using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using Npgsql;

namespace FinlyticCore.Database;

/// <summary>
/// Utility for auto-bootstrapping PostgreSQL databases in a multi-service architecture.
/// Ensures the target catalog database exists prior to EF Core connection and migration execution.
/// </summary>
public static class DatabaseBootstrapper
{
    /// <summary>
    /// Checks if the target PostgreSQL database exists. If not, connects to the default administrative
    /// database ('postgres') and executes CREATE DATABASE so that EF Core migrations can succeed.
    /// </summary>
    public static async Task EnsureDatabaseCreatedAsync(
        string connectionString, 
        ILogger? logger = null, 
        CancellationToken cancellationToken = default)
    {
        if (string.IsNullOrWhiteSpace(connectionString)) return;

        try
        {
            var builder = new NpgsqlConnectionStringBuilder(connectionString);
            string targetDb = builder.Database ?? string.Empty;

            if (string.IsNullOrWhiteSpace(targetDb) || string.Equals(targetDb, "postgres", StringComparison.OrdinalIgnoreCase))
            {
                return;
            }

            // Temporarily connect to the default 'postgres' database to query pg_database
            builder.Database = "postgres";
            string adminConnStr = builder.ConnectionString;

            await using var conn = new NpgsqlConnection(adminConnStr);
            await conn.OpenAsync(cancellationToken);

            await using var checkCmd = new NpgsqlCommand(
                "SELECT 1 FROM pg_database WHERE datname = @dbname;", conn);
            checkCmd.Parameters.AddWithValue("dbname", targetDb);
            var exists = await checkCmd.ExecuteScalarAsync(cancellationToken);

            if (exists == null || exists == DBNull.Value)
            {
                logger?.LogInformation("[DatabaseBootstrapper] Database '{TargetDb}' does not exist on PostgreSQL host. Creating it automatically...", targetDb);
                
                // CREATE DATABASE cannot be executed as a parameterized identifier
                await using var createCmd = new NpgsqlCommand(
                    $"CREATE DATABASE \"{targetDb.Replace("\"", "\"\"")}\";", conn);
                await createCmd.ExecuteNonQueryAsync(cancellationToken);
                
                logger?.LogInformation("[DatabaseBootstrapper] Successfully created database '{TargetDb}'.", targetDb);
            }
        }
        catch (Exception ex)
        {
            logger?.LogWarning(ex, "[DatabaseBootstrapper] Auto-creation check failed or skipped for connection. Continuing with migration.");
        }
    }

    /// <summary>
    /// Combines catalog database auto-creation and EF Core Migration execution in a single call.
    /// </summary>
    public static async Task MigrateWithBootstrapAsync<TContext>(
        this TContext context, 
        string connectionString, 
        ILogger? logger = null, 
        CancellationToken cancellationToken = default) where TContext : DbContext
    {
        await EnsureDatabaseCreatedAsync(connectionString, logger, cancellationToken);
        await context.Database.MigrateAsync(cancellationToken);
    }
}