writeReactLog <- function(file=stdout(), sessionToken = NULL) {
  log <- .graphStack$as_list()
  if (!is.null(sessionToken)) {
    log <- Filter(function(x) {
      is.null(x$session) || identical(x$session, sessionToken)
    }, log)
  }
  cat(toJSON(log, pretty=TRUE), file=file)
}

#' Reactive Log Visualizer
#'
#' Provides an interactive browser-based tool for visualizing reactive
#' dependencies and execution in your application.
#'
#' To use the reactive log visualizer, start with a fresh R session and
#' run the command \code{options(shiny.reactlog=TRUE)}; then launch your
#' application in the usual way (e.g. using \code{\link{runApp}}). At
#' any time you can hit Ctrl+F3 (or for Mac users, Command+F3) in your
#' web browser to launch the reactive log visualization.
#'
#' The reactive log visualization only includes reactive activity up
#' until the time the report was loaded. If you want to see more recent
#' activity, refresh the browser.
#'
#' Note that Shiny does not distinguish between reactive dependencies
#' that "belong" to one Shiny user session versus another, so the
#' visualization will include all reactive activity that has taken place
#' in the process, not just for a particular application or session.
#'
#' As an alternative to pressing Ctrl/Command+F3--for example, if you
#' are using reactives outside of the context of a Shiny
#' application--you can run the \code{showReactLog} function, which will
#' generate the reactive log visualization as a static HTML file and
#' launch it in your default browser. In this case, refreshing your
#' browser will not load new activity into the report; you will need to
#' call \code{showReactLog()} explicitly.
#'
#' For security and performance reasons, do not enable
#' \code{shiny.reactlog} in production environments. When the option is
#' enabled, it's possible for any user of your app to see at least some
#' of the source code of your reactive expressions and observers.
#'
#' @param time A boolean that specifies whether or not to display the
#' time that each reactive.
#'
#' @export
showReactLog <- function(time = TRUE) {
  utils::browseURL(renderReactLog(time = as.logical(time)))
}

renderReactLog <- function(sessionToken = NULL, time = TRUE) {
  templateFile <- system.file('www/reactive-graph.html', package='shiny')
  html <- paste(readLines(templateFile, warn=FALSE), collapse='\r\n')
  tc <- textConnection(NULL, 'w')
  on.exit(close(tc))
  writeReactLog(tc, sessionToken)
  cat('\n', file=tc)
  flush(tc)
  html <- sub('__DATA__', paste(textConnectionValue(tc), collapse='\r\n'), html, fixed=TRUE)
  html <- sub('__TIME__', paste0('"', time, '"'), html, fixed=TRUE)
  file <- tempfile(fileext = '.html')
  writeLines(html, file)
  return(file)
}

.graphAppend <- function(logEntry, domain = getDefaultReactiveDomain()) {
  if (isTRUE(getOption('shiny.reactlog'))) {
    sessionToken <- if (is.null(domain)) NULL else domain$token
    .graphStack$push(c(logEntry, list(
      session = sessionToken,
      time = as.numeric(Sys.time())
    )))
  }

  if (!is.null(domain)) {
    domain$reactlog(logEntry)
  }
}

.graphDependsOn <- function(id, label) {
  .graphAppend(list(action='dep', id=id, dependsOn=label))
}

.graphDependsOnId <- function(id, dependee) {
  .graphAppend(list(action='depId', id=id, dependsOn=dependee))
}

.graphCreateContext <- function(id, label, type, prevId, domain) {
  .graphAppend(list(
    action='ctx', id=id, label=paste(label, collapse='\n'),
    srcref=as.vector(attr(label, "srcref")), srcfile=attr(label, "srcfile"),
    type=type, prevId=prevId
  ), domain = domain)
}

.graphEnterContext <- function(id) {
  .graphAppend(list(action='enter', id=id))
}

.graphExitContext <- function(id) {
  .graphAppend(list(action='exit', id=id))
}

.graphValueChange <- function(label, value) {
  .graphAppend(list(
    action = 'valueChange',
    id = label,
    value = paste(utils::capture.output(utils::str(value)), collapse='\n')
  ))
}

.graphInvalidate <- function(id, domain) {
  .graphAppend(list(action='invalidate', id=id), domain)
}

#' @include stack.R
.graphStack <- Stack$new()