add dora-joy node publishing gamepad axes and buttons

dora_joy/config.py

@@ -0,0 +1,40 @@
+"""Everything the node reads from the environment, parsed once at startup.
+
+Parsing happens here rather than where each value is used, so an unusable
+setting stops the node before it joins the dataflow instead of surfacing the
+first time somebody picks up the gamepad.
+"""
+
+import os
+from dataclasses import dataclass
+
+
+def env_int(name: str, default: int) -> int:
+    """Read a whole number, naming the variable if it cannot be read as one."""
+    value = os.environ.get(name, "").strip()
+    if not value:
+        return default
+    try:
+        return int(value)
+    except ValueError:
+        raise ValueError(f"{name} must be a whole number, not {value!r}") from None
+
+
+@dataclass
+class Config:
+    """The node's settings.
+
+    Short on purpose. A deadzone, a response curve and a speed all describe what
+    a reading should *do*, and this node does not know — it reads a pad and says
+    so. Adding them here would mean two places shaping the same number.
+    """
+
+    joystick_index: int
+
+    @classmethod
+    def from_env(cls) -> "Config":
+        """Build the configuration from the environment, refusing anything unusable."""
+        index = env_int("JOYSTICK_INDEX", 0)
+        if index < 0:
+            raise ValueError(f"JOYSTICK_INDEX must not be negative, not {index}")
+        return cls(joystick_index=index)