using System;
using System.Collections.Generic;

namespace FrameworkBLL.ActionProcessor.Handlers
{
    /// <summary>
    /// Resolves IActionHandler implementations by ActionType.
    /// Handlers are registered via dependency injection and mapped
    /// internally for fast lookup.
    /// </summary>
    public sealed class ActionHandlerResolver : IActionHandlerResolver
    {
        private readonly IReadOnlyDictionary<int, IActionHandler> _map;

    public ActionHandlerResolver(IEnumerable<IActionHandler> handlers)
        {
            if (handlers == null)
                throw new ArgumentNullException(nameof(handlers));

            var map = new Dictionary<int, IActionHandler>();

            foreach (var handler in handlers)
            {
                if (handler == null)
                    continue;

                if (map.ContainsKey(handler.ActionType))
                {
                    throw new InvalidOperationException(
                        $"Duplicate IActionHandler registration for ActionType '{handler.ActionType}'.");
                }

                map.Add(handler.ActionType, handler);
            }

            _map = map;
        }

        /// <summary>
        /// Returns the handler for the specified action type.
        /// Returns null if no handler is registered.
        /// </summary>
        public IActionHandler? Resolve(int actionType)
        {
            return _map.TryGetValue(actionType, out var handler)
                ? handler
                : null;
        }
    }

}