tf_diff: Humanizing the output of `terraform plan` using python `difflib` module

tf_diff.py

#!/usr/bin/env python3
#
# `tf_diff` is a CLI tool for humanizing the output of `terraform plan` using python `difflib` module
# Requirements:
# 1. Python 3.x
# 2. If you want color output then you need to install a python module `colorama` (pip install colorama)
#
# Installation:
# Copy the file into your `bin` directory and make it executable (chmod u+x ~/bin/tf_diff)
#
# Usage:
# terraform plan ... | tf_plan

import sys, os, time, difflib, optparse, re

try:
    from colorama import Fore, Back, Style, init
    init()
except ImportError:  # fallback so that the imported classes always exist
    class ColorFallback():
        __getattr__ = lambda self, name: ''
    Fore = Back = Style = ColorFallback()

def color_diff(diff):
    for line in diff:
        if line.startswith('---') or line.startswith('+++'):
            yield Fore.WHITE + escape_ansi(line).strip('\n') + Fore.RESET
        elif line.startswith('@@'):
            yield Fore.CYAN + escape_ansi(line).strip('\n') + Fore.RESET
        elif line.startswith('+'):
            yield Fore.GREEN + line + Fore.RESET
        elif line.startswith('-'):
            yield Fore.RED + line + Fore.RESET
        elif line.startswith('^'):
            yield Fore.BLUE + line + Fore.RESET
        else:
            yield line


START_MARKER = "Terraform will perform the following actions:"

# Remove the ANSI escape sequences from a string in python
def escape_ansi(line):
    ansi_escape = re.compile(r'(\x9B|\x1B\[)[0-?]*[ -/]*[@-~]')
    return ansi_escape.sub('', line)

def print_line(line):
    print(line, end='', flush=True)


def main():
    usage = "usage: %prog [options]"
    parser = optparse.OptionParser(usage)
    parser.add_option("-c", action="store_true", default=False,
                      help='Produce a context format diff')
    parser.add_option("-u", action="store_true", default=False,
                      help='Produce a unified format diff (default)')
    parser.add_option("-n", action="store_true", default=False,
                      help='Produce a ndiff format diff')
    parser.add_option("-l", "--lines", type="int", default=3,
                      help='Set number of context lines (default 3)')
    (options, args) = parser.parse_args()

    n = options.lines

    state = "init"
    content_name = ""
    content_line = ""

    rx = re.compile(r"\\$", flags=re.MULTILINE)

    for line in sys.stdin:
        if line is None or line == "" or line.strip() == "":
            print_line(line)

        if state == "init":
            if line.startswith(START_MARKER):
                state = "analyze"
            print_line(line)

        elif state == "analyze":
            if escape_ansi(line).strip().startswith("~"):
                state = "expect_content"
                content_name = line.strip()[2:]
            print_line(line)

        elif state == "expect_content":
            res = escape_ansi(line).strip().split(':', 1)
            if len(res) != 2:
                continue
            line = res[1]

            content_line = line.strip()
            content_line = content_line.replace("\\n", "\n")
            content_line = content_line.replace("\\\"", "\"")
            content_line = rx.sub("", content_line)

            left_content, right_content = content_line.split(" => ")
            left_content = left_content.strip("\" ")
            right_content = right_content.strip("\" ")

            left_lines = left_content.split("\n")
            right_lines = right_content.split("\n")

            if options.c:
                diff = difflib.context_diff(left_lines,
                                            right_lines,
                                            "%s old" % content_name,
                                            "%s new" % content_name,
                                            n=n)
            elif options.n:
                diff = difflib.ndiff(left_lines, right_lines)
            else:
                diff = difflib.unified_diff(left_lines,
                                            right_lines,
                                            "%s old" % content_name,
                                            "%s new" % content_name,
                                            n=n)
            # reset color
            print(Fore.RESET, end='')
            diff = color_diff(diff)
            for line in diff:
                print("   ", line.strip("\n"))

            # switch back to analyze phase
            state = "analyze"


if __name__ == "__main__":
    main()