#!/usr/bin/env python
"""Script to smartly chop off portions of the current working directory for
use in the shell prompt"""

from __future__ import print_function
import os

# Constants used to decide when to start chopping
DIRLIM = 5
DIR_L = 3
DIR_R = 2
PWDLEN = 14

def smartwd():
    """Meat of the smartwd script"""
    username = os.environ['USER']
    homedir = os.environ['HOME']
    pwd = os.environ['PWD']

    path = pwd.split('/')

    # Ignore the root path
    if len(path) == 1:
        return pwd

    try:
        username_index = path.index(username)
    except ValueError:
        username_index = None

    if username_index is not None:
        prefix = '/'.join(path[:username_index+1])

        if prefix == homedir:
            pre_path = '~'
        else:
            # The first element is always the empty string.
            # We want the first 4 characters of the second element
            pre_path = path[1][:4] + '~'

        del path[:username_index]
        path[0] = pre_path

        pwd = '/'.join(path)

        # If we exceed the dirlimit and the length of the joined pwd,
        # replace the pwd with left and right elements, with ellipses
        # in between to simulate a long path.
        if len(path) > DIRLIM and len(pwd) > PWDLEN:
            newpwd = '/'.join(path[:DIR_L] + ['...'] + path[-DIR_R:])

            if len(newpwd) < len(pwd):
                pwd = newpwd

    return pwd

if __name__ == "__main__":
    print(smartwd())