index.jl

# Copyright 2025, Jimmy Envall and contributors
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at https://mozilla.org/MPL/2.0/.

import Base.hash

Letter = Int

struct Upper
    letter::Letter
end

struct Lower
    letter::Letter
end

LowerOrUpperIndex = Union{Lower,Upper}
IndexList = Vector{LowerOrUpperIndex}

function flip(index::Lower)
    return Upper(index.letter)
end

function flip(index::Upper)
    return Lower(index.letter)
end

function flip_to(index::Lower, letter::Letter)
    return Upper(letter)
end

function flip_to(index::Upper, letter::Letter)
    return Lower(letter)
end

function same_to(old::Lower, letter::Letter)
    return Lower(letter)
end

function same_to(old::Upper, letter::Letter)
    return Upper(letter)
end

function hash(arg::LowerOrUpperIndex, h::UInt)
    val::UInt = 0
    if typeof(arg) == Lower
        val |= 1
    end
    val |= arg.letter << 1
    hash(val, h)
end