Bond graph ports and drawing added

BEdit/src/bedit/gui/graphics/connection_styles.py

@@ -1,8 +1,12 @@
 from dataclasses import dataclass
+from typing import Literal
 
 from PySide6.QtCore import Qt
 
 
+ArrowStyle = Literal["open", "half", "filled"]
+
+
 @dataclass(frozen=True)
 class ConnectionStyle:
     color: str = "#285f9e"
@@ -13,11 +17,17 @@ class ConnectionStyle:
     arrow_at_source: bool = False
     arrow_at_target: bool = True
     arrow_size: float = 10.0
+    arrow_style: ArrowStyle = "filled"
+
+    def __post_init__(self) -> None:
+        if self.arrow_style not in {"open", "half", "filled"}:
+            raise ValueError(f"Unknown connection arrow style: {self.arrow_style}")
 
 
 # This is the intentional code-level styling point for every port/connection type.
 CONNECTION_STYLES: dict[str, ConnectionStyle] = {
     "signal": ConnectionStyle(),
+    "power": ConnectionStyle(width=3.0, arrow_style="half", color="#000000"),
 }