module advent_of_code.tasks.day_7.Star1

open System.IO

let stream = new StreamReader("tasks/day-7/input.txt")

let containsSplit (s: string) =
    s.Contains("^")

let split (row: string) (pos: int) =
    if row[pos] = '^' then
        [|pos-1; pos+1|] |> Set.ofArray, 1
    else
        [|pos|] |> Set.ofArray, 0

let rec getBeams (manifold: string array) (pos: Set<int>) =
    if manifold.Length = 0 then
        0
    else
        let row, tail = manifold[0], manifold[1..]
        let mapRes = (pos |> Seq.map (split row))
        let newPos = (mapRes |> Seq.map fst) |> Set.ofSeq |> Set.unionMany
        let splits = mapRes |> Seq.map snd |> Seq.sum
        getBeams tail newPos + splits

let main =
    let allLines = stream.ReadToEnd().Split("\n")
    let startLine, manifold = allLines[0], (allLines[1..] |> Array.filter containsSplit)
    let startPos = startLine.IndexOf("S")
    getBeams manifold ([|startPos|] |> Set.ofArray)