(library (sph storage dg data-structure set)
  (export
    dg-ordered-set
    dg-set
    dg-set-add
    dg-set-contains?
    dg-set-delete
    dg-set-delete-relations
    dg-set-elements
    dg-set-elements-intersection)
  (import
    (sph)
    (sph storage dg)
    (sph storage dg one)
    (only (sph list) list-set-equal?))

  (define (dg-set txn . elements)
    "dg-txn integer:node-ids:elements ... -> integer
    create a new set with the given node-ids"
    (let (ids (dg-id-create txn)) (dg-relation-ensure txn ids elements) (first ids)))

  (define (dg-set-add txn ids . elements)
    "dg-txn (integer ...) integer ... ->
    all all elements to all sets identified by \"ids\""
    (dg-relation-ensure txn ids elements))

  (define (dg-set-delete txn ids . elements)
    "dg-txn list integer ... ->
    delete the set and disconnected elements"
    (dg-relation-delete txn ids elements) (dg-delete-disconnected txn elements))

  (define (dg-set-elements-intersection txn ids elements)
    "dg-txn list list -> list
    filter elements that are contained in the sets identified by \"ids\""
    (dg-relation-select-read txn ids elements null (q right)))

  (define (dg-set-contains? txn ids . elements)
    "dg-txn list integer ... -> boolean
    true if the sets identified by \"ids\" contain all elements"
    (list-set-equal? elements (dg-set-elements-intersection txn ids elements)))

  (define (dg-set-intersection txn . ids)
    "dg-txn (integer ...) ... -> (integer ...)
    returns a list of all elements that are contained in all sets"
    (fold (l (id r) (dg-relation-select-read txn (list id) r null (q right))) null ids))

  (define (dg-set-elements txn . ids) "dg-txn integer ... -> list"
    (dg-relation-select-read txn ids null null (q right)))

  (define (dg-ordered-set txn . elements) "dg-txn integer ... -> integer"
    (let (ids (dg-id-create txn))
      (dg-relation-ensure txn ids elements null (l (value) (+ 1 value))) (first ids))))