ScribeJS commandline logfile dumper and filtering tool (python 3)

logcat.py

#!/usr/bin/env python

import json
import argparse
import itertools
import time

from dateutil.parser import parse
import datetime

# date parser
class ParseDate(argparse.Action):
	def __init__(self, option_strings, dest, nargs=None, **kwargs):
		super().__init__(option_strings, dest, **kwargs)

	def __call__(self, parser, namespace, values, option_string=None):
		setattr(namespace, self.dest, parse(values))

# simple follow iterator
def follow(fp):
    fp.seek(0,2) # Go to the end of the file
    while True:
        line = fp.readline()
        if not line:
            time.sleep(1) # Sleep briefly
            continue
        yield line

# argument parser setup
parser = argparse.ArgumentParser(description='Show a ScribeJS logfile.')
parser.add_argument(
	'-t', '--tag',
	type=str,
	action='append',
	nargs=1,
	help='only show log lines with this tag'
)
parser.add_argument(
	'--from',
	type=str,
	action=ParseDate,
	nargs=1,
	dest='from_date',
	help='earliest date to show'
)
parser.add_argument(
	'--to',
	type=str,
	action=ParseDate,
	nargs=1,
	dest='to_date',
	help='latest date to show'
)
parser.add_argument(
	'--type',
	type=str,
	nargs=1,
	dest='type',
	help='type of log messages to show (log|error|info)'
)
parser.add_argument(
	'--file',
	type=str,
	nargs=1,
	action='append',
	dest='file_filter',
	help='only show log entries from that file'
)
parser.add_argument(
	'-c', '--color',
	action='store_true',
	help='if this flag is set display original colored ScribeJS output'
)
parser.add_argument(
	'-f', '--follow',
	action='store_true',
	dest='follow',
	help='follow the log output while the file is written to (like tail -f)'
)
parser.add_argument(
	'file',
	nargs='*',
	type=str,
	help='file to process'
)

args = parser.parse_args()
if args.tag: # flatmap tag list
	args.tag = list(itertools.chain(*args.tag))
if args.file_filter: # flatmap file filter list
	args.file_filter = list(itertools.chain(*args.file_filter))

# bail out on invalid parameter combinations
if args.follow and len(args.file) > 1:
	print("You cannot follow multiple files currently!")
	exit(1)

for file in args.file:

	# if we're going to show multiple files display file headers
	if len(args.file) > 1:
		print(40 * '-')
		print(file)
		print(40 * '-')

	# open the file
	with open(file, 'r') as fp:

		# determine if we follow the file or just dump it completely
		iterator = fp
		if args.follow:
			iterator = follow(fp)

		# iterate over lines
		for line in iterator:

			# parse object
			j = json.loads(line)
			display = True

			# apply type filter
			if args.type:
				display = (j['type'] == args.type[0])

			# apply tag filter (tags are _OR_)
			if args.tag and display:
				display = False
				for tag in j['context']['tags']:
					if tag in args.tag:
						display = True
						break

			# apply from and to date filters
			t = datetime.datetime.utcfromtimestamp(j['context']['time']/1000)
			if args.from_date and display:
				display = t > args.from_date
			if args.to_date and display:
				display = t < args.to_date

			# apply file name filter
			if args.file_filter and display:
				display = False
				for file_filter in args.file_filter:
					if j['context']['location']['filename'] == file_filter:
						display = True
						break

			# all filters determined we want to display the line?
			if display:

				# if the user chose --color, we just dump the original line with fixed indents
				if args.color:
					indent = len(j['contextString'])
					esc = j['contextString'].count('\u001b')
					indent -= esc * 5
					print(j['message'].replace('\n', '\n' + (indent * ' ')))
				else:
					# user did not want color, build a log line ourselves
					indent = 20
					tags = ''

					# exclude tags the user filtered for as they have to be there
					for tag in j['context']['tags']:
						if not args.tag or tag not in args.tag:
							tags += ' [' + tag + ']'
					indent += len(tags)

					# fix indent
					msg = j['argsString'].replace('\n', '\n' + (indent * ' '))

					# print log line
					print('{:%Y-%m-%d %H:%M:%S}{} {}'.format(t, tags, msg))