using System;
using UnityEditor;
using UnityEditor.Build;
using UnityEditor.Build.Reporting;
using UnityEngine;

namespace AOT.Editor.HybridCLR
{
    /// <summary>Limit native WebGL build workers without changing player optimizations.</summary>
    [InitializeOnLoad]
    public sealed class WebGlBuildConcurrency : IPreprocessBuildWithReport, IPostprocessBuildWithReport
    {
        const string BeeVariable = "BEE_BUILD_THREADS";
        const string BinaryenVariable = "BINARYEN_CORES";
        const string WorkerLimit = "4";
        static bool ownsBee;
        static bool ownsBinaryen;

        public int callbackOrder => int.MinValue;

        static WebGlBuildConcurrency()
        {
            // Postprocess callbacks may be skipped when the native build fails.
            EditorApplication.update += RestoreWhenIdle;
            AssemblyReloadEvents.beforeAssemblyReload += Restore;
        }

        public void OnPreprocessBuild(BuildReport report)
        {
            if (Application.platform != RuntimePlatform.WindowsEditor ||
                report.summary.platform != BuildTarget.WebGL) return;

            ownsBee |= SetDefault(BeeVariable);
            ownsBinaryen |= SetDefault(BinaryenVariable);
            Debug.Log($"[WebGlBuildConcurrency] {BeeVariable}={Environment.GetEnvironmentVariable(BeeVariable)}, " +
                $"{BinaryenVariable}={Environment.GetEnvironmentVariable(BinaryenVariable)}");
        }

        public void OnPostprocessBuild(BuildReport report) => Restore();

        static bool SetDefault(string variable)
        {
            // Respect explicit values supplied by the developer or build machine.
            if (!string.IsNullOrEmpty(Environment.GetEnvironmentVariable(variable))) return false;
            Environment.SetEnvironmentVariable(variable, WorkerLimit);
            return true;
        }

        static void RestoreWhenIdle()
        {
            if (!BuildPipeline.isBuildingPlayer) Restore();
        }

        static void Restore()
        {
            RestoreVariable(BeeVariable, ref ownsBee);
            RestoreVariable(BinaryenVariable, ref ownsBinaryen);
        }

        static void RestoreVariable(string variable, ref bool owned)
        {
            if (!owned) return;
            if (Environment.GetEnvironmentVariable(variable) == WorkerLimit)
                Environment.SetEnvironmentVariable(variable, null);
            owned = false;
        }
    }
}