namespace AdventOfCode2023

open System
open System.Collections.Generic
open System.Globalization

[<RequireQualifiedAccess>]
module Day12 =

    let rec solve (line : ReadOnlySpan<char>) (groups : IReadOnlyList<int>) (currentGroupIndex : int) =
        if line.Length = 0 then
            if currentGroupIndex = groups.Count then LanguagePrimitives.GenericOne else LanguagePrimitives.GenericZero
        else
        match line.[0] with
        | '#' ->
            if currentGroupIndex >= groups.Count then LanguagePrimitives.GenericZero else
            let mutable isOk = true
            for i = 1 to groups.[currentGroupIndex] - 1 do
                if isOk && (i >= line.Length || (line.[i] <> '#' && line.[i] <> '?')) then
                    isOk <- false
            if not isOk then LanguagePrimitives.GenericZero else
            if groups.[currentGroupIndex] < line.Length then
                if line.[groups.[currentGroupIndex]] = '#' then
                    LanguagePrimitives.GenericZero
                else
                    solve (line.Slice (groups.[currentGroupIndex] + 1)) groups (currentGroupIndex + 1)
            else
                solve ReadOnlySpan<_>.Empty groups (currentGroupIndex + 1)
        | '.' ->
            solve (line.Slice 1) groups currentGroupIndex
        | '?' ->
            let ifDot = solve (line.Slice 1) groups currentGroupIndex
            let ifHash =
                if currentGroupIndex >= groups.Count then LanguagePrimitives.GenericZero else
                let mutable isOk = true
                for i = 1 to groups.[currentGroupIndex] - 1 do
                    if isOk && (i >= line.Length || (line.[i] <> '#' && line.[i] <> '?')) then
                        isOk <- false
                if not isOk then LanguagePrimitives.GenericZero else
                if groups.[currentGroupIndex] < line.Length then
                    if groups.[currentGroupIndex] < line.Length && line.[groups.[currentGroupIndex]] = '#' then
                        LanguagePrimitives.GenericZero
                    else
                        solve (line.Slice (groups.[currentGroupIndex] + 1)) groups (currentGroupIndex + 1)
                else
                    solve ReadOnlySpan<_>.Empty groups (currentGroupIndex + 1)
            ifDot + ifHash
        | _ ->
            if currentGroupIndex = groups.Count then LanguagePrimitives.GenericOne else LanguagePrimitives.GenericZero


    let part1 (s : string) =
        use mutable lines = StringSplitEnumerator.make '\n' s

        let mutable answer = 0uL
        let arr = ResizeArray ()
        for line in lines do
            if not line.IsEmpty then
                arr.Clear ()
                use ints = StringSplitEnumerator.make' ',' (line.Slice (line.IndexOf ' ' + 1))
                for int in ints do
                    arr.Add (Int32.Parse (int, NumberStyles.None, CultureInfo.InvariantCulture))

                let solved = solve line arr 0
                answer <- answer + solved

        answer

    let part2 (s : string) =
        use mutable lines = StringSplitEnumerator.make '\n' s

        let mutable answer = 0uL
        let arr = ResizeArray ()
        for line in lines do
            if not line.IsEmpty then
                arr.Clear ()
                let spaceIndex =line.IndexOf ' '
                for _ = 0 to 4 do
                    use ints = StringSplitEnumerator.make' ',' (line.Slice (spaceIndex + 1))
                    for int in ints do
                        arr.Add (Int32.Parse (int, NumberStyles.None, CultureInfo.InvariantCulture))

                let sliced = line.Slice(0, spaceIndex).ToString ()
                let line = String.Concat (sliced, '?', sliced, '?', sliced, '?', sliced, '?', sliced)

                let solved = solve (line.AsSpan()) arr 0
                printfn $"%s{line} : %i{solved}"
                answer <- answer + solved

        answer