import { ClockError } from './clock';
export interface LockBackend {
  create(employee:string):Promise<{id:string}>;
  find(employee:string):Promise<{id:string;created:string}|null>;
  remove(id:string):Promise<unknown>;
}
/** Record ID is the ownership token. Never release a lock by employee filter. */
export async function acquireEmployeeLock(backend:LockBackend,employee:string,now=Date.now()) {
  try{return (await backend.create(employee)).id;}
  catch(error) {
    if(![400,409].includes((error as {status:number}).status))throw error;
    const previous=await backend.find(employee);
    if(!previous)throw error;
    const age=now-Date.parse(previous.created);
    if(Number.isFinite(age) && age>120_000) {
      // Concurrent recoverers can only delete this exact expired record. The
      // unique employee lock and unique event predecessor also fence old writers.
      try{await backend.remove(previous.id);}catch(e){if((e as {status:number}).status!==404)throw e;}
      try{return (await backend.create(employee)).id;}
      catch(e){if(![400,409].includes((e as {status:number}).status))throw e;}
    }
    throw new ClockError('Another scan is being saved for this worker. Retry this confirmation; an interrupted scan lock clears after two minutes.',423);
  }
}