using System.Collections.Concurrent;
using System.Text.Json;
using Microsoft.Extensions.Options;

namespace Dpz.Core.Auth.Service;

/// <summary>
/// 管理 Auth 站点的前端资源清单，提供 CSS / JS 文件的带 host 的完整 URL
/// </summary>
/// <remarks>
/// 非开发环境下首次加载后缓存至进程退出；开发环境下监听文件修改时间并按需重载
/// </remarks>
public class AuthAssetService(
    IWebHostEnvironment environment,
    IOptions<AuthAssetOptions> options,
    ILogger<AuthAssetService> logger,
    IConfiguration configuration
)
{
    private static readonly ConcurrentDictionary<string, string[]> Manifest = new(
        StringComparer.OrdinalIgnoreCase
    );

    private readonly AuthAssetOptions _options = options.Value;
    private static DateTime _lastManifestWriteTimeUtc;

    /// <summary>
    /// 获取指定入口的所有样式文件 URL
    /// </summary>
    /// <param name="entryName">入口名称（如 "app"）</param>
    public IReadOnlyList<string> GetStyleUrls(string entryName)
    {
        return GetEntryFiles(entryName, ".css");
    }

    /// <summary>
    /// 获取指定入口的所有脚本文件 URL
    /// </summary>
    /// <param name="entryName">入口名称（如 "app"）</param>
    public IReadOnlyList<string> GetScriptUrls(string entryName)
    {
        return GetEntryFiles(entryName, ".js");
    }

    /// <summary>
    /// 根据入口名和扩展名，从已加载的资源清单中查找对应文件并拼接完整 URL
    /// </summary>
    private List<string> GetEntryFiles(string entryName, string extension)
    {
        LoadManifest();
        var key = $"entries/{entryName}{extension}";
        if (!Manifest.TryGetValue(key, out var paths))
        {
            logger.LogWarning("Auth 资源清单缺少入口：{EntryName}", key);
            return [];
        }

        var host = _options.AssetsHost?.TrimEnd('/') ?? "";
        return paths.Select(path => $"{host}/{path.TrimStart('/')}").ToList();
    }

    /// <summary>
    /// 从磁盘加载 <c>auth-assets-manifest.json</c> 至内存
    /// 非开发环境仅加载一次；开发环境文件变更时自动重载
    /// </summary>
    private void LoadManifest()
    {
        var manifestPath = Path.Combine(environment.WebRootPath, "auth-assets-manifest.json");
        if (!File.Exists(manifestPath))
        {
            logger.LogWarning("Auth 资源清单不存在：{ManifestPath}", manifestPath);
            return;
        }

        var writeTimeUtc = File.GetLastWriteTimeUtc(manifestPath);
        if (!configuration.IsDevelopment && !Manifest.IsEmpty)
        {
            return;
        }
        if (
            configuration.IsDevelopment
            && !Manifest.IsEmpty
            && writeTimeUtc == _lastManifestWriteTimeUtc
        )
        {
            return;
        }

        try
        {
            var manifest =
                JsonSerializer.Deserialize<Dictionary<string, JsonElement>>(
                    File.ReadAllText(manifestPath)
                ) ?? [];
            Manifest.Clear();
            foreach (var (key, value) in manifest)
            {
                if (value.ValueKind == JsonValueKind.Array)
                {
                    Manifest.TryAdd(
                        key,
                        value
                            .EnumerateArray()
                            .Select(x => x.GetString())
                            .Where(x => !string.IsNullOrWhiteSpace(x))
                            .Select(x => x!)
                            .ToArray()
                    );
                    continue;
                }

                var path = value.GetString();
                if (!string.IsNullOrWhiteSpace(path))
                {
                    Manifest.TryAdd(key, [path]);
                }
            }
            _lastManifestWriteTimeUtc = writeTimeUtc;
        }
        catch (Exception e)
        {
            logger.LogError(e, "加载 Auth 资源清单失败");
        }
    }
}