module advent_of_code.tasks.day_7.Star2

open System
open System.IO

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

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

let split (oldTimelines: int64 array) (newTimelines: int64 array) (t: int * char) =
    let index, item = t.Deconstruct()
    let mutable timelines = newTimelines
    if item = '^' then
        timelines[index-1] <- oldTimelines[index] + newTimelines[index-1]
        timelines[index+1] <- oldTimelines[index] + newTimelines[index+1]
    else
        timelines[index] <- oldTimelines[index] + newTimelines[index]
    timelines

let rec getTimelines (manifold: string array) (prevTimelines: int64 array) =
    if manifold.Length = 0 then
        prevTimelines
    else
        let row, tail = manifold[0], manifold[1..]
        let emptyTimeline = [1 .. row.Length] |> Seq.map (fun _ -> 0 |> int64) |> Array.ofSeq
        let newTimeline = row |> seq |> Seq.mapi (fun index item -> index, item) |> Seq.fold (split prevTimelines) emptyTimeline
        getTimelines tail newTimeline
    

let main =
    let allLines = stream.ReadToEnd().Split("\n")
    let startLine, manifold = allLines[0], (allLines[1..] |> Array.filter containsSplit)
    let startPos = startLine.IndexOf("S")
    let initialTimeline = [1..startLine.Length] |> Seq.map (fun _ -> 0 |> int64) |> Array.ofSeq
    initialTimeline[startPos] <- 1
    Array.sum (getTimelines manifold initialTimeline)