### Compute the path for a contraction edge:

# initialize structure

query memclear()

if isDBObject("initsearch") then delete initsearch endif

let initsearch = fun() AllEdges feed head[0] 
  project[Source, Target, SourcePos, TargetPos, Cost, Middle, NEdges]
  extend[Prio: 0.0]
  mcreatepqueue[NEdges, "Path"] count

query initsearch()


if isDBObject("findpath") then delete findpath endif

let findpath = fun(Start: int, Dest: int)
  (fun(a : int) AllEdgesUp orange[a; a] ) (fun(b : int) AllEdgesDown orange[b; b] )
  gbidijkstra[Target, Source, Start, Dest, .Cost]
  replaceAttr[NEdges: 0.0]
  remove[IsForward]
  extend[Prio: 0.0]
  filter[minserttuplepq("Path", ., 0.0, Prio)]
  loopsel[
    "Path" mfeedpq
  filter[fun(t: TUPLE) ifthenelse(attr(t, Middle) = 0, TRUE,
    (AllEdges orange[attr(t, Source), attr(t, Middle); attr(t, Source), attr(t, Middle)]
      ksmallest[1; Cost]
    extend[Prio: 0.0]
    extend[XX: minserttuplepq("Path", ., attr(t, NEdges), Prio)]
    extract[NEdges])
    within[fun (previous: ANY)
    (AllEdges orange[attr(t, Middle), attr(t, Target); attr(t, Middle), attr(t, Target)]
      ksmallest[1; Cost]
    extend[Prio: 0.0]
    extend[XX: minserttuplepq("Path", ., (attr(t, NEdges) + previous), Prio)]
    count = 0)
    ])]
  ]
  consume

if isDBObject("gbi") then delete gbi endif

let gbi = fun(m: int, n: int)
  (fun(a : int) AllEdgesUp orange[a; a] )
  (fun(b : int) AllEdgesDown orange[b; b] )
  gbidijkstra[Target, Source, m, n, .Cost] consume