package sbt
import Relation._
object Relation
{
def empty[A,B]: Relation[A,B] = make(Map.empty, Map.empty)
def make[A,B](forward: Map[A,Set[B]], reverse: Map[B, Set[A]]): Relation[A,B] = new MRelation(forward, reverse)
def reconstruct[A,B](forward: Map[A, Set[B]]): Relation[A,B] =
{
val reversePairs = for( (a,bs) <- forward.view; b <- bs.view) yield (b, a)
val reverse = (Map.empty[B,Set[A]] /: reversePairs) { case (m, (b, a)) => add(m, b, a :: Nil) }
make(forward, reverse)
}
private[sbt] def remove[X,Y](map: M[X,Y], from: X, to: Y): M[X,Y] =
map.get(from) match {
case Some(tos) =>
val newSet = tos - to
if(newSet.isEmpty) map - from else map.updated(from, newSet)
case None => map
}
private[sbt] def combine[X,Y](a: M[X,Y], b: M[X,Y]): M[X,Y] =
(a /: b) { (map, mapping) => add(map, mapping._1, mapping._2) }
private[sbt] def add[X,Y](map: M[X,Y], from: X, to: Traversable[Y]): M[X,Y] =
map.updated(from, get(map, from) ++ to)
private[sbt] def get[X,Y](map: M[X,Y], t: X): Set[Y] = map.getOrElse(t, Set.empty[Y])
private[sbt] type M[X,Y] = Map[X, Set[Y]]
}
trait Relation[A,B]
{
def forward(_1: A): Set[B]
def reverse(_2: B): Set[A]
def +(pair: (A, B)): Relation[A,B]
def +(a: A, b: B): Relation[A,B]
def +(a: A, bs: Traversable[B]): Relation[A,B]
def ++(r: Relation[A,B]): Relation[A,B]
def ++(rs: Traversable[(A,B)]): Relation[A,B]
def --(_1s: Traversable[A]): Relation[A,B]
def --(pairs: TraversableOnce[(A,B)]): Relation[A,B]
def -(_1: A): Relation[A,B]
def -(pair: (A,B)): Relation[A,B]
def _1s: collection.Set[A]
def _2s: collection.Set[B]
def size: Int
def contains(a: A, b: B): Boolean
def filter(f: (A,B) => Boolean): Relation[A,B]
def all: Traversable[(A,B)]
def forwardMap: Map[A, Set[B]]
def reverseMap: Map[B, Set[A]]
}
private final class MRelation[A,B](fwd: Map[A, Set[B]], rev: Map[B, Set[A]]) extends Relation[A,B]
{
def forwardMap = fwd
def reverseMap = rev
def forward(t: A) = get(fwd, t)
def reverse(t: B) = get(rev, t)
def _1s = fwd.keySet
def _2s = rev.keySet
def size = fwd.size
def all: Traversable[(A,B)] = fwd.iterator.flatMap { case (a, bs) => bs.iterator.map( b => (a,b) ) }.toTraversable
def +(pair: (A,B)) = this + (pair._1, Set(pair._2))
def +(from: A, to: B) = this + (from, to :: Nil)
def +(from: A, to: Traversable[B]) =
new MRelation( add(fwd, from, to), (rev /: to) { (map, t) => add(map, t, from :: Nil) })
def ++(rs: Traversable[(A,B)]) = ((this: Relation[A,B]) /: rs) { _ + _ }
def ++(other: Relation[A,B]) = new MRelation[A,B]( combine(fwd, other.forwardMap), combine(rev, other.reverseMap) )
def --(ts: Traversable[A]): Relation[A,B] = ((this: Relation[A,B]) /: ts) { _ - _ }
def --(pairs: TraversableOnce[(A,B)]): Relation[A,B] = ((this: Relation[A,B]) /: pairs) { _ - _ }
def -(pair: (A,B)): Relation[A,B] =
new MRelation( remove(fwd, pair._1, pair._2), remove(rev, pair._2, pair._1) )
def -(t: A): Relation[A,B] =
fwd.get(t) match {
case Some(rs) =>
val upRev = (rev /: rs) { (map, r) => remove(map, r, t) }
new MRelation(fwd - t, upRev)
case None => this
}
def filter(f: (A,B) => Boolean): Relation[A,B] = Relation.empty[A,B] ++ all.filter(f.tupled)
def contains(a: A, b: B): Boolean = forward(a)(b)
override def toString = all.map { case (a,b) => a + " -> " + b }.mkString("Relation [", ", ", "]")
}