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

lib/game/world.test.ts

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+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)
+  })
+})

lib/game/world.ts

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+// Pure, seeded world generation — no DB, no Date, no Math.random. The same seed always
+// yields the same world, which is what makes unit tests (and save regeneration) deterministic.
+
+export interface WorldSystem {
+  name: string
+  x: number // 0–100 coordinate space, rendered directly by NodeGraph
+  y: number
+}
+
+export const START_X = 50
+export const START_Y = 50
+
+const START_RING = 6 // neighbours around the starting system on a new game
+const EXPAND_RING = 4 // new neighbours generated when jumping into an undiscovered system
+const MIN_SPACING = 16 // minimum distance between any two systems in the 0–100 space
+
+// mulberry32 — small fast seeded PRNG; plenty for name/position picking.
+export function mulberry32(seed: number): () => number {
+  let a = seed >>> 0
+  return () => {
+    a |= 0
+    a = (a + 0x6d2b79f5) | 0
+    let t = Math.imul(a ^ (a >>> 15), 1 | a)
+    t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t
+    return ((t ^ (t >>> 14)) >>> 0) / 4294967296
+  }
+}
+
+const FIRST = [
+  'KEPLER', 'VESPER', 'HOLLOW', 'CINDER', 'LANTERN', 'SABLE', 'ORPHEUS', 'MIRE',
+  'THALASSA', 'KUIPER', 'AURELLE', 'BRIMSTONE', 'EMBER', 'FROST', 'GALE', 'IRON',
+]
+const SECOND = ['DRIFT', 'REACH', 'GATE', 'FIELD', 'VOID', 'DEEP', 'BEND', 'SHARD']
+
+function title(word: string): string {
+  return word.charAt(0) + word.slice(1).toLowerCase()
+}
+
+// Picks a name not in `taken` and adds it, so callers can't accidentally reuse one.
+export function makeName(rng: () => number, taken: Set<string>): string {
+  for (;;) {
+    const name = `${title(FIRST[Math.floor(rng() * FIRST.length)])} ${title(SECOND[Math.floor(rng() * SECOND.length)])}`
+    if (!taken.has(name)) {
+      taken.add(name)
+      return name
+    }
+  }
+}
+
+function clamp(v: number): number {
+  return Math.min(96, Math.max(4, v))
+}
+
+// Places `count` systems on a ring around (cx,cy), nudging each candidate until it is at
+// least MIN_SPACING away from every known position. After 12 tries it accepts the last
+// candidate anyway — ponytail: a slightly crowded node beats an infinite loop; with ≤6
+// rings per region and spacing 16 in a 0–100 box this never triggers in practice.
+function placeRing(
+  rng: () => number,
+  cx: number,
+  cy: number,
+  count: number,
+  takenNames: Set<string>,
+  takenPositions: WorldSystem[],
+): WorldSystem[] {
+  const placed: WorldSystem[] = []
+  for (let i = 0; i < count; i++) {
+    const baseAngle = (i / count) * Math.PI * 2 + (rng() - 0.5) * 0.6
+    let x = cx
+    let y = cy
+    for (let attempt = 0; attempt < 12; attempt++) {
+      const angle = baseAngle + attempt * 0.45
+      const radius = 26 + rng() * 8
+      x = clamp(cx + Math.cos(angle) * radius)
+      y = clamp(cy + Math.sin(angle) * radius)
+      if ([...takenPositions, ...placed].every((p) => Math.hypot(p.x - x, p.y - y) >= MIN_SPACING)) break
+    }
+    placed.push({ name: makeName(rng, takenNames), x, y })
+  }
+  return placed
+}
+
+// Edges for a ring of n members around an anchor at index 0: anchor↔each member plus the
+// cycle connecting consecutive members (so every system has ≥2 routes and you can always
+// get back). Pairs are indices into [anchor, ...members].
+function ringEdges(n: number): [number, number][] {
+  const edges: [number, number][] = []
+  for (let i = 0; i < n; i++) {
+    edges.push([0, i + 1])
+    edges.push([i + 1, ((i + 1) % n) + 1])
+  }
+  return edges
+}
+
+export interface StartRegion {
+  start: WorldSystem
+  neighbors: WorldSystem[]
+  edges: [number, number][] // indices into [start, ...neighbors]
+}
+
+// New game: the starting system at chart centre plus a ring of undiscovered neighbours.
+export function generateStartRegion(rng: () => number): StartRegion {
+  const taken = new Set<string>()
+  const start: WorldSystem = { name: makeName(rng, taken), x: START_X, y: START_Y }
+  const neighbors = placeRing(rng, START_X, START_Y, START_RING, taken, [start])
+  return { start, neighbors, edges: ringEdges(neighbors.length) }
+}
+
+export interface RingRegion {
+  systems: WorldSystem[]
+  edges: [number, number][] // indices into [anchor, ...systems] — index 0 is the anchor itself
+}
+
+// Jumping into an undiscovered system grows the chart: a fresh ring of (undiscovered)
+// neighbours around it. `takenNames`/`takenPositions` are every system already in the save.
+export function generateRing(
+  rng: () => number,
+  anchorX: number,
+  anchorY: number,
+  takenNames: Set<string>,
+  takenPositions: WorldSystem[],
+): RingRegion {
+  const systems = placeRing(rng, anchorX, anchorY, EXPAND_RING, takenNames, takenPositions)
+  return { systems, edges: ringEdges(systems.length) }
+}