using System;
using Svrnty.CQRS.Events.PostgreSQL.Configuration;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Npgsql;

namespace Svrnty.CQRS.Events.PostgreSQL.Migration;

/// <summary>
/// Manages database migrations for event streaming schema.
/// </summary>
public class DatabaseMigrator
{
    private readonly PostgresEventStreamStoreOptions _options;
    private readonly ILogger<DatabaseMigrator> _logger;
    private static readonly Regex MigrationFilePattern = new Regex(@"^(\d{3})_(.+)\.sql$", RegexOptions.Compiled);

    public DatabaseMigrator(
        IOptions<PostgresEventStreamStoreOptions> options,
        ILogger<DatabaseMigrator> logger)
    {
        _options = options?.Value ?? throw new ArgumentNullException(nameof(options));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

    /// <summary>
    /// Executes all pending migrations.
    /// </summary>
    public async Task MigrateAsync(CancellationToken cancellationToken = default)
    {
        if (!_options.AutoMigrate)
        {
            _logger.LogInformation("Auto-migration is disabled. Skipping database migration.");
            return;
        }

        _logger.LogInformation("Starting database migration...");

        await using var connection = new NpgsqlConnection(_options.ConnectionString);
        await connection.OpenAsync(cancellationToken);

        // Ensure schema_version table exists
        await EnsureVersionTableExistsAsync(connection, cancellationToken);

        // Get applied versions
        var appliedVersions = await GetAppliedVersionsAsync(connection, cancellationToken);
        _logger.LogInformation("Found {Count} previously applied migrations", appliedVersions.Count);

        // Load all migration files
        var migrations = LoadMigrations();
        _logger.LogInformation("Found {Count} migration files", migrations.Count);

        // Execute pending migrations
        var pendingMigrations = migrations
            .Where(m => !appliedVersions.Contains(m.Version))
            .OrderBy(m => m.Version)
            .ToList();

        if (pendingMigrations.Count == 0)
        {
            _logger.LogInformation("Database is up to date. No migrations to apply.");
            return;
        }

        _logger.LogInformation("Found {Count} pending migrations to apply", pendingMigrations.Count);

        foreach (var migration in pendingMigrations)
        {
            await ExecuteMigrationAsync(connection, migration, cancellationToken);
        }

        _logger.LogInformation("Database migration completed successfully");
    }

    /// <summary>
    /// Gets the current database schema version.
    /// </summary>
    public async Task<int> GetCurrentVersionAsync(CancellationToken cancellationToken = default)
    {
        await using var connection = new NpgsqlConnection(_options.ConnectionString);
        await connection.OpenAsync(cancellationToken);

        await EnsureVersionTableExistsAsync(connection, cancellationToken);

        var appliedVersions = await GetAppliedVersionsAsync(connection, cancellationToken);
        return appliedVersions.Count > 0 ? appliedVersions.Max() : 0;
    }

    private async Task EnsureVersionTableExistsAsync(NpgsqlConnection connection, CancellationToken cancellationToken)
    {
        const string sql = @"
            CREATE SCHEMA IF NOT EXISTS event_streaming;

            CREATE TABLE IF NOT EXISTS event_streaming.schema_version (
                version INT PRIMARY KEY,
                applied_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
                description TEXT NOT NULL
            );";

        await using var command = new NpgsqlCommand(sql, connection);
        await command.ExecuteNonQueryAsync(cancellationToken);
    }

    private async Task<List<int>> GetAppliedVersionsAsync(NpgsqlConnection connection, CancellationToken cancellationToken)
    {
        const string sql = "SELECT version FROM event_streaming.schema_version ORDER BY version";

        await using var command = new NpgsqlCommand(sql, connection);
        await using var reader = await command.ExecuteReaderAsync(cancellationToken);

        var versions = new List<int>();
        while (await reader.ReadAsync(cancellationToken))
        {
            versions.Add(reader.GetInt32(0));
        }

        return versions;
    }

    private List<Migration> LoadMigrations()
    {
        var migrations = new List<Migration>();
        var assembly = Assembly.GetExecutingAssembly();
        var resourceNames = assembly.GetManifestResourceNames()
            .Where(r => r.Contains("Migrations") && r.EndsWith(".sql"))
            .ToList();

        if (resourceNames.Count == 0)
        {
            // Fallback to file system if embedded resources not found
            var migrationsPath = Path.Combine(Path.GetDirectoryName(assembly.Location) ?? "", "Migrations");
            if (Directory.Exists(migrationsPath))
            {
                var files = Directory.GetFiles(migrationsPath, "*.sql");
                foreach (var file in files)
                {
                    var fileName = Path.GetFileName(file);
                    var match = MigrationFilePattern.Match(fileName);
                    if (match.Success)
                    {
                        var version = int.Parse(match.Groups[1].Value);
                        var description = match.Groups[2].Value.Replace("_", " ");
                        var sql = File.ReadAllText(file);

                        migrations.Add(new Migration
                        {
                            Version = version,
                            Description = description,
                            Sql = sql,
                            FileName = fileName
                        });
                    }
                }
            }
        }
        else
        {
            // Load from embedded resources
            foreach (var resourceName in resourceNames)
            {
                var fileName = resourceName.Split('.').TakeLast(2).First() + ".sql";
                var match = MigrationFilePattern.Match(fileName);
                if (match.Success)
                {
                    var version = int.Parse(match.Groups[1].Value);
                    var description = match.Groups[2].Value.Replace("_", " ");

                    using var stream = assembly.GetManifestResourceStream(resourceName);
                    if (stream != null)
                    {
                        using var reader = new StreamReader(stream);
                        var sql = reader.ReadToEnd();

                        migrations.Add(new Migration
                        {
                            Version = version,
                            Description = description,
                            Sql = sql,
                            FileName = fileName
                        });
                    }
                }
            }
        }

        return migrations.OrderBy(m => m.Version).ToList();
    }

    private async Task ExecuteMigrationAsync(
        NpgsqlConnection connection,
        Migration migration,
        CancellationToken cancellationToken)
    {
        _logger.LogInformation("Applying migration {Version}: {Description}", migration.Version, migration.Description);

        await using var transaction = await connection.BeginTransactionAsync(cancellationToken);

        try
        {
            // Execute migration SQL
            await using (var command = new NpgsqlCommand(migration.Sql, connection, transaction))
            {
                command.CommandTimeout = 300; // 5 minutes for large migrations
                await command.ExecuteNonQueryAsync(cancellationToken);
            }

            // Record migration as applied
            const string recordSql = @"
                INSERT INTO event_streaming.schema_version (version, description)
                VALUES (@Version, @Description)
                ON CONFLICT (version) DO NOTHING";

            await using (var command = new NpgsqlCommand(recordSql, connection, transaction))
            {
                command.Parameters.AddWithValue("@Version", migration.Version);
                command.Parameters.AddWithValue("@Description", migration.Description);
                await command.ExecuteNonQueryAsync(cancellationToken);
            }

            await transaction.CommitAsync(cancellationToken);

            _logger.LogInformation("Successfully applied migration {Version}", migration.Version);
        }
        catch (Exception ex)
        {
            await transaction.RollbackAsync(cancellationToken);
            _logger.LogError(ex, "Failed to apply migration {Version}: {Description}", migration.Version, migration.Description);
            throw new InvalidOperationException($"Migration {migration.Version} failed: {ex.Message}", ex);
        }
    }

    private class Migration
    {
        public required int Version { get; init; }
        public required string Description { get; init; }
        public required string Sql { get; init; }
        public required string FileName { get; init; }
    }
}