game: seeded world generation (pure) — start region + expansion rings

lib/game/world.test.ts

@@ -0,0 +1,79 @@
+import { describe, expect, it } from 'vitest'
+import { generateRing, generateStartRegion, makeName, mulberry32 } from './world'
+
+describe('generateStartRegion', () => {
+  const region = generateStartRegion(mulberry32(42))
+
+  it('produces a starting system plus six neighbours', () => {
+    expect(region.neighbors).toHaveLength(6)
+    expect(region.start.x).toBe(50)
+    expect(region.start.y).toBe(50)
+  })
+
+  it('gives every system a unique name and in-bounds coordinates', () => {
+    const all = [region.start, ...region.neighbors]
+    const names = all.map((s) => s.name)
+    expect(new Set(names).size).toBe(names.length)
+    for (const s of all) {
+      expect(s.x).toBeGreaterThanOrEqual(0)
+      expect(s.x).toBeLessThanOrEqual(100)
+      expect(s.y).toBeGreaterThanOrEqual(0)
+      expect(s.y).toBeLessThanOrEqual(100)
+    }
+  })
+
+  it('connects the start to every neighbour and closes the ring cycle', () => {
+    const n = region.neighbors.length
+    // anchor↔each member (n edges) + ring cycle (n edges)
+    expect(region.edges).toHaveLength(n * 2)
+    for (let i = 0; i < n; i++) {
+      expect(region.edges).toContainEqual([0, i + 1])
+      expect(region.edges).toContainEqual([i + 1, ((i + 1) % n) + 1])
+    }
+    // every edge endpoint is a valid index into [start, ...neighbors]
+    for (const [a, b] of region.edges) {
+      expect(a).toBeGreaterThanOrEqual(0)
+      expect(a).toBeLessThan(n + 1)
+      expect(b).toBeGreaterThanOrEqual(0)
+      expect(b).toBeLessThan(n + 1)
+    }
+  })
+
+  it('is deterministic under a fixed seed and differs across seeds', () => {
+    const again = generateStartRegion(mulberry32(42))
+    expect(again).toEqual(region)
+    const other = generateStartRegion(mulberry32(43))
+    expect(other.start.name !== region.start.name || other.neighbors[0].name !== region.neighbors[0].name).toBe(true)
+  })
+})
+
+describe('generateRing (expansion)', () => {
+  it('adds four systems spaced away from the anchor and existing positions', () => {
+    const takenNames = new Set(['Kepler Drift'])
+    const takenPositions = [{ name: 'Kepler Drift', x: 50, y: 50 }]
+    const ring = generateRing(mulberry32(7), 50, 50, takenNames, takenPositions)
+
+    expect(ring.systems).toHaveLength(4)
+    const ringNames = ring.systems.map((s) => s.name)
+    for (const s of ring.systems) {
+      expect(Math.hypot(s.x - 50, s.y - 50)).toBeGreaterThanOrEqual(16)
+      expect(s.name).not.toBe('Kepler Drift') // never reuses a pre-taken name
+    }
+    expect(new Set(ringNames).size).toBe(4) // and makeName claimed them into the set
+    for (const n of ringNames) expect(takenNames.has(n)).toBe(true)
+    expect(ring.edges).toHaveLength(8) // anchor↔each + cycle
+    for (const [a, b] of ring.edges) {
+      expect(a).toBeGreaterThanOrEqual(0)
+      expect(a).toBeLessThan(5)
+      expect(b).toBeGreaterThanOrEqual(0)
+      expect(b).toBeLessThan(5)
+    }
+  })
+
+  it('never reuses a taken name', () => {
+    const rng = mulberry32(1)
+    const taken = new Set<string>()
+    for (let i = 0; i < 40; i++) makeName(rng, taken)
+    expect(taken.size).toBe(40)
+  })
+})