using Chernobyl;
using NUnit.Framework;

namespace System.Utility
{
    /// <summary>
    /// A type used to test the invoking of methods or raising of events.
    /// </summary>
    public class InvokeTester
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="InvokeTester"/> class.
        /// </summary>
        /// <param name="failureMessage">The message that is printed when a test
        /// fails.</param>
        public InvokeTester(string failureMessage)
            : this(false, failureMessage)
        {}

        /// <summary>
        /// Initializes a new instance of the <see cref="InvokeTester" /> class.
        /// </summary>
        /// <param name="pass">True if the test should fail when
        /// <see cref="EventHandler(object, EventArgs)"/> is invoked, false if
        /// otherwise. This property is false by default.</param>
        /// <param name="failureMessage">The message that is printed when a test
        /// fails.</param>
        public InvokeTester(bool pass, string failureMessage)
        {
            Pass = pass;
            FailureMessage = failureMessage;
        }

        /// <summary>
        /// An event handler that, when invoked, either fails or passes the test
        /// based on the value of <see cref="Pass"/>.
        /// </summary>
        /// <param name="sender">The sender of the event.</param>
        /// <param name="e">The <see cref="EventArgs"/> instance containing the
        /// event data.</param>
        public void EventHandler(object sender, EventArgs e)
        {
            if (Pass)
                Assert.Pass();
            else
                Assert.Fail(FailureMessage);
        }

        /// <summary>
        /// True if the test should fail when <see cref="EventHandler(object, EventArgs)"/>
        /// is invoked, false if otherwise. This property is false by default.
        /// </summary>
        public bool Pass { get; set; }

        /// <summary>
        /// The message that is printed when a test fails.
        /// </summary>
        public string FailureMessage
        {
            get => _failureMessage;
            set => _failureMessage = value.ThrowIfNull(nameof(value)).Value;
        }

        /// <summary>
        /// The backing field to <see cref="FailureMessage"/>.
        /// </summary>
        string _failureMessage;
    }
}