_output(x, options)
  }
})