#!/usr/bin/env python
"""

  The idea is to try and import a package and if the import fails 
  then try to download and install the package.

  Yes, you can put the package as a dependency in your pip config for 
  your code.  This is intended for the case when you have a bunch of 
  python libs in some shared repository in your organization.  People 
  check the code out and expect it to run but it has third party 
  dependencies.  There is no install step for your code, per se.

  Tasks.. 
      - tcl/tk ui when cmd line not available (etc wxpython, qt and so on if available).
      - batch require? ask only once for a list of packages

"""
import importlib
import pip
import sys


class IRequireUI:

    @classmethod
    def is_available(cls):
       pass

    def query_do_install(self, package_name):
        return False

    def announce(self, msg):
        pass


class NeverInstallUI(IRequireUI):

    @classmethod
    def is_available(cls):
       return True

    def query_do_install(self, package_name):
        return False

class AlwaysInstallUI(IRequireUI):

    @classmethod
    def is_available(cls):
       return True

    def query_do_install(self, package_name):
        return True


class CmdLineUI(IRequireUI):

    @classmethod
    def is_available(cls):
        return sys.stdin.isatty()

    def query_do_install(self, package_name):
        print("Package: %s needs to install package: %s" % 
              (package_name, package_name))
        print("Type 'y' to install this package or 'n' to exit")

        while True:
            response = raw_input().lower()
            if response in ("y", "yes"):
                return True
            elif response in ("n", "no"):
                return False
            else:
                print("Please enter 'yes' or 'no' to proceed.")            
        return

    def announce(self, msg):
        print(msg)
    


_uis = [NeverInstallUI(), ]

if CmdLineUI.is_available():
    _uis.append(CmdLineUI())


# 
_verbose = True
_require_ui = _uis[-1]
_install_as_root = False


def require(package_name):
    """
    Check if a package is installed.  If it isn't ask the user whether we should 
    download and install it.  If they say yes do what they asked.

    """    
    # try and import the module
    try:
        importlib.import_module(package_name)
    except ImportError:

        # if it fails then we want to ask permission to install?
        if _require_ui.query_do_install(package_name):

            args = ["install" ]
            if not _install_as_root:
                if _verbose:
                    _require_ui.announce("Installing for user!");
                args.append("--user")            
            args.append(package_name)

            try:
                pip.main(args)
            except error:
                _require_ui.announce("Install of %s failed!" % package_name);
                return False
            else:
                if _verbose:
                    _require_ui.announce("Install of %s succeeded." % package_name);
                return True
        else:
            _require_ui.announce("User declined to install package: %s" % package_name)
            return False
    else:

        # if it succeeds we don't have to do any work
        if _verbose:
            _require_ui.announce("Package %s is installed." % package_name)
        return True

    return True


if __name__ == "__main__":

    # proposition is that these would be called as pip.require("foo")
    require("redis")
    require("logist")