using System;
using System.Runtime.CompilerServices;
using UnityEngine;

namespace ADOFAIRenderer.Util
{
    /// <summary>Particle system helpers.</summary>
    internal static class ParticleUtil
    {
        /// <summary>
        /// Renderer found for each particle system. Weak keys: an entry is dropped when its ParticleSystem object is collected.
        /// Main thread.
        /// </summary>
        private static readonly ConditionalWeakTable<ParticleSystem, ParticleSystemRenderer> Cache = new();

        /// <summary>
        /// Returns the ParticleSystemRenderer that belongs to <paramref name="ps"/>. When a GameObject has several particle
        /// systems and renderers, the renderer with the same component index as the particle system is used; otherwise the
        /// first renderer of the GameObject. The result is cached per particle system. Main thread.
        /// </summary>
        /// <param name="ps">Particle system; null or destroyed returns null.</param>
        /// <returns>The renderer, or null when the GameObject has none.</returns>
        public static ParticleSystemRenderer? GetRenderer(this ParticleSystem ps)
        {
            if (!ps) return null;
            if (Cache.TryGetValue(ps, out var renderer) && renderer) return renderer;

            var particleSystems = ps.GetComponents<ParticleSystem>();
            var renderers = ps.GetComponents<ParticleSystemRenderer>();
            var index = Array.IndexOf(particleSystems, ps);

            renderer = index >= 0 && index < renderers.Length ? renderers[index] : ps.GetComponent<ParticleSystemRenderer>();
            if (renderer) Cache.Add(ps, renderer);

            return renderer;
        }
    }
}