adjustcolor

#!/bin/sh

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#
# Copyright 2021 Jeremy Brubaker <јЬruЬаkе@оrіоnаrtѕ.іо>
#
# abstract: Darken or lighten a color by a percentage
#

# Defaults {{{1
#
VERSION='1.0'

# Documentation {{{1
#
print_help() (
    [ -n "$1" ] && printf "%s\n" "$1"

    cat <<EOF
Usage: $0 <darken | lighten> COLOR PERCENTAGE
Darken or lighten a color by a percentage

COLOR is a six-digit hexadecimal string, optionally preceded by a '#'.
PERCENTAGE is a value from 0-100 with an optional trailing '%'.

 -v            display version info and exit
 -h            display this help and exit

subcommands:
  {darken,lighten}
EOF
) >&2

print_version() (
    cat <<EOF
$0 $VERSION
Copyright (C) 2021 Orion Arts
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Jeremy Brubaker.
EOF
) >&2

# Functions {{{1
#
lighten_color() {
    # Lighten a hexadecimal color by a percentage
    # of 0 (do nothing) to 100 (make it white)

    r=$(printf "%.f" "$(echo "(255-$1) * $amt + $1" | bc)")
    b=$(printf "%.f" "$(echo "(255-$2) * $amt + $2" | bc)")
    g=$(printf "%.f" "$(echo "(255-$3) * $amt + $3" | bc)")

    color=$((g | (b << 8) | (r <<16)))
    printf "(%s,%s,%s) #%x\n" "$r" "$b" "$g" "$color"
}

darken_color() {
    # Darken a hexadecimal color by a percentage
    # of 0 (do nothing) to 100 (make it black)

    r=$(printf "%.f" "$(echo "$amt * $1" | bc)")
    b=$(printf "%.f" "$(echo "$amt * $2" | bc)")
    g=$(printf "%.f" "$(echo "$amt * $3" | bc)")

    color=$(((r<<16) + (b<<8) + g))
    printf "#%x (%s,%s,%s)\n" "$color" "$r" "$b" "$g"
}

# Process command line {{{1
#
# Options {{{2
while getopts 'vh' opt; do
    case $opt in
        v)   print_version; exit ;;
        h|?) print_help; exit ;;
    esac
done

# Subcommand {{{2
case "$1" in
    d|da|dar|dark|darke|darken)         cmd=darken ;;
    l|li|lig|ligh|light|lighte|lighten) cmd=lighten ;;
    *) print_help "$0: invalid command: $1"; exit 1 ;;
esac

# Pop the subcommand
shift

# Check for parameters {{{2
if [ "$#" -ne 2 ]; then
    print_help "$0: invalid arguments"
    exit 1
fi

# Run subcommand {{{1
#

# Convert hex string to decimal
color=$(echo "$1" | sed -e 's/^#//' | tr 'a-f' 'A-F')
if ! echo "$color" | grep -Evq "[^0-9A-F]"; then
    printf "%s not hexadecimal\n" "$color" >&2
elif [ "${#color}" -ne 6 ]; then
    printf "#%s is not six digits\n" "$color" >&2
fi
color=$(echo "ibase=16; $color" | bc)

# Convert percentage to decimal
amt=$(echo "$2" | tr -d "%")
amt=$(echo "scale=2; 1-$amt/100" | bc)

# Extract RBG in decimal
r=$(( color >> 16          ))
b=$(((color >> 8)  & 0x00ff))
g=$(( color        & 0x00ff))

case $cmd in
    darken)  darken_color $r $b $g ;;
    lighten) lighten_color $r $b $g ;;
    *) printf "How the heck did we get here?\n" >&2 ;;
esac