#!/usr/bin/env bash
#
#   This file echoes a bunch of 24-bit color codes
#   to the terminal to demonstrate its functionality.
#   The foreground escape sequence is ^[38;2;<r>;<g>;<b>m
#   The background escape sequence is ^[48;2;<r>;<g>;<b>m
#   <r> <g> <b> range from 0 to 255 inclusive.
#   The escape sequence ^[0m returns output to default

setBackgroundColor() {
    echo -en "\x1b[48;2;$1;$2;$3""m"
}

resetOutput() {
    echo -en "\x1b[0m\n"
}

# Gives a color $1/255 % along HSV
# Who knows what happens when $1 is outside 0-255
# Echoes "$red $green $blue" where
# $red $green and $blue are integers
# ranging between 0 and 255 inclusive
rainbowColor()
{
    h=$(($1 / 43))
    f=$(($1 - 43 * h))
    t=$((f * 255 / 43))
    q=$((255 - t))

    if [ "$h" -eq 0 ]; then
        echo "255 $t 0"
    elif [ "$h" -eq 1 ]; then
        echo "$q 255 0"
    elif [ "$h" -eq 2 ]; then
        echo "0 255 $t"
    elif [ "$h" -eq 3 ]; then
        echo "0 $q 255"
    elif [ "$h" -eq 4 ]; then
        echo "$t 0 255"
    elif [ "$h" -eq 5 ]; then
        echo "255 0 $q"
    else
        # execution should never reach here
        echo "0 0 0"
    fi
}

for i in $(seq 0 127); do
    setBackgroundColor "$i" 0 0
    echo -en " "
done
resetOutput
for i in $(seq 255 -1 128); do
    setBackgroundColor "$i" 0 0
    echo -en " "
done
resetOutput

for i in $(seq 0 127); do
    setBackgroundColor 0 "$i" 0
    echo -n " "
done
resetOutput
for i in $(seq 255 -1 128); do
    setBackgroundColor 0 "$i" 0
    echo -n " "
done
resetOutput

for i in $(seq 0 127); do
    setBackgroundColor 0 0 "$i"
    echo -n " "
done
resetOutput
for i in $(seq 255 -1 128); do
    setBackgroundColor 0 0 "$i"
    echo -n " "
done
resetOutput

for i in $(seq 0 127); do
    # shellcheck disable=SC2046
    setBackgroundColor $(rainbowColor "$i")
    echo -n " "
done
resetOutput
for i in $(seq 255 -1 128); do
    # shellcheck disable=SC2046
    setBackgroundColor $(rainbowColor "$i")
    echo -n " "
done
resetOutput