dotfiles/sh/.local/bin/dark_bg

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#!/usr/bin/env sh
#
# Determine if term background is dark or light.
# Uses a couple different heuristics, most of them
# from this:
# https://unix.stackexchange.com/questions/245378/common-environment-variable-to-set-dark-or-light-terminal-background
# unix exchange.
#
# If the background is dark, returns exit code 0 (true).
# If the background is light, returns exit code 1 (false).
# TODO implement alternative $COLORBFG method
is_dark() {
IFS=/ read -r bg_r bg_g bg_b << EOF
${1:-"0000/0000/0000"}
EOF
IFS=/ read -r fg_r fg_g fg_b << EOF
${2:-"ffff/ffff/ffff"}
EOF
calc=$(echo "($bg_r+$bg_g+$bg_b)-($fg_r+$fg_g+$fg_b)" | tr '[:lower:]' '[:upper:]')
luminance=$(echo "ibase=16; $calc" | bc)
if [ "$luminance" -lt 0 ]; then
true
else
false
fi
}
orig_ssty=$(stty -g)
stty raw -echo min 0 time 0
printf '\e]11;?\a'
sleep 0.01
read -r answer
bg="${answer#*;}"
printf '\e]10;?\a'
sleep 0.01
read -r answer
fg="${answer#*;}"
stty "$orig_ssty"
bg=$(echo "${bg}" | sed 's/.*\(rgb:[0-9a-f/]*\).*/\1/')
fg=$(echo "${fg}" | sed 's/.*\(rgb:[0-9a-f/]*\).*/\1/')
# from the amazing
# https://stackoverflow.com/questions/2683279/how-to-detect-if-a-script-is-being-sourced
# answer
sourced=0
if [ -n "$ZSH_VERSION" ]; then
case $ZSH_EVAL_CONTEXT in *:file) sourced=1;; esac
elif [ -n "$KSH_VERSION" ]; then
# shellcheck disable=SC2296
[ "$(cd -- "$(dirname -- "$0")" && pwd -P)/$(basename -- "$0")" != "$(cd -- "$(dirname -- "${.sh.file}")" && pwd -P)/$(basename -- "${.sh.file}")" ] && sourced=1
elif [ -n "$BASH_VERSION" ]; then
(return 0 2>/dev/null) && sourced=1
else
# Detects `sh` and `dash`; add additional shell filenames as needed.
case ${0##*/} in sh|-sh|dash|-dash) sourced=1;; esac
fi
is_dark "${bg#rgb:}" "${fg#rgb:}"
outp="$?"
if [ "$sourced" -eq 1 ]; then
if [ "$outp" -eq 0 ]; then
export TERM_DARK=true
else
export TERM_DARK=false
fi
else
exit "$outp"
fi