using System;
using System.Windows.Input;

namespace MVVM_DEMO.Commands
{
    /// <summary>
    /// A command whose sole purpose is to relay its functionality to other objects by invoking delegates.
    /// The default return value for the CanExecute method is 'true'.
    /// </summary>
    public class RelayCommand : ICommand
    {
        private readonly Action<object?> _execute;
        private readonly Func<object?, bool>? _canExecute;

        /// <summary>
        /// Occurs when changes occur that affect whether or not the command should execute.
        /// </summary>
        public event EventHandler? CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }

        /// <summary>
        /// Creates a new command that can always execute.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        public RelayCommand(Action<object?> execute) : this(execute, null)
        {
        }

        /// <summary>
        /// Creates a new command.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        /// <param name="canExecute">The execution status logic.</param>
        public RelayCommand(Action<object?> execute, Func<object?, bool>? canExecute)
        {
            _execute = execute ?? throw new ArgumentNullException(nameof(execute));
            _canExecute = canExecute;
        }

        /// <summary>
        /// Determines whether this command can execute in its current state.
        /// </summary>
        /// <param name="parameter">Data used by the command. If the command does not require data to be passed, this object can be set to null.</param>
        /// <returns>true if this command can be executed; otherwise, false.</returns>
        public bool CanExecute(object? parameter)
        {
            return _canExecute == null || _canExecute(parameter);
        }

        /// <summary>
        /// Executes the command.
        /// </summary>
        /// <param name="parameter">Data used by the command. If the command does not require data to be passed, this object can be set to null.</param>
        public void Execute(object? parameter)
        {
            _execute(parameter);
        }
    }
}