using System.Diagnostics;
using System.Text.RegularExpressions;
using Microsoft.Data.SqlClient;
using SQLInsight.Connectivity;
using SQLInsight.Core.Configuration;
using SQLInsight.Repository;

namespace SQLInsight.Agent.Setup;

/// <summary>
/// <c>setup-repository [--agent-account &lt;konto&gt;] [--web-account &lt;konto&gt;] [--grant-monitored]</c>
/// <para>
/// Prepares everything the services need, with the rights of whoever runs it (the MSI runs it as the installing user,
/// right after the services are created): the repository database if it is missing, logins and users for the agent
/// (db_owner) and web (db_datareader) accounts, the schema, and with <c>--grant-monitored</c> the least-privilege rights
/// on the configured instances (db/permissions/grant-least-privilege.sql). Safe to run again.
/// </para>
/// The connection string and instances are read from appsettings.json and sqlinsight.ini, like the service does.
/// </summary>
public static partial class RepositorySetup
{
    public const string Command = "setup-repository";
    private const string EventSource = "SQLInsight Pro";

    public static bool Handles(string[] args) => args.FirstOrDefault() == Command;

    public static async Task<int> RunAsync(string[] args, TextWriter output)
    {
        ArgumentNullException.ThrowIfNull(args);
        ArgumentNullException.ThrowIfNull(output);
        var log = new StringWriter();
        var both = new TeeWriter(output, log);
        var agentAccount = Option(args, "--agent-account") ?? @"NT SERVICE\SQLInsight Agent";
        var webAccount = Option(args, "--web-account") ?? @"NT SERVICE\SQLInsight Web";
        var options = CustomRules.RuleCommands.LoadAgentOptions();

        try
        {
            await PrepareRepositoryAsync(options.Repository.ConnectionString, agentAccount, webAccount, both).ConfigureAwait(false);
        }
        catch (Exception ex) when (ex is SqlException or InvalidOperationException or ArgumentException)
        {
            both.WriteLine($"FEJL: {ex.Message}");
            both.WriteLine(Hint(ex));
            Report(log.ToString(), Outcome.Error);
            return 1;
        }

        // The monitored instances are a convenience: an instance that cannot be reached now (or where the installing
        // user is not sysadmin) is reported, but does not stop the installation; grant-least-privilege.sql can be run later.
        var warnings = 0;
        if (args.Contains("--grant-monitored"))
        {
            foreach (var instance in options.Instances.Where(i => !string.IsNullOrWhiteSpace(i.Server)))
            {
                try
                {
                    await GrantMonitoredAsync(instance, agentAccount, both).ConfigureAwait(false);
                }
                catch (Exception ex) when (ex is SqlException or InvalidOperationException)
                {
                    warnings++;
                    both.WriteLine($"ADVARSEL: rettigheder på {instance.Server} kunne ikke gives: {ex.Message}");
                    both.WriteLine("  Kør db/permissions/grant-least-privilege.sql på instansen som sysadmin.");
                }
            }
        }

        Report(log.ToString(), warnings > 0 ? Outcome.Warning : Outcome.Ok);
        return 0;
    }

    private static async Task PrepareRepositoryAsync(string? connectionString, string agentAccount, string webAccount, TextWriter output)
    {
        if (string.IsNullOrWhiteSpace(connectionString))
        {
            throw new InvalidOperationException("SQLInsight:Repository:ConnectionString er ikke sat (sqlinsight.ini eller appsettings.json).");
        }

        var repository = new SqlConnectionStringBuilder(connectionString) { Pooling = false };
        var database = repository.InitialCatalog;
        if (string.IsNullOrWhiteSpace(database))
        {
            throw new ArgumentException("Forbindelsesstrengen mangler Database=…, fx Database=SQLInsight.");
        }

        var master = new SqlConnectionStringBuilder(repository.ConnectionString) { InitialCatalog = "master" };
        await using (var connection = new SqlConnection(master.ConnectionString))
        {
            await connection.OpenAsync().ConfigureAwait(false);
            output.WriteLine($"Forbundet til {repository.DataSource} som {await ScalarAsync(connection, "SELECT SUSER_SNAME()").ConfigureAwait(false)}.");
            var created = await ScalarAsync(connection, """
                IF DB_ID(@db) IS NULL
                BEGIN
                    DECLARE @sql nvarchar(max) = N'CREATE DATABASE ' + QUOTENAME(@db);
                    EXEC (@sql);
                    SELECT N'oprettet';
                END
                ELSE SELECT N'findes';
                """, ("@db", database)).ConfigureAwait(false);
            output.WriteLine($"Database {database}: {created}.");

            // A SQL login in the connection string is what the services use too; there are no Windows accounts to add.
            if (repository.IntegratedSecurity)
            {
                foreach (var (login, _) in RepositoryLogins(agentAccount, webAccount, repository.DataSource))
                {
                    output.WriteLine($"Login {login}: {await EnsureLoginAsync(connection, login).ConfigureAwait(false)}.");
                }
            }
        }

        if (repository.IntegratedSecurity)
        {
            await using var connection = new SqlConnection(repository.ConnectionString);
            await connection.OpenAsync().ConfigureAwait(false);
            foreach (var (login, role) in RepositoryLogins(agentAccount, webAccount, repository.DataSource))
            {
                var user = await ScalarAsync(connection, """
                    DECLARE @user sysname = (SELECT name FROM sys.database_principals WHERE sid = SUSER_SID(@login));
                    IF @user IS NULL
                    BEGIN
                        SET @user = @login;
                        DECLARE @create nvarchar(max) = N'CREATE USER ' + QUOTENAME(@user) + N' FOR LOGIN ' + QUOTENAME(@login);
                        EXEC (@create);
                    END
                    IF @user <> N'dbo' AND IS_ROLEMEMBER(@role, @user) <> 1
                    BEGIN
                        DECLARE @add nvarchar(max) = N'ALTER ROLE ' + QUOTENAME(@role) + N' ADD MEMBER ' + QUOTENAME(@user);
                        EXEC (@add);
                    END
                    SELECT @user;
                    """, ("@login", login), ("@role", role)).ConfigureAwait(false);
                output.WriteLine($"Bruger {user} i {database}: {role}.");
            }
        }

        var applied = await SchemaMigrator.MigrateAsync(repository.ConnectionString).ConfigureAwait(false);
        output.WriteLine(applied > 0 ? $"Skema: {applied} migreringer kørt." : "Skema: opdateret.");
    }

    private static async Task GrantMonitoredAsync(MonitoredInstance instance, string agentAccount, TextWriter output)
    {
        if (instance.Authentication != AuthenticationMode.Windows)
        {
            output.WriteLine($"{instance.Server}: springes over ({instance.Authentication}); giv rettigheder med grant-least-privilege.sql.");
            return;
        }

        var login = ServiceAccounts.LoginFor(agentAccount, instance.Server, Environment.MachineName, Environment.UserDomainName);
        var target = new SqlConnectionStringBuilder
        {
            DataSource = instance.Server,
            InitialCatalog = "master",
            IntegratedSecurity = true,
            Encrypt = instance.Encryption == EncryptionMode.Mandatory ? SqlConnectionEncryptOption.Mandatory : SqlConnectionEncryptOption.Optional,
            TrustServerCertificate = instance.TrustServerCertificate,
            ApplicationName = "SQLInsight Pro setup",
            Pooling = false,
        };
        await using var connection = new SqlConnection(target.ConnectionString);
        connection.InfoMessage += (_, e) => output.WriteLine($"  {e.Message}");
        await connection.OpenAsync().ConfigureAwait(false);
        output.WriteLine($"Login {login} på {instance.Server}: {await EnsureLoginAsync(connection, login).ConfigureAwait(false)}.");

        await using var command = new SqlCommand(GrantScript(), connection) { CommandTimeout = 300 };
        command.Parameters.AddWithValue("@login", login);
        await command.ExecuteNonQueryAsync().ConfigureAwait(false);
        output.WriteLine($"Rettigheder givet på {instance.Server}.");
    }

    /// <summary>
    /// The logins the services connect as, with their role in the repository. Both services on another computer than
    /// SQL Server arrive as the computer account, which then gets db_owner (it covers reading).
    /// </summary>
    public static IReadOnlyList<(string Login, string Role)> RepositoryLogins(string agentAccount, string webAccount, string sqlServer)
    {
        var agent = ServiceAccounts.LoginFor(agentAccount, sqlServer, Environment.MachineName, Environment.UserDomainName);
        var web = ServiceAccounts.LoginFor(webAccount, sqlServer, Environment.MachineName, Environment.UserDomainName);
        return string.Equals(agent, web, StringComparison.OrdinalIgnoreCase)
            ? [(agent, "db_owner")]
            : [(agent, "db_owner"), (web, "db_datareader")];
    }

    private static async Task<string> EnsureLoginAsync(SqlConnection connection, string login) =>
        await ScalarAsync(connection, """
            IF SUSER_ID(@login) IS NULL
            BEGIN
                DECLARE @sql nvarchar(max) = N'CREATE LOGIN ' + QUOTENAME(@login) + N' FROM WINDOWS';
                EXEC (@sql);
                SELECT N'oprettet';
            END
            ELSE SELECT N'findes';
            """, ("@login", login)).ConfigureAwait(false);

    private static async Task<string> ScalarAsync(SqlConnection connection, string sql, params (string Name, string Value)[] parameters)
    {
        await using var command = new SqlCommand(sql, connection) { CommandTimeout = 300 };
        foreach (var (name, value) in parameters)
        {
            command.Parameters.AddWithValue(name, value);
        }

        return Convert.ToString(await command.ExecuteScalarAsync().ConfigureAwait(false), System.Globalization.CultureInfo.InvariantCulture) ?? string.Empty;
    }

    /// <summary>db/permissions/grant-least-privilege.sql with the login as the parameter @login instead of the placeholder.</summary>
    public static string GrantScript()
    {
        using var stream = typeof(RepositorySetup).Assembly.GetManifestResourceStream("grant-least-privilege.sql")
            ?? throw new InvalidOperationException("grant-least-privilege.sql mangler i programmet.");
        using var reader = new StreamReader(stream);
        var script = LoginPlaceholder().Replace(reader.ReadToEnd(), "SET @LoginName = @login;", 1);
        return script.Contains("SET @LoginName = @login;", StringComparison.Ordinal)
            ? script
            : throw new InvalidOperationException("grant-least-privilege.sql: linjen SET @LoginName = N'…' blev ikke fundet.");
    }

    private static string Hint(Exception ex) => ex switch
    {
        SqlException { Number: 18456 } => "Din Windows-konto kan ikke logge ind på SQL Server. Installér som en bruger, der er sysadmin på instansen.",
        SqlException { Number: 262 or 1802 or 15247 } => "Din konto mangler rettighed til at oprette databaser eller logins (dbcreator og securityadmin, eller sysadmin).",
        SqlException { Number: 15401 } => "Windows-kontoen findes ikke på SQL Server-maskinen. Ligger SQL Server på en anden computer, skal computeren være i samme domæne.",
        SqlException { Number: -2146893019 } or SqlException { InnerException: System.Security.Authentication.AuthenticationException } =>
            "SQL Server bruger et certifikat, der ikke er tillid til. Tilføj TrustServerCertificate=true i forbindelsesstrengen.",
        SqlException { Number: 2 or 53 or -1 } => "SQL Server kunne ikke nås. Tjek servernavnet, at instansen kører, og firewallen (TCP 1433).",
        _ => "Installér med SKIP_REPOSITORY_SETUP=1 og opret databasen selv (docs/installation.md, trin 2), hvis det ikke kan løses.",
    };

    private enum Outcome { Ok, Warning, Error }

    private static void Report(string text, Outcome outcome)
    {
        if (!OperatingSystem.IsWindows())
        {
            return;
        }

        try
        {
            var type = outcome switch { Outcome.Error => EventLogEntryType.Error, Outcome.Warning => EventLogEntryType.Warning, _ => EventLogEntryType.Information };
            EventLog.WriteEntry(EventSource, "Opsætning af repository (setup-repository):" + Environment.NewLine + text, type);
        }
        catch (Exception ex) when (ex is InvalidOperationException or System.Security.SecurityException or System.ComponentModel.Win32Exception)
        {
            // The event source is registered by the installer; outside it the console output is enough.
        }
    }

    private static string? Option(string[] args, string name)
    {
        var i = Array.IndexOf(args, name);
        return i >= 0 && i + 1 < args.Length ? args[i + 1] : null;
    }

    [GeneratedRegex(@"SET @LoginName = N'[^']*';[^\r\n]*")]
    private static partial Regex LoginPlaceholder();

    private sealed class TeeWriter(TextWriter first, TextWriter second) : TextWriter
    {
        public override System.Text.Encoding Encoding => first.Encoding;

        public override void Write(char value)
        {
            first.Write(value);
            second.Write(value);
        }

        public override void WriteLine(string? value)
        {
            first.WriteLine(value);
            second.WriteLine(value);
        }
    }
}