# Include file that implements 'getEnv' and friends. Do not import it!

when not declared(os) and not declared(ospaths):
  {.error: "This is an include file for os.nim!".}

from parseutils import skipIgnoreCase

proc c_getenv(env: cstring): cstring {.
  importc: "getenv", header: "<stdlib.h>".}
proc c_putenv(env: cstring): cint {.
  importc: "putenv", header: "<stdlib.h>".}

# Environment handling cannot be put into RTL, because the ``envPairs``
# iterator depends on ``environment``.

var
  envComputed {.threadvar.}: bool
  environment {.threadvar.}: seq[string]

when defined(windows) and not defined(nimscript):
  # because we support Windows GUI applications, things get really
  # messy here...
  when useWinUnicode:
    when defined(cpp):
      proc strEnd(cstr: WideCString, c = 0'i32): WideCString {.
        importcpp: "(NI16*)wcschr((const wchar_t *)#, #)", header: "<string.h>".}
    else:
      proc strEnd(cstr: WideCString, c = 0'i32): WideCString {.
        importc: "wcschr", header: "<string.h>".}
  else:
    proc strEnd(cstr: cstring, c = 0'i32): cstring {.
      importc: "strchr", header: "<string.h>".}

  proc getEnvVarsC() =
    if not envComputed:
      environment = @[]
      when useWinUnicode:
        var
          env = getEnvironmentStringsW()
          e = env
        if e == nil: return # an error occurred
        while true:
          var eend = strEnd(e)
          add(environment, $e)
          e = cast[WideCString](cast[ByteAddress](eend)+2)
          if eend[1].int == 0: break
        discard freeEnvironmentStringsW(env)
      else:
        var
          env = getEnvironmentStringsA()
          e = env
        if e == nil: return # an error occurred
        while true:
          var eend = strEnd(e)
          add(environment, $e)
          e = cast[cstring](cast[ByteAddress](eend)+1)
          if eend[1] == '\0': break
        discard freeEnvironmentStringsA(env)
      envComputed = true

else:
  const
    useNSGetEnviron = (defined(macosx) and not defined(ios)) or defined(nimscript)

  when useNSGetEnviron:
    # From the manual:
    # Shared libraries and bundles don't have direct access to environ,
    # which is only available to the loader ld(1) when a complete program
    # is being linked.
    # The environment routines can still be used, but if direct access to
    # environ is needed, the _NSGetEnviron() routine, defined in
    # <crt_externs.h>, can be used to retrieve the address of environ
    # at runtime.
    proc NSGetEnviron(): ptr cstringArray {.
      importc: "_NSGetEnviron", header: "<crt_externs.h>".}
  else:
    var gEnv {.importc: "environ".}: cstringArray

  proc getEnvVarsC() =
    # retrieves the variables of char** env of C's main proc
    if not envComputed:
      environment = @[]
      when useNSGetEnviron:
        var gEnv = NSGetEnviron()[]
      var i = 0
      while true:
        if gEnv[i] == nil: break
        add environment, $gEnv[i]
        inc(i)
      envComputed = true

proc findEnvVar(key: string): int =
  getEnvVarsC()
  var temp = key & '='
  for i in 0..high(environment):
    when defined(windows):
      if skipIgnoreCase(environment[i], temp) == len(temp): return i
    else:
      if startsWith(environment[i], temp): return i
  return -1

proc getEnv*(key: string, default = ""): TaintedString {.tags: [ReadEnvEffect].} =
  ## Returns the value of the `environment variable`:idx: named `key`.
  ##
  ## If the variable does not exist, `""` is returned. To distinguish
  ## whether a variable exists or it's value is just `""`, call
  ## `existsEnv(key) proc <#existsEnv,string>`_.
  ##
  ## See also:
  ## * `existsEnv proc <#existsEnv,string>`_
  ## * `putEnv proc <#putEnv,string,string>`_
  ## * `envPairs iterator <#envPairs.i>`_
  runnableExamples:
    assert getEnv("unknownEnv") == ""
    assert getEnv("unknownEnv", "doesn't exist") == "doesn't exist"

  when nimvm:
    discard "built into the compiler"
  else:
    var i = findEnvVar(key)
    if i >= 0:
      return TaintedString(substr(environment[i], find(environment[i], '=')+1))
    else:
      var env = c_getenv(key)
      if env == nil: return TaintedString(default)
      result = TaintedString($env)

proc existsEnv*(key: string): bool {.tags: [ReadEnvEffect].} =
  ## Checks whether the environment variable named `key` exists.
  ## Returns true if it exists, false otherwise.
  ##
  ## See also:
  ## * `getEnv proc <#getEnv,string,string>`_
  ## * `putEnv proc <#putEnv,string,string>`_
  ## * `envPairs iterator <#envPairs.i>`_
  runnableExamples:
    assert not existsEnv("unknownEnv")

  when nimvm:
    discard "built into the compiler"
  else:
    if c_getenv(key) != nil: return true
    else: return findEnvVar(key) >= 0

proc putEnv*(key, val: string) {.tags: [WriteEnvEffect].} =
  ## Sets the value of the `environment variable`:idx: named `key` to `val`.
  ## If an error occurs, `OSError` is raised.
  ##
  ## See also:
  ## * `getEnv proc <#getEnv,string,string>`_
  ## * `existsEnv proc <#existsEnv,string>`_
  ## * `envPairs iterator <#envPairs.i>`_

  # Note: by storing the string in the environment sequence,
  # we guarantee that we don't free the memory before the program
  # ends (this is needed for POSIX compliance). It is also needed so that
  # the process itself may access its modified environment variables!
  when nimvm:
    discard "built into the compiler"
  else:
    var indx = findEnvVar(key)
    if indx >= 0:
      environment[indx] = key & '=' & val
    else:
      add environment, (key & '=' & val)
      indx = high(environment)
    when defined(windows) and not defined(nimscript):
      when useWinUnicode:
        var k = newWideCString(key)
        var v = newWideCString(val)
        if setEnvironmentVariableW(k, v) == 0'i32: raiseOSError(osLastError())
      else:
        if setEnvironmentVariableA(key, val) == 0'i32: raiseOSError(osLastError())
    else:
      if c_putenv(environment[indx]) != 0'i32:
        raiseOSError(osLastError())

iterator envPairs*(): tuple[key, value: TaintedString] {.tags: [ReadEnvEffect].} =
  ## Iterate over all `environments variables`:idx:.
  ##
  ## In the first component of the tuple is the name of the current variable stored,
  ## in the second its value.
  ##
  ## See also:
  ## * `getEnv proc <#getEnv,string,string>`_
  ## * `existsEnv proc <#existsEnv,string>`_
  ## * `putEnv proc <#putEnv,string,string>`_
  getEnvVarsC()
  for i in 0..high(environment):
    var p = find(environment[i], '=')
    yield (TaintedString(substr(environment[i], 0, p-1)),
           TaintedString(substr(environment[i], p+1)))
