fix(live-atc): match the D-registration to the aircraft class

VFR scenarios drew from a fixed pool of D-E** registrations regardless of type,
so an A320 was assigned "D-ETMO". The letter after "D-" is assigned by weight
and type class (LuftVZO Anlage 1): D-E is single-engine pistons up to 2 t, so
an airliner has to be D-A.

Pick the class from the ICAO type designator — D-A for airliners, D-I for light
twins, D-H for helicopters, D-E for light singles and anything unrecognised,
since VFR scenarios are overwhelmingly light aircraft.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/shared/registration.test.ts

@@ -0,0 +1,73 @@
+import { test } from 'node:test'
+import assert from 'node:assert/strict'
+import {
+  generateGermanRegistration,
+  germanRegistrationPrefix,
+} from '../../shared/utils/registration.ts'
+
+// German registrations encode a weight/type class in the first letter after
+// "D-" (LuftVZO Anlage 1): D-A above 20 t, D-I multi-engine 2–5.7 t,
+// D-E single-engine piston up to 2 t, D-H helicopters.
+
+test('airliners get a D-A registration', () => {
+  for (const type of ['A320', 'A319', 'A321', 'B738', 'B39M', 'A333', 'A359', 'B77W', 'B788', 'B744', 'A388', 'E190', 'CRJ9']) {
+    assert.equal(germanRegistrationPrefix(type), 'A', `${type} should be a D-A registration`)
+  }
+})
+
+test('single-engine light aircraft get a D-E registration', () => {
+  for (const type of ['C172', 'PA28', 'DA40', 'C152', 'SR22', 'DR40', 'P28A']) {
+    assert.equal(germanRegistrationPrefix(type), 'E', `${type} should be a D-E registration`)
+  }
+})
+
+test('light twins get a D-I registration', () => {
+  for (const type of ['BE58', 'PA34', 'C310', 'BE76']) {
+    assert.equal(germanRegistrationPrefix(type), 'I', `${type} should be a D-I registration`)
+  }
+})
+
+test('helicopters get a D-H registration', () => {
+  for (const type of ['R44', 'R22', 'EC35', 'H125', 'AS50']) {
+    assert.equal(germanRegistrationPrefix(type), 'H', `${type} should be a D-H registration`)
+  }
+})
+
+test('an unknown type falls back to the light single class', () => {
+  // VFR scenarios are overwhelmingly light aircraft, so that is the safe guess.
+  assert.equal(germanRegistrationPrefix('ZZZZ'), 'E')
+  assert.equal(germanRegistrationPrefix(''), 'E')
+  assert.equal(germanRegistrationPrefix(undefined as unknown as string), 'E')
+})
+
+test('the type is matched case-insensitively and ignores a trailing variant', () => {
+  assert.equal(germanRegistrationPrefix('a320'), 'A')
+  assert.equal(germanRegistrationPrefix('A320/M'), 'A')
+  assert.equal(germanRegistrationPrefix(' c172 '), 'E')
+})
+
+test('generateGermanRegistration produces a well-formed registration for the class', () => {
+  for (let i = 0; i < 200; i++) {
+    const { registration } = generateGermanRegistration('A320')
+    assert.match(registration, /^D-A[A-Z]{3}$/, registration)
+  }
+  for (let i = 0; i < 200; i++) {
+    const { registration } = generateGermanRegistration('C172')
+    assert.match(registration, /^D-E[A-Z]{3}$/, registration)
+  }
+})
+
+test('the abbreviated callsign is the first letter plus the last two', () => {
+  // German ATC abbreviates D-EMIL to "D-IL" after first contact.
+  const { registration, short } = generateGermanRegistration('C172')
+  const letters = registration.slice(2)
+  assert.equal(short, `D-${letters.slice(-2)}`)
+  assert.match(short, /^D-[A-Z]{2}$/)
+})
+
+test('an A320 never gets the light-aircraft registration that prompted this', () => {
+  for (let i = 0; i < 500; i++) {
+    const { registration } = generateGermanRegistration('A320')
+    assert.ok(!registration.startsWith('D-E'), `A320 got ${registration}`)
+  }
+})