using System.Diagnostics;
using System.Security.Cryptography;
using System.Text.Json;
using Jiaowu.Api.Infrastructure.Persistence;
using Microsoft.Data.Sqlite;
using MySql.Data.MySqlClient;

namespace Jiaowu.Api.Infrastructure.Operations;

public sealed record BackupArtifact(
    string Id,
    string FileName,
    string Provider,
    DateTime CreatedAt,
    long SizeBytes,
    string Sha256,
    string? Note,
    DateTime? LastDrillAt,
    bool? LastDrillSucceeded,
    string? LastDrillDetail,
    long? LastDrillDurationMilliseconds);

public sealed record RestoreDrillResult(
    string BackupId,
    bool Succeeded,
    DateTime CompletedAt,
    string Detail,
    long DurationMilliseconds,
    int? TableCount);

public sealed class DatabaseBackupService(
    DatabaseOptions databaseOptions,
    OperationsOptions options,
    IConfiguration configuration,
    IHostEnvironment environment,
    ILogger<DatabaseBackupService> logger)
{
    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web)
    {
        WriteIndented = true
    };

    private readonly SemaphoreSlim operationLock = new(1, 1);
    private readonly string backupDirectory = ResolveBackupDirectory(
        options.BackupDirectory,
        environment.ContentRootPath);

    public async Task<IReadOnlyCollection<BackupArtifact>> ListAsync(
        CancellationToken cancellationToken)
    {
        Directory.CreateDirectory(backupDirectory);
        var items = new List<BackupArtifact>();
        foreach (var metadataPath in Directory.EnumerateFiles(
                     backupDirectory,
                     "*.metadata.json",
                     SearchOption.TopDirectoryOnly))
        {
            cancellationToken.ThrowIfCancellationRequested();
            try
            {
                await using var stream = File.OpenRead(metadataPath);
                var artifact = await JsonSerializer.DeserializeAsync<BackupArtifact>(
                    stream,
                    JsonOptions,
                    cancellationToken);
                if (artifact is not null &&
                    File.Exists(Path.Combine(backupDirectory, artifact.FileName)))
                {
                    items.Add(artifact);
                }
            }
            catch (Exception exception) when (
                exception is IOException or UnauthorizedAccessException or JsonException)
            {
                logger.LogWarning(
                    exception,
                    "Unable to read backup metadata {MetadataFile}.",
                    Path.GetFileName(metadataPath));
            }
        }

        return items
            .OrderByDescending(x => x.CreatedAt)
            .ToArray();
    }

    public async Task<BackupArtifact> CreateAsync(
        string? note,
        CancellationToken cancellationToken)
    {
        await operationLock.WaitAsync(cancellationToken);
        try
        {
            Directory.CreateDirectory(backupDirectory);
            var createdAt = DateTime.UtcNow;
            var id = $"{createdAt:yyyyMMddHHmmss}-{Guid.NewGuid():N}"[..29];
            var provider = NormalizeProvider(databaseOptions.Provider);
            var extension = provider == "SQLite" ? ".sqlite" : ".sql";
            var fileName = $"jiaowu-{id}{extension}";
            var backupPath = Path.Combine(backupDirectory, fileName);

            try
            {
                if (provider == "SQLite")
                    await CreateSqliteBackupAsync(backupPath, cancellationToken);
                else
                    await CreateMySqlBackupAsync(backupPath, cancellationToken);

                var fileInfo = new FileInfo(backupPath);
                var artifact = new BackupArtifact(
                    id,
                    fileName,
                    provider,
                    createdAt,
                    fileInfo.Length,
                    await ComputeHashAsync(backupPath, cancellationToken),
                    NormalizeNote(note),
                    null,
                    null,
                    null,
                    null);
                await WriteMetadataAsync(artifact, cancellationToken);
                return artifact;
            }
            catch
            {
                if (File.Exists(backupPath))
                    File.Delete(backupPath);
                throw;
            }
        }
        finally
        {
            operationLock.Release();
        }
    }

    public async Task<RestoreDrillResult> RunRestoreDrillAsync(
        string backupId,
        CancellationToken cancellationToken)
    {
        await operationLock.WaitAsync(cancellationToken);
        try
        {
            var artifact = (await ListAsync(cancellationToken))
                .SingleOrDefault(x => x.Id.Equals(backupId, StringComparison.Ordinal));
            if (artifact is null)
                throw new FileNotFoundException("未找到指定备份。");

            var backupPath = Path.Combine(backupDirectory, artifact.FileName);
            var actualHash = await ComputeHashAsync(backupPath, cancellationToken);
            if (!CryptographicOperations.FixedTimeEquals(
                    Convert.FromHexString(artifact.Sha256),
                    Convert.FromHexString(actualHash)))
            {
                var damaged = await CompleteDrillAsync(
                    artifact,
                    false,
                    "备份文件校验和不一致，恢复演练已中止。",
                    0,
                    null,
                    cancellationToken);
                return damaged;
            }

            var stopwatch = Stopwatch.StartNew();
            RestoreDrillResult result;
            try
            {
                var tableCount = artifact.Provider == "SQLite"
                    ? await DrillSqliteAsync(backupPath, cancellationToken)
                    : await DrillMySqlAsync(backupPath, cancellationToken);
                stopwatch.Stop();
                result = await CompleteDrillAsync(
                    artifact,
                    true,
                    $"已在隔离数据库完成恢复并通过完整性检查，共发现 {tableCount} 张业务表。",
                    stopwatch.ElapsedMilliseconds,
                    tableCount,
                    cancellationToken);
            }
            catch (Exception exception) when (exception is not OperationCanceledException)
            {
                stopwatch.Stop();
                logger.LogError(
                    exception,
                    "Restore drill failed for backup {BackupId}.",
                    artifact.Id);
                result = await CompleteDrillAsync(
                    artifact,
                    false,
                    $"恢复演练失败：{SafeMessage(exception)}",
                    stopwatch.ElapsedMilliseconds,
                    null,
                    cancellationToken);
            }

            return result;
        }
        finally
        {
            operationLock.Release();
        }
    }

    private async Task CreateSqliteBackupAsync(
        string backupPath,
        CancellationToken cancellationToken)
    {
        var sourceBuilder = new SqliteConnectionStringBuilder(
            configuration.GetConnectionString("SQLite")
            ?? throw new InvalidOperationException("缺少 ConnectionStrings:SQLite。"));
        if (!Path.IsPathRooted(sourceBuilder.DataSource))
        {
            sourceBuilder.DataSource = Path.GetFullPath(
                sourceBuilder.DataSource,
                environment.ContentRootPath);
        }

        var destinationBuilder = new SqliteConnectionStringBuilder
        {
            DataSource = backupPath,
            Mode = SqliteOpenMode.ReadWriteCreate,
            Pooling = false
        };
        await using var source = new SqliteConnection(sourceBuilder.ConnectionString);
        await using var destination = new SqliteConnection(destinationBuilder.ConnectionString);
        await source.OpenAsync(cancellationToken);
        await destination.OpenAsync(cancellationToken);
        source.BackupDatabase(destination);
    }

    private async Task CreateMySqlBackupAsync(
        string backupPath,
        CancellationToken cancellationToken)
    {
        var connection = GetMySqlConnectionBuilder();
        var arguments = new List<string>
        {
            "--protocol=tcp",
            $"--host={connection.Server}",
            $"--port={connection.Port}",
            $"--user={connection.UserID}",
            "--single-transaction",
            "--quick",
            "--routines",
            "--triggers",
            "--events",
            "--hex-blob",
            "--default-character-set=utf8mb4"
        };
        arguments.AddRange(options.MySqlAdditionalArguments);
        arguments.Add(connection.Database);

        await using var output = new FileStream(
            backupPath,
            FileMode.CreateNew,
            FileAccess.Write,
            FileShare.None,
            81920,
            FileOptions.Asynchronous);
        await RunToolAsync(
            options.MySqlDumpPath,
            arguments,
            connection.Password,
            standardInput: null,
            standardOutput: output,
            cancellationToken);
    }

    private static async Task<int> DrillSqliteAsync(
        string backupPath,
        CancellationToken cancellationToken)
    {
        var drillPath = Path.Combine(
            Path.GetDirectoryName(backupPath)!,
            $".restore-drill-{Guid.NewGuid():N}.sqlite");
        try
        {
            var sourceBuilder = new SqliteConnectionStringBuilder
            {
                DataSource = backupPath,
                Mode = SqliteOpenMode.ReadOnly,
                Pooling = false
            };
            var drillBuilder = new SqliteConnectionStringBuilder
            {
                DataSource = drillPath,
                Mode = SqliteOpenMode.ReadWriteCreate,
                Pooling = false
            };
            await using var source = new SqliteConnection(sourceBuilder.ConnectionString);
            await using var drill = new SqliteConnection(drillBuilder.ConnectionString);
            await source.OpenAsync(cancellationToken);
            await drill.OpenAsync(cancellationToken);
            source.BackupDatabase(drill);

            await using var integrity = drill.CreateCommand();
            integrity.CommandText = "PRAGMA integrity_check;";
            var integrityResult = Convert.ToString(
                await integrity.ExecuteScalarAsync(cancellationToken));
            if (!string.Equals(integrityResult, "ok", StringComparison.OrdinalIgnoreCase))
                throw new InvalidDataException($"SQLite 完整性检查返回 {integrityResult ?? "空结果"}。");

            await using var tables = drill.CreateCommand();
            tables.CommandText =
                "SELECT COUNT(*) FROM sqlite_master " +
                "WHERE type = 'table' AND name NOT LIKE 'sqlite_%';";
            return Convert.ToInt32(await tables.ExecuteScalarAsync(cancellationToken));
        }
        finally
        {
            if (File.Exists(drillPath))
                File.Delete(drillPath);
            if (File.Exists($"{drillPath}-shm"))
                File.Delete($"{drillPath}-shm");
            if (File.Exists($"{drillPath}-wal"))
                File.Delete($"{drillPath}-wal");
        }
    }

    private async Task<int> DrillMySqlAsync(
        string backupPath,
        CancellationToken cancellationToken)
    {
        var connection = GetMySqlConnectionBuilder();
        var drillDatabase = $"jiaowu_restore_drill_{DateTime.UtcNow:yyyyMMddHHmmss}_" +
                            Guid.NewGuid().ToString("N")[..8];
        var adminBuilder = new MySqlConnectionStringBuilder(connection.ConnectionString)
        {
            Database = ""
        };

        await using var admin = new MySqlConnection(adminBuilder.ConnectionString);
        await admin.OpenAsync(cancellationToken);
        try
        {
            await using (var create = admin.CreateCommand())
            {
                create.CommandText =
                    $"CREATE DATABASE `{drillDatabase}` CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;";
                await create.ExecuteNonQueryAsync(cancellationToken);
            }

            var arguments = new List<string>
            {
                "--protocol=tcp",
                $"--host={connection.Server}",
                $"--port={connection.Port}",
                $"--user={connection.UserID}",
                "--default-character-set=utf8mb4"
            };
            arguments.AddRange(options.MySqlAdditionalArguments);
            arguments.Add($"--database={drillDatabase}");
            await using (var input = new FileStream(
                             backupPath,
                             FileMode.Open,
                             FileAccess.Read,
                             FileShare.Read,
                             81920,
                             FileOptions.Asynchronous))
            {
                await RunToolAsync(
                    options.MySqlClientPath,
                    arguments,
                    connection.Password,
                    input,
                    standardOutput: null,
                    cancellationToken);
            }

            await using var count = admin.CreateCommand();
            count.CommandText =
                "SELECT COUNT(*) FROM information_schema.tables " +
                "WHERE table_schema = @schema AND table_type = 'BASE TABLE';";
            count.Parameters.AddWithValue("@schema", drillDatabase);
            return Convert.ToInt32(await count.ExecuteScalarAsync(cancellationToken));
        }
        finally
        {
            try
            {
                await using var drop = admin.CreateCommand();
                drop.CommandText = $"DROP DATABASE IF EXISTS `{drillDatabase}`;";
                await drop.ExecuteNonQueryAsync(CancellationToken.None);
            }
            catch (Exception exception)
            {
                logger.LogCritical(
                    exception,
                    "Unable to remove isolated restore drill database {DatabaseName}.",
                    drillDatabase);
            }
        }
    }

    private async Task RunToolAsync(
        string executable,
        IReadOnlyCollection<string> arguments,
        string password,
        Stream? standardInput,
        Stream? standardOutput,
        CancellationToken cancellationToken)
    {
        var startInfo = new ProcessStartInfo
        {
            FileName = executable,
            UseShellExecute = false,
            RedirectStandardError = true,
            RedirectStandardInput = standardInput is not null,
            RedirectStandardOutput = standardOutput is not null,
            CreateNoWindow = true
        };
        foreach (var argument in arguments)
            startInfo.ArgumentList.Add(argument);
        if (!string.IsNullOrEmpty(password))
            startInfo.Environment["MYSQL_PWD"] = password;

        using var process = Process.Start(startInfo)
            ?? throw new InvalidOperationException($"无法启动数据库工具 {executable}。");
        using var timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        timeout.CancelAfter(TimeSpan.FromMinutes(options.ToolTimeoutMinutes));
        var errorTask = process.StandardError.ReadToEndAsync(timeout.Token);
        var inputTask = standardInput is null
            ? Task.CompletedTask
            : CopyInputAsync(standardInput, process.StandardInput.BaseStream, timeout.Token);
        var outputTask = standardOutput is null
            ? Task.CompletedTask
            : process.StandardOutput.BaseStream.CopyToAsync(
                standardOutput,
                timeout.Token);

        try
        {
            await Task.WhenAll(
                process.WaitForExitAsync(timeout.Token),
                inputTask,
                outputTask);
        }
        catch (OperationCanceledException)
        {
            if (!process.HasExited)
                process.Kill(entireProcessTree: true);
            throw;
        }

        var error = await errorTask;
        if (process.ExitCode != 0)
            throw new InvalidOperationException(
                $"数据库工具执行失败（退出码 {process.ExitCode}）：{TrimToolError(error)}");
    }

    private static async Task CopyInputAsync(
        Stream input,
        Stream processInput,
        CancellationToken cancellationToken)
    {
        await input.CopyToAsync(processInput, cancellationToken);
        await processInput.FlushAsync(cancellationToken);
        processInput.Close();
    }

    private MySqlConnectionStringBuilder GetMySqlConnectionBuilder()
    {
        var value = configuration.GetConnectionString("OperationsMySql");
        if (string.IsNullOrWhiteSpace(value))
        {
            throw new InvalidOperationException(
                "MySQL 备份与恢复演练必须配置独立的 " +
                "ConnectionStrings:OperationsMySql 运维账号，不能复用日常业务账号。");
        }
        var builder = new MySqlConnectionStringBuilder(value);
        if (string.IsNullOrWhiteSpace(builder.Database))
            throw new InvalidOperationException(
                "OperationsMySql 连接字符串未指定业务数据库名称。");
        return builder;
    }

    private async Task<RestoreDrillResult> CompleteDrillAsync(
        BackupArtifact artifact,
        bool succeeded,
        string detail,
        long durationMilliseconds,
        int? tableCount,
        CancellationToken cancellationToken)
    {
        var completedAt = DateTime.UtcNow;
        var updated = artifact with
        {
            LastDrillAt = completedAt,
            LastDrillSucceeded = succeeded,
            LastDrillDetail = detail,
            LastDrillDurationMilliseconds = durationMilliseconds
        };
        await WriteMetadataAsync(updated, cancellationToken);
        return new RestoreDrillResult(
            artifact.Id,
            succeeded,
            completedAt,
            detail,
            durationMilliseconds,
            tableCount);
    }

    private async Task WriteMetadataAsync(
        BackupArtifact artifact,
        CancellationToken cancellationToken)
    {
        var metadataPath = Path.Combine(
            backupDirectory,
            $"{artifact.Id}.metadata.json");
        var temporaryPath = $"{metadataPath}.{Guid.NewGuid():N}.tmp";
        try
        {
            await using (var stream = new FileStream(
                             temporaryPath,
                             FileMode.CreateNew,
                             FileAccess.Write,
                             FileShare.None,
                             16384,
                             FileOptions.Asynchronous))
            {
                await JsonSerializer.SerializeAsync(
                    stream,
                    artifact,
                    JsonOptions,
                    cancellationToken);
            }
            File.Move(temporaryPath, metadataPath, overwrite: true);
        }
        finally
        {
            if (File.Exists(temporaryPath))
                File.Delete(temporaryPath);
        }
    }

    private static async Task<string> ComputeHashAsync(
        string path,
        CancellationToken cancellationToken)
    {
        await using var stream = File.OpenRead(path);
        return Convert.ToHexString(
            await SHA256.HashDataAsync(stream, cancellationToken));
    }

    private static string ResolveBackupDirectory(
        string configuredPath,
        string contentRoot)
    {
        if (string.IsNullOrWhiteSpace(configuredPath))
            throw new InvalidOperationException("Operations:BackupDirectory 不能为空。");
        return Path.IsPathRooted(configuredPath)
            ? Path.GetFullPath(configuredPath)
            : Path.GetFullPath(configuredPath, contentRoot);
    }

    private static string NormalizeProvider(string provider) =>
        provider.Equals("SQLite", StringComparison.OrdinalIgnoreCase)
            ? "SQLite"
            : provider.Equals("MySql", StringComparison.OrdinalIgnoreCase)
                ? "MySql"
                : throw new InvalidOperationException($"不支持数据库 Provider '{provider}'。");

    private static string? NormalizeNote(string? note)
    {
        if (string.IsNullOrWhiteSpace(note)) return null;
        var trimmed = note.Trim();
        return trimmed.Length <= 200 ? trimmed : trimmed[..200];
    }

    private static string SafeMessage(Exception exception)
    {
        var message = exception.GetBaseException().Message;
        return message.Length <= 500 ? message : message[..500];
    }

    private static string TrimToolError(string error)
    {
        var trimmed = error.Trim();
        if (trimmed.Length == 0) return "未返回错误详情。";
        return trimmed.Length <= 500 ? trimmed : trimmed[..500];
    }
}