Improve justfile init phase

Justfile

@@ -1,21 +1,30 @@
 # https://github.com/casey/just
 
-vbin   := "./venv/bin"
-pip    := vbin / "pip"
-python := vbin / "python"
+venv   := "./venv"
+pip    := venv / "bin/pip"
+python := venv / "bin/python"
 
 last_commit_sha1   := `git rev-parse --short HEAD`
 remote_image_name  := "gitea.gdemontauzan.fr/maxenceg2m/github-release-notifier"
 remote_build_image := remote_image_name + ":" + last_commit_sha1
 
 # Run the script
-run: init
+run: _ensure_venv_is_ok
     {{ python }} notifier.py
 
 # Init python virtual env
 init:
     python3 -m venv venv
     {{ pip }} install --requirement requirements.txt
+    sha256sum requirements.txt > {{ venv }}/requirements.sha
+
+# Inspiration: https://github.com/behave/behave/blob/afb6b6716cd0f3e028829416475312db804a6aa9/justfile
+_ensure_venv_is_ok:
+    #!/usr/bin/env python3
+    from subprocess import run
+    from os import path
+    if run("sha256sum -c {{ venv }}/requirements.sha", shell=True).returncode != 0:
+        run("just init", shell=True)
 
 # Clean workspace - remove venv - and init
 reinit: hclean init