glitch_automata_lab/backend/test/caEngines.test.ts

import { describe, expect, it } from 'vitest'
import { listCaEngineRuntimes, registerCaEngineRuntime, stepCaCells } from '../admin/src/caEngines.js'
import type { Cells, SceneParams } from '../admin/src/types.js'

function cells(width: number, height: number, alive: Array<[number, number]> = []): Cells {
  const grid = Array.from({ length: height }, () => Array.from({ length: width }, () => false))
  for (const [x, y] of alive) grid[y][x] = true
  return grid
}

function settings(params: SceneParams = {}): SceneParams {
  return {
    ...params,
    simulation: {
      engineId: 'game-of-life-2d',
      ruleId: 'B3/S23',
      neighborhoodId: 'moore',
      ...params.simulation
    }
  }
}

describe('CA engine runtimes', () => {
  it('registers built-in runtimes that can be selected by engine id', () => {
    expect(listCaEngineRuntimes().map((engine) => engine.id)).toEqual(
      expect.arrayContaining([
        'game-of-life-2d',
        'outer-totalistic-2d',
        'elementary-1d',
        'wildfire-2d',
        'generic-voxel-ca',
        'noop'
      ])
    )
  })

  it('allows a drop-in engine to register and step cells through the shared contract', () => {
    registerCaEngineRuntime({
      id: 'test-fill-runtime',
      label: 'Test fill runtime',
      step: (current) => current.map((row) => row.map(() => true))
    })

    expect(stepCaCells(cells(2, 2), settings({ simulation: { engineId: 'test-fill-runtime' } }))).toEqual([
      [true, true],
      [true, true]
    ])
  })

  it('rejects duplicate engine runtime ids', () => {
    expect(() =>
      registerCaEngineRuntime({
        id: 'game-of-life-2d',
        label: 'Duplicate Life',
        step: (current) => current
      })
    ).toThrow('already registered')
  })

  it('rejects engine output that changes the grid contract', () => {
    registerCaEngineRuntime({
      id: 'test-invalid-shape-runtime',
      label: 'Test invalid shape runtime',
      step: () => [[true]]
    })

    expect(() => stepCaCells(cells(2, 2), settings({ simulation: { engineId: 'test-invalid-shape-runtime' } }))).toThrow(
      'preserve the input grid dimensions'
    )
  })

  it('does not mutate the input cell grid while stepping', () => {
    const current = cells(3, 3, [
      [0, 1],
      [1, 1],
      [2, 1]
    ])
    const before = current.map((row) => [...row])

    const next = stepCaCells(current, settings())

    expect(current).toEqual(before)
    expect(next).not.toBe(current)
    expect(next[0]).not.toBe(current[0])
  })

  it('steps Conway Life oscillators with the outer-totalistic B/S rule contract', () => {
    const blinker = cells(5, 5, [
      [2, 1],
      [2, 2],
      [2, 3]
    ])

    expect(stepCaCells(blinker, settings())).toEqual(
      cells(5, 5, [
        [1, 2],
        [2, 2],
        [3, 2]
      ])
    )
  })

  it('steps elementary 1D rules on the active source row', () => {
    const current = cells(3, 3, [[1, 0]])

    expect(
      stepCaCells(current, settings({ simulation: { engineId: 'elementary-1d', ruleId: 'Rule 90' } }))
    ).toEqual(cells(3, 3, [
      [0, 0],
      [2, 0]
    ]))
  })

  it('uses fixed boundaries for elementary 1D edge samples when requested', () => {
    const current = cells(3, 3, [[0, 0]])

    expect(
      stepCaCells(current, settings({ simulation: { engineId: 'elementary-1d', ruleId: 'Rule 90', grid: { boundary: 'fixed' } } }))
    ).toEqual(cells(3, 3, [[1, 0]]))
  })

  it('steps binary wildfire by cooling burning cells and igniting von Neumann neighbours', () => {
    const current = cells(3, 3, [[1, 1]])

    expect(
      stepCaCells(current, settings({ simulation: { engineId: 'wildfire-2d', spreadProbability: 1 } }))
    ).toEqual(cells(3, 3, [
      [1, 0],
      [0, 1],
      [2, 1],
      [1, 2]
    ]))
  })

  it('lets binary wildfire suppress spread with deterministic probability settings', () => {
    const current = cells(3, 3, [[1, 1]])

    expect(
      stepCaCells(current, settings({ simulation: { engineId: 'wildfire-2d', spreadProbability: 0 } }))
    ).toEqual(cells(3, 3))
  })

  it('defaults boundaries to wrap when the node does not specify a boundary condition', () => {
    const current = cells(3, 3, [
      [2, 2],
      [2, 0],
      [0, 2]
    ])

    expect(stepCaCells(current, settings())[0][0]).toBe(true)
  })

  it('supports fixed boundaries and legacy wrap=false nodes', () => {
    const current = cells(3, 3, [
      [2, 2],
      [2, 0],
      [0, 2]
    ])

    expect(stepCaCells(current, settings({ simulation: { grid: { boundary: 'fixed' } } }))[0][0]).toBe(false)
    expect(stepCaCells(current, settings({ simulation: { grid: { wrap: false } } }))[0][0]).toBe(false)
  })

  it('supports mirror boundaries by reflecting out-of-bounds neighbour samples', () => {
    const current = cells(3, 3, [
      [0, 0],
      [1, 0],
      [0, 1]
    ])

    expect(stepCaCells(current, settings({ simulation: { grid: { boundary: 'fixed' } } }))[0][0]).toBe(true)
    expect(stepCaCells(current, settings({ simulation: { grid: { boundary: 'mirror' } } }))[0][0]).toBe(false)
  })
})