feat: initial implementation (#1)

Author: mdjastrzebski

Diff for: src/__tests__/index.test.tsx

@@ -1 +1,76 @@
-it.todo('write a test');
+type RegexComponent = string | RegexQuantifier;
+
+type RegexQuantifier = OneOrMore | Optionally;
+
+type OneOrMore = {
+  type: 'oneOrMore';
+  children: RegexComponent[];
+};
+
+function oneOrMore(...children: RegexComponent[]): OneOrMore {
+  return {
+    type: 'oneOrMore',
+    children,
+  };
+}
+
+type Optionally = {
+  type: 'optionally';
+  children: RegexComponent[];
+};
+
+function optionally(...children: RegexComponent[]): Optionally {
+  return {
+    type: 'optionally',
+    children,
+  };
+}
+
+function compile(...children: RegexComponent[]): string {
+  return children.map((c) => compileSingle(c)).join('');
+}
+
+function compileSingle(component: RegexComponent): string {
+  if (typeof component === 'string') {
+    return component;
+  }
+
+  const { type, children } = component;
+  if (type === 'oneOrMore') {
+    return `${wrapGroup(compile(...children))}+`;
+  }
+
+  if (type === 'optionally') {
+    return `${wrapGroup(compile(...children))}?`;
+  }
+
+  throw new Error(`Unknown component ${component}`);
+}
+
+function wrapGroup(input: string): string {
+  return input.length === 1 ? input : `(${input})`;
+}
+
+function regex(...children: RegexComponent[]): RegExp {
+  const pattern = compile(...children);
+  return new RegExp(pattern);
+}
+
+test('basic quantifies', () => {
+  expect(compile('a')).toEqual('a');
+  expect(compile('a', 'b')).toEqual('ab');
+
+  expect(compile(oneOrMore('a'))).toEqual('a+');
+  expect(compile(optionally('a'))).toEqual('a?');
+
+  expect(compile('a', oneOrMore('b'))).toEqual('ab+');
+  expect(compile('a', oneOrMore('bc'))).toEqual('a(bc)+');
+  expect(compile('a', oneOrMore('bc'))).toEqual('a(bc)+');
+
+  expect(compile(optionally('a'), 'b')).toEqual('a?b');
+});
+
+test('regex constructor', () => {
+  expect(regex('a').test('a')).toBeTruthy();
+  expect(regex('a').test('b')).toBeFalsy();
+});