(*
 * SPDX-FileCopyrightText: Copyright 2025 Alexandre Jesus <https://adbjesus.com>
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *)

let parse_data ch =
  In_channel.input_all ch
  |> String.trim
  |> String.split_on_char '\n'
  |> List.map String.trim
  |> List.filter (fun s -> String.length s > 0)
  |> List.fold_left
       (fun (r, v) s ->
         match String.split_on_char '-' s with
         | [ n ] -> (r, int_of_string n :: v)
         | [ a; b ] ->
             let a = int_of_string a in
             let b = int_of_string b in
             let rng = if a < b then (a, b) else (b, a) in
             (rng :: r, v)
         | _ -> failwith (Printf.sprintf "Invalid line: %s" s))
       ([], [])

let part1 ch =
  let r, v = parse_data ch in
  let is_fresh v (a, b) = v >= a && v <= b in
  let is_fresh v = List.exists (is_fresh v) r in
  (* O(|v| * |r|) which is good enough *)
  (* Could be O((|v|+|r|) log (|v| + |r|)) with a line-sweep similar to part 2 *)
  List.map is_fresh v
  |> List.map Bool.to_int
  |> List.fold_left ( + ) 0
  |> Printf.printf "%d\n"

let part2 ch =
  parse_data ch
  |> fst
  |> List.fold_left (fun acc (a, b) -> (b + 1, 0) :: (a, 1) :: acc) []
  |> List.sort compare
  |> List.fold_left
       (* (c, a, s) gives (count, active, start) *)
       (* (v, t) gives (value, type) *)
       (fun (c, a, s) (v, t) ->
         match (t, a) with
         | 0, 1 -> (c + v - s, 0, v)
         | 0, _ -> (c, a - 1, s)
         | _, 0 -> (c, 1, v)
         | _ -> (c, a + 1, s))
       (0, 0, 0)
  |> fun (c, _, _) -> Printf.printf "%d\n" c