feat: have option for terraform_tfsec hook to only run in relevant mo…

…dified directories (#135)

README.md

@@ -121,7 +121,22 @@ if they are present in `README.md`.
 
 ## Notes about terraform_tfsec hooks
 
-1. `terraform_tfsec` will recurse all directories/modules.
+1. `terraform_tfsec` will consume modified files that pre-commit
+    passes to it, so you can perform whitelisting of directories
+    or files to run against via [files](https://pre-commit.com/#config-files)
+    pre-commit flag
+
+    1. Example:
+    ```yaml
+    hooks:
+      - id: terraform_tfsec
+        files: ^prd-infra/
+    ```
+
+    The above will tell pre-commit to pass down files from the `prd-infra/` folder
+    only such that the underlying `tfsec` tool can run against changed files in this
+    directory, ignoring any other folders at the root level
+
 1. To ignore specific warnings, follow the convention from the
 [documentation](https://github.com/liamg/tfsec#ignoring-warnings).
     1. Example:

terraform_tfsec.sh

@@ -5,8 +5,26 @@ main() {
   initialize_
   parse_cmdline_ "$@"
 
-  # Don't pass any files tfsec will recurse directories anyway.
-  tfsec "$ARGS" .
+  # propagate $FILES to custom function
+  tfsec_ "$ARGS" "$FILES"
+}
+
+tfsec_() {
+  # consume modified files passed from pre-commit so that
+  # tfsec runs against only those relevant directories
+  for file_with_path in $FILES; do
+    file_with_path="${file_with_path// /__REPLACED__SPACE__}"
+    paths[index]=$(dirname "$file_with_path")
+
+    let "index+=1"
+  done
+
+  for path_uniq in $(echo "${paths[*]}" | tr ' ' '\n' | sort -u); do
+    path_uniq="${path_uniq//__REPLACED__SPACE__/ }"
+    pushd "$path_uniq" > /dev/null
+    tfsec $ARGS
+    popd > /dev/null
+  done
 }
 
 initialize_() {
@@ -41,7 +59,7 @@ parse_cmdline_() {
         ;;
       --)
         shift
-        # ignore any parameters, as they're not used
+        FILES+=("$@")
         break
         ;;
     esac
@@ -50,5 +68,6 @@ parse_cmdline_() {
 
 # global arrays
 declare -a ARGS=()
+declare -a FILES=()
 
 [[ ${BASH_SOURCE[0]} != "$0" ]] || main "$@"