colortail

#!/usr/bin/python3
"""
This script has been derived from a billion android adb logcat scripts
floating around the internet.

Produces coloured logfile output with a different colour for each line based on
the logging level (debug, info, warning, etc.). Works as a `tail -f` replacement
or accepts piped input:

    ~# colortail /var/log/myservice.log
    ~# colortail < /var/log/myservice.log
    ~# cat /some/file | colortail

The format that the script expects is output produced by python's logging
formatters, with basic "%(asctime)s %(name)s %(levelname)s %(message)s" setup,
however any log file that has <timestamp> <anything> <loglevel> at the
beginning of each line will (probably) work. The first fields before the log
level need to be space-separated, there can be maximum three fields before the
loglevel and loglevel must be in capital letters.

Author: Mikko Mensonen <mikko@mensonen.com>
"""
import os
import sys
import re
import io

# The log line syntax to highlight:
# <timestamp> <user (optional)> <producer> <loglevel> <msg>
log_fmt = re.compile(r"^([\d\s,:-]+)([\da-z@_.]+\s+)?([A-Za-z0-9_.]+\s+)([A-Z]{4,})(.*)$")

BLACK: int = 0
RED: int = 1
GREEN: int = 2
YELLOW: int = 3
BLUE: int = 4
MAGENTA: int = 5
CYAN: int = 6
WHITE: int = 7


def fmt_text(fg: int = None, bg: int = None, bright: bool = False,
             bold: bool = False, dim: bool = False, reset: bool = False) -> str:
    """Produce an ANSI escape sequence to start a colour.

    Manually derived from http://en.wikipedia.org/wiki/ANSI_escape_code#Codes
    """
    codes = []
    if reset:
        codes.append("0")
    else:
        if fg is not None:
            codes.append(f"3{fg:d}")
        if bg is not None:
            if not bright:
                codes.append(f"4{bg:d}")
            else:
                codes.append(f"10{bg:d}")
        if bold:
            codes.append("1")
        elif dim:
            codes.append("2")
        else:
            codes.append("22")
    return f"\033[{';'.join(codes)}m"


def allocate_color(tag: str) -> str:
    """Pick an ANSI colour start sequence for a log level."""
    if tag not in KNOWN_TAGS:
        return fmt_text(fg=WHITE, dim=True)
    return KNOWN_TAGS[tag]


KNOWN_TAGS: dict[str, str] = {
    "DEBUG": fmt_text(fg=GREEN, dim=True),
    "INFO": fmt_text(fg=CYAN),
    "WARNING": fmt_text(fg=YELLOW, bright=True),
    "WARN": fmt_text(fg=YELLOW, bright=True),
    "ERROR": fmt_text(fg=BLACK, bg=RED),
    "CRITICAL": fmt_text(fg=WHITE, bg=RED)}


args = ''.join(sys.argv[1:])
pipe = False

# If someone is piping in to us, use stdin as input. If not, invoke tail
if os.isatty(sys.stdin.fileno()):
    input_lines = os.popen("tail -n 80 -F %s" % args)
else:
    pipe = True
    input_lines = sys.stdin

while True:
    try:
        line = input_lines.readline()
        if pipe and not line:
            break
    except KeyboardInterrupt:
        break

    match = log_fmt.match(line)
    if match is not None:
        timestamp, user, owner, loglevel, message = match.groups()
        linebuf = io.StringIO()
        if not user:
            user = ""
        if not owner:
            owner = ""

        color = allocate_color(loglevel.strip())
        linebuf.write(f"{fmt_text(fg=WHITE, dim=True)}{timestamp}{user}"
                      f"{fmt_text(reset=True)}")
        linebuf.write(f"{color}{owner}")
        linebuf.write(loglevel)
        linebuf.write(f"{message}{fmt_text(reset=True)}")
        line = linebuf.getvalue()
    else:
        line = line.rstrip()

    print(line)