using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using UnityEngine;

namespace ShrinkModFramework
{
    /// <summary>
    /// 把工程内程序集和外部 DLL 的当前 revision 投影为延迟组件源。
    /// 同一路径的旧外部程序集无法从 Mono AppDomain 卸载，但不会再进入候选集合。
    /// </summary>
    internal static class ShrinkModComponentDiscovery
    {
        public static IReadOnlyList<ShrinkModComponentSource> Discover(
            ShrinkModFrameworkSettings settings,
            bool verboseLogging,
            IEnumerable<string> authorizedDllPaths)
        {
            ShrinkExternalModAssemblyLoader.ScanExternalAssemblyRevisions(
                settings, verboseLogging, authorizedDllPaths);
            var results = new List<ShrinkModComponentSource>();
            var prefixes = settings?.assemblyNamePrefixes;

            foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies())
            {
                if (ShrinkExternalModAssemblyLoader.IsExternalAssembly(assembly) &&
                    !ShrinkExternalModAssemblyLoader.TryGetCurrentRevision(assembly, out _))
                {
                    continue;
                }
                if (!ShouldScanAssembly(assembly, prefixes))
                    continue;

                var assemblyRevision = GetAssemblyRevision(assembly);
                foreach (var type in GetTypesSafely(assembly))
                {
                    if (type == null || type.IsAbstract || type.IsInterface)
                        continue;

                    var modAttribute = type.GetCustomAttribute<ShrinkModAttribute>(false);
                    if (modAttribute == null)
                        continue;
                    if (!typeof(IShrinkMod).IsAssignableFrom(type))
                    {
                        Debug.LogWarning(
                            $"[ShrinkModFramework] 类型 {type.FullName} 标记了 ShrinkMod，但没有实现 IShrinkMod，已跳过。");
                        continue;
                    }
                    if (type.GetConstructor(Type.EmptyTypes) == null)
                        throw new InvalidOperationException($"模组 {type.FullName} 缺少无参构造函数，无法实例化。");

                    var dependencies = type
                        .GetCustomAttributes<ShrinkModDependencyAttribute>(false)
                        .Select(attribute => new ShrinkModDependency(
                            attribute.ModId, attribute.MinimumVersion, attribute.Optional))
                        .ToArray();
                    var info = new ShrinkModInfo(
                        modAttribute.ModId,
                        modAttribute.DisplayName,
                        modAttribute.Version,
                        modAttribute.LoadOrder,
                        type,
                        modAttribute.AutoApplyHarmonyPatches,
                        dependencies);
                    var revision = $"{assemblyRevision}:{type.FullName}";
                    results.Add(new ShrinkModComponentSource(info, revision,
                        () => (IShrinkMod)Activator.CreateInstance(type)));
                }
            }

            return results;
        }

        private static string GetAssemblyRevision(Assembly assembly)
        {
            if (ShrinkExternalModAssemblyLoader.TryGetCurrentRevision(assembly, out var externalRevision))
                return externalRevision;

            try
            {
                return assembly.ManifestModule.ModuleVersionId.ToString("N");
            }
            catch
            {
                return assembly.FullName ?? assembly.GetName().Name ?? "unknown";
            }
        }

        private static bool ShouldScanAssembly(Assembly assembly, string[] prefixes)
        {
            var name = assembly.GetName().Name;
            if (string.IsNullOrEmpty(name))
                return false;
            if (name.StartsWith("Unity", StringComparison.Ordinal) ||
                name.StartsWith("System", StringComparison.Ordinal) ||
                name.StartsWith("mscorlib", StringComparison.Ordinal) ||
                name.StartsWith("netstandard", StringComparison.Ordinal))
            {
                return false;
            }
            if (prefixes == null || prefixes.Length == 0)
                return true;

            return prefixes.Any(prefix => !string.IsNullOrWhiteSpace(prefix) &&
                                          name.StartsWith(prefix, StringComparison.OrdinalIgnoreCase));
        }

        private static IEnumerable<Type> GetTypesSafely(Assembly assembly)
        {
            try
            {
                return assembly.GetTypes();
            }
            catch (ReflectionTypeLoadException exception)
            {
                return exception.Types.Where(type => type != null);
            }
            catch
            {
                return Array.Empty<Type>();
            }
        }
    }
}