go.property("acceleration", 100)
go.property("deceleration", 200)
go.property("max_speed", 400)
go.property("rotation_speed", 180)

-- unit vector pointing up
local UP = vmath.vector3(0, 1, 0)

function init(self)
    -- make sure the script will receive user input
    msg.post(".", "acquire_input_focus")

    -- movement input
    self.input = vmath.vector3()

    -- the current speed (pixels/second)
    self.speed = 0
end

function update(self, dt)
    -- accelerating?
    if self.input.y > 0 then
        -- increase speed
        self.speed = self.speed + self.acceleration * dt
        -- cap speed
        self.speed = math.min(self.speed, self.max_speed)
    else
        -- decrease speed when not accelerating
        self.speed = self.speed - self.deceleration * dt
        self.speed = math.max(self.speed, 0)
    end

    -- apply rotation based on self.input.x (left/right)
    local rot = go.get_rotation()
    -- amount to rotate (in radians)
    local rot_amount = math.rad(self.rotation_speed * self.input.x * dt)
    -- apply rotation as a quaternion created from a rotation of 'rot_amount' degrees around the z-axis
    rot = rot * vmath.quat_rotation_z(rot_amount)
    go.set_rotation(rot)

    -- move the game object
    local p = go.get_position()
    -- amount to move (pixels)
    local move_amount = UP * self.speed * dt
    -- apply rotation to movement vector to move game object in the direction of rotation
    p = p + vmath.rotate(rot, move_amount)
    go.set_position(p)

    -- reset input
    self.input = vmath.vector3()
end

function on_input(self, action_id, action)
    -- update direction of movement based on currently pressed keys
    if action_id == hash("up") then
        self.input.y = 1
    elseif action_id == hash("down") then
        self.input.y = -1
    elseif action_id == hash("left") then
        self.input.x = 1
    elseif action_id == hash("right") then
        self.input.x = -1
    end
end