'''
This is a basic Python program to allow a user of mongodb to login with her
user name and password and perform some basic operations. Here are the 
steps.

1. Import the MongoClient package from pymongo as
   from pymongo import MongoClient

2. Connect to the mongodb server as
   client = MongoClient('mongodb://eg-mongodb.bucknell.edu')

   Note that the client connection doesn't contain user name or password.

3. Select the database to be used as
   db = client.[db-name]
   e.g.,
   db = client.xmeng

   Note that here the database we connect to in the example is 'xmeng', 
   one should choose a valid database.

4. Authenticate with proper user name and password as
   db.authenticate('user-name', 'password')

   The operation should return 'true' if succeeding, 'false' otherwise.
'''
from pymongo import MongoClient
from getpass import getpass
import sys

def connectDB():
    """Connect to DB with given credentials
       Use input redict to avoid typing on the terminal directly"""

    the_url      = 'mongodb://eg-mongodb.bucknell.edu'
    the_user     = input('User name : ')   # owner
    print('Password : ', end = '')         # non-echo to read password
    the_pass     = getpass()

    client      = MongoClient(the_url)
    db          = client.xmeng                        # database name is xmeng
    try:
        auth_result = db.authenticate(the_user, the_pass)# auth for this db only
        print('authentication result : ' + str(auth_result))
        if (auth_result == True):
            return db
        else:
            return None
    except:
        print('Authentication problem')
        sys.exit(1)

def testInsert():
    """Inser a doc into the 'post' collection"""
    print('Insert a doc into the "post" collection ...')
    insrt_result = db.post.insert_one({"title":"fifth world", "by":"newcomer", "likes":28})
    print(insrt_result)

def printDocs(docs):
    """Print the entire 'docs' collection"""
    i = 0
    for document in docs:
        print(str(i) + 'th doc : ', end = '')
        print(document)
        i = i + 1
        print()

    print('a total of ' + str(i) + ' documents.')

def printAll(db):
    """Retrieve and print the entire 'post' colletion"""
    '''
    cursor = db.post.find()    # query the 'post' collection
                               # without criteria returns all docs

    print('----- Entire database ----- ')
    printDocs(cursor)
    '''
    db.post.find().pretty()

def testQuery(db):
    """Query by specified condition on a field (column)"""
    cursor = db.post.find({"likes":{"$gt":25}})

    print('----- All documents that have more than 25 "likes" ----- ')
    printDocs(cursor)

db = connectDB()
#testInsert()
printAll(db)
#testQuery(db)