local world = require("world")

local function getCurrentTimeMilliseconds()
    return love.timer.getTime() * 1000
end

local Animation = {
    animation = {
        initialMs = T.number,
        msPerFrame = T.number,
        frames = Arr({ drawable = T.Drawable }),
    },
    position = T.XyPair,
    drawAsSprite = T.Drawable
}

---@return { initialMs: number, frames: Entity[], msPerFrame: number }
function BuildAnimation(frames, msPerFrame)
    return {
        initialMs = getCurrentTimeMilliseconds(),
        frames = frames,
        msPerFrame = msPerFrame,
    }
end

local currentMs = getCurrentTimeMilliseconds()

local animation = world:filteredSystem("animation", Animation, function(e, _, system)
    local nextFrameIndex = 1 + math.floor((currentMs - e.animation.initialMs) / e.animation.msPerFrame)
    if nextFrameIndex > #e.animation.frames then
        e.animation = nil
        system.world:addEntity(e)
    else
        e.drawAsSprite = e.animation.frames[nextFrameIndex]
    end

end)

function animation:preProcess()
    currentMs = getCurrentTimeMilliseconds()
end