functional-programming-snake/e2e/lib/oracle.mjs

// The oracle: the pure JS solutions, run in Node, say what a page must draw for a given seed, stored best and list of
// inputs. Nothing here touches a browser.
//
// A program (`main`, `pongMain`, `replayMain(recording)`, `lifeMain`) is an IO that yields a stream; `trace` answers
// its RandomSeed and LoadBest ops with the test's seed and best, exactly as the course's `play(main, seed, events,
// best)` does (js/solutions/app.js). The Model then steps that stream one input at a time and traces each IO it emits,
// so it knows, per input, which shapes are drawn and which scores are saved. Flattened, its output equals `play`'s
// (tests/techniques.spec.mjs checks that); grouped per input, it lines up with the page's recorded frames.
//
// Next to the program, the Model steps a stream of the program's *states*, built from the same pieces as the program
// (e.g. `clampTime(sessions(seed, best, speedActions), MAX_GAP_MS)` for Snake). It is used only to plan inputs and to
// state assertions in game terms ("the head moved one cell"); every judgement of the page is made on its drawing.
import { readFileSync } from 'node:fs'
import { trace } from '../../js/solutions/io.js'
import { clampTime } from '../../js/solutions/stream.js'
import { main, play, sessions, sessionView, speedActions, MAX_GAP_MS, FRAME_MS } from '../../js/solutions/app.js'
import { movesEvery } from '../../js/solutions/game.js'
import { newGame } from '../../js/solutions/spawn.js'
import { pongMain, pongStates, pongActions, FRAME_MS_PONG } from '../../js/solutions/pong/app.js'
import { pongView } from '../../js/solutions/pong/view.js'
import { replayMain, viewerStates, replayActions, viewerView, frames as replayFrames, REPLAY_MS } from '../../js/solutions/replay.js'
import { lifeMain, lifeStates, lifeActions, GEN_MS } from '../../js/solutions/life/app.js'
import { lifeView } from '../../js/solutions/life/view.js'
import { LCELL, LW, LH } from '../../js/solutions/life/model.js'

export const recording = JSON.parse(readFileSync(new URL('../../fixtures/replay-sample.json', import.meta.url), 'utf8'))

/** The four pages of a track, the program each runs, and the matching stream of states. */
export const programs = {
  snake: {
    page: 'index.html',
    main: () => main,
    states: (seed, best) => clampTime(sessions(seed, best, speedActions), MAX_GAP_MS),
  },
  pong: {
    page: 'pong.html',
    main: () => pongMain,
    states: (seed) => clampTime(pongStates(seed, pongActions), MAX_GAP_MS),
  },
  replay: {
    page: 'replay.html',
    main: () => replayMain(recording),
    states: () => clampTime(viewerStates(replayFrames(recording).length - 1, replayActions), MAX_GAP_MS),
  },
  life: {
    page: 'life.html',
    main: () => lifeMain,
    states: (seed) => clampTime(lifeStates(seed, lifeActions), MAX_GAP_MS),
  },
}

export class Model {
  constructor(name, { seed, best = 0 }) {
    const program = programs[name]
    this.name = name
    this.seed = seed
    this.best = best
    const traced = trace(program.main(), seed, best)
    this.startOps = traced.ops // RandomSeed, LoadBest: what the program asks before it starts
    this.stream = traced.result
    this.stateStream = program.states(seed, best)
    this.state = null // latest state the program emitted
    this.inputs = [] // every input fed so far
    this.frames = [] // per input that drew anything: {input, shapes}
    this.saves = [] // scores passed to SaveBest, in order
  }

  /** Feed inputs, in order, as the page received them. */
  feed(inputs) {
    for (const input of inputs) {
      const [ios, next] = this.stream.step(input)
      this.stream = next
      const ops = ios.flatMap((io) => trace(io, this.seed, this.best).ops)
      const shapes = ops.filter((op) => op.tag === 'Draw').map((op) => op.shape)
      this.saves.push(...ops.filter((op) => op.tag === 'SaveBest').map((op) => op.score))
      if (shapes.length > 0) this.frames.push({ input, shapes })
      const [states, nextStates] = this.stateStream.step(input)
      this.stateStream = nextStates
      if (states.length > 0) this.state = states[states.length - 1]
      this.inputs.push(input)
    }
    return this
  }

  /** What the state would be after these inputs, without feeding them. Streams are values, so this is free. */
  peek(inputs) {
    const [states] = inputs.reduce(([acc, s], input) => {
      const [out, next] = s.step(input)
      return [out.length > 0 ? out[out.length - 1] : acc, next]
    }, [this.state, this.stateStream])
    return states
  }

  /** The course's own one-equality run of the program over every input fed so far. */
  play() {
    return play(programs[this.name].main(), this.seed, this.inputs, this.best)
  }

  lastFrame() {
    return this.frames.length === 0 ? null : this.frames[this.frames.length - 1]
  }
}

// Re-exported for tests that state expectations directly in model terms.
export { sessionView, newGame, movesEvery, pongView, viewerView, replayFrames, lifeView }
export { FRAME_MS, MAX_GAP_MS, FRAME_MS_PONG, REPLAY_MS, GEN_MS, LCELL, LW, LH }