

#' Python configuration
#'
#' Retrieve information about the version of Python currently being used by
#' `reticulate`.
#'
#' If Python has not yet been initialized, then calling `py_config()` will force
#' the initialization of Python. See [py_discover_config()] for more details.
#'
#' @return Information about the version of Python in use, as an \R list with
#'   class `"py_config"`.
#'
#' @export
py_config <- function() {
  ensure_python_initialized()
  .globals$py_config
}

#' Python version
#'
#' Get the version of Python currently being used by `reticulate`.
#'
#' @return The version of Python currently used, or `NULL` if Python has
#'   not yet been initialized by `reticulate`.
#'
#' @export
py_version <- function() {

  if (!py_available(initialize = FALSE))
    return(NULL)

  config <- py_config()
  numeric_version(config$version)

}

#' Python executable
#'
#' Get the path to the Python executable that `reticulate` has been configured
#' to use. If Python has already been initialized, then `reticulate` will
#' choose the currently-active copy of Python.
#'
#' This can occasionally be useful if you'd like to interact with Python (or its
#' modules) via a subprocess; for example you might choose to install a package
#' with `pip`:
#'
#' ```
#' system2(py_exe(), c("-m", "pip", "install", "numpy"))
#' ```
#'
#' and so you can also have greater control over how these modules are invoked.
#'
#' @return The path to the Python executable `reticulate` has been configured
#'   to use.
#'
#' @export
py_exe <- function() {

  # if python has already been initialized, use that
  if (!is.null(.globals$py_config))
    return(.globals$py_config$python)

  # otherwise, guess what version of python we'd use
  py_discover_config()$python

}


#' Build Python configuration error message
#'
#' @param prefix Error message prefix
#'
#' @keywords internal
#' @export
py_config_error_message <- function(prefix) {
  message <- prefix
  config <- py_config()
  if (!is.null(config)) {
    message <- paste0(message, "\n\nDetected Python configuration:\n\n",
                      str(config), "\n")
  }
  message
}

#' Check if Python is available on this system
#'
#' @param initialize `TRUE` to attempt to initialize Python bindings if they
#'   aren't yet available (defaults to `FALSE`).
#'
#' @return Logical indicating whether Python is initialized.
#'
#' @note The `py_numpy_available` function is a superset of the
#'  `py_available` function (it calls `py_available` first before
#'  checking for NumPy).
#'
#' @export
py_available <- function(initialize = FALSE) {

  if (is_python_initialized())
    return(.globals$py_config$available)

  if (!initialize)
    return(FALSE)

  tryCatch({
    ensure_python_initialized()
    .globals$py_config$available
  }, error = function(e) FALSE)

}


#' @rdname py_available
#' @export
py_numpy_available <- function(initialize = FALSE) {

  if (!py_available(initialize = initialize))
    return(FALSE)

  py_numpy_available_impl()

}


#' Check if a Python module is available on this system.
#'
#' Note that this function will also attempt to initialize Python
#' before checking if the requested module is available.
#'
#' @param module The name of the module.
#'
#' @return `TRUE` if the module is available and can be loaded;
#'   `FALSE` otherwise.
#'
#' @export
py_module_available <- function(module) {
  tryCatch({ import(module); TRUE }, error = clear_error_handler(FALSE))
}


#' Discover the version of Python to use with reticulate.
#'
#' This function enables callers to check which versions of Python will be
#' discovered on a system as well as which one will be chosen for use with
#' reticulate.
#'
#' @param required_module A optional module name that will be used to select the
#'   Python environment used.
#'
#' @param use_environment An optional virtual/conda environment name to prefer
#'   in the search.
#'
#' @return Python configuration object.
#'
#' @export
py_discover_config <- function(required_module = NULL, use_environment = NULL) {

  if (is.null(required_module) && length(.globals$delay_load_imports$module))
    required_module <- .globals$delay_load_imports$module[[1L]]
  if (!is.null(required_module))
    required_module <- strsplit(required_module, ".", fixed = TRUE)[[1L]][[1L]]

  # check if python symbols can already be found in the current process
  main_process_info <- main_process_python_info()
  if (!is.null(main_process_info)) {
    python_version <- normalize_python_path(main_process_info$python)$path
    try(return(python_config(python_version, required_module,
                             forced = "the current process")))
  }

  # if PYTHON_SESSION_INITIALIZED is specified then use it without scanning
  # further (this is a "hard" requirement because an embedding process may
  # set this to indicate that the python interpreter is already loaded)
  py_session_initialized <- py_session_initialized_binary()
  if (!is.null(py_session_initialized)) {
    python_version <- normalize_python_path(py_session_initialized)$path
    try(return(python_config(python_version, required_module,
                             forced = "PYTHON_SESSION_INITIALIZED")))
  }

  # if RETICULATE_PYTHON is specified then use it without scanning further
  reticulate_env <- Sys.getenv("RETICULATE_PYTHON", unset = NA)
  if (!is.na(reticulate_env)) {

    python_version <- normalize_python_path(reticulate_env)
    if (!python_version$exists)
      stop("Python specified in RETICULATE_PYTHON (", reticulate_env, ") does not exist")

    python_version <- python_version$path
    try(return(python_config(python_version, required_module,
                             forced = "RETICULATE_PYTHON")))

  }

  # if RETICULATE_PYTHON_ENV is specified then use that
  # can be a bare envname or a path
  reticulate_python_env <- Sys.getenv("RETICULATE_PYTHON_ENV", unset = NA)
  if (!is.na(reticulate_python_env)) {

    # resolve the path to the environment directory
    tryCatch({
      python <- py_resolve(reticulate_python_env)
    }, error = function(e) {
      stop("Python specified in RETICULATE_PYTHON_ENV (", reticulate_python_env, ") does not exist")
    })

    try(return(python_config(python, required_module,
                             forced = "RETICULATE_PYTHON_ENV")))

  }

  # look for a required python version
  # (e.g. use_python("/usr/bin/python", required = TRUE))
  required_version <- .globals$required_python_version
  if (!is.null(required_version)) {
    python_version <- normalize_python_path(required_version)$path
    try(return(python_config(python_version, required_module,
                             forced = "use_python() function")))
  }

  # check if we're running in an activated venv
  if (is_virtualenv(envpath <- Sys.getenv("VIRTUAL_ENV", NA))) {
    # If this check ends up being too strict, we can alternatively do:
    # if (python_info(Sys.which("python"))$type == "virtualenv") {
    try(return(python_config(
      virtualenv_python(envpath), required_module,
      forced = "VIRTUAL_ENV")))
  }

  # if we're working within a project that contains a pyproject.toml file,
  # then use the copy of Python associated with the poetry environment
  config <- tryCatch(poetry_config(required_module), error = identity)
  if (!inherits(config, "error") && !is.null(config))
    return(config)

  # if we're working within a project that contains a Pipfile, then
  # use the copy of Python associated with that pipenv
  config <- tryCatch(pipenv_config(required_module), error = identity)
  if (!inherits(config, "error") && !is.null(config))
    return(config)

  # if the current directory contains a venv, use it:
  for (dirpath in c("./venv", "./virtualenv", "./.venv", "./.virtualenv")) {
    if (dir.exists(dirpath) && is_virtualenv(dirpath)) {
      python <- virtualenv_python(dirpath)
      try(return(python_config(
        python, required_module,
        forced = sprintf("'%s' existing in the current working directory", dirpath))))
    }
  }

  # look for any environment names supplied in a call like:
  #  import("bar", delayed = list(environment = "r-barlyr"))
  for (envname in c(use_environment, .globals$delay_load_imports$environment)) {
    if (is.na(envname))
      next
    python <- tryCatch(py_resolve(envname), error = identity)
    if (!inherits(python, "error"))
      try(return(python_config(
        python, required_module,
        forced = sprintf('import("%s")', required_module)
      )))
  }

  # check for `use_python(required = FALSE)`. This should rarely be triggered
  # any more by users, since the default value for `required` changed from FALSE to TRUE.
  # excepting if the use_*() call is within a `.onLoad()` call of a package.
  # first call of use_*(,required = FALSE) wins
  optional_requested_use_pythons <- reticulate_python_versions()
  for (python in optional_requested_use_pythons) {
    try(return(python_config(
      python, required_module,
      forced = "use_python(, required = FALSE)"
      )))
  }

  # look in virtual environments that have a required module derived name,
  # e.g., given a call to import("bar"), look for an environment named "r-bar"
  for (module in c(required_module, .globals$delay_load_imports$module)) {
    envname <- paste0("r-", module)
    python <- tryCatch(py_resolve(envname), error = identity)
    if (!inherits(python, "error"))
      try(return(python_config(
        python, required_module,
        forced = sprintf('import("%s")', required_module)
      )))
  }

  # if RETICULATE_PYTHON_FALLBACK is specified then use it
  reticulate_env <- Sys.getenv("RETICULATE_PYTHON_FALLBACK", unset = NA)
  if (!is.na(reticulate_env)) {
    python_version <- normalize_python_path(reticulate_env)
    if (!python_version$exists)
      stop("Python specified in RETICULATE_PYTHON_FALLBACK (", reticulate_env, ") does not exist")
    python_version <- python_version$path
    try(return(python_config(python_version, required_module, python_version,
                             forced = "RETICULATE_PYTHON_FALLBACK")))
  }


  ## At this point, the user, (and package authors on behalf of the user), has
  ## expressed no preference for any particular python installation, or the
  ## preference expressed is for a python environment that don't exist.
  ##
  ## In other words,
  ##  - no use_python(), use_virtualenv(), use_condaenv()
  ##  - no RETICULATE_PYTHON, RETICULATE_PYTHON_ENV, or RETICULATE_PYTHON_FALLBACK env vars
  ##  - no env named 'r-bar' if there was a call like `import('foo', delay_load = list(environment = "r-bar"))`
  ##  - no env named 'r-foo' if there was a call like `import('foo')`
  ##  - we're not running under an already activated venv (i.e., no VIRTUAL_ENV env var)
  ##  - no configured poetry or pipfile or venv in the current working directory

  # Look for a "r-reticulate" venv or condaenv. if found, use that.
  # If not found, try to get permission to create one.
  # This is the default in the absence of any expressed preference by the user.
  python <- tryCatch(py_resolve("r-reticulate"), error = function(e) {
    envpath <- try_create_default_virtualenv(package = "reticulate")
    if (!is.null(envpath))
      virtualenv_python(envpath)
    else
      e
  })
  if (!inherits(python, "error"))
    try(return(python_config(python, required_module)))


  # At this point, user has expressed no preference, and we do not have user permission
  # to create the "r-reticulate" venv

  # fall back to using the PATH python, or fail.
  # We intentionally do not go on a fishing expedition for every possible python,
  # for two reasons:
  #   - the default workflow should be to use venvs
  #   - which python is found should be predictable.

  # create a list of possible python versions to bind to
  python_versions <- unique(c(
    Sys.which("python3"),
    Sys.which("python")
  ))

  windows_registry_python <- character()
  if (is_windows()) {
    append(python_versions) <- windows_registry_python <-
      local({
        df <- py_versions_windows()
        df$executable_path[df$type == "PythonCore"]
      })
  }

  # filter locations by existence
  if (length(python_versions) > 0)
    python_versions <- python_versions[file.exists(python_versions)]

  if (is_windows()) {
    # remove 'fake' / inaccessible python executables
    # https://github.com/rstudio/reticulate/issues/534
    info <- suppressWarnings(file.info(python_versions))
    size <- ifelse(is.na(info$size), 0, info$size)
    python_versions <- python_versions[size != 0]

    # remove msys2 / cygwin python executables.
    # path translation going to and from msys2 currently not implemented.
    # E.g.: "C:\foo\bar" -> "/c/foo/bar" and  "/foo/bar" -> "C:\rtools43\foo\bar"
    # https://github.com/rstudio/reticulate/issues/1325
    python_sys_platforms <- vapply(
      python_versions, system2, "",
      args = c("-c", shQuote("import sys; print(sys.platform)")),
      stdout = TRUE)

    python_versions <- python_versions[python_sys_platforms != "cygwin"]
  }

  # scan until we find a version of python that meets our qualifying conditions
  valid_python_versions <- c()
  for (python_version in python_versions) {

    # get the config
    config <- try(python_config(python_version, required_module, python_versions,
                                forced = if (python_version %in% windows_registry_python)
                                  "Windows Registry" else "PATH"))
    if(inherits(config, "try-error"))
      next

    # if we have a required module ensure it's satisfied.
    # also check architecture (can be an issue on windows)
    has_python_gte_27 <- as.numeric_version(config$version) >= "2.7"
    has_compatible_arch <- !is_incompatible_arch(config)
    has_preferred_numpy <- !is.null(config$numpy) && config$numpy$version >= "1.6"
    if (has_compatible_arch && has_preferred_numpy)
      valid_python_versions <- c(valid_python_versions, python_version)
    has_required_module <- is.null(config$required_module) || !is.null(config$required_module_path)
    if (has_python_gte_27 && has_compatible_arch && has_preferred_numpy && has_required_module)
      return(config)
  }

  # no preferred found, return first with valid config if we have it or NULL
  if (length(valid_python_versions) > 0)
    try(return(python_config(valid_python_versions[[1]], required_module, python_versions)))
  else if (length(python_versions) > 0)
    try(return(python_config(python_versions[[1]], required_module, python_versions)))
  else
    return(NULL)
}

py_discover_config_fallbacks <- function() {

  # prefer conda python if available
  conda <- find_conda()[[1L]]
  if (!is.null(conda) && file.exists(conda)) {

    pythons <- tryCatch(
      conda_python(envname = "base", conda = conda, all = TRUE),
      error = identity
    )

    if (is.character(pythons))
      return(pythons)

  }

  # on Windows, try looking in the registry
  if (is_windows())
    return(py_versions_windows()$executable_path)

  # otherwise, just search some default locations
  prefixes <- c(
    "/opt/local/python",
    "/opt/python",
    "/usr/local",
    "/usr"
  )

  suffixes <- c("bin/python3", "bin/python")
  grid <- expand.grid(
    prefix = prefixes,
    suffix = suffixes,
    KEEP.OUT.ATTRS = FALSE,
    stringsAsFactors = FALSE
  )

  paste(grid$prefix, grid$suffix, sep = "/")

}

try_create_default_virtualenv <- function(package = "reticulate", ...) {

  # If the environment already exists, use it
  envname <- paste0("r-", package)
  if (virtualenv_exists(envname))
    return(virtualenv_python(envname))

  if (!isTRUE(getOption("reticulate.python.initializing")))
    return(NULL)

  permission <- tolower(Sys.getenv("RETICULATE_AUTOCREATE_PACKAGE_VENV", ""))

  if (permission %in% c("false", "0", "no"))
    return(NULL)

  if (permission == "") {
    if (is_interactive()) {
      permission <- utils::askYesNo(sprintf(
        "Would you like to create a default python environment for the %s package?",
        package))
      if (!isTRUE(permission))
        return(NULL)
      permission <- "true"
    }
  }

  if (!permission %in% c("true", "yes", "1"))
    return(NULL)

  virtualenv_create(
    envname = envname,
    ...
  )

}


#' Discover versions of Python installed on a Windows system
#'
#' @return Data frame with `type`, `hive`, `install_path`, `executable_path`,
#'   and `version`.
#'
#' @keywords internal
#' @export
py_versions_windows <- function() {
  rbind(
    read_python_versions_from_registry("HCU", key = "PythonCore"),
    read_python_versions_from_registry("HLM", key = "PythonCore"),
    windows_registry_anaconda_versions()
  )
}

python_virtualenv_versions <- function() {
  home <- virtualenv_root()
  bins <- python_environments(home)
  data.frame(
    name = basename(dirname(dirname(bins))),
    python = bins,
    stringsAsFactors = FALSE
  )
}

python_conda_versions <- function() {

  if (is_windows()) {

    # list all conda environments
    conda_envs <- data.frame(name = character(),
                             python = character(),
                             stringsAsFactors = FALSE)
    registry_versions <- py_versions_windows()
    anaconda_registry_versions <- subset(registry_versions, registry_versions$type == "Anaconda")
    for (conda in file.path(anaconda_registry_versions$install_path, "Scripts", "conda.exe")) {
      conda_envs <- rbind(conda_envs, conda_list(conda = conda))
    }

    conda_envs

  } else {

    env_dirs <- c("~/anaconda/envs",
                  "~/anaconda2/envs",
                  "~/anaconda3/envs",
                  "~/anaconda4/envs",
                  "~/miniconda/envs",
                  "~/miniconda2/envs",
                  "~/miniconda3/envs",
                  "~/miniconda4/envs",
                  "/anaconda/envs",
                  "/anaconda2/envs",
                  "/anaconda3/envs",
                  "/anaconda4/envs",
                  "/miniconda/envs",
                  "/miniconda2/envs",
                  "/miniconda3/envs",
                  "/miniconda4/envs",
                  "~/opt/anaconda/envs",
                  "~/opt/anaconda2/envs",
                  "~/opt/anaconda3/envs",
                  "~/opt/anaconda4/envs",
                  "~")

    python_env_binaries <- python_environments(env_dirs)
    data.frame(name = basename(dirname(dirname(python_env_binaries))),
               python = python_env_binaries,
               stringsAsFactors = FALSE)
  }

}

python_environments <- function(env_dirs, required_module = NULL) {

  # filter env_dirs by existence
  env_dirs <- env_dirs[utils::file_test("-d", env_dirs)]

  # envs to return
  envs <- character()

  # python bin differs by platform
  python_bin <- ifelse(is_windows(), "python.exe", "bin/python")

  for (env_dir in env_dirs) {
    # filter by required module if requested
    if (!is.null(required_module)) {
      module_envs <- c(paste0("r-", required_module), required_module)
      envs <- c(envs, path.expand(sprintf("%s/%s/%s", env_dir, module_envs, python_bin)))

      # otherwise return all
    } else {
      envs <- c(envs, path.expand(sprintf("%s/%s",
                                          list.dirs(env_dir, recursive = FALSE),
                                          python_bin)))
    }
  }

  # filter by existence
  if (length(envs) > 0)
    envs[file.exists(envs)]
  else
    envs
}

python_munge_path <- function(python) {

  # add the python bin dir to the PATH (so that any execution of python from
  # within the interpreter, from a system call, or from within a terminal
  # hosted within the front end will use the same version of python.
  #
  # we do this up-front in python_config as otherwise attempts to discover
  # and load numpy can fail, especially on Windows
  # https://github.com/rstudio/reticulate/issues/367
  python_home <- dirname(python)
  python_dirs <- c(normalizePath(python_home))

  # fix rpath for anaconda libmkl
  if (is_osx()) {
    libmkl <- file.path(python_home, "../lib/libmkl_intel_thread.dylib")
    if (file.exists(libmkl)) {
      libmkl <- normalizePath(libmkl)
      args <- c("-add_rpath", shQuote(dirname(libmkl)), libmkl)
      system2("install_name_tool", args, stdout = FALSE, stderr = FALSE)
    }
  }



  if (is_conda_python(python)) {
    conda_info <- get_python_conda_info(python)

    new_path <- conda_run2(
      "python",
      c("-c", shQuote("import os; print(os.environ['PATH'])")),
      conda = conda_info$conda,
      envname = conda_info$root,
      intern = TRUE
    )
    # maybe discard unsilenceable warnings, see issue #1303
    new_path <- new_path[length(new_path)]

    old_path <- Sys.getenv("PATH")
    Sys.setenv("PATH" = new_path)
    return(old_path)
  }

  if (is_windows()) {

    # include the Scripts path, as well
    python_scripts <- file.path(python_home, "Scripts")
    if (file.exists(python_scripts))
      python_dirs <- c(python_dirs, normalizePath(python_scripts))

    # we saw some crashes occurring when Python modules attempted to load
    # dynamic libraries at runtime; e.g.
    #
    #   Intel MKL FATAL ERROR: Cannot load mkl_intel_thread.dll
    #
    # we work around this by putting the associated binary directory
    # on the PATH so it can be successfully resolved
    python_library_bin <- file.path(python_home, "Library/bin")
    if (file.exists(python_library_bin))
      python_dirs <- c(python_dirs, normalizePath(python_library_bin))
  }


  path_prepend(python_dirs)

}

python_config_impl <- function(python) {

  if(!file.exists(python)) {
    # Test if `python` is broken symlink, which can happen with a venv if the
    # venv starter is moved/removed
    msg <- paste0("Error running ", shQuote(python), ": No such file.")
    info <- python_info(python)
    if (info$type == "virtualenv") {
      msg <- paste0(sep = "", c(msg, "\n",
          "The Python installation used to create the virtualenv has been moved or removed",
          if(is.null(info$starter)) "." else ":\n  ", shQuote(info$starter)
        ))
    }
    stop(msg)
  }

  script <- system.file("config/config.py", package = "reticulate")
  config <- tryCatch(system2(
    command = python,
    args    = shQuote(script),
    stdout  = TRUE,
    stderr  = FALSE
  ), error = function(e) {
    e$message <- paste(e$message, shQuote(python))
    stop(e)
  })

  # check for error
  status <- attr(config, "status")
  if (!is.null(status)) {
    errmsg <- attr(config, "errmsg")
    stop("Error ", status, " occurred running ", python, ": ", errmsg)
  }

  # on macOS, if we see some variables referencing /Applications/Xcode.app
  # but that doesn't actually exist, then redirect to default CLT
  if (is_osx()) {
    clt <- "/Library/Developer/CommandLineTools"
    xcode <- "/Applications/Xcode.app/Contents/Developer"
    if (file.exists(clt))
      config <- gsub(xcode, clt, config, fixed = TRUE)
  }

  # return config
  config

}

python_config <- function(python,
                          required_module = NULL,
                          python_versions = python,
                          forced = NULL)
{
  # normalize and remove duplicates
  python <- canonical_path(python)
  python_versions <- canonical_path(python_versions)
  python_versions <- unique(python_versions)

  # update and restore PATH when done
  oldpath <- python_munge_path(python)
  on.exit(Sys.setenv(PATH = oldpath), add = TRUE)

  # set LD_LIBRARY_PATH on Linux as well, just to make sure Python libraries
  # can be resolved if necessary (also need to guard against users who munge
  # LD_LIBRARY_PATH in a way that breaks dynamic lookup of Python libraries)
  if (is_linux()) {
    libpath <- file.path(dirname(dirname(python)), "lib")
    if (file.exists(libpath)) {
      oldlibpath <- Sys.getenv("LD_LIBRARY_PATH", unset = NA)
      newlibpath <- paste(libpath, oldlibpath, sep = ":")
      Sys.setenv(LD_LIBRARY_PATH = newlibpath)
      on.exit({
        if (is.na(oldlibpath))
          Sys.unsetenv("LD_LIBRARY_PATH")
        else
          Sys.setenv(LD_LIBRARY_PATH = oldlibpath)
      }, add = TRUE)
    }
  }

  # collect configuration information
  if (!is.null(required_module)) {
    Sys.setenv(RETICULATE_REQUIRED_MODULE = required_module)
    on.exit(Sys.unsetenv("RETICULATE_REQUIRED_MODULE"), add = TRUE)
  }

  # execute config script
  config <- python_config_impl(python)

  # read output as dcf
  config_connection <- textConnection(config)
  on.exit(close(config_connection), add = TRUE)
  config <- read.dcf(config_connection, all = TRUE)

  # get the full textual version and the numeric version, check for anaconda
  version_string <- config$Version
  version <- config$VersionNumber
  anaconda <- grepl("anaconda|continuum", version_string, ignore.case = TRUE)
  architecture <- config$Architecture

  # determine the location of libpython
  # see also: https://github.com/JuliaPy/PyCall.jl/blob/master/deps/build.jl
  main_process_info <- main_process_python_info()
  if (!is.null(main_process_info)) {
    # either we have the main process libpython, or NA in case of PIE executable
    libpython <- main_process_info$libpython
  } else if (is_windows()) {

    # construct DLL name
    dll <- sprintf("python%s.dll", gsub(".", "", version, fixed = TRUE))

    # default to just using dll as libpython path (implies lookup on PATH)
    libpython <- dll

    # search for python DLL in one of the declared prefixes
    roots <- c(
      dirname(python),
      config$Prefix,
      config$ExecPrefix,
      config$BaseExecPrefix
    )

    for (root in roots) {
      candidate <- file.path(root, dll)
      if (file.exists(candidate)) {
        libpython <- canonical_path(candidate)
        break
      }
    }

  } else {

    # default to NULL
    libpython <- NULL

    # check multiple library directories
    # (necessary for virtualenvs that don't copy over the shared library)
    libsrcs <- c("LIBPL", "LIBDIR", "Prefix", "ExecPrefix", "BaseExecPrefix")
    for (libsrc in libsrcs) {

      # skip null entries in config
      src <- config[[libsrc]]
      if (is.null(src))
        next

      # get appropriate libpython extension for platform
      ext <- switch(
        Sys.info()[["sysname"]],
        Darwin  = ".dylib",
        Windows = ".dll",
        ".so"
      )

      # try to resolve libpython in this location
      pattern <- sprintf("^libpython%sd?m?%s", version, ext)
      candidates <- list.files(src, pattern = pattern, full.names = TRUE)
      if (length(candidates)) {
        libpython <- candidates
        break
      }

    }
  }

  # determine PYTHONHOME
  pythonhome <- NULL
  if (!is.null(config$Prefix)) {
    pythonhome <- canonical_path(config$Prefix)
    if (!is_windows()) {
      exec_prefix <- canonical_path(config$ExecPrefix)
      pythonhome <- paste(pythonhome, exec_prefix, sep = ":")
    }
  }

  as_numeric_version <- function(version) {
    version <- clean_version(version)
    numeric_version(version)
  }

  # check for numpy
  numpy <- NULL
  if (!is.null(config$NumpyPath)) {
    numpy <- list(
      path = canonical_path(config$NumpyPath),
      version = as_numeric_version(config$NumpyVersion)
    )
  }

  # check to see if this is a Python virtualenv
  root <- dirname(dirname(python))
  virtualenv <- if (is_virtualenv(root))
    root
  else
    ""

  # check for virtualenv activate script
  activate_this <- file.path(dirname(python), "activate_this.py")
  if (file.exists(activate_this))
    virtualenv_activate <- activate_this
  else
    virtualenv_activate <- ""

  # check for required module
  required_module_path <- config$RequiredModulePath

  # return config info
  info <- list(
    python               = python,
    libpython            = libpython[1],
    pythonhome           = pythonhome,
    pythonpath           = config$PythonPath,
    prefix               = config$Prefix,
    exec_prefix          = config$ExecPrefix,
    base_exec_prefix     = config$BaseExecPrefix,
    virtualenv           = virtualenv,
    virtualenv_activate  = virtualenv_activate,
    executable           = config$Executable, # sys.executable
    base_executable      = config$BaseExecutable, # sys._base_executable; exe for venv starter
    version_string       = version_string,
    version              = version,
    architecture         = architecture,
    anaconda             = anaconda,
    conda                = config$IsConda,
    numpy                = numpy,
    required_module      = required_module,
    required_module_path = required_module_path,
    available            = FALSE,
    python_versions      = python_versions,
    forced               = forced
  )

  class(info) <- "py_config"
  info
}

#' @export
str.py_config <- function(object, ...) {
  NextMethod()
}

#' @export
format.py_config <- function(x, ...) {

  out <- ""
  out <- paste0(out, "python:         ", x$python, "\n")
  out <- paste0(out, "libpython:      ", ifelse(is.null(x$libpython), "[NOT FOUND]", x$libpython), ifelse(is_windows() || is.null(x$libpython) || is.na(x$libpython) || file.exists(x$libpython), "", "[NOT FOUND]"), "\n")
  out <- paste0(out, "pythonhome:     ", ifelse(is.null(x$pythonhome), "[NOT FOUND]", x$pythonhome), "\n")

  if (nzchar(x$virtualenv_activate))
    out <- paste0(out, "virtualenv:     ", x$virtualenv_activate, "\n")

  out <- paste0(out, "version:        ", x$version_string, "\n")

  if (is_windows())
    out <- paste0(out, "Architecture:   ", x$architecture, "\n")

  if (!is.null(x$numpy)) {
    out <- paste0(out, "numpy:          ", x$numpy$path, "\n")
    out <- paste0(out, "numpy_version:  ", as.character(x$numpy$version), "\n")
  } else {
    out <- paste0(out, "numpy:           [NOT FOUND]\n")
  }

  if (!is.null(x$required_module)) {
    out <- paste0(out, sprintf("%-16s", paste0(x$required_module, ":")))
    if (!is.null(x$required_module_path))
      out <- paste0(out, x$required_module_path, "\n")
    else
      out <- paste0(out, "[NOT FOUND]\n")
  }

  if (!is.null(x$forced)) {
    out <- paste0(out, "\nNOTE: Python version was forced by ", x$forced, "\n")
  }

  if (length(x$python_versions) > 1) {
    out <- paste0(out, "\npython versions found: \n")
    python_versions <- paste0(" ", x$python_versions, collapse = "\n")
    out <- paste0(out, python_versions, sep = "\n")
  }

  out
}

#' @export
print.py_config <- function(x, ...) {
  cat(format(x))
}


is_windows <- function() {
  identical(.Platform$OS.type, "windows")
}

is_unix <- function() {
  identical(.Platform$OS.type, "unix")
}

is_osx <- function() {
  Sys.info()["sysname"] == "Darwin"
}

is_macos <- is_osx

is_linux <- function() {
  identical(tolower(Sys.info()[["sysname"]]), "linux")
}

is_ubuntu <- function() {
  # check /etc/lsb-release
  if (is_unix() && file.exists("/etc/lsb-release")) {
    lsbRelease <- readLines("/etc/lsb-release")
    any(grepl("Ubuntu", lsbRelease))
  } else {
    FALSE
  }
}


is_fedora <- function() {
  if (is_unix() && file.exists("/etc/os-release")) {
    os_info <- readLines("/etc/os-release")
    any(grepl("Fedora", os_info))
  } else {
    FALSE
  }
}

is_rstudio <- function() {
  exists("RStudio.Version", envir = globalenv())
}

is_rstudio_desktop <- function() {
  if (!exists("RStudio.Version", envir = globalenv()))
    return(FALSE)

  RStudio.Version <- get("RStudio.Version", envir = globalenv())
  version <- RStudio.Version()
  identical(version$mode, "desktop")
}

clean_version <- function(version) {
  gsub("\\.$", "", gsub("[A-Za-z_+].*$", "", version))
}

reticulate_python_versions <- function() {

  # python versions to return
  python_versions <- c()

  # get versions specified via use_* functions
  reticulate_python_options <- .globals$use_python_versions

  # determine python versions to return
  if (length(reticulate_python_options) > 0) {
    for (i in 1:length(reticulate_python_options)) {
      python <- normalize_python_path(reticulate_python_options[[i]])
      if (python$exists)
        python_versions <- c(python_versions, python$path)
    }
  }

  # return them
  python_versions
}


normalize_python_path <- function(python) {

  # normalize trailing slash and expand
  python <- gsub("[\\/]+$", "", python)
  python <- path.expand(python)

  # check for existence
  if (!utils::file_test("-d", python) &&
      !utils::file_test("-f", python)) {
    list(
      path = python,
      exists = FALSE
    )
  } else {

    # append binary if it's a directory
    if (utils::file_test("-d", python))
      python <- file.path(python, "python")

    # append .exe if necessary on windows
    # accept .bat for pyenv-win shim
    if (is_windows() && (!grepl("^.*\\.(exe|bat)$", tolower(python))))
      python <- paste0(python, ".exe")

    # return
    list(
      path = python,
      exists = TRUE
    )
  }

}


windows_registry_anaconda_versions <- function() {
  rbind(read_python_versions_from_registry("HCU", key = "ContinuumAnalytics", type = "Anaconda"),
        read_python_versions_from_registry("HLM", key = "ContinuumAnalytics", type = "Anaconda"))
}

read_python_versions_from_registry <- function(hive, key, type=key) {

  python_core_key <- tryCatch(utils::readRegistry(
    key = paste0("SOFTWARE\\Python\\", key), hive = hive, maxdepth = 3),
    error = function(e) NULL)


  types <- c()
  hives <- c()
  install_paths <- c()
  executable_paths <- c()
  versions <- c()
  archs <- c()

  if (length(python_core_key) > 0) {
    for (version in names(python_core_key)) {
      version_key <- python_core_key[[version]]
      if (is.list(version_key) && !is.null(version_key$InstallPath)) {
        version_dir <- version_key$InstallPath$`(Default)`
        if (!is.null(version_dir) && utils::file_test("-d", version_dir)) {

          # determine install_path and executable_path
          install_path <- version_dir
          executable_path <- file.path(install_path, "python.exe")

          # proceed if it exists
          if (file.exists(executable_path)) {

            # determine version and arch
            if (type == "Anaconda") {
              matches <- regexec("^Anaconda.*(32|64).*$", version)
              matches <- regmatches(version, matches)[[1]]
              if (length(matches) == 2) {
                version <- version_key$SysVersion
                arch <- matches[[2]]
              } else {
                warning("Unexpected format for Anaconda version: ", version,
                        "\n(Please install a more recent version of Anaconda)")
                arch <- NA
              }
            } else { # type == "PythonCore"
              matches <- regexec("^(\\d+)\\.(\\d+)(?:-(32|64))?$", version)
              matches <- regmatches(version, matches)[[1]]
              if (length(matches) == 4) {
                version <- paste(matches[[2]], matches[[3]], sep = ".")
                arch <- matches[[4]]
                if (!nzchar(arch)) {
                  if (numeric_version(version) >= "3.0")
                    arch <- "64"
                  else {
                    python_arch <- python_arch(executable_path)
                    arch <- gsub("bit", "", python_arch, fixed = TRUE)
                  }
                }
              } else {
                warning("Unexpected format for PythonCore version: ", version)
                arch <- NA
              }
            }

            if (!is.na(arch)) {
              # convert to R arch
              if (arch == "32")
                arch <- "i386"
              else if (arch == "64")
                arch <- "x64"

              # append to vectors
              types <- c(types, type)
              hives <- c(hives, hive)
              install_paths <- c(install_paths, utils::shortPathName(install_path))
              executable_paths <- c(executable_paths, utils::shortPathName(executable_path))
              versions <- c(versions, version)
              archs <- c(archs, arch)
            }
          }
        }
      }
    }
  }

  data.frame(
    type = types,
    hive = hives,
    install_path = install_paths,
    executable_path = executable_paths,
    version = versions,
    arch = archs,
    stringsAsFactors = FALSE
  )
}


# get the architecture from a python binary
python_arch <- function(python) {

  # run command
  result <- system2(python, stdout = TRUE, args = c("-c", shQuote(
    "import sys; import platform; sys.stdout.write(platform.architecture()[0])")))

  # check for error
  error_status <- attr(result, "status")
  if (!is.null(error_status))
    stop("Error ", error_status, " occurred while checking for python architecture", call. = FALSE)

  # return arch
  result

}

# convert R arch to python arch
current_python_arch <- function() {
  if (.Platform$r_arch == "i386")
    "32bit"
  else if (.Platform$r_arch == "x64")
    "64bit"
  else
    "Unknown"
}


# check for compatible architecture
is_incompatible_arch <- function(config) {
  if (is_windows()) {
    !identical(current_python_arch(),config$architecture)
  } else {
    FALSE
  }
}


py_session_initialized_binary <- function() {

  # binary to return
  python_binary <- NULL

  # check environment variable
  py_session <- Sys.getenv("PYTHON_SESSION_INITIALIZED", unset = NA)
  if (!is.na(py_session)) {
    py_session <- strsplit(py_session, ":", fixed = TRUE)[[1]]
    py_session <- strsplit(py_session, "=", fixed = TRUE)
    keys <- character()
    py_session <- lapply(py_session, function(x) {
      keys <<- c(keys, x[[1]])
      x[[2]]
    })
    if (all(c("current_pid", "sys.executable") %in% keys)) {
      names(py_session) <- keys
      # verify it's from the current process
      if (identical(as.character(Sys.getpid()), py_session$current_pid)) {
        python_binary <- py_session$sys.executable
      }
    } else {
      warning("PYTHON_SESSION_INITIALIZED does not include current_pid and sys.executable",
              call. = FALSE)
    }
  }

  # return
  python_binary
}
