using System.Data.Common;
using Microsoft.Data.SqlClient;
using Microsoft.Extensions.Configuration;

namespace Infrastructure.Repository.Sql;

/// <summary>
/// Default <see cref="ISqlConnectionFactory"/> implementation that creates SQL Server connections,
/// resolving the connection string from environment variables or application configuration.
/// </summary>
/// <param name="configuration">The application configuration, used as a fallback source for the connection string.</param>
public class DefaultSqlConnectionFactory(IConfiguration configuration)
    : ISqlConnectionFactory
{
    private readonly string _connectionString = GetConnectionString(
        configuration
    );

    /// <summary>
    /// Resolves the SQL Server connection string, preferring (in order): the <c>DB_CONNECTION_STRING</c>
    /// environment variable, a connection string built from individual <c>DB_*</c> environment variables
    /// via <see cref="SqlConnectionStringHelper.BuildConnectionString"/>, and finally the <c>"Default"</c>
    /// connection string from <paramref name="configuration"/>.
    /// </summary>
    /// <param name="configuration">The application configuration to fall back to.</param>
    /// <returns>The resolved SQL Server connection string.</returns>
    /// <exception cref="InvalidOperationException">
    /// Thrown when no connection string can be resolved from any of the supported sources.
    /// </exception>
    private static string GetConnectionString(IConfiguration configuration)
    {
        // Check for full connection string first
        var fullConnectionString = Environment.GetEnvironmentVariable(
            "DB_CONNECTION_STRING"
        );
        if (!string.IsNullOrEmpty(fullConnectionString))
        {
            return fullConnectionString;
        }

        // Try to build from individual environment variables (preferred method for Docker)
        try
        {
            return SqlConnectionStringHelper.BuildConnectionString();
        }
        catch (InvalidOperationException)
        {
            // Fall back to configuration-based connection string if env vars are not set
            var connString = configuration.GetConnectionString("Default");
            if (!string.IsNullOrEmpty(connString))
            {
                return connString;
            }

            throw new InvalidOperationException(
                "Database connection string not configured. Set DB_CONNECTION_STRING or DB_SERVER, DB_NAME, DB_USER, DB_PASSWORD env vars or ConnectionStrings:Default."
            );
        }
    }

    /// <summary>
    /// Creates a new, unopened <see cref="SqlConnection"/> using the resolved connection string.
    /// </summary>
    /// <returns>A new <see cref="SqlConnection"/> instance.</returns>
    public DbConnection CreateConnection()
    {
        return new SqlConnection(_connectionString);
    }
}