Expose grouped Truthtrance current-fact questions

game/truth-fact-expression.ts

@@ -0,0 +1,39 @@
+import type { TruthFact } from './truthtrance';
+
+// Existing parser limits. These bound structured input; they are not printed
+// restrictions on which game-related yes/no questions may be asked.
+export const TRUTH_FACT_MAX_NODES = 16;
+export const TRUTH_FACT_MAX_DEPTH = 4;
+export const TRUTH_FACT_MAX_TERMS = 8;
+export const TRUTH_FACT_SIZE_ERROR =
+  'Truthtrance supports at most 16 clauses and four levels of grouping.';
+export const TRUTH_FACT_GROUP_ERROR =
+  'Combine two to eight fact clauses with AND or OR.';
+
+export function truthFactExpressionSize(fact: TruthFact): { nodes: number; depth: number } {
+  if (fact.kind !== 'and' && fact.kind !== 'or') return { nodes: 1, depth: 0 };
+  const children = fact.terms.map(truthFactExpressionSize);
+  return {
+    nodes: 1 + children.reduce((sum, child) => sum + child.nodes, 0),
+    depth: 1 + Math.max(0, ...children.map(child => child.depth)),
+  };
+}
+
+/** Structural input feedback; leaf eligibility remains with the existing
+ * entitled field validators and the authoritative question parser. */
+export function truthFactExpressionError(fact: TruthFact): string | null {
+  const size = truthFactExpressionSize(fact);
+  if (size.nodes > TRUTH_FACT_MAX_NODES || size.depth > TRUTH_FACT_MAX_DEPTH)
+    return TRUTH_FACT_SIZE_ERROR;
+  const groupError = (node: TruthFact): string | null => {
+    if (node.kind !== 'and' && node.kind !== 'or') return null;
+    if (node.terms.length < 2 || node.terms.length > TRUTH_FACT_MAX_TERMS)
+      return TRUTH_FACT_GROUP_ERROR;
+    for (const term of node.terms) {
+      const error = groupError(term);
+      if (error) return error;
+    }
+    return null;
+  };
+  return groupError(fact);
+}