lib/preview: refactor into a function

This allows future use like `bash-it preview`. Alsö, allows to use `$BASH_PREVIEW` to specify a particular theme to preview instead of just doing all of them.

clean_files.txt

@@ -85,6 +85,7 @@ lib/colors.bash
 lib/helpers.bash
 lib/log.bash
 lib/preexec.bash
+lib/preview.bash
 lib/search.bash
 lib/utilities.bash
 

lib/preview.bash

@@ -1,19 +1,30 @@
-if [[ "${BASH_PREVIEW:-}" ]];
-then
-  unset BASH_PREVIEW #Prevent infinite looping
-  echo "
+# shellcheck shell=bash
+#
+# Displays the prompt from each _Bash It_ theme.
 
-  Previewing Bash-it Themes
+function _bash-it-preview() {
+	local BASH_IT_THEME BASH_IT_LOG_LEVEL
+	local themes theme
 
-  "
+	printf '\n\n\t%s\n\n' "Previewing Bash-it Themes"
 
-  THEMES="$BASH_IT/themes/*/*.theme.bash"
-  for theme in $THEMES
-  do
-    BASH_IT_THEME=${theme%.theme.bash}
-    BASH_IT_THEME=${BASH_IT_THEME##*/}
-    echo "
-    $BASH_IT_THEME"
-    echo "" | bash --init-file "${BASH_IT}/bash_it.sh" -i
-  done
+	if [[ -n "${1:-}" && -s "${BASH_IT?}/themes/${1}/${1}.theme.bash" ]]; then
+		themes=("${1}")
+	else
+		themes=("${BASH_IT?}/themes"/*/*.theme.bash)
+	fi
+
+	# shellcheck disable=SC2034
+	for theme in "${themes[@]}"; do
+		BASH_IT_THEME="${theme%.theme.bash}"
+		BASH_IT_THEME="${BASH_IT_THEME##*/}"
+		BASH_IT_LOG_LEVEL=0
+
+		bash --init-file "${BASH_IT_BASHRC:-${BASH_IT?}/bash_it.sh}" -i <<< '_bash-it-flash-term "${#BASH_IT_THEME}" "${BASH_IT_THEME}"'
+	done
+}
+
+if [[ -n "${BASH_PREVIEW:-}" ]]; then
+	_bash-it-preview "${BASH_PREVIEW}" "$@"
+	unset BASH_PREVIEW #Prevent infinite looping
 fi