#' @useDynLib shiny
NULL

suppressPackageStartupMessages({
  library(websockets)
  library(RJSONIO)
})

ShinyApp <- setRefClass(
  'ShinyApp',
  fields = list(
    .websocket = 'list',
    .outputs = 'Map',
    .invalidatedOutputValues = 'Map',
    session = 'Values'
  ),
  methods = list(
    initialize = function(ws) {
      .websocket <<- ws
      .outputs <<- Map$new()
      .invalidatedOutputValues <<- Map$new()
      session <<- Values$new()
    },
    defineOutput = function(name, func) {
      "Binds an output generating function to this name. The function can either
      take no parameters, or have named parameters for \\code{name} and
      \\code{shinyapp} (in the future this list may expand, so it is a good idea
      to also include \\code{...} in your function signature)."
      if (is.function(func)) {
        if (length(formals(func)) != 0) {
          orig <- func
          func <- function() {
            orig(name=name, shinyapp=.self)
          }
        }
        .outputs$set(name, func)
      }
      else {
        stop(paste("Unexpected", class(func), "output for", name))
      }
    },
    instantiateOutputs = function() {
      lapply(.outputs$keys(),
             function(key) {
               func <- .outputs$remove(key)
               Observer$new(function() {
                 value <- func()
                 .invalidatedOutputValues$set(key, value)
               })
             })
    },
    flushOutput = function() {
      if (length(.invalidatedOutputValues) == 0)
        return(invisible())
      
      data <- .invalidatedOutputValues
      .invalidatedOutputValues <<- Map$new()
      # cat(c("SEND", toJSON(as.list(data)), "\n"))
      websocket_write(toJSON(as.list(data)), .websocket)
    }
  )
)

.createOutputWriter <- function(shinyapp) {
  ow <- list(impl=shinyapp)
  class(ow) <- 'shinyoutput'
  return(ow)
}

#' @S3method $<- shinyoutput
`$<-.shinyoutput` <- function(x, name, value) {
  x[['impl']]$defineOutput(name, value)
  return(invisible(x))
}

httpServer <- function(handlers) {
  handler <- joinHandlers(handlers)
  function(ws, header) {
    response <- handler(ws, header)
    if (!is.null(response))
      return(response)
    else
      return(http_response(ws, 404, content="<h1>Not Found</h1>"))
  }
}

joinHandlers <- function(handlers) {
  handlers <- lapply(handlers, function(h) {
    if (is.character(h))
      return(staticHandler(h))
    else
      return(h)
  })
  
  if (length(handlers) < 2)
    return(handlers)
  
  function(ws, header) {
    for (handler in handlers) {
      response <- handler(ws, header)
      if (!is.null(response))
        return(response)
    }
    return(NULL)
  }
}

staticHandler <- function(root) {
  root <- normalizePath(root, mustWork=T)
  
  resolve <- function(dir, relpath) {
    abs.path <- file.path(dir, relpath)
    if (!file.exists(abs.path))
      return(NULL)
    abs.path <- normalizePath(abs.path, mustWork=T)
    if (nchar(abs.path) <= nchar(dir) + 1)
      return(NULL)
    if (substr(abs.path, 1, nchar(dir)) != dir ||
        !(substr(abs.path, nchar(dir)+1, nchar(dir)+1) %in% c('/', '\\'))) {
      return(NULL)
    }
    return(abs.path)
  }
  
  return(function(ws, header) {
    path <- header$RESOURCE
    
    if (is.null(path))
      return(http_response(ws, 400, content="<h1>Bad Request</h1>"))
    
    if (path == '/')
      path <- '/index.html'
    
    abs.path <- resolve(root, path)
    if (is.null(abs.path))
      return(NULL)
    
    ext <- tools::file_ext(abs.path)
    content.type <- switch(ext,
                           html='text/html; charset=UTF-8',
                           htm='text/html; charset=UTF-8',
                           js='text/javascript',
                           css='text/css',
                           png='image/png',
                           jpg='image/jpeg',
                           jpeg='image/jpeg',
                           gif='image/gif',
                           'application/octet-stream')
    response.content <- readBin(abs.path, 'raw', n=file.info(abs.path)$size)
    return(http_response(ws, 200, content.type, response.content))
  })
}

apps <- Map$new()

# Provide a character representation of the WS that can be used
# as a key in a Map.
wsToKey <- function(WS) {
  as.character(WS$socket)
}

#' Creates a new app with the given properties.
#' 
#' @param client Path to the root of the application-specific www files (which
#'   should include index.html); or, a function that knows how to serve up www
#'   files (TODO: document); or, a list of one or more paths and/or functions.
#' @param server If a character string, a path to the R file that contains the 
#'   server application logic. If a function, the actual server application 
#'   logic (should take \code{input} and \code{output} parameters).
#' @param sys.www.root Path to the system www root, that is, the assets that are
#'   shared by all Shiny applications (shiny.css, shiny.js, etc.).
#' @param port The TCP port that the application should listen on.
startApp <- function(client = './www',
                     server = './app.R',
                     sys.www.root = system.file('www', package='shiny'),
                     port=8101L) {
  
  ws_env <- create_server(
    port=port,
    webpage=httpServer(c(client, sys.www.root)))
  
  set_callback('established', function(WS, ...) {
    shinyapp <- ShinyApp$new(WS)
    apps$set(wsToKey(WS), shinyapp)
  }, ws_env)
  
  set_callback('closed', function(WS, ...) {
    apps$remove(wsToKey(WS))
  }, ws_env)
  
  set_callback('receive', function(DATA, WS, ...) {
    # cat(c("RECV", rawToChar(DATA), "\n"))
    
    if (identical(charToRaw("\003\xe9"), DATA))
      return()
    
    shinyapp <- apps$get(wsToKey(WS))
    
    msg <- fromJSON(rawToChar(DATA), asText=T, simplify=F)
    switch(
      msg$method,
      init = {
        shinyapp$session$mset(msg$data)
        flushReact()
        local({
          input <- .createValuesReader(shinyapp$session)
          output <- .createOutputWriter(shinyapp)
          
          if (is.function(server))
            server(input=input, output=output)
          else if (is.character(server))
            source(server, local=T)
          else
            warning("app must be a function or filename")
        })
        shinyapp$instantiateOutputs()
      },
      update = {
        shinyapp$session$mset(msg$data)
      })
    flushReact()
    shinyapp$flushOutput()
  }, ws_env)
  
  cat(paste('\nListening on port ', port, "\n", sep=''))
  
  return(ws_env)
}

#' Run an application that was created by \code{\link{startApp}}. This
#' function should normally be called in a \code{while(T)} loop.
#' 
#' @param ws_env The return value from \code{\link{startApp}}.
serviceApp <- function(ws_env) {
  if (timerCallbacks$executeElapsed()) {
    flushReact()
     lapply(apps$values(), function(shinyapp) {
       shinyapp$flushOutput()
       NULL
     })
  }

  # If this R session is interactive, then call service() with a short timeout
  # to keep the session responsive to user input
  maxTimeout <- ifelse(interactive(), 100, 5000)
  
  timeout <- max(1, min(maxTimeout, timerCallbacks$timeToNextEvent()))
  service(server=ws_env, timeout=timeout)
}

#' Run an application. This function normally does not return.
#' 
#' @param client Path to the root of the application-specific www files (which
#'   should include index.html).
#' @param server If a character string, a path to the R file that contains the 
#'   server application logic. If a function, the actual server application 
#'   logic (should take \code{input} and \code{output} parameters).
#' @param sys.www.root Path to the system www root, that is, the assets that are
#'   shared by all Shiny applications (shiny.css, shiny.js, etc.).
#' @param port The TCP port that the application should listen on.
#' @param launch.browser If true, the system's default web browser will be 
#'   launched automatically after the app is started. Defaults to true in 
#'   interactive sessions only.
#'   
#' @export
runApp <- function(client = './www',
                   server = './app.R',
                   sys.www.root = system.file('www', package='shiny'),
                   port=8101L,
                   launch.browser=interactive()) {
  ws_env <- startApp(server=server, 
                     client=client,
                     sys.www.root=sys.www.root,
                     port=port)
  
  if (launch.browser) {
    appUrl <- paste("http://localhost:", port, sep="")
    utils::browseURL(appUrl)
  }
  
  tryCatch(
    while (T) {
      serviceApp(ws_env)
    },
    finally = {
      websocket_close(ws_env)
    }
  )
}