#!/usr/bin/env python

__author__ = "Mislav Novakovic <mislav.novakovic@sartura.hr>"
__copyright__ = "Copyright 2016, Deutsche Telekom AG"
__license__ = "Apache 2.0"

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# This sample application demonstrates use of Python programming language bindings for sysrepo library.
# Original c application was rewritten in Python to show similarities and differences
# between the two.
#
# Most notable difference is in the very different nature of languages, c is weakly statically typed language
# while Python is strongly dynamiclally typed. Python code is much easier to read and logic easier to comprehend
# for smaller scripts. Memory safety is not an issue but lower performance can be expected.
#
# The original c implementation is also available in the source, so one can refer to it to evaluate trade-offs.

import libsysrepoPython2 as sr
import sys

# Helper function for printing changes given operation, old and new value.
def print_change(op, old_val, new_val):
    if (op == sr.SR_OP_CREATED):
           print "CREATED: ",
           print new_val.to_string(),
    elif (op == sr.SR_OP_DELETED):
           print "DELETED: ",
           print old_val.to_string(),
    elif (op == sr.SR_OP_MODIFIED):
           print "MODIFIED: ",
           print "old value",
           print old_val.to_string(),
           print "new value",
           print new_val.to_string(),
    elif (op == sr.SR_OP_MOVED):
        print "MOVED: " + new_val.xpath() + " after " + old_val.xpath()

# Helper function for printing events.
def ev_to_str(ev):
    if (ev == sr.SR_EV_VERIFY):
        return "verify"
    elif (ev == sr.SR_EV_APPLY):
        return "apply"
    elif (ev == sr.SR_EV_ABORT):
        return "abort"
    else:
        return "abort"

# Function to print current configuration state.
# It does so by loading all the items of a session and printing them out.
def print_current_config(session, module_name):
    select_xpath = "/" + module_name + ":*//*"

    values = session.get_items(select_xpath)

    for i in range(values.val_cnt()):
        print values.val(i).to_string(),

# Function to be called for subscribed client of given session whenever configuration changes.
def module_change_cb(sess, module_name, event, private_ctx):
    print "\n\n ========== CONFIG HAS CHANGED, CURRENT RUNNING CONFIG: ==========\n"

    try:
        print "\n\n ========== Notification " + ev_to_str(event) + " =============================================\n"
        if (sr.SR_EV_APPLY == event):
            print "\n ========== CONFIG HAS CHANGED, CURRENT RUNNING CONFIG: ==========\n"
            print_current_config(sess, module_name);

        print "\n ========== CHANGES: =============================================\n"

        change_path = "/" + module_name + ":*"

        it = sess.get_changes_iter(change_path);

        while True:
            change = sess.get_change_next(it)
            if change == None:
                break
            print_change(change.oper(), change.old_val(), change.new_val())

        print "\n\n ========== END OF CHANGES =======================================\n"

    except Exception as e:
        print e

    return sr.SR_ERR_OK

# Notable difference between c implementation is using exception mechanism for open handling unexpected events.
# Here it is useful because `Conenction`, `Session` and `Subscribe` could throw an exception.
try:
    module_name = "ietf-interfaces"
    if len(sys.argv) > 1:
        module_name = sys.argv[1]
    else:
        print "\nYou can pass the module name to be subscribed as the first argument"

    print "Application will watch for changes in " +  module_name + "\n"

    # connect to sysrepo
    conn = sr.Connection("example_application")

    # start session
    sess = sr.Session(conn)

    # subscribe for changes in running config */
    subscribe = sr.Subscribe(sess)

    subscribe.module_change_subscribe(module_name, module_change_cb)

    print "\n\n ========== READING STARTUP CONFIG: ==========\n"
    try:
        print_current_config(sess, module_name);
    except Exception as e:
        print e

    print "\n\n ========== STARTUP CONFIG APPLIED AS RUNNING ==========\n"

    sr.global_loop()

    print "Application exit requested, exiting.\n";

except Exception as e:
    print e
