Build standalone CiviCRM check-in middleware

lib/conditional.ts

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+/**
+ * Visibility engine for form sections and fields.
+ *
+ * Evaluates a VisibilityRule tree against the current form state.
+ * Form state is a plain object {fieldName: value}. Missing fields are
+ * treated as undefined.
+ *
+ * Rule semantics:
+ *   - SimpleCondition: tests a single field with an operator
+ *   - {all: [...]}:    AND
+ *   - {any: [...]}:    OR
+ *
+ * Operator semantics:
+ *   - equals       : field value === rule.value
+ *   - notEquals    : field value !== rule.value
+ *   - in           : rule.values includes the field value
+ *   - notIn        : rule.values does not include the field value
+ *   - isEmpty      : field is undefined / null / "" / [] / {}
+ *   - isNotEmpty   : negation of isEmpty
+ *
+ * If a rule is malformed, evaluate returns false (field stays hidden) rather
+ * than throwing, so a config typo can never break the page.
+ */
+
+import type {
+  VisibilityRule,
+  SimpleCondition,
+  AllCondition,
+  AnyCondition,
+} from "@/types/form";
+
+type FormState = Record<string, unknown>;
+
+function isSimple(r: VisibilityRule): r is SimpleCondition {
+  return typeof (r as SimpleCondition).field === "string";
+}
+
+function isAll(r: VisibilityRule): r is AllCondition {
+  return Array.isArray((r as AllCondition).all);
+}
+
+function isAny(r: VisibilityRule): r is AnyCondition {
+  return Array.isArray((r as AnyCondition).any);
+}
+
+function isEmpty(v: unknown): boolean {
+  if (v === undefined || v === null) return true;
+  if (typeof v === "string") return v.length === 0;
+  if (Array.isArray(v)) return v.length === 0;
+  if (typeof v === "object") return Object.keys(v as object).length === 0;
+  return false;
+}
+
+function evalSimple(c: SimpleCondition, state: FormState): boolean {
+  const v = state[c.field];
+  switch (c.op) {
+    case "equals":
+      return v === c.value;
+    case "notEquals":
+      return v !== c.value;
+    case "in":
+      return Array.isArray(c.values) && c.values.includes(v as string | number | boolean);
+    case "notIn":
+      return Array.isArray(c.values) && !c.values.includes(v as string | number | boolean);
+    case "isEmpty":
+      return isEmpty(v);
+    case "isNotEmpty":
+      return !isEmpty(v);
+    default:
+      return false;
+  }
+}
+
+export function evaluate(rule: VisibilityRule | undefined, state: FormState): boolean {
+  if (!rule) return true;
+  if (isSimple(rule)) return evalSimple(rule, state);
+  if (isAll(rule)) return rule.all.every((r) => evaluate(r, state));
+  if (isAny(rule)) return rule.any.some((r) => evaluate(r, state));
+  return false;
+}