;; clojure.core — collection tier. Pure, eager fns expressed as compositions of
;; already-frozen core primitives (reduce/assoc/get/conj/filter/vec/count/>=).
;; No host internals, no laziness, no macros — so they compile cleanly and stay
;; redefinable. Loaded after the seq tier; self-hosted in compile mode.
;;
;; Same migration rule as the seq tier (see 10-seq.clj): not in core-renames, no
;; internal Janet callers, not used by the self-hosted compiler.

;; Base is (hash-map), not the {} literal: a literal map is a struct that doesn't
;; canonicalize collection keys across representations (a {:a 1} literal vs
;; (hash-map :a 1) key), whereas a PHM does — so counting/grouping by collection
;; value needs the PHM base (the prior Janet impl used make-phm for this reason).
(defn frequencies [coll]
  (reduce (fn [counts x] (assoc counts x (inc (get counts x 0)))) (hash-map) coll))

(defn group-by [f coll]
  (reduce (fn [ret x] (let [k (f x)] (assoc ret k (conj (get ret k []) x)))) (hash-map) coll))

(defn not-empty [coll]
  (if (or (nil? coll) (zero? (count coll))) nil coll))

(defn filterv [pred coll]
  (vec (filter pred coll)))

;; Greatest/least x by (k x). Canonical Clojure multi-arity: the first pair uses
;; strict < / > and the fold uses <= / >= — this exact ordering reproduces the
;; JVM IEEE-754 NaN behavior (e.g. (min-key identity 1 ##NaN) => ##NaN). > / <
;; throw on non-numbers, as Clojure does.
(defn max-key
  ([k x] x)
  ([k x y] (if (> (k x) (k y)) x y))
  ([k x y & more]
   (let [kx (k x) ky (k y)
         v (if (> kx ky) x y)
         kv (if (> kx ky) kx ky)]
     (loop [v v kv kv more more]
       (if (seq more)
         (let [w (first more) kw (k w)]
           (if (>= kw kv) (recur w kw (next more)) (recur v kv (next more))))
         v)))))

(defn min-key
  ([k x] x)
  ([k x y] (if (< (k x) (k y)) x y))
  ([k x y & more]
   (let [kx (k x) ky (k y)
         v (if (< kx ky) x y)
         kv (if (< kx ky) kx ky)]
     (loop [v v kv kv more more]
       (if (seq more)
         (let [w (first more) kw (k w)]
           (if (<= kw kv) (recur w kw (next more)) (recur v kv (next more))))
         v)))))

;; Function combinators (pure HOFs).
(defn juxt [& fs]
  (fn [& args] (mapv (fn [f] (apply f args)) fs)))

(defn every-pred [& preds]
  (fn [& xs] (every? (fn [p] (every? p xs)) preds)))

(defn some-fn [& preds]
  (fn [& xs] (some (fn [p] (some p xs)) preds)))

(defn not-any? [pred coll] (not (some pred coll)))

(defn not-every? [pred coll] (not (every? pred coll)))

(defn split-at [n coll] [(take n coll) (drop n coll)])

(defn split-with [pred coll] [(take-while pred coll) (drop-while pred coll)])

(defn ident? [x] (or (keyword? x) (symbol? x)))

(defn qualified-ident? [x] (or (qualified-symbol? x) (qualified-keyword? x)))

(defn simple-ident? [x] (or (simple-symbol? x) (simple-keyword? x)))