adding decoder logic

src/peakrdl_busdecoder/body/if_body.py

@@ -0,0 +1,84 @@
+from __future__ import annotations
+from types import EllipsisType
+from typing import Self
+from .body import Body, SupportsStr
+
+
+class IfBody(Body):
+    def __init__(self, *, indent: int = 4) -> None:
+        super().__init__()
+        # (None means 'else')
+        self._branches: list[tuple[SupportsStr | None, Body]] = []
+        self._has_else = False
+        self._indent = " " * indent
+
+    # --- Item access: if/else-if via condition; else via Ellipsis/None ---
+    def __getitem__(self, condition: SupportsStr | EllipsisType | None) -> Body:
+        if self._has_else:
+            raise RuntimeError("Cannot add branches after an 'else' branch.")
+        if condition is Ellipsis or condition is None:
+            if self._has_else:
+                raise RuntimeError("Only one 'else' branch is allowed.")
+            self._has_else = True
+            b = Body()
+            self._branches.append((None, b))
+            return b
+        # conditional branch
+        b = Body()
+        self._branches.append((condition, b))
+        return b
+
+    # --- In-place or: if/else-if via (cond, Body); else via Body ---
+    def __ior__(self, other: tuple[SupportsStr, Body] | Body) -> Self:
+        if isinstance(other, Body):
+            if self._has_else:
+                raise RuntimeError("Only one 'else' branch is allowed.")
+            if self._has_else or (self._branches and self._branches[-1][0] is None):
+                raise RuntimeError("Cannot add branches after an 'else' branch.")
+            self._branches.append((None, other))
+            self._has_else = True
+            return self
+
+        cond, body = other
+        if self._has_else:
+            raise RuntimeError("Cannot add branches after an 'else' branch.")
+        self._branches.append((cond, body))
+        return self
+
+    # --- Context manager for a branch ---
+    class _BranchCtx:
+        def __init__(self, outer: IfBody, condition: SupportsStr | None) -> None:
+            self._outer = outer
+            # route through __getitem__ to reuse validation logic
+            self._body = outer[Ellipsis if condition is None else condition]
+
+        def __enter__(self) -> Body:
+            return self._body
+
+        def __exit__(
+            self,
+            exc_type: type[BaseException] | None,
+            exc: BaseException | None,
+            tb: object | None,
+        ) -> bool:
+            return False
+
+    def cm(self, condition: SupportsStr | None) -> "IfBody._BranchCtx":
+        """Use with: with ifb.cm('cond') as b: ...  ; use None for else."""
+        return IfBody._BranchCtx(self, condition)
+
+    # --- Rendering ---
+    def __str__(self) -> str:
+        out: list[str] = []
+        for i, (cond, body) in enumerate(self._branches):
+            if i == 0 and cond is not None:
+                out.append(f"if ({cond}) begin")
+            elif cond is not None:
+                out.append(f"else if ({cond}) begin")
+            else:
+                out.append("else begin")
+            body_str = str(body)
+            if body_str:
+                out.extend(self._indent + ln for ln in body_str.splitlines())
+            out.append("end")
+        return "\n".join(out)