vifm: Fancy markdown display with glow or bat

For anything markdown or that gets displayed as markdown
(e.g. docx files) in the vifm preview, we now use glow
or bat to display a nicely styled and colored version.

For glow I added a script which tries to detect the
current terminal background between dark/light to
correctly set the color scheme.

sh/.config/sh/env

@@ -50,6 +50,8 @@ export LANG="en_US.UTF-8"
 export SHELL="${SHELL:-/bin/bash}"
 
 export TERM=xterm-256color
+# set env var to current shell background luminosity (used by vifm)
+. dark_bg
 
 if exist fzf; then
     export FZF_DEFAULT_OPTS="--bind 'tab:toggle+down,shift-tab:toggle+up,ctrl-g:top,ctrl-t:toggle-preview,ctrl-d:preview-half-page-down,ctrl-u:preview-half-page-up' --color=light -1 -m --delimiter :"

sh/.local/bin/dark_bg

@@ -0,0 +1,72 @@
+#!/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

terminal/.config/vifm/scripts/vifm-default-viewer

@@ -21,5 +21,5 @@ charset=${info#*=}
 if [ "x$charset" == "xbinary" ]; then
     hexdump -e '"%08_ax: "' -e '8/1 "%02x " "  " 8/1 "%02x "' -e '" |" 16/1 "%_p"' -e '"\n"' -v -n $nbytes "$1"
 else
-    head -$nlines "$1" | enconv -g -L $language -x $encoding
+    head -$nlines "$1" | enconv -g -L $language -x $encoding | bat --color=always --style=plain
 fi

terminal/.config/vifm/vifmrc

@@ -552,7 +552,8 @@ filetype *.docx
             \ pandoc -s -t markdown %f | nvim,
             \ docx2txt %f - | nvim
 fileviewer *.docx
-            \ pandoc -s -t markdown %f,
+            \ [ "$TERM_DARK" = "true" ] && pandoc -s -t markdown %f |  glow --style=dark - || pandoc -s -t markdown %f | glow --style=light -,
+            \ pandoc -s -t markdown %f | bat --color=always --style=plain
             \ docx2txt %f -
 
 " TuDu files
@@ -569,6 +570,11 @@ fileviewer */
         \ exa --color always --tree -L2,
         \ tree -L 2,
 
+" markdown text
+fileviewer *.md
+        \ [ "$TERM_DARK" = "true" ] && glow --style=dark %c || glow --style=light %c,
+        \ bat --color=always --style=plain
+
 " use custom viewer script for rest
 fileviewer * vifm-default-viewer %c