package com.twitter.recos.graph_common

import com.twitter.graphjet.stats.StatsReceiver
import com.twitter.graphjet.bipartite.MultiSegmentPowerLawBipartiteGraph

/**
 * The GraphBuilder builds a MultiSegmentPowerLawBipartiteGraph given a set of parameters.
 */
object MultiSegmentPowerLawBipartiteGraphBuilder {

  /**
   * This encapsulates all the state needed to initialize the in-memory graph.
   *
   * @param maxNumSegments           is the maximum number of segments we'll add to the graph.
   *                                 At that point, the oldest segments will start getting dropped
   * @param maxNumEdgesPerSegment    determines when the implementation decides to fork off a
   *                                 new segment
   * @param expectedNumLeftNodes     is the expected number of left nodes that would be inserted in
   *                                 the segment
   * @param expectedMaxLeftDegree    is the maximum degree expected for any left node
   * @param leftPowerLawExponent     is the exponent of the LHS power-law graph. see
   *                                 [[com.twitter.graphjet.bipartite.edgepool.PowerLawDegreeEdgePool]]
   *                                 for details
   * @param expectedNumRightNodes    is the expected number of right nodes that would be inserted in
   *                                 the segment
   * @param expectedMaxRightDegree   is the maximum degree expected for any right node
   * @param rightPowerLawExponent    is the exponent of the RHS power-law graph. see
   *                                 [[com.twitter.graphjet.bipartite.edgepool.PowerLawDegreeEdgePool]]
   *                                 for details
   */
  case class GraphBuilderConfig(
    maxNumSegments: Int,
    maxNumEdgesPerSegment: Int,
    expectedNumLeftNodes: Int,
    expectedMaxLeftDegree: Int,
    leftPowerLawExponent: Double,
    expectedNumRightNodes: Int,
    expectedMaxRightDegree: Int,
    rightPowerLawExponent: Double)

  /**
   * This apply function returns a mutuable bipartiteGraph
   *
   * @param graphBuilderConfig         is the graph builder config
   *
   */
  def apply(
    graphBuilderConfig: GraphBuilderConfig,
    statsReceiver: StatsReceiver
  ): MultiSegmentPowerLawBipartiteGraph = {
    new MultiSegmentPowerLawBipartiteGraph(
      graphBuilderConfig.maxNumSegments,
      graphBuilderConfig.maxNumEdgesPerSegment,
      graphBuilderConfig.expectedNumLeftNodes,
      graphBuilderConfig.expectedMaxLeftDegree,
      graphBuilderConfig.leftPowerLawExponent,
      graphBuilderConfig.expectedNumRightNodes,
      graphBuilderConfig.expectedMaxRightDegree,
      graphBuilderConfig.rightPowerLawExponent,
      new ActionEdgeTypeMask(),
      statsReceiver
    )
  }
}