day_1.gleam

import gleam/dict
import gleam/int
import gleam/list
import gleam/option
import gleam/result
import gleam/string

// Expects both lists to be sorted
fn solve_part_one(left: List(Int), right: List(Int), distance_accumulator: Int) {
  case left {
    [first, ..rest] -> {
      let right_remaining = list.rest(right) |> result.unwrap([])
      let right_value = list.first(right) |> result.unwrap(0)
      let distance =
        first
        |> int.subtract(right_value)
        |> int.absolute_value

      solve_part_one(rest, right_remaining, { distance_accumulator + distance })
    }
    _ -> distance_accumulator
  }
}

pub fn pt_1(input: String) {
  let #(left, right) =
    input
    |> string.split(on: "\n")
    |> list.map(fn(line) {
      let sections =
        line
        |> string.split("   ")

      let left =
        list.first(sections)
        |> result.unwrap("0")
        |> int.parse()
        |> result.unwrap(0)

      let right =
        list.last(sections)
        |> result.unwrap("0")
        |> int.parse()
        |> result.unwrap(0)

      #(left, right)
    })
    |> list.unzip

  let left = list.sort(left, by: int.compare)
  let right = list.sort(right, by: int.compare)

  solve_part_one(left, right, 0)
}

pub fn get_frequencies(
  values: List(Int),
  accum: dict.Dict(Int, Int),
) -> dict.Dict(Int, Int) {
  case values {
    [item, ..rest] -> {
      let accum =
        accum
        |> dict.upsert(item, fn(x) {
          case x {
            option.Some(i) -> {
              i + 1
            }
            option.None -> 1
          }
        })
      get_frequencies(rest, accum)
    }
    _ -> accum
  }
}

pub fn pt_2(input: String) {
  let #(left, right) =
    input
    |> string.split(on: "\n")
    |> list.map(fn(line) {
      let sections =
        line
        |> string.split("   ")

      let left =
        list.first(sections)
        |> result.unwrap("0")
        |> int.parse()
        |> result.unwrap(0)

      let right =
        list.last(sections)
        |> result.unwrap("0")
        |> int.parse()
        |> result.unwrap(0)

      #(left, right)
    })
    |> list.unzip

  let frequencies = get_frequencies(right, dict.new())

  left
  |> list.fold(0, fn(current, value) {
    let exists =
      frequencies
      |> dict.get(value)
      |> result.unwrap(0)

    current + { value * exists }
  })
}