"""
This module is responsible for finding the necessary programs for all of the
desired calculations in the MMPBSA calculation.

Methods:
         find_progs(INPUT): Determines which programs are needed and sees if
                            they can be found. Returns dictionary of programs
         which(program): Internal; searches AMBERHOME/bin and optionally
                         PATH to see if a program can be found

Classes: ExternProg: External program class
"""

from MMPBSA_mods.exceptions import MMPBSA_Error

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def find_progs(INPUT):
   """ Find the necessary programs based in the user INPUT """
   # List all of the used programs with the conditions that they are needed
   used_progs = { 'cpptraj' : True,
                  'ptraj' : bool(INPUT['entropy']),
                  'mmpbsa_py_energy' : ((INPUT['pbrun'] or INPUT['gbrun'])
                                        and not (INPUT['use_sander'] or
                                                 INPUT['decomprun'])),
                  'sander' : (INPUT['decomprun'] or INPUT['use_sander'] or
                              INPUT['ifqnt'] == 1),
                  'sander.APBS' : INPUT['sander_apbs'] == 1,
                  'mmpbsa_py_nabnmode' : INPUT['nmoderun'],
                  'rism3d.snglpnt' : INPUT['rismrun']
                }

   # The returned dictionary:
   my_progs = {}

   search_path = INPUT['search_path']

   for prog in used_progs.keys():
      my_progs[prog] = ExternProg(prog, used_progs[prog], search_path)
      if used_progs[prog]: 
         if not my_progs[prog].full_path:
            raise MMPBSA_Error('Could not find necessary program [%s]' % prog)
         print '%s found! Using %s' % (prog, str(my_progs[prog]))
   
   return my_progs

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def which(program, search_path = False):
   """ Searches for a program in $AMBERHOME first, then PATH if we allow
       PATH searching.
   """
   import os

   def is_exe(filename):
      return os.path.exists(filename) and os.access(filename, os.X_OK)

   def get_amberhome():
      ambhome = os.getenv('AMBERHOME')
      if ambhome == None:
         raise MMPBSA_Error('AMBERHOME is not set!') 
      return ambhome

   # Check to see that a path was provided in the program name
   fpath, fname = os.path.split(program)
   if fpath:
      if is_exe(program): return program

   # If not (and it generally isn't), then look in AMBERHOME
   amberhome = get_amberhome()

   if is_exe(os.path.join(amberhome, 'bin', program)):
      return os.path.join(amberhome, 'bin', program)

   # If we can search the path, look through it
   if search_path:
      for path in os.environ["PATH"].split(os.pathsep):
         exe_file = os.path.join(path, program)
         if is_exe(exe_file):
            return exe_file # if it's executable, return the file

   return None  # if program can still not be found... return None

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class ExternProg(object):
   """ An external program """
   def __init__(self, prog_name, needed=False, search_path=False):
      # We need to initialize the program name that we're looking for, whether
      # or not it is necessary by default, and the conditions upon which we
      # must look for it. The full_path is the attribute that stores this
      # program's full PATH name. We also need to know if we are going to search
      # through the whole PATH or just AMBERHOME.
      self.prog_name = prog_name
      self.full_path = None
      self.search_path = search_path
      if needed: self.find()

   def find(self):
      """ Find the program """
      self.full_path = which(self.prog_name, self.search_path)

   def __str__(self):
      if self.full_path:
         return self.full_path
      else:
         return self.prog_name

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