using { /Fortnite.com/Devices }
using { /Verse.org/Simulation }
using { /Verse.org/Simulation/Tags }
using { /UnrealEngine.com/Temporary/SpatialMath }
using { /UnrealEngine.com/Temporary/Diagnostics }

# BUILD THE CAR PRIMITIVE — Part 1 of "Scene Graph: Car Primitive".
#
# A "car" in UEFN can mean two very different things. The real modular wheeled
# vehicle (engine + suspension + wheels) is built from `modular_vehicle_*`
# scene-graph components that are ALL Epic-internal in build 41.00 — a creator
# cannot assemble one from Verse. So we build the honest, creator-usable version:
# a PRIMITIVE. A primitive is just a placed prop (a mesh body) that we claim as
# "the car", find from Verse, and move on command. That is the foundation every
# later lesson builds on: colour it (Part 2), drive a camera into it (Part 3),
# and make it actually move under input (the capstone).
#
# We use TAG DISCOVERY (the proven working-island idiom) instead of @editable
# wiring: the car body is any placed prop carrying the `car_body_tag`, and the
# ignition is any button carrying the `car_ignition_tag`. Press the ignition and
# the car nudges forward — proof we have a live handle on a real placed prop.

# A tag is any class deriving from `tag`. Put the matching string on the actors
# in the editor (set the actor's Tags array) so Verse discovers them with no
# Details-panel binding.
car_body_tag := class(tag) {}
car_ignition_tag := class(tag) {}

car_build_primitive_device := class(creative_device):

    # How far (cm) the car nudges forward on each ignition press.
    @editable
    NudgeDistance : float = 250.0

    # How long (seconds) the nudge takes.
    @editable
    NudgeSeconds : float = 0.6

    OnBegin<override>()<suspends> : void =
        # Find the ignition button(s) by tag and react to each press.
        for (Obj : FindCreativeObjectsWithTag(car_ignition_tag)):
            if (Ignition := button_device[Obj]):
                Ignition.InteractedWithEvent.Subscribe(OnIgnition)
                Print("CarPrimitive: ignition wired.")
        # Confirm we actually found a car body to drive.
        for (Obj : FindCreativeObjectsWithTag(car_body_tag)):
            if (Body := creative_prop[Obj]):
                Print("CarPrimitive: car body found and ready.")

    OnIgnition(Agent : agent) : void =
        spawn { NudgeForward() }

    # Move every tagged car body one nudge along its own forward (+X) direction.
    NudgeForward()<suspends> : void =
        for (Obj : FindCreativeObjectsWithTag(car_body_tag)):
            if (Body := creative_prop[Obj]):
                spawn { NudgeOne(Body) }

    NudgeOne(Body : creative_prop)<suspends> : void =
        Current : transform = Body.GetTransform()
        # GetLocalForward gives the prop's own +X axis as a unit vector; scale it
        # by NudgeDistance and add it to the current position. The rotation is
        # unchanged so the car keeps facing the same way.
        Forward : vector3 = Current.Rotation.GetLocalForward()
        Target : vector3 = Current.Translation + Forward * NudgeDistance
        Body.MoveTo(Target, Current.Rotation, NudgeSeconds)
        Print("CarPrimitive: car nudged forward.")