using System;
using System.Collections.Generic;

namespace Jovian.EncounterSystem {
    /// <summary>
    /// Dispatches <see cref="IEncounterEvent"/> instances (authored on dialog options) to per-type
    /// handlers registered at composition time. Unknown event types are silently skipped.
    /// </summary>
    /// <remarks>
    /// The resolver stores handlers keyed by concrete event <see cref="Type"/>. Registration wraps a
    /// typed delegate in a closure that casts back to the concrete type — the cast is safe because
    /// we only ever invoke the wrapped delegate via the dictionary lookup under the same key.
    /// </remarks>
    public class EncounterResolver {
        private readonly Dictionary<Type, Action<IEncounterEvent, EncounterContext>> handlers = new();

        /// <summary>Register a handler for a concrete event type. Replaces any prior registration.</summary>
        /// <typeparam name="T">The event type to handle.</typeparam>
        /// <param name="handler">The delegate invoked with the cast event and the resolution context.</param>
        public void Register<T>(Action<T, EncounterContext> handler) where T : IEncounterEvent {
            handlers[typeof(T)] = (evt, ctx) => handler((T)evt, ctx);
        }

        /// <summary>Remove the handler registered for event type <typeparamref name="T"/>, if any.</summary>
        public void Unregister<T>() where T : IEncounterEvent {
            handlers.Remove(typeof(T));
        }

        /// <summary>Dispatch each event in <paramref name="events"/> to its registered handler, in order.
        /// Null events and events with no registered handler are skipped.</summary>
        /// <param name="events">The ordered event list (typically from an <see cref="EncounterDialogOption"/>).</param>
        /// <param name="context">Per-resolution context passed to every handler.</param>
        public void Resolve(IEnumerable<IEncounterEvent> events, EncounterContext context) {
            if(events == null) {
                return;
            }

            foreach(var evt in events) {
                if(evt == null) {
                    continue;
                }

                if(handlers.TryGetValue(evt.GetType(), out var handler)) {
                    handler(evt, context);
                }
            }
        }
    }
}