1 files changed, 68 insertions, 0 deletions
diff --git a/motus/lib/freq_analysis.ml b/motus/lib/freq_analysis.ml
new file mode 100644
index 0000000..12f5fef
--- /dev/null
+++ b/motus/lib/freq_analysis.ml
@@ -0,0 +1,68 @@
+open StdLabels
+
+let () = Random.self_init ()
+
+type t = (char * int) list
+
+let update_freq : (char, int) Hashtbl.t -> char -> unit =
+ fun freq c ->
+  match Hashtbl.find_opt freq c with
+  | None -> Hashtbl.add freq c 1
+  | Some value -> Hashtbl.replace freq c (value + 1)
+
+
+(** Evaluate the score for each char (lower is better) *)
+let analyse : Wordlist.t -> (char * int) list =
+ fun data ->
+  let freq = Hashtbl.create 26 in
+  Seq.iter
+    (fun word -> String.iter word ~f:(update_freq freq))
+    (Wordlist.words data);
+
+  let number_2 = Wordlist.list_size data / 2 in
+  Hashtbl.fold (fun k v acc -> (k, abs (v - number_2)) :: acc) freq []
+
+
+(** Get the word which with the most information in it.
+
+The information is the score given to each character, representing each
+frequency in the whole word list (lower is better). If the same letter is
+present many times, we consider that succeding letters does not give any more
+informations (do not consider the position here) *)
+let pick_next_word : Wordlist.t -> (char * int) list -> string =
+ fun data scores ->
+  let list_size = Wordlist.list_size data / 2 in
+
+  let p' : (string list * int) option -> string -> (string list * int) option =
+   fun prec word ->
+    (* evaluate the score for this word *)
+    let _, eval =
+      String.fold_left
+        ~f:(fun (scores, score) c ->
+          match List.assoc_opt c scores with
+          | None ->
+              (* if the character has no score associated, we consider that it
+                 does not provide any more information, and give it the max
+                 score available *)
+              (scores, score + list_size)
+          | Some v ->
+              let new_scores =
+                List.filter ~f:(fun (c', _) -> not (Char.equal c c')) scores
+              in
+              (new_scores, score + v) )
+        ~init:(scores, 0)
+        word
+    in
+    match prec with
+    | None -> Some ([ word ], eval)
+    | Some (_, prec_score) when eval < prec_score -> Some ([ word ], eval)
+    | Some (w, prec_score) when eval = prec_score -> Some (word :: w, eval)
+    | _ -> prec
+  in
+  match Seq.fold_left p' None (Wordlist.words data) with
+  | None -> ""
+  | Some (words, _) ->
+      (* Pick a reandom word from the list *)
+      let elements = List.length words in
+      let number = Random.int elements in
+      List.nth words number