graph: add a command to graph just one item

graph.py

@@ -12,6 +12,25 @@ def graph_all(recipes: dict) -> None:
     print("}")
 
 
+def graph_one(recipes: dict, target: str) -> None:
+    print("digraph G {")
+
+    seen = set()
+    remain = set()
+    remain.add(target)
+
+    while remain:
+        output = remain.pop()
+
+        for need in recipes[output][0]['input']:
+            print(f"{need} -> {output}")
+            if need not in seen:
+                remain.add(need)
+
+        seen.add(output)
+    print("}")
+
+
 def load_recipes(recipe_root: str) -> dict:
     recipes = dict()
 
@@ -28,6 +47,23 @@ def load_recipes(recipe_root: str) -> dict:
 
 
 if __name__ == '__main__':
+    def main():
+        import argparse
+
         root = os.path.dirname(__file__)
         recipe_root = os.path.join(root, 'data', 'recipes')
-    graph_all(load_recipes(recipe_root))
+
+        parser = argparse.ArgumentParser()
+        parser.add_argument('--data', type=str, default=recipe_root)
+        parser.add_argument('--target', type=str, required=False)
+
+        args = parser.parse_args()
+
+        recipes = load_recipes(args.data)
+
+        if args.target:
+            graph_one(recipes, args.target)
+        else:
+            graph_all(recipes)
+
+    main()