export type Release = { release: () => void };

export default class DocumentLock {
   private locks = new Map<string, (() => void)[]>();

   getLocks() {
      return Array.from(this.locks.keys())
   }

   async lock(collection: string = "", document: string = "") {
      let key = collection + "/" + document;
      let l = this.locks.get(key);
      if (l)
         await new Promise(resolve => { l.push(resolve); this.locks.set(key, l) });
      else {
         l = [];
         this.locks.set(key, l);
      }

      return () => {
         if (l.length > 0)
            setImmediate(() => l.shift()());
         else
            this.locks.delete(key)
      }
   }
}