using Avalonia_Common.Infrastructure;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Migrations;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace Avalonia_EFCore.Database
{
    /// <summary>
    /// 数据库管理器 —— 负责连接测试、自动迁移、种子数据、版本检查。
    /// 在应用启动时调用，确保数据库结构与应用代码同步。
    /// </summary>
    public class DatabaseManager<TContext> where TContext : AppDbContext
    {
        private readonly TContext _context;
        private readonly DatabaseConfiguration _config;
        private readonly IServiceProvider? _serviceProvider;

        public DatabaseManager(TContext context, DatabaseConfiguration config, IServiceProvider? serviceProvider = null)
        {
            _context = context;
            _config = config;
            _serviceProvider = serviceProvider;
        }

        /// <summary>
        /// 初始化数据库：测试连接 → 自动迁移 → 种子数据。
        /// </summary>
        public async Task InitializeAsync(Action<TContext, IServiceProvider?>? seeder = null)
        {
            // 1. 测试数据库连接
            var canConnect = await CanConnectAsync();
            if (!canConnect)
            {
                throw new InvalidOperationException(
                    $"无法连接到数据库 [{_config.Provider}]，请检查连接字符串和数据库服务状态。");
            }

            // 2. 自动迁移（如果启用）
            if (_config.AutoMigrate)
            {
                await MigrateAsync();
            }

            // 3. 种子数据
            if (seeder != null)
            {
                seeder(_context, _serviceProvider);
                await _context.SaveChangesAsync();
            }
        }

        /// <summary>
        /// 测试数据库连接是否正常。
        /// </summary>
        public async Task<bool> CanConnectAsync()
        {
            try
            {
                return await _context.Database.CanConnectAsync();
            }
            catch
            {
                return false;
            }
        }

        /// <summary>
        /// 执行待处理的迁移。
        /// 使用 EF Core 原生迁移机制，自动检测并应用 Schema 变更。
        /// </summary>
        public async Task MigrateAsync()
        {
            try
            {
                var pendingMigrations = await _context.Database.GetPendingMigrationsAsync();

                if (pendingMigrations.Any())
                {
                    AppLog.Information(
                        "检测到 {Count} 个待执行的数据库迁移: {Migrations}",
                        pendingMigrations.Count(),
                        string.Join(", ", pendingMigrations));

                    await _context.Database.MigrateAsync();

                    AppLog.Information("数据库迁移完成（{Count} 个迁移已应用）", pendingMigrations.Count());
                }
                else
                {
                    AppLog.Information("数据库已是最新版本，无需迁移");
                }
            }
            catch (Exception ex)
            {
                AppLog.Error(ex, "数据库迁移失败");
                throw;
            }
        }

        /// <summary>
        /// 获取数据库当前版本信息。
        /// </summary>
        public async Task<DatabaseVersionInfo> GetVersionInfoAsync()
        {
            var appliedMigrations = await _context.Database.GetAppliedMigrationsAsync();
            var pendingMigrations = await _context.Database.GetPendingMigrationsAsync();

            return new DatabaseVersionInfo
            {
                Provider = _config.Provider.ToString(),
                AppliedMigrations = appliedMigrations.ToList(),
                PendingMigrations = pendingMigrations.ToList(),
                IsLatest = !pendingMigrations.Any(),
                CanConnect = await CanConnectAsync(),
            };
        }

        /// <summary>
        /// 生成从指定迁移到最新版本的 SQL 脚本（用于生产环境审计）。
        /// </summary>
        public string GenerateMigrationScript(string? fromMigration = null)
        {
            var migrator = _context.GetService<IMigrator>();
            return fromMigration is null
                ? migrator.GenerateScript()
                : migrator.GenerateScript(fromMigration);
        }

        /// <summary>
        /// 确保数据库已创建（不执行迁移，适用于简单场景）。
        /// </summary>
        public bool EnsureCreated()
        {
            return _context.Database.EnsureCreated();
        }
    }

    /// <summary>
    /// 数据库版本信息 DTO。
    /// </summary>
    public class DatabaseVersionInfo
    {
        public string Provider { get; set; } = string.Empty;
        public List<string> AppliedMigrations { get; set; } = new();
        public List<string> PendingMigrations { get; set; } = new();
        public bool IsLatest { get; set; }
        public bool CanConnect { get; set; }
    }
}