using System;
using System.Collections.Generic;

namespace AlicizaX.UI.Runtime
{
    /// <summary>
    /// UI State Machine - Validates state transitions for UI lifecycle.
    /// Helps catch bugs early and ensures proper UI lifecycle management.
    /// </summary>
    internal static class UIStateMachine
    {
        private static readonly Dictionary<UIState, HashSet<UIState>> _validTransitions = new()
        {
            [UIState.Uninitialized] = new() { UIState.CreatedUI },
            [UIState.CreatedUI] = new() { UIState.Loaded },
            [UIState.Loaded] = new() { UIState.Initialized },
            [UIState.Initialized] = new() { UIState.Opened },
            [UIState.Opened] = new() { UIState.Closed, UIState.Destroying },
            [UIState.Closed] = new() { UIState.Opened, UIState.Destroying },
            [UIState.Destroying] = new() { UIState.Destroyed },
            [UIState.Destroyed] = new() { }
        };

        /// <summary>
        /// Checks if a state transition is valid.
        /// </summary>
        /// <param name="from">Current state</param>
        /// <param name="to">Target state</param>
        /// <returns>True if transition is valid</returns>
        public static bool IsValidTransition(UIState from, UIState to)
        {
            return _validTransitions.TryGetValue(from, out var validStates) && validStates.Contains(to);
        }

        /// <summary>
        /// Validates a state transition and logs error if invalid.
        /// </summary>
        /// <param name="uiName">Name of the UI for logging</param>
        /// <param name="from">Current state</param>
        /// <param name="to">Target state</param>
        /// <returns>True if transition is valid</returns>
        public static bool ValidateTransition(string uiName, UIState from, UIState to)
        {
            if (IsValidTransition(from, to))
                return true;

            Log.Error($"[UI] Invalid state transition for {uiName}: {from} -> {to}");
            return false;
        }

        /// <summary>
        /// Gets all valid next states from the current state.
        /// </summary>
        /// <param name="currentState">Current state</param>
        /// <returns>Set of valid next states</returns>
        public static HashSet<UIState> GetValidNextStates(UIState currentState)
        {
            return _validTransitions.TryGetValue(currentState, out var states)
                ? states
                : new HashSet<UIState>();
        }

        /// <summary>
        /// Gets a human-readable description of the state.
        /// </summary>
        public static string GetStateDescription(UIState state)
        {
            return state switch
            {
                UIState.Uninitialized => "Not yet created",
                UIState.CreatedUI => "UI logic created, awaiting resource load",
                UIState.Loaded => "Resources loaded, awaiting initialization",
                UIState.Initialized => "Initialized, ready to open",
                UIState.Opened => "Currently visible and active",
                UIState.Closed => "Hidden but cached",
                UIState.Destroying => "Being destroyed",
                UIState.Destroyed => "Fully destroyed",
                _ => "Unknown state"
            };
        }
    }
}