const { Space, BodyAdapter, Brain } = require("@srk0102/plexa")
const { OllamaBrain } = require("@srk0102/plexa/bridges/ollama")
// -- Pure JS cart-pole physics --
class CartpolePhysics {
constructor() { this.reset() }
reset() { this.x = 0; this.v = 0; this.theta = (Math.random() - 0.5) * 0.1; this.omega = 0; this.force = 0 }
step(dt = 1 / 60) {
const g = 9.8, mC = 1.0, mP = 0.1, L = 0.5
const total = mC + mP
const sinT = Math.sin(this.theta), cosT = Math.cos(this.theta)
const temp = (this.force + mP * L * this.omega * this.omega * sinT) / total
const alpha = (g * sinT - cosT * temp) / (L * (4 / 3 - (mP * cosT * cosT) / total))
const accX = temp - (mP * L * alpha * cosT) / total
this.v += accX * dt; this.x += this.v * dt
this.omega += alpha * dt; this.theta += this.omega * dt
this.v *= 0.999; this.omega *= 0.999; this.force = 0
if (Math.abs(this.theta) > 1.2 || Math.abs(this.x) > 2.5) { this.reset(); return true }
return false
}
apply(direction, magnitude = 0.5) {
const f = Math.min(1, Math.max(0, magnitude)) * 15
this.force = direction === "left" ? -f : f
}
}
// -- Body --
class CartpoleBody extends BodyAdapter {
static bodyName = "cartpole"
static tools = {
apply_force: {
description: "push the cart left or right",
parameters: {
direction: { type: "string", enum: ["left", "right"], required: true },
magnitude: { type: "number", min: 0, max: 1, required: true },
},
},
hold: { description: "no-op", parameters: {} },
}
constructor() { super(); this.physics = new CartpolePhysics() }
async apply_force({ direction, magnitude }) {
this.physics.apply(direction, magnitude); return { applied: direction, magnitude }
}
async hold() { this.physics.force = 0; return { ok: true } }
async tick() {
await super.tick()
this.physics.step()
this.setState({ pole_angle: this.physics.theta, cart_pos: this.physics.x })
// Reflex: emergency damping when the pole is past the danger threshold.
if (Math.abs(this.physics.theta) > 0.5) {
this.physics.apply(this.physics.theta > 0 ? "left" : "right", 0.6)
}
if (Math.abs(this.physics.theta) > 0.8) {
this.emit("pole_critical", { angle: this.physics.theta }, "CRITICAL")
}
}
}
// -- Stub brain (used if Ollama is not running) --
class StubBrain extends Brain {
constructor() { super({ model: "stub" }); this._i = 0 }
async _rawCall() {
this._i++
const choices = [
{ tool: "apply_force", parameters: { direction: "left", magnitude: 0.5 } },
{ tool: "apply_force", parameters: { direction: "right", magnitude: 0.5 } },
{ tool: "hold", parameters: {} },
]
const c = choices[this._i % choices.length]
return JSON.stringify({ target_body: "cartpole", tool: c.tool, parameters: c.parameters })
}
}
// -- Main --
async function main() {
const space = new Space("cartpole_demo", { tickHz: 60, brainIntervalMs: 1500 })
space.addBody(new CartpoleBody())
const ollamaUp = await OllamaBrain.isAvailable()
space.setBrain(ollamaUp ? new OllamaBrain({ model: "llama3.2", maxTokens: 80 }) : new StubBrain())
space.setGoal("balance the pole upright")
space.on("tool_dispatched", (e) =>
console.log(`[plexa] ${e.body}.${e.tool}(${JSON.stringify(e.parameters)})`)
)
space.installShutdownHandlers()
await space.run()
console.log(`[plexa] running at ${space.tickHz}Hz, brain=${ollamaUp ? "ollama" : "stub"}`)
}
main()
