#!/usr/bin/env bash
# ^^^^^^^^^^^^ Use env rather than assume we've got /bin/bash.
# This works better on OSX where /bin/bash is brain dead.

#   Copyright (C) 2019-2020, Rocky Bernstein <rocky@gnu.org>
#   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 2, 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; see the file COPYING.  If not, write to
#   the Free Software Foundation, 59 Temple Place, Suite 330, Boston,
#   MA 02111 USA.

# Try to determine if we have dark or light terminal background

typeset -i success=0
typeset    method="xterm control"

# On return, variable is_dark_bg is set
# We follow Emacs logic (at least initially)
get_default_colorfgbg() {
  if [[ -n $COLORFGBG ]]; then
    method="COLORFGBG"
    is_dark_colorfgbg
  elif [[ -n $TERM ]]; then
    case $TERM in
    xterm-256color)
      # 382.5 = (* .6 (+ 255 255 255))
      TERMINAL_COLOR_MIDPOINT=${TERMINAL_COLOR_MIDPOINT:-383}
      ;;
    xterm* | dtterm | eterm*)
      # 117963 = (* .6 (+ 65535 65535 65535))
      TERMINAL_COLOR_MIDPOINT=${TERMINAL_COLOR_MIDPOINT:-117963}
      is_dark_bg=0
      ;;

    *)
      TERMINAL_COLOR_MIDPOINT=${TERMINAL_COLOR_MIDPOINT:-117963}
      is_dark_bg=1
      ;;
    esac
  fi
}

# Pass as parameters R G B values in hex
# Compare FG to BG for light/dark, not just FB and midpoint
# NOTE: We could have FG=#403020 BG=#203040 and tie
# On return, variable is_dark_bg is set
is_dark_rgb() {
  typeset fg_r fg_g fg_b
  typeset bg_r bg_g bg_b
  fg_r=$1
  fg_g=$2
  fg_b=$3
  bg_r=$4
  bg_g=$5
  bg_b=$6
  a_fg=$((16#"$fg_r" + 16#"$fg_g" + 16#"$fg_b"))
  a_bg=$((16#"$bg_r" + 16#"$bg_g" + 16#"$bg_b"))
  if [[ $a_fg -gt $a_bg ]]; then
    is_dark_bg=1
  else
    is_dark_bg=0
  fi
}

# Consult (environment) variable COLORFGB
# On return, variable is_dark_bg is set
is_dark_colorfgbg() {
  case $COLORFGBG in
  '15;0' | '15;default;0')
    is_dark_bg=1
    success=1
    ;;
  '0;15' | '0;default;15')
    is_dark_bg=0
    success=1
    ;;
  *)
    is_dark_bg=-1
    ;;
  esac
}

is_sourced() {
  if [[ $0 == ${BASH_SOURCE[0]} ]]; then
    return 1
  else
    return 0
  fi
}

# Exit if we are not source.
# if sourced, then we just set exitrc
# which was assumed to be declared outside
exit_if_not_sourced() {
  exitrc=${1:-0}
  if ! is_sourced; then
    exit "$exitrc"
  fi
}

# From:
# http://unix.stackexchange.com/questions/245378/common-environment-variable-to-set-dark-or-light-terminal-background/245381#245381
# and:
# https://bugzilla.gnome.org/show_bug.cgi?id=733423#c1
#
# User should set up RGB_fg and RGB_bg arrays
xterm_compatible_fg_bg() {
  typeset fg bg
  # Turn TTY off
  stty -echo 2>/dev/null
  # Issue command to get foreground
  echo -ne '\e]10;?\a'
  # Read back in terminal program reporting its OSC fg values
  IFS=: read -t 0.1 -d $'\a' x fg
  # Turn TTY back on
  stty echo 2>/dev/null
  # Remove any escape or control characters
  # Note: gnome-terminal tacked \e at end
  fg=$(echo "$fg" | sed 's/[^a-zA-Z0-9/]//g')
  [[ -z $fg ]] && return 1
  # Convert to array
  typeset -p fg
  IFS='/' read -ra RGB_fg <<<"$fg"
  typeset -p RGB_fg

  # Turn TTY off
  stty -echo 2>/dev/null
  # Issue command to get background
  echo -ne '\e]11;?\a'
  # Read back in terminal program reporting its OSC bg values
  # purposely reading x, then discarding it.
  IFS=: read -t 0.1 -d $'\a' x bg
  # Turn TTY back on
  stty echo 2>/dev/null
  # Remove any escape or control characters
  # Note: gnome-terminal tacked \e at end
  bg=$(echo "$bg" | sed 's/[^a-zA-Z0-9/]//g')
  [[ -z $bg ]] && return 1
  # Convert to array
  typeset -p bg
  IFS='/' read -ra RGB_bg <<<"$bg"
  typeset -p RGB_bg
  xterm_osc_done=1
  return 0
}

# From a comment left by user "duthen" in my StackOverflow answer cited above.
osx_get_terminal_fg_bg() {
  if [[ -n $COLORFGBG ]]; then
    method="COLORFGBG"
    is_dark_colorfgbg
  else
    RGB_bg=($(osascript -e 'tell application "Terminal" to get the background color of the current settings of the selected tab of front window'))
    retsts=$?
    # typeset -p RGB_bg
    ((retsts != 0)) && return 1
    is_dark_rgb ${RGB_fg[@]} ${RGB_bg[@]}
    method="OSX osascript"
    success=1
  fi
}

typeset -i success=0
typeset -i is_dark_bg=0
typeset -i exitrc=0
typeset -i xterm_osc_done=0

# Pre-analysis for non-COLORFGBG terminals
if (( 3711 < VTE_VERSION )) && [[ -z "$COLORFGBG" ]]; then
  # Try Xterm Operating System Command (OSC) (Esc-])
  if xterm_compatible_fg_bg; then
    is_dark_rgb ${RGB_fg[@]} ${RGB_bg[@]}
    if [[ $is_dark_bg == 1 ]]; then
      # Even though, we're xterm, assist COLORFGBG
      export COLORFGBG='0;15'
    else
      # Even though, we're xterm, assist COLORFGBG
      export COLORFGBG='15;0'
    fi
  else
    echo "xterm/vte Esc-] OSC has empty string"
    get_default_colorfgbg
  fi
  unset x fg bg avg_RGB_fg avg_RGB_bg
fi

if [[ ${BASH_VERSINFO[5]} == *"darwin"* ]]; then
  osx_get_terminal_fg_bg
fi

if ((!success)) && [[ -n $TERM ]]; then
  case $TERM in
  xterm* | gnome | rxvt* | linux)
    typeset -a RGB_fg RGB_bg
    if [[ $xterm_osc_done -eq 1 ]]; then
      if xterm_compatible_fg_bg; then
        is_dark_rgb ${RGB_fg[@]} ${RGB_bg[@]}
      fi
      success=1
    fi
    ;;
  *) ;;

  esac
fi

if ((success)); then
  if ((is_dark_bg == 1)); then
    echo "Dark background from ${method}"
  else
    echo "Light background from ${method}"
  fi
elif [[ -n $COLORFGBG ]]; then
  # Note that this can be wrong if
  # COLORFGBG was set prior invoking a terminal
  is_dark_colorfgbg
  case $is_dark_bg in
  0)
    echo "Light background from COLORFGBG"
    ;;
  1)
    echo "Dark background from COLORFGBG"
    ;;
  -1 | *)
    echo "Can't decide from COLORFGBG"
    exit_if_not_sourced 1
    ;;
  esac
else
  echo "Can't decide"
  exit_if_not_sourced 1
fi

# If we were sourced, then set
# some environment variables
if is_sourced; then
  if ((exitrc == 0)); then
    if ((is_dark_bg == 1)); then
      export DARK_BG=1 # deprecated
      export LC_DARK_BG=1
      [[ -z $COLORFGBG ]] && export COLORFGBG='0;15'
    else
      export DARK_BG=0
      export LC_DARK_BG=0
      [[ -z $COLORFGBG ]] && export COLORFGBG='15;0'
    fi
  fi
else
  exit 0
fi
