// SceneGraph.swift
// Observable scene graph that owns all objects and drives the outliner + renderer.

import Observation
import Metal
import simd

@Observable
final class SceneGraph {

    // All top-level objects (children are nested inside each)
    var rootObjects: [SceneObject] = []

    // Quick access to the selected object
    var selectedObject: SceneObject? {
        allObjects.first { $0.isSelected }
    }

    // Flattened list of every object in the hierarchy
    var allObjects: [SceneObject] {
        var result: [SceneObject] = []
        func walk(_ objects: [SceneObject]) {
            for obj in objects {
                result.append(obj)
                walk(obj.children)
            }
        }
        walk(rootObjects)
        return result
    }

    // MARK: - Stats

    var totalVertexCount: Int {
        allObjects.compactMap { $0.meshHandle?.vertexCount }.reduce(0, +)
    }

    var totalFaceCount: Int {
        allObjects.compactMap { $0.meshHandle?.faceCount }.reduce(0, +)
    }

    // MARK: - Mutation

    func addObject(_ object: SceneObject) {
        rootObjects.append(object)
    }

    func removeObject(_ object: SceneObject) {
        object.removeFromParent()
        rootObjects.removeAll { $0.id == object.id }
    }

    func select(_ object: SceneObject?) {
        for obj in allObjects {
            obj.isSelected = (obj.id == object?.id)
        }
    }

    func deselectAll() {
        for obj in allObjects {
            obj.isSelected = false
        }
    }

    // MARK: - Default Scene

    /// Creates the classic Blender startup scene: Cube + Camera + Light.
    static func defaultScene(device: MTLDevice) -> SceneGraph {
        let graph = SceneGraph()

        // Default cube
        let cube = SceneObject(name: "Cube", type: .mesh)
        let cubeMeshData = PrimitiveGenerator.cube(size: 2.0, color: SIMD4(0.63, 0.63, 0.63, 1))
        cube.meshHandle = MeshUploader.upload(
            vertices: cubeMeshData.vertices,
            wireVertices: cubeMeshData.wireVertices,
            faceCount: cubeMeshData.faceCount,
            edgeCount: cubeMeshData.edgeCount,
            label: "Cube",
            device: device
        )
        cube.isSelected = true
        graph.addObject(cube)

        // Camera
        let camera = SceneObject(name: "Camera", type: .camera,
                                 position: SIMD3(7.36, 4.95, -6.93))
        camera.transform.rotation = SIMD3(1.11, 0.0, 2.17)
        let cameraMeshData = PrimitiveGenerator.cameraWireframe()
        camera.meshHandle = MeshUploader.upload(
            vertices: [],
            wireVertices: cameraMeshData.wireVertices,
            faceCount: 0,
            edgeCount: cameraMeshData.edgeCount,
            label: "Camera",
            device: device
        )
        camera.color = SIMD4(0.4, 0.4, 0.4, 1.0)
        graph.addObject(camera)

        // Light
        let light = SceneObject(name: "Light", type: .light,
                                position: SIMD3(4.08, 5.90, -1.0))
        let lightMeshData = PrimitiveGenerator.lightIcon()
        light.meshHandle = MeshUploader.upload(
            vertices: [],
            wireVertices: lightMeshData.wireVertices,
            faceCount: 0,
            edgeCount: lightMeshData.edgeCount,
            label: "Light",
            device: device
        )
        light.color = SIMD4(1.0, 0.85, 0.4, 1.0)
        graph.addObject(light)

        return graph
    }
}

// MARK: - Mesh Uploader Utility

enum MeshUploader {
    static func upload(
        vertices: [MeshVertex],
        wireVertices: [MeshVertex],
        faceCount: Int,
        edgeCount: Int,
        label: String,
        device: MTLDevice
    ) -> MeshHandle {
        let vBuf: MTLBuffer?
        if !vertices.isEmpty {
            vBuf = device.makeBuffer(
                bytes: vertices,
                length: MemoryLayout<MeshVertex>.stride * vertices.count,
                options: .storageModeShared
            )
        } else {
            // Empty placeholder buffer (1 byte) for objects with no solid geometry
            vBuf = device.makeBuffer(length: 1, options: .storageModeShared)
        }

        let wBuf: MTLBuffer?
        if !wireVertices.isEmpty {
            wBuf = device.makeBuffer(
                bytes: wireVertices,
                length: MemoryLayout<MeshVertex>.stride * wireVertices.count,
                options: .storageModeShared
            )
        } else {
            wBuf = nil
        }

        return MeshHandle(
            vertexBuffer: vBuf!,
            vertexCount: vertices.count,
            wireVertexBuffer: wBuf,
            wireVertexCount: wireVertices.count,
            faceCount: faceCount,
            edgeCount: edgeCount,
            label: label
        )
    }
}