fix(882): fixes negative number submission for employees input (#1130)

* fix(882): fixes negative number submission for employees input

* formatting

* fix linting

front/src/utils/cast-as-positive-integer-or-null.ts

@@ -0,0 +1,64 @@
+export function canBeCastAsPositiveIntegerOrNull(
+  probablePositiveNumberOrNull: string | undefined | number | null,
+): probablePositiveNumberOrNull is number | null {
+  if (probablePositiveNumberOrNull === undefined) {
+    return false;
+  }
+
+  if (typeof probablePositiveNumberOrNull === 'number') {
+    return (
+      Number.isInteger(probablePositiveNumberOrNull) &&
+      Math.sign(probablePositiveNumberOrNull) === 1
+    );
+  }
+
+  if (probablePositiveNumberOrNull === null) {
+    return true;
+  }
+
+  if (probablePositiveNumberOrNull === '') {
+    return true;
+  }
+
+  if (typeof probablePositiveNumberOrNull === 'string') {
+    const stringAsNumber = +probablePositiveNumberOrNull;
+
+    if (isNaN(stringAsNumber)) {
+      return false;
+    }
+
+    if (Number.isInteger(stringAsNumber) && Math.sign(stringAsNumber) === 1) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+export function castAsPositiveIntegerOrNull(
+  probablePositiveNumberOrNull: string | undefined | number | null,
+): number | null {
+  if (
+    canBeCastAsPositiveIntegerOrNull(probablePositiveNumberOrNull) === false
+  ) {
+    throw new Error('Cannot cast to positive number or null');
+  }
+
+  if (probablePositiveNumberOrNull === null) {
+    return null;
+  }
+
+  if (probablePositiveNumberOrNull === '') {
+    return null;
+  }
+
+  if (typeof probablePositiveNumberOrNull === 'number') {
+    return probablePositiveNumberOrNull;
+  }
+
+  if (typeof probablePositiveNumberOrNull === 'string') {
+    return +probablePositiveNumberOrNull;
+  }
+
+  return null;
+}