✨ Slice C of #854: ask bounded Elicit forms in the REPL

packages/cli/src/repl/components/actions.ts

@@ -15,10 +15,17 @@
 import type { ReplDrawerRef, ReplSurface } from "../route.ts";
 
 export type ReplAction =
-  /** Text for whichever field has focus. */
-  | { readonly kind: "type"; readonly text: string }
-  /** Remove the last decoded text unit from whichever field has focus. */
-  | { readonly kind: "erase" }
+  /**
+   * Text for one named field, or for the entry draft when it names none.
+   *
+   * The name travels with the text because focus belongs to the mounted tree
+   * and this vocabulary does not: a control that emitted bare text would have
+   * its characters delivered to whichever field the application last recorded,
+   * which is not necessarily the one under the cursor.
+   */
+  | { readonly kind: "type"; readonly text: string; readonly field?: string }
+  /** Remove the last Unicode scalar value from one named field, or the draft. */
+  | { readonly kind: "erase"; readonly field?: string }
   /** Admit the draft as this execution's one entry. */
   | { readonly kind: "submit" }
   | { readonly kind: "select-surface"; readonly surface: ReplSurface }
@@ -33,5 +40,17 @@ export type ReplAction =
   | { readonly kind: "go-live" }
   | { readonly kind: "pause" }
   | { readonly kind: "continue" }
-  /** Answer the question waiting right now. */
-  | { readonly kind: "answer" };
+  /** Answer the question waiting right now, from the form as it stands. */
+  | { readonly kind: "answer" }
+  /** Give this form field the focus that text and Backspace act on. */
+  | { readonly kind: "select-field"; readonly field: string }
+  /** Put one offered enum value into one field. */
+  | { readonly kind: "choose"; readonly field: string; readonly option: string }
+  /**
+   * Move the read-only message region by whole lines.
+   *
+   * A delta rather than a position, because the control that emits it knows
+   * which way it points and nothing else: how far the region can go is the
+   * frame's to decide, and clamping belongs where the height is known.
+   */
+  | { readonly kind: "scroll"; readonly delta: number };

packages/cli/src/repl/components/rows.ts

@@ -140,6 +140,26 @@ function activation(input: ReplViewData): ReplAction | undefined {
   if (select === "close") {
     return { kind: "close-drawer" };
   }
+  if (select === "form-field") {
+    const field = named["field"];
+    return typeof field === "string" ? { kind: "select-field", field } : undefined;
+  }
+  if (select === "form-choice") {
+    const field = named["field"];
+    const option = named["option"];
+    return typeof field === "string" && typeof option === "string"
+      ? { kind: "choose", field, option }
+      : undefined;
+  }
+  if (select === "form-submit") {
+    return { kind: "answer" };
+  }
+  if (select === "scroll") {
+    // A direction, not a position: the control knows which way it points, and
+    // how far the region may travel is the frame's to decide.
+    const delta = named["delta"];
+    return typeof delta === "number" ? { kind: "scroll", delta } : undefined;
+  }
   return undefined;
 }
 
@@ -159,14 +179,19 @@ export const FIELD: ReplComponent<ReplAction> = component<ReplAction>({
     node.render(rendered(node.input));
     node.onInput((input: ReplViewData) => node.render(rendered(input)));
     node.claim((event: ReplInputEvent): ReplAction | undefined => {
+      // The field this line edits, read off its own description. Text reaches
+      // the field the person is actually on rather than whichever one the
+      // application last recorded as selected.
+      const named = optional(node.input, "field");
+      const owns: { readonly field?: string } = named === undefined ? {} : { field: named };
       if (event.kind === "text") {
-        return { kind: "type", text: event.text };
+        return { kind: "type", text: event.text, ...owns };
       }
       if (event.kind === "pointer") {
         return undefined;
       }
       if (event.key === "Backspace") {
-        return { kind: "erase" };
+        return { kind: "erase", ...owns };
       }
       if (event.key === "Enter") {
         return submission(node.input);