Custom-element registry, builder, and TS codegen

common/components/custom_elements.py

@@ -0,0 +1,104 @@
+"""Custom-element builder, registry, and TypeScript codegen.
+
+A custom element is a light-DOM Web Component: the Python builder emits a
+semantic tag whose typed props become kebab-case attributes and whose behavior
+lives in a compiled TS module (loaded via Media). One ``TypedDict`` per element
+is the single source of truth for the server<->client contract;
+``gen_element_types`` turns each registered spec into a TS interface + attribute
+reader so drift fails ``tsc``.
+"""
+
+from dataclasses import dataclass
+from typing import Mapping, TypedDict, get_type_hints
+
+from common.components.core import Children, Element, HTMLAttribute, Media, Node
+
+
+@dataclass(frozen=True)
+class ElementSpec:
+    tag: str  # e.g. "game-status-selector"
+    ts_name: str  # e.g. "GameStatusSelector"
+    props: type  # a TypedDict subclass
+
+
+ELEMENT_REGISTRY: list[ElementSpec] = []
+
+
+def register_element(tag: str, ts_name: str, props: type) -> None:
+    """Register an element so codegen can emit its TS contract."""
+    ELEMENT_REGISTRY.append(ElementSpec(tag, ts_name, props))
+
+
+def _kebab(name: str) -> str:
+    return name.replace("_", "-")
+
+
+def custom_element(
+    tag: str, props: Mapping[str, object], *, children: Children = None
+) -> Node:
+    """Emit ``<tag kebab-attrs>children</tag>`` and declare its compiled module.
+
+    The module path mirrors the source layout: ``ts/elements/<tag>.ts`` compiles
+    to ``dist/elements/<tag>.js``, which ``Media`` loads via ``ModuleScript``."""
+    attributes: list[HTMLAttribute] = [
+        (_kebab(key), value)  # type: ignore[misc]
+        for key, value in props.items()
+    ]
+    return Element(tag, attributes, children).with_media(
+        Media(js=(f"dist/elements/{tag}.js",))
+    )
+
+
+# ── Codegen ──────────────────────────────────────────────────────────────────
+
+_TYPE_MAP = {int: "number", float: "number", str: "string", bool: "boolean"}
+
+
+def _camel(name: str) -> str:
+    head, *tail = name.split("_")
+    return head + "".join(part.title() for part in tail)
+
+
+def _reader_expr(name: str, python_type: type) -> str:
+    attr = _kebab(name)
+    if python_type in (int, float):
+        return f'Number(el.getAttribute("{attr}"))'
+    if python_type is bool:
+        return f'el.getAttribute("{attr}") === "true"'
+    return f'el.getAttribute("{attr}") ?? ""'
+
+
+def _ts_for_spec(spec: ElementSpec) -> str:
+    hints = get_type_hints(spec.props)
+    interface_lines = "\n".join(
+        f"  {_camel(name)}: {_TYPE_MAP[python_type]};"
+        for name, python_type in hints.items()
+    )
+    reader_lines = "\n".join(
+        f"    {_camel(name)}: {_reader_expr(name, python_type)},"
+        for name, python_type in hints.items()
+    )
+    return (
+        f"export interface {spec.ts_name}Props {{\n{interface_lines}\n}}\n\n"
+        f"export function read{spec.ts_name}Props(el: HTMLElement): "
+        f"{spec.ts_name}Props {{\n  return {{\n{reader_lines}\n  }};\n}}"
+    )
+
+
+def render_props_module() -> str:
+    """The full ``ts/generated/props.ts`` content for every registered element."""
+    header = "// GENERATED by `manage.py gen_element_types` — do not edit.\n"
+    blocks = [_ts_for_spec(spec) for spec in ELEMENT_REGISTRY]
+    return header + "\n" + "\n\n".join(blocks) + "\n"
+
+
+# ── Element prop schemas (registered at import time) ─────────────────────────
+
+
+class GameStatusSelectorProps(TypedDict):
+    game_id: int
+    status: str
+    csrf: str
+
+
+register_element("game-status-selector", "GameStatusSelector", GameStatusSelectorProps)