using System.Text.Json;
using Microsoft.Extensions.Logging;
using Npgsql;
using Fengling.Console.Data;
using Microsoft.EntityFrameworkCore;

namespace Fengling.Console.Services;

/// <summary>
/// 配置变更通知服务接口
/// </summary>
public interface INotificationService
{
    /// <summary>
    /// 发布通知到指定通道
    /// </summary>
    Task PublishAsync(string channel, string payload, CancellationToken cancellationToken = default);
    
    /// <summary>
    /// 发布配置变更事件
    /// </summary>
    Task PublishConfigChangeAsync(
        string eventType, 
        string action, 
        object? details = null,
        CancellationToken cancellationToken = default);
}

/// <summary>
/// 配置变更事件数据
/// </summary>
public class ConfigChangeEvent
{
    public string EventType { get; set; } = ""; // service, route, instance, gateway
    public string Action { get; set; } = "";    // create, update, delete, reload
    public DateTime Timestamp { get; set; } = DateTime.UtcNow;
    public object? Details { get; set; }
}

/// <summary>
/// PostgreSQL 通知服务实现
/// 使用 PostgreSQL NOTIFY/LISTEN 机制广播配置变更
/// </summary>
public class PgSqlNotificationService : INotificationService
{
    private readonly ILogger<PgSqlNotificationService> _logger;
    private readonly string _connectionString;

    public const string GatewayConfigChangedChannel = "gateway_config_changed";

    public PgSqlNotificationService(DbContextOptions<ConsoleDbContext> dbContextOptions, ILogger<PgSqlNotificationService> logger)
    {
        _logger = logger;
        
        // 从 DbContextOptions 获取连接字符串
        string? connectionString = null;
        
        foreach (var ext in dbContextOptions.Extensions)
        {
            var extType = ext.GetType();
            if (extType.Name.Contains("Npgsql"))
            {
                var prop = extType.GetProperty("ConnectionString");
                if (prop != null && prop.PropertyType == typeof(string))
                {
                    connectionString = prop.GetValue(ext) as string;
                    break;
                }
            }
        }
        
        _connectionString = connectionString 
            ?? throw new InvalidOperationException("DefaultConnection not configured");
    }

    /// <inheritdoc/>
    public async Task PublishAsync(string channel, string payload, CancellationToken cancellationToken = default)
    {
        try
        {
            await using var connection = new NpgsqlConnection(_connectionString);
            await connection.OpenAsync(cancellationToken);
            
            await using var cmd = new NpgsqlCommand(
                $"SELECT pg_notify(@channel, @payload)",
                connection);
            
            cmd.Parameters.AddWithValue("channel", channel);
            cmd.Parameters.AddWithValue("payload", payload);
            
            await cmd.ExecuteNonQueryAsync(cancellationToken);
            
            _logger.LogInformation("Published notification to channel '{Channel}': {Payload}", channel, payload);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to publish notification to channel '{Channel}'", channel);
        }
    }

    /// <summary>
    /// 创建配置变更事件并发布
    /// </summary>
    public async Task PublishConfigChangeAsync(
        string eventType, 
        string action, 
        object? details = null,
        CancellationToken cancellationToken = default)
    {
        var configEvent = new ConfigChangeEvent
        {
            EventType = eventType,
            Action = action,
            Timestamp = DateTime.UtcNow,
            Details = details
        };

        var payload = JsonSerializer.Serialize(configEvent);
        await PublishAsync(GatewayConfigChangedChannel, payload, cancellationToken);
    }
}

/// <summary>
/// 通知服务扩展方法
/// </summary>
public static class NotificationServiceExtensions
{
    public static IServiceCollection AddNotificationService(this IServiceCollection services)
    {
        services.AddScoped<INotificationService, PgSqlNotificationService>();
        return services;
    }
}