let get_one_line file =
  try Some (input_line file) with
    End_of_file -> None

let get_lines file =
  let rec input lines =
    match get_one_line file with
      Some line -> input (line :: lines)
    | None -> List.rev lines
  in input []

(* --- *)

type password_set = { min : int; max : int; chr : char; pw : string };;

let line_to_set line = (* convert a line from the file into a password_set *)
  let [rng; chr; pw] = String.split_on_char ' ' line in (* split on spaces *)
  let chr = String.get chr 0 in (* strip colon and convert to char *)
  let [min; max] = List.map int_of_string (String.split_on_char '-' rng) in (* pull out the min and max from the range, map to Int *)
  { min; max; chr; pw }

(* stolen from SO.. *)
let explode s = (* convert a string to a list of chars *)
  let rec exp i l =
   if i < 0 then l else exp (i - 1) (s.[i] :: l) in
  exp (String.length s - 1) [];;

let char_count el str =
  List.length (List.filter (fun c -> c == el) (explode str))

let is_valid_day1_password set =
  let count = char_count set.chr set.pw in
  (*Printf.printf "%s %c count: %i min: %i, max: %i, in range: %b\n" set.pw set.chr count set.min set.max (count >= set.min && count <= set.max);*)
  count >= set.min && count <= set.max

let is_valid_day2_password set =
  let is_valid = ((String.get set.pw (set.min-1)) == set.chr) <> ((String.get set.pw (set.max-1)) == set.chr) in
  (*Printf.printf "%s %c min: %i, max: %i, char-at-min: %c, char-at-max: %c, valid: %b\n" set.pw set.chr set.min set.max (String.get set.pw (set.min-1)) (String.get set.pw (set.max-1)) is_valid;*)
  is_valid

let file = "day2.txt"
let channel = open_in(file)
let lines = get_lines channel
let sets = List.map line_to_set lines

let valid_day1_passwords = List.filter is_valid_day1_password sets;;
Printf.printf "valid day1 password count: %i\n" (List.length valid_day1_passwords)

let valid_day2_passwords = List.filter is_valid_day2_password sets;;
Printf.printf "valid day2 password count: %i\n" (List.length valid_day2_passwords)