import { describe, expect, it } from 'vitest'
import { Rng, seedToRng } from '../src/renderer/game/engine/kernel/rng'

describe('Rng.sfc32 特性', () => {
  it('同一种子产生的序列完全一致', () => {
    const a = new Rng(seedToRng('ser1'))
    const b = new Rng(seedToRng('ser1'))
    for (let i = 0; i < 5000; i++) {
      expect(a.next()).toBe(b.next())
    }
  })

  it('不同种子产生不同序列', () => {
    const a = new Rng(seedToRng('seed-a'))
    const b = new Rng(seedToRng('seed-b'))
    let diff = 0
    for (let i = 0; i < 100; i++) {
      if (a.next() !== b.next()) diff++
    }
    expect(diff).toBeGreaterThan(90)
  })

  it('输出始终落在 [0,1)', () => {
    const rng = new Rng(seedToRng('domain'))
    for (let i = 0; i < 20000; i++) {
      const v = rng.next()
      expect(v).toBeGreaterThanOrEqual(0)
      expect(v).toBeLessThan(1)
    }
  })

  it('分布均值接近 0.5（20000 样本）', () => {
    const rng = new Rng(seedToRng('mean'))
    let sum = 0
    const n = 20000
    for (let i = 0; i < n; i++) sum += rng.next()
    const mean = sum / n
    expect(Math.abs(mean - 0.5)).toBeLessThan(0.02)
  })

  it('int 端点全部可取（长抽样覆盖 min 与 max）', () => {
    const rng = new Rng(seedToRng('ends'))
    let minSeen: number | null = null
    let maxSeen: number | null = null
    for (let i = 0; i < 5000; i++) {
      const v = rng.int(1, 6)
      expect(v).toBeGreaterThanOrEqual(1)
      expect(v).toBeLessThanOrEqual(6)
      if (v === 1) minSeen = v
      if (v === 6) maxSeen = v
    }
    expect(minSeen).toBe(1)
    expect(maxSeen).toBe(6)
  })

  it('pick 返回数组内元素', () => {
    const rng = new Rng(seedToRng('pick'))
    const pool = ['a', 'b', 'c']
    for (let i = 0; i < 200; i++) {
      expect(pool).toContain(rng.pick(pool))
    }
  })

  it('pick 空数组抛错（进行防御性约束）', () => {
    const rng = new Rng(seedToRng('empty'))
    expect(() => rng.pick([])).toThrow()
  })

  it('chance 边界行为：p=0 恒否、p=1 恒是', () => {
    const rng = new Rng(seedToRng('chance'))
    for (let i = 0; i < 50; i++) {
      expect(rng.chance(0)).toBe(false)
      expect(rng.chance(1)).toBe(true)
    }
  })

  it('shuffle 保持乱序且不丢元素', () => {
    const rng = new Rng(seedToRng('shuffle'))
    const src = Array.from({ length: 30 }, (_, i) => i)
    const shuffled = rng.shuffle(src)
    expect(shuffled.length).toBe(30)
    expect([...shuffled].sort((a, b) => a - b)).toEqual(src)
    // 30 个元素单次打乱完全与原序相同概率几乎为 0
    expect(shuffled.some((v, i) => v !== src[i])).toBe(true)
  })

  it('between 落在区间内', () => {
    const rng = new Rng(seedToRng('between'))
    for (let i = 0; i < 500; i++) {
      const v = rng.between(2.5, 7.5)
      expect(v).toBeGreaterThanOrEqual(2.5)
      expect(v).toBeLessThanOrEqual(7.5)
    }
  })

  it('getState 返回副本：修改不影响原', () => {
    const rng = new Rng(seedToRng('copy'))
    rng.next()
    const snap = rng.getState()
    snap.a = 999999
    const c = new Rng(rng.getState())
    expect(c.next()).toBe(rng.next())
  })

  it('全零种子被安全修复不会退化为常数', () => {
    const state = { a: 0, b: 0, c: 0, d: 0 }
    const rng = new Rng(state)
    const v1 = rng.next()
    const v2 = rng.next()
    expect(v1).not.toBe(v2)
  })

  it('空字符串种子可稳定初始化', () => {
    const a = new Rng(seedToRng(''))
    const b = new Rng(seedToRng(''))
    expect(a.next()).toBe(b.next())
  })
})