json-log

#!/usr/bin/python3
import sys
import json
import argparse
from jinja2 import Environment, FileSystemLoader

FIELDS = '@fields'
DEFAULT_TEMPLATE = '[{{timestamp}}] {{fields.level}} {{message}}'


def make_log_filter(condition=None):
    if condition is not None:
        split_condition = condition.split('=')
        field = split_condition[0].split('.')[1]
        value = split_condition[1]
        condition = {field: value}
    else:
        condition = {}

    def filter(entry):
        for k, v in condition.items():
            if entry[FIELDS][k] not in v:
                return False
        return True

    return filter


def make_formatter(template_file=None):
    if template_file is not None:
        env = Environment(loader=FileSystemLoader(searchpath='/'))
        template = env.get_template(template_file)
    else:
        template = Environment().from_string(DEFAULT_TEMPLATE)

    def render(entry):
        for k, v in entry.items():
            if k.startswith('@'):
                del entry[k]
                entry[k.lstrip('@')] = v
        return template.render(**entry)

    return render


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Read from stdin and filter json-like log')
    parser.add_argument('--filter', dest='condition', help='Filter condition')
    parser.add_argument('--template', dest='template', help='Formatting template.')
    args = parser.parse_args()

    line_filter = make_log_filter(args.condition)
    formatter = make_formatter(args.template)

    try:
        for line in map(formatter, filter(line_filter, map(json.loads, sys.stdin))):
            print(line)
    except KeyboardInterrupt:
        print('Stopped')
        sys.exit(0)
    except ValueError:
        print('Log entry is not valid json')
        sys.exit(1)
    except IndexError:
        print('Wrong format of filter. Please use @fields.your_field=your_value')
        sys.exit(1)