Bejeweled Initial Fill

BejeweledFill.fs

let init settings =
    let getJewel a b =
        let rnd m = rand() * (float (settings.JewelTypes - m)) |> floor |> int
        let shift j jewl = if jewl >= j then jewl + 1 else jewl
        match a, b with
        | None, None -> rnd 0
        | None, Some i
        | Some i, None -> rnd 1 |> shift i
        | Some i, Some j when i = j -> rnd 1 |> shift j
        | Some i, Some j -> rnd 2 |> shift (min i j) |> shift (max i j)
    let addJewel = function
        | n, _, _, _, _, _ when n = settings.GridSize -> None
        | n, top, mid, m, i, j ->
            let a = if j = i || j = m then j else None
            let mid, top, m2, b =
                match mid with
                | [] -> [], [], None, None
                | m2 :: mid ->
                    match top with
                    | t :: top when m2 = t ->
                        mid, top, Some m2, Some m2
                    | _ :: top | top ->
                        let eq = Some m2 = j || Some m2 = m || not mid.IsEmpty && mid.Head = m2
                        mid, top, Some m2, if eq then Some m2 else None
            let jewel = getJewel a b
            Some (jewel, (n+1, top, mid, m2, j, Some jewel))
    let addLine = function
        | n, _, _ when n = settings.GridSize -> None
        | n, top, mid ->
            let line = Seq.unfold addJewel (0, top, mid, None, None, None) |> Seq.toList
            Some (line, (n + 1, mid, line))
    Seq.unfold addLine (0, [], [])