/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author  Martin Odersky
 */


package scala
package tools.nsc
package backend.icode.analysis

import scala.collection.{ mutable, immutable }

/** A generic framework for data flow analysis.
 */
trait DataFlowAnalysis[L <: SemiLattice] {
  /** A type for program points. */
  type P <: ProgramPoint[P]
  val  lattice: L

  val worklist: mutable.Set[P]          = new mutable.LinkedHashSet
  val in:  mutable.Map[P, lattice.Elem] = new mutable.HashMap
  val out: mutable.Map[P, lattice.Elem] = new mutable.HashMap
  val visited: mutable.HashSet[P]       = new mutable.HashSet

  /** collect statistics? */
  var stat = true

  /** the number of times we iterated before reaching a fixpoint. */
  var iterations = 0

  /* Implement this function to initialize the worklist.  */
  def init(f: => Unit): Unit = {
    iterations = 0
    in.clear(); out.clear(); worklist.clear(); visited.clear()
    f
  }

  def run(): Unit

  /** Implements forward dataflow analysis: the transfer function is
   *  applied when inputs to a Program point change, to obtain the new
   *  output value.
   *
   *  @param f the transfer function.
   */
  def forwardAnalysis(f: (P, lattice.Elem) => lattice.Elem): Unit = try {
    while (!worklist.isEmpty) {
      if (stat) iterations += 1
      //Console.println("worklist in: " + worklist);
      val point = worklist.iterator.next(); worklist -= point; visited += point
      //Console.println("taking out point: " + point + " worklist out: " + worklist);
      val output = f(point, in(point))

      if ((lattice.bottom == out(point)) || output != out(point)) {
        // Console.println("Output changed at " + point
        //                 + " from: " + out(point) + " to: " + output
        //                 + " for input: " + in(point) + " and they are different: " + (output != out(point)))
        out(point) = output
        val succs = point.successors
        succs foreach { p =>
          val updated = lattice.lub(in(p) :: (p.predecessors map out.apply), p.exceptionHandlerStart)
          if(updated != in(p)) {
            in(p) = updated
            if (!worklist(p)) { worklist += p; }
          }
        }
      }
    }
  } catch {
    case e: NoSuchElementException =>
      Console.println("in: " + in.mkString("", "\n", ""))
      Console.println("out: " + out.mkString("", "\n", ""))
      e.printStackTrace
      sys.error("Could not find element " + e.getMessage)
  }

  def backwardAnalysis(f: (P, lattice.Elem) => lattice.Elem): Unit =
    while (worklist.nonEmpty) {
      if (stat) iterations += 1
      val point = worklist.head
      worklist -= point

      out(point) = lattice.lub(point.successors map in.apply, exceptional = false) // TODO check for exception handlers
      val input = f(point, out(point))

      if ((lattice.bottom == in(point)) || input != in(point)) {
        in(point) = input
        worklist ++= point.predecessors
      }
    }

}
