/*
See the LICENSE.txt file for this sample’s licensing information.

Abstract:
Component and System for controlling portal crossing lighting behavior.
*/

import RealityKit

struct EnvironmentLightingFadeComponent: Component {

    init() {
        EnvironmentLightingFadeComponent.registerComponent()
        EnvironmentLightingFadeSystem.registerSystem()
    }
}

final class EnvironmentLightingFadeSystem: System {

    var elapsedTime: TimeInterval = 0
    init(scene: RealityKit.Scene) {
    }

    func update(context: SceneUpdateContext) {
        elapsedTime += context.deltaTime

        let portals = context.entities(matching: EntityQuery(where: .has(PortalComponent.self)), updatingSystemWhen: .rendering)
        let portal = portals.first { entity in
            entity.components[PortalComponent.self] != nil
        }

        guard let portal else { return }

        for entity in context.entities(matching: EntityQuery(where: .has(EnvironmentLightingFadeComponent.self)), updatingSystemWhen: .rendering) {

            let distance = computeDistanceFromPortal(entity: entity, portal: portal)
            let weight = mapDistanceToWeight(distance: distance)

            portal.components.set(EnvironmentLightingConfigurationComponent(environmentLightingWeight: weight))
        }
    }

    func computeDistanceFromPortal(entity: Entity, portal: Entity) -> Float {
        let vector = entity.position(relativeTo: nil) - portal.position(relativeTo: nil)
        let portalForward = portal.transformMatrix(relativeTo: nil).forward * -1
        let distance = SIMD3<Float>.dot(portalForward, vector)
        return distance
    }

    func mapDistanceToWeight(distance: Float) -> Float {
        let maxDistance: Float = 0.15
        let minDistance: Float = 0.1
        if distance > maxDistance {
            return 1.0
        } else if distance > minDistance {
            return (distance - minDistance) / (maxDistance - minDistance)
        } else {
            return 0
        }
    }
}