feat: add cli flags for input, template & output

main.py

@@ -1,3 +1,4 @@
+import argparse
 import json
 from pathlib import Path
 from jinja2 import Environment, FileSystemLoader
@@ -5,31 +6,59 @@ from jinja2 import Environment, FileSystemLoader
 from schema import DocumentInput
 
 
+def parse_args() -> argparse.Namespace:
+    # keep cli parsing separate so main stays about workflow
+    parser = argparse.ArgumentParser(description="Render document from JSON + Jinja2 template")
+
+    parser.add_argument(
+        "--input",
+        "-i",
+        type=Path,
+        required=True,
+        help="Path to input JSON file (e.g. examples/input.json)"
+    )
+    parser.add_argument(
+        "--template",
+        "-t",
+        default="doc.md.j2",
+        help="Template file (e.g. doc.md.j2)"
+    )
+    parser.add_argument(
+        "--output",
+        "-o",
+        type=Path,
+        required=True,
+        help="Path to write rendered output (e.g. out.md)"
+    )
+
+    return parser.parse_args()
+
+
+def render_template(template_name: str, data: dict) -> str:
+    # Jinja env points at templates/
+    env = Environment(loader=FileSystemLoader("templates"),
+                      trim_blocks=True,
+                      lstrip_blocks=True)
+    template = env.get_template(template_name)
+    return template.render(data)
+
+
 def main():
+    args = parse_args()
+
     # load input data
     # path() over hardcoding str
-    data = json.loads(Path("examples/input.json").read_text(encoding="utf-8"))
+    data = json.loads(args.input.read_text(encoding="utf-8"))
 
     # validate + normalise input
     doc_input = DocumentInput(**data)
 
-    # setup template eng
-    # create jinja2 env for templates
-    env = Environment(
-        # look in templates/
-        loader=FileSystemLoader("templates"),
-        # trim whitespaces
-        trim_blocks=True,
-        lstrip_blocks=True,
-    )
     # load template to render
-    # **data spreads dict so keys become template vars
-    template = env.get_template("doc.md.j2")
-    out = template.render(**doc_input.model_dump())
+    out = render_template(args.template, doc_input.model_dump())
 
     # write output - render md to file
-    Path("out.md").write_text(out, encoding="utf-8")
-    print("wrote out.md")
+    args.output.write_text(out, encoding="utf-8")
+    print(f"wrote {args.output}")
 
 
 if __name__ == "__main__":