Format cortextool diff output as Markdown diff code section

format-diff-file-as-markdown.sh

#!/bin/bash

# this script will:
# 1. read in file argument 1, $DIFF_FILE_IN
# 2. format text to Markdown diff code section
# 3. write out file argument 2, $DIFF_FILE_OUT

# https://gitlab.com/gitlab-org/gitlab/-/issues/15582
set -e

DIFF_START='```diff\n'
DIFF_HEADER="The following rule changes will be applied upon successful rules sync,\
 based on rules files changes in this commit:\n"
DIFF_END='\n```'
DIFF_WRAPPER="${DIFF_HEADER}${DIFF_START}%s${DIFF_END}"

# check input file variable, use $DIFF_FILE_IN from ./gitlab-ci.yml by default
DIFF_FILE_IN="${1:-$DIFF_FILE_IN}"
if [ -z "$DIFF_FILE_IN" ]; then
    echo "Error: input variable 1 'DIFF_FILE_IN' is not defined."
    exit 1
elif test -f "${DIFF_FILE_IN}"; then
    # print diff to pipeline
    echo
    echo
    echo "rules diff below"
    cat "${DIFF_FILE_IN}"
    echo
    echo
else
    echo "Error: Input file \"${DIFF_FILE_IN}\" does not exist."
    exit 1
fi

# check input variable 2, use $DIFF_FILE_OUT from ./gitlab-ci.yml by default
DIFF_FILE_OUT="${2:-$DIFF_FILE_OUT}"
if [ -z "$DIFF_FILE_OUT" ]; then
    echo "Error: input variable 2 'DIFF_FILE_OUT' is not defined."
    exit 1
fi

# remove all occurences of unwanted characters from diff text
DIFF_OLD=$(cat -v ${DIFF_FILE_IN})          # read in file with "show-all" characters flag
DIFF_OLD=`echo -e "${DIFF_OLD//'[0m'/}"`    # remove all SGR ASCII reset codes '[0m'
DIFF_OLD=`echo -e "${DIFF_OLD//'$'/}"`      # remove all newline characters '$'
DIFF_OLD=`echo -e "${DIFF_OLD//'^['/}"`     # remove all escape characters '^['
DIFF_OLD=`echo -e "${DIFF_OLD//'+'/}"`      # remove all '+'
DIFF_OLD=`echo -e "${DIFF_OLD//'-'/}"`      # remove all '-'

# replace sgr color codes with characters, eg. '[32m' with '+'
declare -A MAP_SGR_TO_CHAR=( ['[32m']='+' ['[31m']='-' ['[33m']='~' )
while read -r line; do                      # loop each line in $diff variable
    # check line for each color code
    for sgr_code in "${!MAP_SGR_TO_CHAR[@]}"; do
        # if found, replace with new character from associative array
        if [[ $line == *"$sgr_code"* ]]; then
            new_char="${MAP_SGR_TO_CHAR[$sgr_code]}"
            printf -v line '%s' "${new_char}${line/sgr_code/}"
        fi
    done
DIFF_NEW+=`echo -e "$line\n"`               # append markdown newline '  '
done <<< "${DIFF_OLD}"

# wrap with markdown diff code section formatting ticks
printf -v DIFF_NEW "${DIFF_WRAPPER}" "${DIFF_NEW}"
echo -e "${DIFF_NEW}" > "${DIFF_FILE_OUT}"    # write new diff file

# print diff to pipeline
echo
echo
echo "Markdown-formatted diff below"
cat "${DIFF_FILE_OUT}"