import {readFile,writeFile} from 'node:fs/promises'
import {pathToFileURL} from 'node:url'

const keys=(value,allowed)=>Object.keys(value).filter(key=>!allowed.includes(key))
const safeId=value=>typeof value==='string'&&/^[a-z][a-z0-9-]{0,63}$/.test(value)
export function validateScenario(value){
  const errors=[]
  if(!value||typeof value!=='object'||Array.isArray(value))return['scenario must be an object']
  for(const key of keys(value,['schema','synthetic','requests']))errors.push(`unknown scenario field: ${key}`)
  if(value.schema!=='martybytes-synthetic-gateway/v1')errors.push('schema must be martybytes-synthetic-gateway/v1')
  if(value.synthetic!==true)errors.push('synthetic must be true')
  if(!Array.isArray(value.requests)||value.requests.length===0)errors.push('requests must be a nonempty array')
  else {
    const requestIds=new Set()
    value.requests.forEach((request,index)=>{
      const prefix=`requests[${index}]`
      if(!request||typeof request!=='object'||Array.isArray(request)){errors.push(`${prefix} must be an object`);return}
      for(const key of keys(request,['requestId','budgetUnits','attempts']))errors.push(`${prefix} unknown field: ${key}`)
      if(!safeId(request.requestId))errors.push(`${prefix}.requestId must be a safe stable id`)
      else if(requestIds.has(request.requestId))errors.push(`${prefix}.requestId must be unique`)
      else requestIds.add(request.requestId)
      if(!Number.isInteger(request.budgetUnits)||request.budgetUnits<0)errors.push(`${prefix}.budgetUnits must be a nonnegative integer`)
      if(!Array.isArray(request.attempts)||request.attempts.length===0)errors.push(`${prefix}.attempts must be a nonempty array`)
      else {
        const providers=new Set()
        request.attempts.forEach((attempt,attemptIndex)=>{
          const at=`${prefix}.attempts[${attemptIndex}]`
          if(!attempt||typeof attempt!=='object'||Array.isArray(attempt)){errors.push(`${at} must be an object`);return}
          for(const key of keys(attempt,['provider','model','outcome','syntheticDurationTicks','estimate']))errors.push(`${at} unknown field: ${key}`)
          if(!safeId(attempt.provider))errors.push(`${at}.provider must be a safe id`)
          else if(providers.has(attempt.provider))errors.push(`${at}.provider must be unique per request`)
          else providers.add(attempt.provider)
          if(!safeId(attempt.model))errors.push(`${at}.model must be a safe id`)
          if(!['success','timeout','rate-limit','error'].includes(attempt.outcome))errors.push(`${at}.outcome is invalid`)
          if(!Number.isInteger(attempt.syntheticDurationTicks)||attempt.syntheticDurationTicks<0)errors.push(`${at}.syntheticDurationTicks must be a nonnegative integer`)
          const estimate=attempt.estimate
          if(!estimate||typeof estimate!=='object'||Array.isArray(estimate))errors.push(`${at}.estimate must be an object`)
          else {
            for(const key of keys(estimate,['units','source','basis']))errors.push(`${at}.estimate unknown field: ${key}`)
            if(!Number.isInteger(estimate.units)||estimate.units<0)errors.push(`${at}.estimate.units must be a nonnegative integer`)
            if(!safeId(estimate.source))errors.push(`${at}.estimate.source must be a safe id`)
            if(typeof estimate.basis!=='string'||estimate.basis.trim().length<4)errors.push(`${at}.estimate.basis must explain provenance`)
          }
        })
      }
    })
  }
  return errors
}

export function runScenario(scenario){
  const errors=validateScenario(scenario)
  if(errors.length)throw new Error(errors.join('; '))
  return {schema:'martybytes-synthetic-gateway-result/v1',synthetic:true,requests:scenario.requests.map(request=>{
    let usedUnits=0
    const attempts=[]
    let finalOutcome='exhausted'
    let selectedProvider=null
    for(let index=0;index<request.attempts.length;index++){
      const candidate=request.attempts[index]
      if(usedUnits+candidate.estimate.units>request.budgetUnits){
        finalOutcome='budget-stopped'
        attempts.push({attempt:index+1,provider:candidate.provider,model:candidate.model,outcome:'not-attempted-budget-stop',syntheticDurationTicks:0,estimate:candidate.estimate,cumulativeEstimateUnits:usedUnits})
        break
      }
      usedUnits+=candidate.estimate.units
      attempts.push({attempt:index+1,provider:candidate.provider,model:candidate.model,outcome:candidate.outcome,syntheticDurationTicks:candidate.syntheticDurationTicks,estimate:candidate.estimate,cumulativeEstimateUnits:usedUnits})
      if(candidate.outcome==='success'){finalOutcome='success';selectedProvider=candidate.provider;break}
    }
    return {requestId:request.requestId,budgetUnits:request.budgetUnits,finalOutcome,selectedProvider,totalEstimatedUnits:usedUnits,attempts}
  })}
}

async function main(){
  const [inputPath,outputPath]=process.argv.slice(2)
  if(!inputPath||!outputPath)throw new Error('Usage: node gateway-attribution-lab.mjs scenario.json result.json')
  const scenario=JSON.parse(await readFile(inputPath,'utf8'))
  const result=runScenario(scenario)
  await writeFile(outputPath,`${JSON.stringify(result,null,2)}\n`,{encoding:'utf8',flag:'wx'})
  process.stdout.write(`${JSON.stringify(result,null,2)}\n`)
}
if(process.argv[1]&&import.meta.url===pathToFileURL(process.argv[1]).href)main().catch(error=>{process.stderr.write(`${JSON.stringify({ok:false,error:error.message})}\n`);process.exitCode=1})