session.worker.js

import {loadModel,ModelSimulation} from './model.js'
let simulation,adapter,queue=Promise.resolve()
const emit=data=>self.postMessage({event:data})
self.onmessage=({data})=>{
  // Control notifications must stay responsive during an adapter's paced rollout.
  if(data.command){try{adapter?.command(data.command)}catch(error){emit({type:'error',error:String(error)})}return}
  queue=queue.then(async()=>{
    try{
      let value
      if(data.method==='load'){
        if(simulation||adapter)throw Error('Session already loaded')
        if(data.args.adapterUrl){
          const module=await import(data.args.adapterUrl)
          adapter=await module.createAdapter({config:data.args,emit,loadModel})
          value=await adapter.describe()
        }else{
          const {mj,model}=await loadModel(data.args,message=>emit({type:'loading',message}))
          simulation=new ModelSimulation(mj,model);value=simulation.describe()
        }
      }else{
        const target=adapter||simulation
        if(!target)throw Error('Load a model first')
        if(!['reset','step','snapshot','describe'].includes(data.method)||typeof target[data.method]!=='function')throw Error(`Unsupported operation: ${data.method}`)
        value=await target[data.method](data.args)
      }
      self.postMessage({id:data.id,value})
    }catch(error){self.postMessage({id:data.id,error:error.stack||String(error)})}
  })
}