using System.Collections.Concurrent;
using System.Reflection;

namespace Kit.Helpers.SqlHelperAbstract
{
    /// <summary>
    /// SQL-тексты библиотеки, хранятся EmbeddedResource-файлами в SqlHelperAbstract\Sql\*.sql (см. Kit.Helpers.csproj).
    /// </summary>
    internal static class SqlTexts
    {
        private static readonly ConcurrentDictionary<string, string> _cache = new();

        /// <summary>Lookup «хранимой функции» в sys_functions (SQLite).</summary>
        public static string SelectStoredFunction => Load("sys_function_select.sql");

        private static string Load(string fileName)
        {
            return _cache.GetOrAdd(fileName, key =>
            {
                Assembly assembly = typeof(SqlTexts).Assembly;
                string resourceName = assembly.GetManifestResourceNames().SingleOrDefault(x => x.EndsWith(key, StringComparison.Ordinal))
                    ?? throw new InvalidOperationException($"Embedded sql resource not found: {key}");

                using Stream stream = assembly.GetManifestResourceStream(resourceName)
                    ?? throw new InvalidOperationException($"Embedded sql resource is empty: {resourceName}");
                using var reader = new StreamReader(stream);
                return reader.ReadToEnd().Trim();
            });
        }
    }
}