let input = Reuse.split "inputs/day02.txt" ','

let is_valid ((start, ending): string * string) : bool =
  let start_length = String.length start in
  let end_length = String.length ending in
  let filtered_out =   start_length mod 2 != 0 && end_length mod 2 != 0 && start_length == end_length in
  not filtered_out
  


let generate_tuple (value : string) : (string * string) =
  let split = String.split_on_char '-' value in
  match split with
  | first :: second :: [] -> (first, second)
  | _ -> failwith("Expected exactly 2 values in list entry" ^ value)

let generate_pairs (inputs: string list) : (string * string ) list =
  List.map generate_tuple inputs
  
let is_invalid (number: int) : bool = 
  let number_string = string_of_int number in
  let length = String.length number_string in
  let is_even = length mod 2 == 0 in
  let half = length / 2 in
  let first_part = String.sub number_string 0 half in
  let last_part = String.sub number_string half half in
  let invalid = is_even && first_part = last_part in
  invalid

  let is_invalid_2 (number: int) : bool =
    let number_string = string_of_int number in
    let pattern = Str.regexp "\\(.+\\)\\1+$" in
    Str.string_match pattern number_string 0
  
let calculate_for_line ((start, ending) : (string * string)) (inv: int -> bool) : int =
  let start_number = int_of_string start in
  let end_number = int_of_string ending in
  let rec loop i acc = 
    if i > end_number then acc
    else loop (i + 1) (acc + if inv i then i else 0)
  in
  loop start_number 0
  
let calculate_invalidities entries inv =
  List.fold_left (fun acc entry -> acc + calculate_for_line entry inv) 0 entries

let solve_part1 (inputs: string list) : int = 
  let inputs = generate_pairs inputs in 
  let filtered = List.filter is_valid inputs in
  calculate_invalidities filtered is_invalid

  

let solve_part2 (inputs: string list) : int = 
  let inputs = generate_pairs inputs in
  calculate_invalidities inputs is_invalid_2
  
let day2_part1 : int = 
  solve_part1 input

let day2_part2 : int = 
  solve_part2 input

module Tests = struct
  let test_input = "11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124"
  
  let test_lines = String.split_on_char ',' test_input
  
  let run_tests () = 
    let part1_result = solve_part1 test_lines in
    let part2_result = solve_part2 test_lines in
    if part1_result <> 1227775554 then
      failwith ("Day 2 Part 1 test failed: expected 1227775554, got " ^ string_of_int part1_result);
      
    if part2_result <> 4174379265 then
        failwith ("Day 2 Part 2 test failed: expected 4174379265, got " ^ string_of_int part2_result);
      
    Printf.printf "All day 2 tests passed!\n"
end
  
let () = Tests.run_tests()