(* This file is free software, part of containers. See file "license" for more details. *)

(** {1 Map specialized for Int keys} *)

(* "Fast Mergeable Integer Maps", Okasaki & Gill.
   We use big-endian trees. *)

(** Masks with exactly one bit active *)
module Bit : sig
  type t = private int
  val highest : int -> t
  val min_int : t
  val equal : t -> t -> bool
  val is_0 : bit:t -> int -> bool
  val is_1 : bit:t -> int -> bool
  val mask : mask:t -> int -> int   (* zeroes the bit, puts all lower bits to 1 *)
  val lt : t -> t -> bool
  val gt : t -> t -> bool
  val equal_int : int -> t -> bool
end = struct
  type t = int

  let min_int = min_int

  let equal : t -> t -> bool = Stdlib.(=)

  let rec highest_bit_naive x m =
    if x=m then m
    else highest_bit_naive (x land (lnot m)) (2*m)

  let mask_20_ = 1 lsl 20
  let mask_40_ = 1 lsl 40

  let highest x =
    if x<0 then min_int
    else if Sys.word_size > 40 && x > mask_40_ then (
      (* remove least significant 40 bits *)
      let x' = x land (lnot (mask_40_ -1)) in
      highest_bit_naive x' mask_40_
    ) else if x> mask_20_ then (
      (* small shortcut: remove least significant 20 bits *)
      let x' = x land (lnot (mask_20_ -1)) in
      highest_bit_naive x' mask_20_
    ) else (
      highest_bit_naive x 1
    )

  let is_0 ~bit x = x land bit = 0
  let is_1 ~bit x = x land bit = bit

  let mask ~mask x = (x lor (mask -1)) land (lnot mask)
  (* low endian: let mask_ x ~mask = x land (mask - 1) *)

  let gt a b = (b != min_int) && (a = min_int || a > b)
  let lt a b = gt b a
  let equal_int = Stdlib.(=)
end

(*$inject
  let highest2 x : int =
    let rec aux i =
      if i=0 then i
      else if 1 = (x lsr i) then 1 lsl i else aux (i-1)
    in
    if x<0 then min_int else aux (Sys.word_size-2)
*)

(*$QR & ~count:1_000
  Q.int (fun x ->
    if Bit.equal_int (highest2 x) (Bit.highest x) then true
    else QCheck.Test.fail_reportf "x=%d, highest=%d, highest2=%d@." x
      (Bit.highest x :> int) (highest2 x))
  *)

(*$inject
  let _list_uniq l = CCList.sort_uniq ~cmp:(fun a b-> Stdlib.compare (fst a)(fst b)) l
*)

type +'a t =
  | E  (* empty *)
  | L of int * 'a  (* leaf *)
  | N of int (* common prefix *) * Bit.t (* bit switch *) * 'a t * 'a t

let empty = E

let is_empty = function
  | E -> true
  | _ -> false

(*$Q
  Q.(small_list (pair int int)) (fun l -> \
    let m = of_list l in \
    is_empty m = (cardinal m = 0))
  *)

let is_prefix_ ~prefix y ~bit =
  prefix = Bit.mask y ~mask:bit

(*$Q
  Q.int (fun i -> \
    let b = Bit.highest i in \
    ((b:>int) land i = (b:>int)) && (i < 0 || ((b:>int) <= i && (i-(b:>int)) < (b:>int))))
  Q.int (fun i -> (Bit.highest i = Bit.min_int) = (i < 0))
  Q.int (fun i -> ((Bit.highest i:>int) < 0) = (Bit.highest i = Bit.min_int))
  Q.int (fun i -> let j = (Bit.highest i :> int) in  j land (j-1) = 0)
*)

(*$T
  (Bit.highest min_int :> int) = min_int
  (Bit.highest 2 :> int) = 2
  (Bit.highest 17 :> int)  = 16
  (Bit.highest 300 :> int) = 256
*)

(* helper:

    let b_of_i i =
      let rec f acc i =
        if i=0 then acc else let q, r = i/2, abs (i mod 2)
      in
      f (r::acc) q in f [] i;;
*)

(* low endian: let branching_bit_ a _ b _ = lowest_bit_ (a lxor b) *)
let branching_bit_ a b = Bit.highest (a lxor b)

(* TODO use hint in branching_bit_ *)

let check_invariants t =
  (* check that keys are prefixed by every node in their path *)
  let rec check_keys path t = match t with
    | E -> true
    | L (k, _) ->
      List.for_all
        (fun (prefix, switch, side) ->
           is_prefix_ ~prefix k ~bit:switch &&
           begin match side with
             | `Left -> Bit.is_0 k ~bit:switch
             | `Right -> Bit.is_1 k ~bit:switch
           end)
        path
    | N (prefix, switch, l, r) ->
      check_keys ((prefix, switch, `Left) :: path) l &&
      check_keys ((prefix, switch, `Right) :: path) r
  in
  check_keys [] t

(*$Q
  Q.(list (pair int bool)) (fun l -> \
    check_invariants (of_list l))
*)

let rec find_exn k t = match t with
  | E -> raise Not_found
  | L (k', v) when k = k' -> v
  | L _ -> raise Not_found
  | N (prefix, m, l, r) ->
    if is_prefix_ ~prefix k ~bit:m then (
      if Bit.is_0 k ~bit:m
      then find_exn k l
      else find_exn k r
    ) else (
      raise Not_found
    )

(* XXX could test with lt_unsigned_? *)

    (*
    if k <= prefix (* search tree *)
    then find_exn k l
    else find_exn k r
       *)

let find k t =
  try Some (find_exn k t)
  with Not_found -> None

(*$Q
  Q.(list (pair int int)) (fun l -> \
    let l = _list_uniq l in \
    let m = of_list l in \
    List.for_all (fun (k,v) -> find k m = Some v) l)
*)

let mem k t =
  try ignore (find_exn k t); true
  with Not_found -> false

(*$Q
  Q.(list (pair int int)) (fun l -> \
    let m = of_list l in \
    List.for_all (fun (k,_) -> mem k m) l)
*)

let mk_node_ prefix switch l r = match l, r with
  | E, o | o, E -> o
  | _ -> N (prefix, switch, l, r)

(* join trees t1 and t2 with prefix p1 and p2 respectively
   (p1 and p2 do not overlap) *)
let join_ t1 p1 t2 p2 =
  let switch = branching_bit_ p1 p2 in
  let prefix = Bit.mask p1 ~mask:switch in
  if Bit.is_0 p1 ~bit:switch then (
    assert (Bit.is_1 p2 ~bit:switch);
    mk_node_ prefix switch t1 t2
  ) else (
    assert (Bit.is_0 p2 ~bit:switch);
    mk_node_ prefix switch t2 t1
  )

let singleton k v = L (k, v)

(* c: conflict function *)
let rec insert_ c k v t = match t with
  | E -> L (k, v)
  | L (k', v') ->
    if k=k'
    then L (k, c ~old:v' v)
    else join_ t k' (L (k, v)) k
  | N (prefix, switch, l, r) ->
    if is_prefix_ ~prefix k ~bit:switch then (
      if Bit.is_0 k ~bit:switch
      then N(prefix, switch, insert_ c k v l, r)
      else N(prefix, switch, l, insert_ c k v r)
    ) else (
      join_ (L(k,v)) k t prefix
    )

let add k v t = insert_ (fun ~old:_ v -> v) k v t

(*$Q & ~count:20
  Q.(list (pair int int)) (fun l -> \
    let l = _list_uniq l in let m = of_list l in \
    List.for_all (fun (k,v) -> find_exn k m = v) l)
*)

let rec remove k t = match t with
  | E -> E
  | L (k', _) -> if k=k' then E else t
  | N (prefix, switch, l, r) ->
    if is_prefix_ ~prefix k ~bit:switch then (
      if Bit.is_0 k ~bit:switch
      then mk_node_ prefix switch (remove k l) r
      else mk_node_ prefix switch l (remove k r)
    ) else (
      t (* not present *)
    )

(*$Q & ~count:20
  Q.(list (pair int int)) (fun l -> \
    let l =  _list_uniq l in let m = of_list l in \
    List.for_all (fun (k,_) -> mem k m && not (mem k (remove k m))) l)
*)

let update k f t =
  try
    let v = find_exn k t in
    begin match f (Some v) with
      | None -> remove k t
      | Some v' -> add k v' t
    end
  with Not_found ->
  match f None with
    | None -> t
    | Some v -> add k v t

(*$= & ~printer:Q.Print.(list (pair int int))
  [1,1; 2, 22; 3, 3] \
  (of_list [1,1;2,2;3,3] \
    |> update 2 (function None -> assert false | Some _ -> Some 22) \
    |> to_list |> List.sort Stdlib.compare)
*)

let doubleton k1 v1 k2 v2 = add k1 v1 (singleton k2 v2)

let rec equal ~eq a b =
  Stdlib.(==) a b ||
  begin match a, b with
    | E, E -> true
    | L (ka, va), L (kb, vb) -> ka = kb && eq va vb
    | N (pa, sa, la, ra), N (pb, sb, lb, rb) ->
      pa=pb && Bit.equal sa sb && equal ~eq la lb && equal ~eq ra rb
    | E, _
    | N _, _
    | L _, _ -> false
  end

(*$Q
  Q.(list (pair int bool)) ( fun l -> \
    equal ~eq:(=) (of_list l) (of_list (List.rev l)))
*)

let rec iter f t = match t with
  | E -> ()
  | L (k, v) -> f k v
  | N (_, _, l, r) -> iter f l; iter f r

let rec fold f t acc = match t with
  | E -> acc
  | L (k, v) -> f k v acc
  | N (_, _, l, r) ->
    let acc = fold f l acc in
    fold f r acc

let cardinal t = fold (fun _ _ n -> n+1) t 0

let rec mapi f t = match t with
  | E -> E
  | L (k, v) -> L (k, f k v)
  | N (p, s, l, r) ->
    N (p, s, mapi f l, mapi f r)

let rec map f t = match t with
  | E -> E
  | L (k, v) -> L (k, f v)
  | N (p, s, l, r) ->
    N (p, s, map f l, map f r)

let rec choose_exn = function
  | E -> raise Not_found
  | L (k, v) -> k, v
  | N (_, _, l, _) -> choose_exn l

let choose t =
  try Some (choose_exn t)
  with Not_found -> None

(** {2 Whole-collection operations} *)

let rec union f t1 t2 =
  match t1, t2 with
    | E, o | o, E -> o
    | L (k, v), o
    | o, L (k, v) ->
      (* insert k, v into o *)
      insert_ (fun ~old v -> f k old v) k v o
    | N (p1, m1, l1, r1), N (p2, m2, l2, r2) ->
      if p1 = p2 && Bit.equal m1 m2 then (
        mk_node_ p1 m1 (union f l1 l2) (union f r1 r2)
      ) else if Bit.gt m1 m2 && is_prefix_ ~prefix:p1 p2 ~bit:m1 then (
        if Bit.is_0 p2 ~bit:m1
        then N (p1, m1, union f l1 t2, r1)
        else N (p1, m1, l1, union f r1 t2)
      ) else if Bit.lt m1 m2 && is_prefix_ ~prefix:p2 p1 ~bit:m2 then (
        if Bit.is_0 p1 ~bit:m2
        then N (p2, m2, union f t1 l2, r2)
        else N (p2, m2, l2, union f t1 r2)
      ) else (
        join_ t1 p1 t2 p2
      )

(*$Q & ~small:(fun (a,b) -> List.length a + List.length b)
  Q.(pair (list (pair int bool)) (list (pair int bool))) (fun (l1,l2) -> \
    check_invariants (union (fun _ _ x -> x) (of_list l1) (of_list l2)))
  Q.(pair (list (pair int bool)) (list (pair int bool))) (fun (l1,l2) -> \
    check_invariants (inter (fun _ _ x -> x) (of_list l1) (of_list l2)))
*)

(* associativity of union *)
(*$Q & ~small:(fun (a,b,c) -> List.(length a + length b + length c))
  Q.(let p = list (pair int int) in triple p p p) (fun (l1,l2,l3) -> \
    let m1 = of_list l1 and m2 = of_list l2 and m3 = of_list l3 in \
    let f _ x y = max x y in \
    equal ~eq:(=) (union f (union f m1 m2) m3) (union f m1 (union f m2 m3)))
*)

(*$R
  assert_equal ~cmp:(equal ~eq:(=)) ~printer:(CCFormat.to_string (pp CCString.pp))
    (of_list [1, "1"; 2, "2"; 3, "3"; 4, "4"])
    (union (fun _ a b -> a)
      (of_list [1, "1"; 3, "3"]) (of_list [2, "2"; 4, "4"]));
*)

(*$R
  assert_equal ~cmp:(equal ~eq:(=)) ~printer:(CCFormat.to_string (pp CCString.pp))
    (of_list [1, "1"; 2, "2"; 3, "3"; 4, "4"])
    (union (fun _ a b -> a)
      (of_list [1, "1"; 2, "2"; 3, "3"]) (of_list [2, "2"; 4, "4"]))
*)

(*$Q
   Q.(list (pair int bool)) (fun l -> \
    equal ~eq:(=) (of_list l) (union (fun _ a _ -> a) (of_list l)(of_list l)))
*)

(*$inject
  let union_l l1 l2 =
    let l2' = List.filter (fun (x,_) -> not @@ List.mem_assoc x l1) l2 in
    _list_uniq (l1 @ l2')

  let inter_l l1 l2 =
    let l2' = List.filter (fun (x,_) -> List.mem_assoc x l1) l2 in
    _list_uniq l2'
*)

(*$QR
  Q.(pair (small_list (pair small_int unit)) (small_list (pair small_int unit)))
    (fun (l1,l2) ->
      union_l l1 l2 = _list_uniq @@ to_list (union (fun _ _ _ ->())(of_list l1) (of_list l2)))
  *)

(*$QR
  Q.(pair (small_list (pair small_int unit)) (small_list (pair small_int unit)))
    (fun (l1,l2) ->
      inter_l l1 l2 = _list_uniq @@ to_list (inter (fun _ _ _ ->()) (of_list l1) (of_list l2)))
  *)

let rec inter f a b =
  match a, b with
    | E, _ | _, E -> E
    | L (k, v), o
    | o, L (k, v) ->
      begin try
          let v' = find_exn k o in
          L (k, f k v v')
        with Not_found -> E
      end
    | N (p1, m1, l1, r1), N (p2, m2, l2, r2) ->
      if p1 = p2 && Bit.equal m1 m2 then (
        mk_node_ p1 m1 (inter f l1 l2) (inter f r1 r2)
      ) else if Bit.gt m1 m2 && is_prefix_ ~prefix:p1 p2 ~bit:m1 then (
        if Bit.is_0 p2 ~bit:m1
        then inter f l1 b
        else inter f r1 b
      ) else if Bit.lt m1 m2 && is_prefix_ ~prefix:p2 p1 ~bit:m2 then (
        if Bit.is_0 p1 ~bit:m2
        then inter f a l2
        else inter f a r2
      ) else E

(*$R
  assert_equal ~cmp:(equal ~eq:(=)) ~printer:(CCFormat.to_string (pp CCString.pp))
    (singleton 2 "2")
    (inter (fun _ a b -> a)
      (of_list [1, "1"; 2, "2"; 3, "3"]) (of_list [2, "2"; 4, "4"]))
*)

(*$Q
   Q.(list (pair int bool)) (fun l -> \
    equal ~eq:(=) (of_list l) (inter (fun _ a _ -> a) (of_list l)(of_list l)))
*)

(* associativity of inter *)
(*$Q & ~small:(fun (a,b,c) -> List.(length a + length b + length c))
  Q.(let p = list (pair int int) in triple p p p) (fun (l1,l2,l3) -> \
    let m1 = of_list l1 and m2 = of_list l2 and m3 = of_list l3 in \
    let f _ x y = max x y in \
    equal ~eq:(=) (inter f (inter f m1 m2) m3) (inter f m1 (inter f m2 m3)))
*)

let rec disjoint_union_ t1 t2 : _ t = match t1, t2 with
  | E, o | o, E -> o
  | L (k,v), o
  | o, L(k,v) -> insert_ (fun ~old:_ _ -> assert false) k v o
  | N (p1,m1,l1,r1), N(p2,m2,l2,r2) ->
    if p1 = p2 && Bit.equal m1 m2 then (
      mk_node_ p1 m1 (disjoint_union_ l1 l2) (disjoint_union_ r1 r2)
    ) else if Bit.gt m1 m2 && is_prefix_ ~prefix:p1 p2 ~bit:m1 then (
      if Bit.is_0 p2 ~bit:m1
      then mk_node_ p1 m1 (disjoint_union_ l1 t2) r1
      else mk_node_ p1 m1 l1 (disjoint_union_ r1 t2)
    ) else if Bit.lt m1 m2 && is_prefix_ ~prefix:p2 p1 ~bit:m2 then (
      if Bit.is_0 p1 ~bit:m2
      then mk_node_ p2 m2 (disjoint_union_ t1 l2) r2
      else mk_node_ p2 m2 l2 (disjoint_union_ t1 r2)
    ) else (
      join_ t1 p1 t2 p2
    )

let rec filter f m = match m with
  | E -> E
  | L (k,v) ->
    if f k v then m else E
  | N (_,_,l,r) ->
    disjoint_union_ (filter f l) (filter f r)

(*$QR
  Q.(pair (fun2 Observable.int Observable.int bool) (small_list (pair int int))) (fun (f,l) ->
    let QCheck.Fun(_,f) = f in
    _list_uniq (List.filter (fun (x,y) -> f x y) l) =
    (_list_uniq @@ to_list @@ filter f @@ of_list l)
  )
*)

let rec filter_map f m = match m with
  | E -> E
  | L (k,v) ->
    begin match f k v with
      | None -> E
      | Some v' -> L(k,v')
    end
  | N (_,_,l,r) ->
    disjoint_union_ (filter_map f l) (filter_map f r)

(*$QR
  Q.(pair (fun2 Observable.int Observable.int @@ option bool) (small_list (pair int int))) (fun (f,l) ->
    let QCheck.Fun(_,f) = f in
    _list_uniq (CCList.filter_map (fun (x,y) -> CCOpt.map (CCPair.make x) @@ f x y) l) =
    (_list_uniq @@ to_list @@ filter_map f @@ of_list l)
  )
*)

let rec merge ~f t1 t2 : _ t =
  let merge1 t =
    filter_map (fun k v -> f k (`Left v)) t
  and merge2 t =
    filter_map (fun k v -> f k (`Right v)) t
  and add_some k opt m = match opt with
    | None -> m
    | Some v -> insert_ (fun ~old:_ _ -> assert false) k v m
  in
  match t1, t2 with
  | E, o -> merge2 o
  | o, E -> merge1 o
  | L (k, v), o ->
    let others = merge2 (remove k o) in
    add_some k
      (try f k (`Both (v,find_exn k o))
       with Not_found -> f k (`Left v)) others
  | o, L (k, v) ->
    let others = merge1 (remove k o) in
    add_some k
      (try f k (`Both (find_exn k o,v))
       with Not_found -> f k (`Right v)) others
  | N (p1, m1, l1, r1), N (p2, m2, l2, r2) ->
    if p1 = p2 && Bit.equal m1 m2 then (
      mk_node_ p1 m1 (merge ~f l1 l2) (merge ~f r1 r2)
    ) else if Bit.gt m1 m2 && is_prefix_ ~prefix:p1 p2 ~bit:m1 then (
      if Bit.is_0 p2 ~bit:m1
      then mk_node_ p1 m1 (merge ~f l1 t2) (merge1 r1)
      else mk_node_ p1 m1 (merge1 l1) (merge ~f r1 t2)
    ) else if Bit.lt m1 m2 && is_prefix_ ~prefix:p2 p1 ~bit:m2 then (
      if Bit.is_0 p1 ~bit:m2
      then mk_node_ p2 m2 (merge ~f t1 l2) (merge2 r2)
      else mk_node_ p2 m2 (merge2 l2) (merge ~f t1 r2)
    ) else (
      join_ (merge1 t1) p1 (merge2 t2) p2
    )

(*$inject
  let merge_union _x o = match o with
    | `Left v | `Right v | `Both (v,_) -> Some v
  let merge_inter _x o = match o with
    | `Left _ | `Right _ -> None
    | `Both (v,_) -> Some v
*)

(*$QR
  Q.(let p = small_list (pair small_int small_int) in pair p p) (fun (l1,l2) ->
    check_invariants
      (merge ~f:merge_union (of_list l1) (of_list l2)))
  *)

(*$QR
  Q.(let p = small_list (pair small_int small_int) in pair p p) (fun (l1,l2) ->
    check_invariants
      (merge ~f:merge_inter (of_list l1) (of_list l2)))
  *)

(*$QR
  Q.(let p = small_list (pair small_int unit) in pair p p) (fun (l1,l2) ->
    let l1 = _list_uniq l1 and l2 = _list_uniq l2 in
    equal Stdlib.(=)
      (union (fun _ v1 _ -> v1) (of_list l1) (of_list l2))
      (merge ~f:merge_union (of_list l1) (of_list l2)))
  *)

(*$QR
  Q.(let p = small_list (pair small_int unit) in pair p p) (fun (l1,l2) ->
    let l1 = _list_uniq l1 and l2 = _list_uniq l2 in
    equal Stdlib.(=)
      (inter (fun _ v1 _ -> v1) (of_list l1) (of_list l2))
      (merge ~f:merge_inter (of_list l1) (of_list l2)))
  *)

(** {2 Conversions} *)

type 'a sequence = ('a -> unit) -> unit
type 'a gen = unit -> 'a option
type 'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]

let add_list t l = List.fold_left (fun t (k,v) -> add k v t) t l

let of_list l = add_list empty l

let to_list t = fold (fun k v l -> (k,v) :: l) t []

(*$Q
  Q.(list (pair int int)) (fun l -> \
    let l = List.map (fun (k,v) -> abs k,v) l in \
    let rec is_sorted = function [] | [_] -> true \
      | x::y::tail -> x <= y && is_sorted (y::tail) in \
    of_list l |> to_list |> List.rev_map fst |> is_sorted)
*)

(*$Q
  Q.(list (pair int int)) (fun l -> \
    of_list l |> cardinal = List.length l)
*)

let add_seq t seq =
  let t = ref t in
  seq (fun (k,v) -> t := add k v !t);
  !t

let of_seq seq = add_seq empty seq

let to_seq t yield = iter (fun k v -> yield (k,v)) t

let keys t yield = iter (fun k _ -> yield k) t

let values t yield = iter (fun _ v -> yield v) t

let rec add_gen m g =  match g() with
  | None -> m
  | Some (k,v) -> add_gen (add k v m) g

let of_gen g = add_gen empty g

let to_gen m =
  let st = Stack.create () in
  Stack.push m st;
  let rec next() =
    if Stack.is_empty st then None
    else explore (Stack.pop st)
  and explore n = match n with
    | E -> next()  (* backtrack *)
    | L (k,v) -> Some (k,v)
    | N (_, _, l, r) ->
      Stack.push r st;
      explore l
  in
  next

(*$T
  doubleton 1 "a" 2 "b" |> to_gen |> of_gen |> to_list \
    |> List.sort Stdlib.compare = [1, "a"; 2, "b"]
*)

(*$Q
  Q.(list (pair int bool)) (fun l -> \
    let m = of_list l in equal ~eq:(=) m (m |> to_gen |> of_gen))
*)

(* E < L < N; arbitrary order for switches *)
let compare ~cmp a b =
  let rec cmp_gen cmp a b = match a(), b() with
    | None, None -> 0
    | Some _, None -> 1
    | None, Some _ -> -1
    | Some (ka, va), Some (kb, vb) ->
      if ka=kb then (
        let c = cmp va vb in
        if c=0 then cmp_gen cmp a b else c
      ) else (
        compare ka kb
      )
  in
  cmp_gen cmp (to_gen a) (to_gen b)

(*$Q
  Q.(list (pair int bool)) ( fun l -> \
    let m1 = of_list l and m2 = of_list (List.rev l) in \
    compare ~cmp:Stdlib.compare m1 m2 = 0)

*)

(*$QR
  Q.(pair (list (pair int bool)) (list (pair int bool))) (fun (l1, l2) ->
    let l1 = List.map (fun (k,v) -> abs k,v) l1 in
    let l2 = List.map (fun (k,v) -> abs k,v) l2 in
    let m1 = of_list l1 and m2 = of_list l2 in
    let c = compare ~cmp:Stdlib.compare m1 m2
    and c' = compare ~cmp:Stdlib.compare m2 m1 in
    (c = 0) = (c' = 0) && (c < 0) = (c' > 0) && (c > 0) = (c' < 0))
*)

(*$QR
  Q.(pair (list (pair int bool)) (list (pair int bool))) (fun (l1, l2) ->
    let l1 = List.map (fun (k,v) -> abs k,v) l1 in
    let l2 = List.map (fun (k,v) -> abs k,v) l2 in
    let m1 = of_list l1 and m2 = of_list l2 in
    (compare ~cmp:Stdlib.compare m1 m2 = 0) = equal ~eq:(=) m1 m2)
*)

let rec add_klist m l = match l() with
  | `Nil -> m
  | `Cons ((k,v), tl) -> add_klist (add k v m) tl

let of_klist l = add_klist empty l

let to_klist m =
  (* [st]: stack of alternatives *)
  let rec explore st m () = match m with
    | E -> next st ()
    | L (k,v) -> `Cons ((k, v), next st)
    | N (_, _, l, r) -> explore (r::st) l ()
  and next st () = match st with
    | [] -> `Nil
    | x :: st' -> explore st' x ()
  in
  next [m]

(*$Q
  Q.(list (pair int bool)) (fun l -> \
    let m = of_list l in equal ~eq:(=) m (m |> to_klist |> of_klist))
*)

type 'a tree = unit -> [`Nil | `Node of 'a * 'a tree list]

let rec as_tree t () = match t with
  | E -> `Nil
  | L (k, v) -> `Node (`Leaf (k, v), [])
  | N (prefix, switch, l, r) ->
    `Node (`Node (prefix, (switch:>int)), [as_tree l; as_tree r])

(** {2 IO} *)

type 'a printer = Format.formatter -> 'a -> unit

let pp pp_x out m =
  Format.fprintf out "@[<hov2>intmap {@,";
  let first = ref true in
  iter
    (fun k v ->
       if !first then first := false else Format.pp_print_string out ", ";
       Format.fprintf out "%d -> " k;
       pp_x out v;
       Format.pp_print_cut out ()
    ) m;
  Format.fprintf out "}@]"

(* Some thorough tests from Jan Midtgaar
   https://github.com/jmid/qc-ptrees
*)

(*$inject
  let test_count = 2_500

  open QCheck

  type instr_tree =
    | Empty
    | Singleton of int * int
    | Add of int * int * instr_tree
    | Remove of int * instr_tree
    | Union of instr_tree * instr_tree
    | Inter of instr_tree * instr_tree

  let rec to_string (a:instr_tree): string =
    let int_to_string = string_of_int in
    match a with
    | Empty -> "Empty"
    | Singleton (k,v) -> Printf.sprintf "Singleton(%d,%d)" k v
    | Add (k,v,t) -> Printf.sprintf "Add(%d,%d," k v ^ (to_string t) ^ ")"
    | Remove (n,t) -> "Remove (" ^ (int_to_string n) ^ ", " ^ (to_string t) ^ ")"
    | Union (t,t') -> "Union (" ^ (to_string t) ^ ", " ^ (to_string t') ^ ")"
    | Inter (t,t') -> "Inter (" ^ (to_string t) ^ ", " ^ (to_string t') ^ ")"

  let merge_f _ x y = min x y

  let rec interpret t : _ t = match t with
    | Empty -> empty
    | Singleton (k,v)  -> singleton k v
    | Add (k,v,t) -> add k v (interpret t)
    | Remove (n,t) -> remove n (interpret t)
    | Union (t,t') ->
      let s  = interpret t in
      let s' = interpret t' in
      union merge_f s s'
    | Inter (t,t') ->
      let s  = interpret t in
      let s' = interpret t' in
      inter merge_f s s'

  let tree_gen int_gen : instr_tree Q.Gen.t =
    let open Gen in
    sized
      (fix (fun recgen n -> match n with
        | 0 -> oneof [return Empty;
                      Gen.map2 (fun i j -> Singleton (i,j)) int_gen int_gen]
        | _ ->
          frequency
            [ (1, return Empty);
              (1, map2 (fun k v -> Singleton (k,v)) int_gen int_gen);
              (2, map3 (fun i j t -> Add (i,j,t)) int_gen int_gen (recgen (n-1)));
              (2, map2 (fun i t -> Remove (i,t)) int_gen (recgen (n-1)));
              (2, map2 (fun l r -> Union (l,r)) (recgen (n/2)) (recgen (n/2)));
              (2, map2 (fun l r -> Inter (l,r)) (recgen (n/2)) (recgen (n/2)));
            ]))

  let (<+>) = Q.Iter.(<+>)

  let rec tshrink t : instr_tree Q.Iter.t = match t with
    | Empty -> Iter.empty
    | Singleton (k,v) ->
      (Iter.return Empty)
      <+> (Iter.map (fun k' -> Singleton (k',v)) (Shrink.int k))
      <+> (Iter.map (fun v' -> Singleton (k,v')) (Shrink.int v))
    | Add (k,v,t) ->
      (Iter.of_list [Empty; t; Singleton (k,v)])
      <+> (Iter.map (fun t' -> Add (k,v,t')) (tshrink t))
      <+> (Iter.map (fun k' -> Add (k',v,t)) (Shrink.int k))
      <+> (Iter.map (fun v' -> Add (k,v',t)) (Shrink.int v))
    | Remove (i,t) ->
      (Iter.of_list [Empty; t])
      <+> (Iter.map (fun t' -> Remove (i,t')) (tshrink t))
      <+> (Iter.map (fun i' -> Remove (i',t)) (Shrink.int i))
    | Union (t0,t1) ->
      (Iter.of_list [Empty;t0;t1])
      <+> (Iter.map (fun t0' -> Union (t0',t1)) (tshrink t0))
      <+> (Iter.map (fun t1' -> Union (t0,t1')) (tshrink t1))
    | Inter (t0,t1) ->
      (Iter.of_list [Empty;t0;t1])
      <+> (Iter.map (fun t0' -> Inter (t0',t1)) (tshrink t0))
      <+> (Iter.map (fun t1' -> Inter (t0,t1')) (tshrink t1))

  let arb_int =
    frequency
      [(5,small_signed_int);
       (3,int);
       (1, oneofl [min_int;max_int])]

  let arb_tree =
    make ~print:to_string ~shrink:tshrink
      (tree_gen arb_int.gen)

  let empty_m = []
  let singleton_m k v = [k,v]
  let mem_m i s = List.mem_assoc i s
  let rec remove_m i s = match s with
    | [] -> []
    | (j,v)::s' -> if i=j then s' else (j,v)::(remove_m i s')
  let add_m k v s = List.sort Stdlib.compare ((k,v)::remove_m k s)
  let rec union_m s s' = match s,s' with
    | [], _ -> s'
    | _, [] -> s
    | (k1,v1)::is,(k2,v2)::js ->
        if k1<k2 then (k1,v1)::(union_m is s') else
        if k1>k2 then (k2,v2)::(union_m s js) else
        (k1,min v1 v2)::(union_m is js)
  let rec inter_m s s' = match s with
    | [] -> []
    | (k,v)::s ->
      if List.mem_assoc k s'
      then (k,min v (List.assoc k s'))::(inter_m s s')
      else inter_m s s'

  let abstract s = List.sort Stdlib.compare (fold (fun k v acc -> (k,v)::acc) s [])
*)

(* A bunch of agreement properties *)

(*$=
  empty_m (let s = empty in abstract s)
*)

(*$QR & ~count:test_count
  (Q.pair arb_int arb_int) (fun (k,v) ->
    abstract (singleton k v) = singleton_m k v)
*)

(*$QR & ~count:test_count
  Q.(pair arb_tree arb_int)
      (fun (t,n) ->
        let s = interpret t in
        mem n s = mem_m n (abstract s))
*)

(*$QR & ~count:test_count
  (triple arb_tree arb_int arb_int)
    (fun (t,k,v) ->
      let s = interpret t in
      abstract (add k v s) = add_m k v (abstract s))
*)

(*$QR & ~count:test_count
  (pair arb_tree arb_int)
    (fun (t,n) ->
      let s = interpret t in
      abstract (remove n s) = remove_m n (abstract s))
*)

(*$QR & ~count:test_count
  (pair arb_tree arb_tree)
  (fun (t,t') ->
    let s  = interpret t in
    let s' = interpret t' in
    abstract (union merge_f s s') = union_m (abstract s) (abstract s'))
*)

(*$QR & ~count:test_count
  Q.(pair arb_tree arb_tree)
    (fun (t,t') ->
      let s  = interpret t in
      let s' = interpret t' in
      abstract (inter merge_f s s') = inter_m (abstract s) (abstract s'))
*)