import { sleep } from './sleep'

import type { Query, Row } from '@rocicorp/zero'

type ServerWithQuery = {
  query: (cb: (q: any) => any) => Promise<any>
}

export function createBatchQuery(server: ServerWithQuery) {
  return async function batchQuery<Q extends Query<any, any, any>, Item extends Row<Q>>(
    buildQuery: (q: any) => Q,
    mapper: (items: Item[]) => Promise<void>,
    {
      chunk,
      pause = 0,
      stopAfter = 100_000,
    }: {
      chunk: number
      pause?: number
      stopAfter?: number
    } = { chunk: 20 }
  ) {
    let hasMore = true
    let last: Item | null = null
    let iterations = 0

    while (hasMore) {
      const results = await server.query((q: any) => {
        let query = buildQuery(q).limit(chunk)

        if (last) {
          query = query.start(last)
        }

        return query
      })

      await mapper(results as Item[])

      if (results.length < chunk) {
        hasMore = false
      }

      if (iterations > stopAfter) {
        console.error(`[batchQuery] ‼️ stopping batch, ran ${stopAfter} chunks`)
        break
      }

      if (pause) {
        await sleep(pause)
      }
    }
  }
}