(ns Stream
  "Elixir Stream module — lazy, composable enumerables.

   In CljElixir: (Stream/map coll f), (Stream/filter coll f), etc.
   Streams are lazy: operations are only executed when the stream is consumed
   (e.g., by Enum/to-list, Enum/take, etc.).")

(defn map
  "Lazily maps `fun` over `enumerable`.
   (-> [1 2 3] (Stream/map (fn [x] (* x 2))) (Enum/to-list)) ;=> [2 4 6]"
  [enumerable fun])

(defn filter
  "Lazily filters elements.
   (-> [1 2 3 4] (Stream/filter (fn [x] (> x 2))) (Enum/to-list)) ;=> [3 4]"
  [enumerable fun])

(defn reject
  "Lazily rejects elements where `fun` returns truthy."
  [enumerable fun])

(defn flat-map
  "Lazily maps and flattens."
  [enumerable fun])

(defn take
  "Lazily takes `count` elements.
   (-> (Stream/iterate 0 inc) (Stream/take 5) (Enum/to-list)) ;=> [0 1 2 3 4]"
  [enumerable count])

(defn take-while
  "Lazily takes while `fun` returns truthy."
  [enumerable fun])

(defn take-every
  "Lazily takes every `nth` element."
  [enumerable nth])

(defn drop
  "Lazily drops `count` elements."
  [enumerable count])

(defn drop-while
  "Lazily drops while `fun` returns truthy."
  [enumerable fun])

(defn chunk-by
  "Lazily chunks by result of `fun`."
  [enumerable fun])

(defn chunk-every
  "Lazily chunks into groups of `count`.
   (-> [1 2 3 4 5] (Stream/chunk-every 2) (Enum/to-list)) ;=> [[1 2] [3 4] [5]]"
  ([enumerable count])
  ([enumerable count step])
  ([enumerable count step leftover]))

(defn chunk-while
  "Lazily chunks with custom accumulator logic."
  [enumerable acc chunk-fun after-fun])

(defn concat
  "Lazily concatenates enumerables.
   (-> (Stream/concat [1 2] [3 4]) Enum/to-list) ;=> [1 2 3 4]"
  ([enumerables])
  ([first rest]))

(defn dedup
  "Lazily removes consecutive duplicates."
  ([enumerable]))

(defn dedup-by
  "Lazily removes consecutive duplicates by `fun`."
  [enumerable fun])

(defn each
  "Lazily invokes `fun` for side effects. Elements pass through.
   (-> [1 2 3] (Stream/each (fn [x] (IO/puts x))) Enum/to-list)"
  [enumerable fun])

(defn scan
  "Lazily emits successive reduced values.
   (-> [1 2 3 4] (Stream/scan 0 +) Enum/to-list) ;=> [1 3 6 10]"
  ([enumerable fun])
  ([enumerable acc fun]))

(defn transform
  "Lazily transforms with an accumulator."
  [enumerable acc reducer after-fun])

(defn uniq
  "Lazily removes duplicates."
  [enumerable])

(defn uniq-by
  "Lazily removes duplicates by `fun`."
  [enumerable fun])

(defn with-index
  "Lazily adds indices.
   (-> [:a :b :c] Stream/with-index Enum/to-list) ;=> [{:a 0} {:b 1} {:c 2}]"
  ([enumerable])
  ([enumerable offset]))

(defn zip
  "Lazily zips enumerables.
   (-> (Stream/zip [1 2 3] [:a :b :c]) Enum/to-list) ;=> [{1 :a} {2 :b} {3 :c}]"
  ([enumerables])
  ([enum1 enum2]))

(defn zip-with
  "Lazily zips with a merge function."
  ([enumerables zip-fun])
  ([enum1 enum2 zip-fun]))

;; --- Generators ---

(defn iterate
  "Generates an infinite stream by repeatedly applying `fun`.
   (-> (Stream/iterate 0 inc) (Stream/take 5) Enum/to-list) ;=> [0 1 2 3 4]"
  [start-value next-fun])

(defn repeatedly
  "Generates a stream by calling `fun` repeatedly.
   (-> (Stream/repeatedly (fn [] (rand 10))) (Stream/take 3) Enum/to-list)"
  ([fun])
  ([count fun]))

(defn unfold
  "Generates a stream with an accumulator. `fun` returns {emit, next-acc} or nil.
   (-> (Stream/unfold 5 (fn [n] (if (> n 0) {n (- n 1)} nil)))
       Enum/to-list) ;=> [5 4 3 2 1]"
  [acc fun])

(defn resource
  "Creates a stream with setup/cleanup. Useful for external resources.
   (Stream/resource
     (fn [] (File/open! \"file.txt\"))
     (fn [file] ...)
     (fn [file] (File/close file)))"
  [start-fun next-fun after-fun])

(defn cycle
  "Repeats an enumerable infinitely.
   (-> (Stream/cycle [1 2 3]) (Stream/take 7) Enum/to-list) ;=> [1 2 3 1 2 3 1]"
  [enumerable])

(defn interval
  "Emits incrementing integers at `interval` milliseconds.
   (-> (Stream/interval 1000) (Stream/take 3) Enum/to-list) ;=> [0 1 2] (1s apart)"
  [interval])

(defn timer
  "Emits a single value of 0 after `delay` milliseconds.
   (-> (Stream/timer 1000) Enum/to-list) ;=> [0]"
  [delay])

(defn run
  "Consumes the stream for side effects. Returns :ok."
  [stream])

(defn intersperse
  "Lazily intersperses `separator` between elements."
  [enumerable separator])

(defn map-every
  "Lazily maps `fun` over every `nth` element."
  [enumerable nth fun])