paginatedquery

paginatedQuery.ts

type Result = { rows: any[]; nextPage?: () => void }
class PaginatedQuery {
  constructor(public query: string, public params: any[] = []) {}

  private ctx = getContext()
  private fetchSize = 10
  private nextPromise = new Promise<Result>((resolve, reject) => {
    this.nextResolve = resolve
    this.nextReject = reject
  })
  private nextResolve!: Function
  private nextReject!: Function

  async init() {
    const client = await this.ctx.cassandra.getClient()
    let that = this
    client.eachRow(
      this.query,
      this.params,
      { fetchSize: this.fetchSize },
      function eachRow(/*n, row*/) {},
      function eachPage(err: any, result: Result) {
        if (err) return that.nextReject(err)
        that.nextResolve(result)
      }
    )
  }

  async readNext(): Promise<Result | undefined> {
    if (!this.nextPromise) return undefined
    let result = await this.nextPromise
    if (result.nextPage) {
      this.nextPromise = new Promise((resolve, reject) => {
        this.nextResolve = resolve
        this.nextReject = reject
      })
      result.nextPage()
    } else {
      this.nextPromise = undefined as any
      this.nextResolve = undefined as any
    }
    return result
  }
}

const resultsCache = new Map<string, PaginatedQuery>()
    
  // if (queryId) {
  //   const found = resultsCache.get(queryId)
  //   if (found) return found.readNext()
  //   throw Error("queryId expired or not found.")
  // }
  // const query = new PaginatedQuery("")
  // await query.init()
  // const newQueryId = v4()
  // resultsCache.set(newQueryId, query)
  // setTimeout(() => {
  //   resultsCache.delete(newQueryId)
  // }, 30000)
  // return query.readNext()