update_hooks = {}

-- https://pico-8.fandom.com/wiki/Qsort
function qsort(a, c, l, r)
    c, l, r = c or function(a, b) return a < b end, l or 1, r or #a
    if l < r then
        if c(a[r], a[l]) then
            a[l], a[r] = a[r], a[l]
        end
        local lp, k, rp, p, q = l + 1, l + 1, r - 1, a[l], a[r]
        while k <= rp do
            local swaplp = c(a[k], p)
            -- "if a or b then else"
            -- saves a token versus
            -- "if not (a or b) then"
            if swaplp or c(a[k], q) then
            else
                while c(q, a[rp]) and k < rp do
                    rp -= 1
                end
                a[k], a[rp], swaplp = a[rp], a[k], c(a[rp], p)
                rp -= 1
            end
            if swaplp then
                a[k], a[lp] = a[lp], a[k]
                lp += 1
            end
            k += 1
        end
        lp -= 1
        rp += 1
        -- sometimes lp==rp, so
        -- these two lines *must*
        -- occur in sequence;
        -- don't combine them to
        -- save a token!
        a[l], a[lp] = a[lp], a[l]
        a[r], a[rp] = a[rp], a[r]
        qsort(a, c, l, lp - 1)
        qsort(a, c, lp + 1, rp - 1)
        qsort(a, c, rp + 1, r)
    end
    return a
end

function filter(a, pred)
    filtered = {}
    for k, v in pairs(a) do
        if pred(v) then
            filtered[k] = v
        end
    end
    return filtered
end

function fmt(x, depth)
    depth = depth or 1
    if (depth > 4) then return "STACK_OVERFLOW" end

    if x == nil then
        return "nil"
    end

    t = type(x)
    if t == "number" then
        return "" .. x
    elseif t == "string" then
        return x
    elseif t == "table" then
        s = "{"
        i = 0
        for k, v in pairs(x) do
            if i ~= 0 then s = s .. ", " end
            i += 1
            s = s .. fmt(k, depth + 1) .. "=" .. fmt(v, depth + 1)
        end
        return s .. "}"
    elseif t == "function" then
        return "F()"
    elseif t == "boolean" and x then
        return "true"
    elseif t == "boolean" and not x then
        return "false"
    end
    return "_unknown_"
end

_button_states = {}
function _update_button_states(_dt)
    for button = 0, 20 do
        if btn(button) then
            if _button_states[button] == "up" then
                _button_states[button] = "just_pressed"
            else
                _button_states[button] = "held"
            end
        else
            _button_states[button] = "up"
        end
    end
end
update_hooks[1] = _update_button_states
function button_just_pressed(id)
    return _button_states[id] == "just_pressed"
end