#!/bin/bash

# This script generates a PNG image with the current hostname /  IP address / MAC
# AUTHOR : Marc Schütze
# LICENSE: MIT

# Get the current local IP as a variable
IP=$(ip route | sed -n 's/.* src \(.*\) metric .*/\1/p' | uniq)

# get the current MAC address for the current ip address
MAC=$(cat /sys/class/net/$(ip route show default | awk '/default/ {print $5}')/address)

# Get the hostname of the current IP and remove trailing . from the output
HOSTNAME=$(dig -x $IP +short | sed 's/\.$//')

#Get the CRC32 of the hostname and convert it to uppercase
HOSTNAME_CRC32=$(echo -n $HOSTNAME | crc32 /dev/stdin | tr '[:lower:]' '[:upper:]')

# remove the last two chars from string to extract color in hex form
COLOR_HEX=$(echo $HOSTNAME_CRC32 | sed 's/..$//')

# split the hex color into three parts
a=`echo $COLOR_HEX | cut -c-2`
b=`echo $COLOR_HEX | cut -c3-4`
c=`echo $COLOR_HEX | cut -c5-6`

# convert hex to decimal
r=`echo "ibase=16; $a" | bc`
g=`echo "ibase=16; $b" | bc`
b=`echo "ibase=16; $c" | bc`

# calc the luminance of the color
LUMINANCE=$(echo "scale=2;(0.299*$r + 0.587*$g + 0.114*$b)/255" | bc)

# if luminance is less than 0.5, set the text color to white, otherwise set it to black
if (( $(echo "$LUMINANCE < 0.5" | bc -l) )); then
    TEXT_COLOR="white"
else
    TEXT_COLOR="black"
fi

# generate the image with hostname and IP in two lines

FONT="DejaVu-Sans-Bold"
FONT_SIZE=80

convert \
-size 1920x1080 \
-background "#$COLOR_HEX" \
-gravity center \
-pointsize $FONT_SIZE \
-fill $TEXT_COLOR \
label:"$HOSTNAME \\n $IP \\n $MAC" \
hostinfo.png