use Universal == < > >=
use Optional None Some

namespace Sequence where

  map : (a -> b) -> [a] -> [b]
  map f a =
    go i as acc = case Sequence.at i as of
      None -> acc
      Some a -> go (i + 1) as (acc `snoc` f a)
    go 0 a []

  zip : [a] -> [b] -> [(a,b)]
  zip as bs =
    go acc i = case (at i as, at i bs) of
      (None,_) -> acc
      (_,None) -> acc
      (Some a, Some b) -> go (acc `snoc` (a,b)) (i + 1)
    go [] 0

  insert : Nat -> a -> [a] -> [a]
  insert i a as = take i as ++ [a] ++ drop i as

  replace : Nat -> a -> [a] -> [a]
  replace i a as = take i as ++ [a] ++ drop (i + 1) as

  slice : Nat -> Nat -> [a] -> [a]
  slice start stopExclusive s =
    take (stopExclusive `Nat.drop` start) (drop start s)

  unsafeAt : Nat -> [a] -> a
  unsafeAt n as = case at n as of
    Some a -> a
    None -> Debug.watch "oh noes" (unsafeAt n as) -- Debug.crash "oh noes!"

  foldl : (b -> a -> b) -> b -> [a] -> b
  foldl f b as =
    go b i = case Sequence.at i as of
      None -> b
      Some a -> go (f b a) (i + 1)
    go b 0

  foldb : (a -> b) -> (b -> b -> b) -> b -> [a] -> b
  foldb f op z as =
    if Sequence.size as == 0 then z
    else if Sequence.size as == 1 then f (unsafeAt 0 as)
    else case halve as of (left, right) ->
       foldb f op z left `op` foldb f op z right

  reverse : [a] -> [a]
  reverse as = foldl (acc a -> cons a acc) [] as

  indexed : [a] -> [(a, Nat)]
  indexed as = as `zip` range 0 (size as)

  sortBy : (a -> b) -> [a] -> [a]
  sortBy f as =
    tweak p = (f (at1 p), at2 p, at1 p)
    Heap.sort (map tweak (indexed as)) |> map at3

  halve : [a] -> ([a], [a])
  halve s =
    n = size s / 2
    (take n s, drop n s)

  unfold : s -> (s -> Optional (a, s)) -> [a]
  unfold s0 f =
    go f s acc = case f s of
      None -> acc
      Some (a, s) -> go f s (acc `snoc` a)
    go f s0 []

  uncons : [a] -> Optional (a, [a])
  uncons as = case at 0 as of
    None -> None
    Some a -> Some (a, drop 1 as)

  unsnoc : [a] -> Optional ([a], a)
  unsnoc as =
    i = size as `drop` 1
    case at i as of
      None -> None
      Some a -> Some (take i as, a)

  join : [[a]] -> [a]
  join = foldl (++) []

  flatMap : (a -> [b]) -> [a] -> [b]
  flatMap f as = join (map f as)

  range : Nat -> Nat -> [Nat]
  range start stopExclusive =
    f i = if i < stopExclusive then Some (i, i + 1) else None
    unfold start f

  distinct : [a] -> [a]
  distinct as =
    go i seen acc = case Sequence.at i as of
      None -> acc
      Some a -> if Set.contains a seen then go (i + 1) seen acc
                else go (i + 1) (Set.insert a seen) (acc `snoc` a)
    go 0 Set.empty []

-- > Sequence.foldb "" (t t2 -> "(" ++ t ++ " " ++ t2 ++ ")") (x -> x) ["Alice", "Bob", "Carol", "Dave", "Eve", "Frank", "Gerald", "Henry"]

-- Sorted maps, represented as a pair of sequences
-- Use binary search to do lookups and find insertion points
-- This relies on the underlying sequence having efficient
-- slicing and concatenation
type Map k v = Map [k] [v]

use Map Map

namespace Search where

  indexOf : a -> [a] -> Optional Nat
  indexOf a s =
    ao = Some a
    Search.exact (i -> ao `compare` Sequence.at i s) 0 (size s)

  lubIndexOf' : a -> Nat -> [a] -> Nat
  lubIndexOf' a start s =
    ao = Some a
    Search.lub (i -> ao `compare` Sequence.at i s) start (size s)

  lubIndexOf : a -> [a] -> Nat
  lubIndexOf a s = lubIndexOf' a 0 s

  lub : (Nat -> Int) -> Nat -> Nat -> Nat
  lub hit bot top =
    if bot >= top then top
    else
      mid = (bot + top) / 2
      case hit mid of
        +0 -> mid
        -1 -> lub hit bot mid
        +1 -> lub hit (mid + 1) top

  exact : (Nat -> Int) -> Nat -> Nat -> Optional Nat
  exact hit bot top =
    if bot >= top then None
    else
      mid = (bot + top) / 2
      case hit mid of
        +0 -> Some mid
        -1 -> exact hit bot mid
        +1 -> exact hit (mid + 1) top

-- > ex = [0,2,4,6,77,192,3838,12000]
-- > Sequence.map (e -> indexOf e ex) ex
-- > lubIndexOf 193 ex

use Pair Pair

namespace Tuple where
  at1 : Pair a b -> a
  at1 p = case p of Pair a _ -> a

  at2 : Pair a (Pair b c) -> b
  at2 p = case p of Pair _ (Pair b _) -> b

  at3 : Pair a (Pair b (Pair c d)) -> c
  at3 p = case p of Pair _ (Pair _ (Pair c _)) -> c

  at4 : Pair a (Pair b (Pair c (Pair d e))) -> d
  at4 p = case p of Pair _ (Pair _ (Pair _ (Pair d _))) -> d

(|>) : a -> (a -> b) -> b
a |> f = f a

(<|) : (a -> b) -> a -> b
f <| a = f a

id : a -> a
id a = a

namespace Map where

  empty : Map k v
  empty = Map [] []

  singleton : k -> v -> Map k v
  singleton k v = Map [k] [v]

  fromSequence : [(k,v)] -> Map k v
  fromSequence kvs =
    go acc i = case Sequence.at i kvs of
      None -> acc
      Some (k,v) -> go (insert k v acc) (i + 1)
    go empty 0

  toSequence : Map k v -> [(k,v)]
  toSequence m = Sequence.zip (keys m) (values m)

  size : Map k v -> Nat
  size s = Sequence.size (keys s)

  lookup : k -> Map k v -> Optional v
  lookup k m = case m of
    Map ks vs -> case Search.indexOf k ks of
      None -> None
      Some i -> at i vs

  contains : k -> Map k v -> Boolean
  contains k m = case m of Map ks _ -> case Search.indexOf k ks of
    None -> false
    _ -> true

  insert : k -> v -> Map k v -> Map k v
  insert k v m = case m of Map ks vs ->
    use Search lubIndexOf
    i = lubIndexOf k ks
    case at i ks of
      Some k' ->
        if k == k' then Map ks (Sequence.replace i v vs)
        else Map (Sequence.insert i k ks) (Sequence.insert i v vs)
      None -> Map (ks `snoc` k) (vs `snoc` v)

  map : (v -> v2) -> Map k v -> Map k v2
  map f m = Map (keys m) (Sequence.map f (values m))

  union : Map k v -> Map k v -> Map k v
  union = unionWith (_ v -> v)

  unionWith : (v -> v -> v) -> Map k v -> Map k v -> Map k v
  unionWith f m1 m2 = case (m1, m2) of (Map k1 v1, Map k2 v2) ->
    go i j ko vo = case (at i k1, at j k2) of
      (None, _) -> Map (ko ++ drop j k2) (vo ++ drop j v2)
      (_, None) -> Map (ko ++ drop i k1) (vo ++ drop i v1)
      (Some kx, Some ky) ->
        use Sequence slice unsafeAt
        use Search lubIndexOf'
        if kx == ky then
          go (i + 1) (j + 1)
             (ko `snoc` kx)
             (vo `snoc` f (unsafeAt i v1) (unsafeAt j v2))
        else if kx < ky then
          i' = lubIndexOf' ky i k1
          go i' j (ko ++ slice i i' k1) (vo ++ slice i i' v1)
        else
          j' = lubIndexOf' kx j k2
          go i j' (ko ++ slice j j' k2) (vo ++ slice j j' v2)
    go 0 0 [] []

  intersect : Map k v -> Map k v -> Map k v
  intersect = intersectWith (_ v -> v)

  intersectWith : (v -> v -> v2) -> Map k v -> Map k v -> Map k v2
  intersectWith f m1 m2 = case (m1, m2) of (Map k1 v1, Map k2 v2) ->
    go i j ko vo = case (at i k1, at j k2) of
      (None, _) -> Map ko vo
      (_, None) -> Map ko vo
      (Some kx, Some ky) ->
        if kx == ky then
          go (i + 1) (j + 1)
             (ko `snoc` kx)
             (vo `snoc` f (Sequence.unsafeAt i v1) (Sequence.unsafeAt j v2))
        else if kx < ky then
          i' = Search.lubIndexOf' ky i k1
          go i' j ko vo
        else
          j' = Search.lubIndexOf' kx j k2
          go i j' ko vo
    go 0 0 [] []

  keys : Map k v -> [k]
  keys m = case m of Map ks _ -> ks

  values : Map k v -> [v]
  values m = case m of Map _ vs -> vs

namespace Multimap where

  insert : k -> v -> Map k [v] -> Map k [v]
  insert k v m = case Map.lookup k m of
    None -> Map.insert k [v] m
    Some vs -> Map.insert k (vs `snoc` v) m

  lookup : k -> Map k [v] -> [v]
  lookup k m = Optional.orDefault [] (Map.lookup k m)

type Set a = Set (Map a ())
use Set Set

namespace Set where

  empty : Set k
  empty = Set Map.empty

  underlying : Set k -> Map k ()
  underlying s = case s of Set s -> s

  toMap : (k -> v) -> Set k -> Map k v
  toMap f s = case s of Set (Map ks vs) -> Map ks (Sequence.map f ks)

  fromSequence : [k] -> Set k
  fromSequence ks = Set (Map.fromSequence (Sequence.map (k -> (k,())) ks))

  toSequence : Set k -> [k]
  toSequence s = case s of Set (Map ks _) -> ks

  contains : k -> Set k -> Boolean
  contains k s = case s of Set m -> Map.contains k m

  insert : k -> Set k -> Set k
  insert k s = case s of Set s -> Set (Map.insert k () s)

  union : Set k -> Set k -> Set k
  union s1 s2 = Set (Map.union (underlying s1) (underlying s2))

  size : Set k -> Nat
  size s = Map.size (underlying s)

  intersect : Set k -> Set k -> Set k
  intersect s1 s2 = Set (Map.intersect (underlying s1) (underlying s2))

type Heap k v = Heap Nat k v [Heap k v]
use Heap Heap

namespace Heap where

  singleton : k -> v -> Heap k v
  singleton k v = Heap 1 k v []

  size : Heap k v -> Nat
  size h = case h of Heap n _ _ _ -> n

  union : Heap k v -> Heap k v -> Heap k v
  union h1 h2 = case (h1, h2) of
    (Heap n k1 v1 hs1, Heap m k2 v2 hs2) ->
      if k1 >= k2 then Heap (n + m) k1 v1 (cons h2 hs1)
      else Heap (n + m) k2 v2 (cons h1 hs2)

  pop : Heap k v -> Optional (Heap k v)
  pop h =
    go h subs =
      use Sequence drop size unsafeAt
      if size subs == 0 then h
      else if size subs == 1 then h `union` unsafeAt 0 subs
      else union h (unsafeAt 0 subs) `union` go (unsafeAt 1 subs) (drop 2 subs)
    case uncons (children h) of
      None -> None
      Some (s0, subs) -> Some (go s0 subs)

  children : Heap k v -> [Heap k v]
  children h = case h of Heap _ _ _ cs -> cs

  max : Heap k v -> (k, v)
  max h = case h of Heap _ k v _ -> (k, v)

  maxKey : Heap k v -> k
  maxKey h = case h of Heap _ k _ _ -> k

  fromSequence : [(k,v)] -> Optional (Heap k v)
  fromSequence kvs =
    op a b = case a of
      None -> b
      Some a -> case b of
        None -> Some a
        Some b -> Some (union a b)
    single kv = Some (singleton (Tuple.at1 kv) (Tuple.at2 kv))
    Sequence.foldb single op None kvs

  fromKeys : [a] -> Optional (Heap a a)
  fromKeys as = fromSequence (Sequence.map (a -> (a,a)) as)

  sortDescending : [a] -> [a]
  sortDescending as =
    step o = case o of
      None -> None
      Some h -> Some (max h, pop h)
    Sequence.unfold (fromKeys as) step |> Sequence.map Tuple.at1

  sort : [a] -> [a]
  sort as = sortDescending as |> reverse

-- > sort [11,9,8,4,5,6,7,3,2,10,1]

Optional.map : (a -> b) -> Optional a -> Optional b
Optional.map f o = case o of
  None -> None
  Some a -> Some (f a)

Optional.orDefault : a -> Optional a -> a
Optional.orDefault a o = case o of
  None -> a
  Some a -> a