package com.twitter.product_mixer.component_library.selector

import com.twitter.product_mixer.core.functional_component.common.AllPipelines
import com.twitter.product_mixer.core.functional_component.common.CandidateScope
import com.twitter.product_mixer.core.functional_component.selector.Selector
import com.twitter.product_mixer.core.functional_component.selector.SelectorResult
import com.twitter.product_mixer.core.model.common.presentation.CandidateWithDetails
import com.twitter.product_mixer.core.pipeline.PipelineQuery
import com.twitter.product_mixer.core.pipeline.PipelineResult
import com.twitter.timelines.configapi.Param

/**
 * Drop all results if the minimum item threshold is not met. Some products would rather return
 * nothing than, for example, a single tweet. This lets us leverage existing client logic for
 * handling no results such as logic to not render the product at all.
 */
case class DropTooFewResults(minResultsParam: Param[Int]) extends Selector[PipelineQuery] {

  override val pipelineScope: CandidateScope = AllPipelines

  override def apply(
    query: PipelineQuery,
    remainingCandidates: Seq[CandidateWithDetails],
    result: Seq[CandidateWithDetails]
  ): SelectorResult = {
    val minResults = query.params(minResultsParam)
    assert(minResults > 0, "Min results must be greater than zero")

    if (PipelineResult.resultSize(result) < minResults) {
      SelectorResult(remainingCandidates = remainingCandidates, result = Seq.empty)
    } else {
      SelectorResult(remainingCandidates = remainingCandidates, result = result)
    }
  }
}