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"""Option type for package Variables.

This file defines the option type for SCons implementing 'package activation'.

To be used whenever a 'package' may be enabled/disabled and the
package path may be specified.

Usage example:

  Examples:
      x11=no   (disables X11 support)
      x11=yes  (will search for the package installation dir)
      x11=/usr/local/X11 (will check this path for existence)

  To replace autoconf's --with-xxx=yyy ::


      opts = Variables()
      opts.Add(PackageVariable('x11',
                             'use X11 installed here (yes = search some places',
                             'yes'))
      ...
      if env['x11'] == True:
          dir = ... search X11 in some standard places ...
          env['x11'] = dir
      if env['x11']:
          ... build with x11 ...
"""

__all__ = ['PackageVariable',]

import SCons.Errors

__enable_strings  = ('1', 'yes', 'true',  'on', 'enable', 'search')
__disable_strings = ('0', 'no',  'false', 'off', 'disable')

def _converter(val):
    """
    """
    lval = val.lower()
    if lval in __enable_strings: return True
    if lval in __disable_strings: return False
    #raise ValueError("Invalid value for boolean option: %s" % val)
    return val


def _validator(key, val, env, searchfunc):
    # NB: searchfunc is currently undocumented and unsupported
    """
    """
    # TODO write validator, check for path
    import os
    if env[key] is True:
        if searchfunc:
            env[key] = searchfunc(key, val)
    elif env[key] and not os.path.exists(val):
        raise SCons.Errors.UserError(
            'Path does not exist for option %s: %s' % (key, val))


def PackageVariable(key, help, default, searchfunc=None):
    # NB: searchfunc is currently undocumented and unsupported
    """
    The input parameters describe a 'package list' option, thus they
    are returned with the correct converter and validator appended. The
    result is usable for input to opts.Add() .

    A 'package list' option may either be 'all', 'none' or a list of
    package names (separated by space).
    """
    help = '\n    '.join(
        (help, '( yes | no | /path/to/%s )' % key))
    return (key, help, default,
            lambda k, v, e: _validator(k,v,e,searchfunc),
            _converter)

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