using System;
using System.Reflection;
using System.Resources;
using MelonLoader;
using UnityEngine;

namespace ADOFAIRenderer.Util;

/// <summary>
/// Loads the Unity asset bundles (fonts, shaders) embedded in the mod DLL as manifest resources. One bundle set is
/// embedded per platform (Bundle/Win64, Bundle/OSX, Bundle/Linux).
/// Main thread (AssetBundle loading).
/// </summary>
internal static class BundleLoader
{
    /// <summary>Resource folder of the running platform: "Win64" on Windows, "OSX" on macOS, "Linux" otherwise.</summary>
    private static readonly string BundlePlatform;
    /// <summary>The mod assembly that contains the bundle resources.</summary>
    private static readonly Assembly? ExecutingAssembly;

    static BundleLoader()
    {
        BundlePlatform = Application.platform switch
        {
            RuntimePlatform.WindowsPlayer => "Win64",
            RuntimePlatform.OSXPlayer => "OSX",
            _ => "Linux"
        };
        ExecutingAssembly = Assembly.GetExecutingAssembly();
    }

    /// <summary>
    /// Loads the bundle stored as manifest resource "ADOFAIRenderer.Bundle.&lt;platform&gt;.&lt;resourcePath&gt;" with
    /// AssetBundle.LoadFromStream. The resource stream is disposed when this method returns. The caller owns the returned
    /// bundle.
    /// Reference: https://docs.unity3d.com/ScriptReference/AssetBundle.LoadFromStream.html
    /// </summary>
    /// <param name="resourcePath">Bundle name inside the platform folder, for example "fonts" or "shaders".</param>
    /// <returns>The loaded bundle, or null when Unity fails to load it.</returns>
    /// <exception cref="MissingManifestResourceException">The resource is not embedded in the DLL.</exception>
    /// <exception cref="InvalidOperationException">The executing assembly is not available.</exception>
    public static AssetBundle GetBundle(string resourcePath)
    {
        if (ExecutingAssembly != null)
        {
            var bundlePath = $"ADOFAIRenderer.Bundle.{BundlePlatform}.{resourcePath}";
            using var resourceStream = ExecutingAssembly.GetManifestResourceStream(bundlePath);
            if (resourceStream != null)
            {
                return AssetBundle.LoadFromStream(resourceStream);
            }
                
            Melon<RenderMod>.Logger.Error($"Could not find bundle resource in DLL.\n{bundlePath}");
            throw new MissingManifestResourceException("Could not find bundle resource in DLL.");
        }
            
        Melon<RenderMod>.Logger.Error("Executing assembly has not been set properly.");
        throw new InvalidOperationException("ExecutingAssembly has not been set."); 
    }
}