_gcolors

#!/usr/bin/env bash
# Copyright 2022-2023 GlitchyByte
# SPDX-License-Identifier: MIT

# _gcolors v1.2.1

# Find out terminal color support.
if [[ -t 1 ]]; then
  readonly _tput_colors="$(tput colors 2>/dev/null)"
  if [[ -n "${_tput_colors}" && "${_tput_colors}" != "0" ]]; then
    readonly term_color_count="${_tput_colors}"
  else
    readonly term_color_count="0"
  fi
else
  readonly term_color_count="0"
fi

# Define basic colors.
if [ "${term_color_count}" -eq "0" ]; then
  # Color control.
  readonly c_reset=""
  readonly c_bold=""
  # Foreground colors.
  readonly cf_black=""
  readonly cf_red=""
  readonly cf_green=""
  readonly cf_yellow=""
  readonly cf_blue=""
  readonly cf_magenta=""
  readonly cf_cyan=""
  readonly cf_white=""
  # Background colors.
  readonly cb_black=""
  readonly cb_red=""
  readonly cb_green=""
  readonly cb_yellow=""
  readonly cb_blue=""
  readonly cb_magenta=""
  readonly cb_cyan=""
  readonly cb_white=""
else
  # Color control.
  readonly c_reset="$(tput sgr0)"
  readonly c_bold="$(tput bold)"
  # Foreground colors.
  readonly cf_black="$(tput setaf 0)"
  readonly cf_red="$(tput setaf 1)"
  readonly cf_green="$(tput setaf 2)"
  readonly cf_yellow="$(tput setaf 3)"
  readonly cf_blue="$(tput setaf 4)"
  readonly cf_magenta="$(tput setaf 5)"
  readonly cf_cyan="$(tput setaf 6)"
  readonly cf_white="$(tput setaf 7)"
  # Background colors.
  readonly cb_black=$(tput setab 0)
  readonly cb_red=$(tput setab 1)
  readonly cb_green=$(tput setab 2)
  readonly cb_yellow=$(tput setab 3)
  readonly cb_blue=$(tput setab 4)
  readonly cb_magenta=$(tput setab 5)
  readonly cb_cyan=$(tput setab 6)
  readonly cb_white=$(tput setab 7)
fi

# Pick from 256 colors.
color256() {
  if [ "${term_color_count}" -lt "256" ]; then
    echo ""
    return
  fi
  local r=$1
  local g=$2
  local b=$3
  local value=$((16 + (36 * r) + (6 * g) + b))
  echo "$(tput setaf ${value})"
}

# Custom colors.
if [ "${term_color_count}" -eq "0" ]; then
  readonly cc_error=""
elif [ "${term_color_count}" -eq "8" ]; then
  readonly cc_error="${c_reset}${cf_red}${c_bold}"
else
  readonly cc_error="${c_reset}$(color256 5 0 1)"
fi

# Echo to stderr.
echoerr() {
  >&2 echo "${cc_error}$@${c_reset}"
}

# Snippet to test and pick colors.
# for c in {16..255}; do tput setaf $c; echo "${c}"; done | column -c 200