#!/usr/bin/env python3
  
  import os
  import sys
  
  def bail(msg):
      print(msg, file=sys.stderr)
      sys.exit(1)
  
  _MARKER = '@@'
  def transform_line(line):
      # Substitute any special markers of this form:
      # @@ENV@@
      # with the value of ENV, split into meson array syntax.
      start = line.find(_MARKER)
      if start == -1:
          return line
  
      end = line.rfind(_MARKER)
      if end == start:
          return line
  
      # Lookup value of the env var.
      var = line[start+len(_MARKER):end]
      try:
          val = os.environ[var]
      except KeyError:
          bail('cannot generate meson.cross; env var %s not set' % var)
  
      # Transform into meson array.
      val = ["'%s'" % x for x in val.split()]
      val = ', '.join(val)
      val = '[%s]' % val
  
      before = line[:start]
      after = line[end+len(_MARKER):]
  
      return '%s%s%s' % (before, val, after)
  
  # Make sure this is really an SDK extraction environment.
  try:
      sysroot = os.environ['OECORE_NATIVE_SYSROOT']
  except KeyError:
      bail('OECORE_NATIVE_SYSROOT env var must be set')
  
  cross_file = os.path.join(sysroot, 'usr/share/meson/meson.cross')
  tmp_cross_file = '%s.tmp' % cross_file
  
  # Read through and transform the current meson.cross.
  lines = []
  with open(cross_file, 'r') as f:
      for line in f:
          lines.append(transform_line(line))
  
  # Write the transformed result to a tmp file and atomically rename it. In case
  # we crash during the file write, we don't want an invalid meson.cross file.
  with open(tmp_cross_file, 'w') as f:
      for line in lines:
          f.write(line)
      f.flush()
      os.fdatasync(f.fileno())
  os.rename(tmp_cross_file, cross_file)