bignum = require "_openssl.bignum"

function find(card, deck, times)
    local revert = false
    local increment = bignum.new(0)
    local multiply = bignum.new(1)
    for line in io.lines(arg[1]) do
        if line:find("^deal into new stack$") then
            revert = not revert
        elseif line:find("^cut %-?%d+$") then
            local val = tonumber(line:match("^cut (%-?%d+)$"))
            if not revert then
                increment = (increment - val) % deck
            else
                increment = (increment + val) % deck
            end
        elseif line:find("^deal with increment %d+$") then
            local val = tonumber(line:match("^deal with increment (%d+)$"))
            multiply = (multiply * val) % deck
            increment = (increment * val) % deck
            if revert then
                increment = (increment + (val - 1)) % deck
            end
        end
    end

    print(card, multiply, increment, deck)
    card = (card * multiply * times + increment * times) % deck
    if revert then
        card = deck - (card + 1)
    end
    return card
end

function revfind(card, deck, times)
    local revert = false
    local increment = bignum.new(0)
    local multiply = bignum.new(1)
    for line in io.lines(arg[1]) do
        if line:find("^deal into new stack$") then
            revert = not revert
        elseif line:find("^cut %-?%d+$") then
            local val = tonumber(line:match("^cut (%-?%d+)$"))
            if not revert then
                increment = (increment - val) % deck
            else
                increment = (increment + val) % deck
            end
        elseif line:find("^deal with increment %d+$") then
            local val = tonumber(line:match("^deal with increment (%d+)$"))
            multiply = (multiply * val) % deck
            increment = (increment * val) % deck
            if revert then
                increment = (increment + (val - 1)) % deck
            end
        end
    end

    print(card, multiply, increment, deck)
    card = (card * multiply * times + increment * times) % deck
    if revert then
        card = deck - (card + 1)
    end
    return card
end

print("Part 1:", find(2019, 10007, 1))
print("Part 2:", find(2020, 119315717514047, 101741582076661))

print("Part 1:", revfind(7744, 10007, 1))
print("Part 2:", revfind(2020, 119315717514047, 101741582076661))