fix check_call usages

app.py

@@ -24,8 +24,8 @@ def convert_to_wav(file_name: str):
     print(f"{extension=}")
     command = [
         "tape2wav",
-        file_name,
-        f"${output}.wav",
+        os.path.join("uploads", file_name),
+        os.path.join("uploads", f"${output}.wav"),
     ]
     try:
         check_call(command)
@@ -35,10 +35,13 @@ def convert_to_wav(file_name: str):
 
 
 def run_cassetta(cassetta: str):
-    command = f"aplay uploads/{cassetta}"
+    command = [
+        "aplay",
+        os.path.join("uploads", cassetta),
+    ]
 
     try:
-        check_call(command.split())
+        check_call(command)
     except CalledProcessError as exc:
         print(f"aplay failed: {exc.output=}\n{exc.stderr=}")
 
@@ -72,7 +75,10 @@ def upload_file():
         return "No file?"
 
     save_path = os.path.join("uploads", file.filename)
-    assert not os.path.exists(save_path)
+    if os.path.exists(save_path):
+        response = make_response(make_response("file already exists", 400))
+        response.headers["Location"] = "/"
+        response.status_code = 400
 
     try:
         file.save(save_path)