//
//  DirtTextureFactory.swift
//  GasTankAR
//
//  Created by Dennis Nemec on 28.08.26.
//

import RealityKit
import UIKit

/// Erzeugt prozedural eine kachelbare Erd-/Dreck-Textur (ohne Bild-Asset) für die Grubenwand,
/// damit sichtbar wird, dass sich der Tank unter der Erde befindet.
@MainActor
enum DirtTextureFactory {
    /// Einmalig erzeugte, wiederverwendete Textur.
    static let texture: TextureResource? = makeTexture()

    private static func makeTexture() -> TextureResource? {
        let size = CGSize(width: 256, height: 256)
        let image = UIGraphicsImageRenderer(size: size).image { context in
            let rect = CGRect(origin: .zero, size: size)

            // Erd-Grundton.
            UIColor(red: 0.42, green: 0.30, blue: 0.18, alpha: 1).setFill()
            context.fill(rect)

            // Größere Erdflecken / Steine für Struktur.
            for _ in 0..<70 {
                let diameter = CGFloat.random(in: 6...26)
                let origin = CGPoint(x: .random(in: -10...size.width), y: .random(in: -10...size.height))
                let brightness = CGFloat.random(in: -0.12...0.12)
                UIColor(
                    red: max(0, min(1, 0.42 + brightness)),
                    green: max(0, min(1, 0.30 + brightness)),
                    blue: max(0, min(1, 0.18 + brightness)),
                    alpha: 1
                ).setFill()
                context.cgContext.fillEllipse(in: CGRect(x: origin.x, y: origin.y, width: diameter, height: diameter))
            }

            // Feine Körnung (helle + dunkle Sprenkel).
            for _ in 0..<2000 {
                let point = CGPoint(x: .random(in: 0..<size.width), y: .random(in: 0..<size.height))
                let diameter = CGFloat.random(in: 0.5...2.5)
                let isDark = Bool.random()
                let color = isDark
                    ? UIColor(white: 0, alpha: .random(in: 0.05...0.2))
                    : UIColor(white: 1, alpha: .random(in: 0.03...0.12))
                color.setFill()
                context.cgContext.fillEllipse(in: CGRect(x: point.x, y: point.y, width: diameter, height: diameter))
            }
        }

        guard let cgImage = image.cgImage else { return nil }
        return try? TextureResource.generate(from: cgImage, options: .init(semantic: .color))
    }
}