SlowLoadableComponent implementation

SlowLoadableComponent.cs

// <copyright file="SlowLoadableComponent.cs" company="WebDriver Committers">
// Copyright 2007-2011 WebDriver committers
// Copyright 2007-2011 Google Inc.
// Portions copyright 2011 Software Freedom Conservancy
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// </copyright>

using System;
using System.Linq;
using System.Threading;
using System.Globalization;

namespace OpenQA.Selenium.Support.UI
{
    ///<summary>
    /// A <see cref="LoadableComponent<T>"/> which might not have finished loading when Load() returns. After a
    /// call to Load(), the IsLoaded() method should continue to fail until the component has fully
    /// loaded. Use the IsError() methd to check for error conditions which caused the Load() to fail.
    /// 
    /// <pre class="code">
    /// new SlowHypotheticalComponent().Load();
    /// </pre>
    ///</summary>
    ///<typeparam name="T">The type to be returned (normally the subclass' type)</typeparam>
    ///
    public abstract class SlowLoadableComponent<T> : LoadableComponent<T> where T : SlowLoadableComponent<T>
    {
        private readonly IClock clock;
        private readonly TimeSpan timeOut;
        
        public SlowLoadableComponent(int timeoutInSeconds) : this(new SystemClock(), timeoutInSeconds) { }

        public SlowLoadableComponent(TimeSpan timeout) : this(new SystemClock(), timeout) { }

        public SlowLoadableComponent(IClock clock, int timeOutInSeconds) : this(clock, TimeSpan.FromSeconds(timeOutInSeconds)) { }

        public SlowLoadableComponent(IClock clock, TimeSpan timeout)
        {
            this.clock = clock;
            this.timeOut = timeout;
        }

        public override T Load()
        {
            if (this.IsLoaded)
            {
                return (T)this;
            }
            else
            {
                this.TryLoad();
            }

            DateTime end = clock.LaterBy(timeOut);

            while (clock.IsNowBefore(end))
            {
                if (this.IsLoaded)
                {
                    return (T)this;
                }

                IsError();
                WaitFor();
            }

            if (this.IsLoaded)
            {
                return (T)this;
            }
            else
            {
                string timeoutMessage = string.Format(CultureInfo.InvariantCulture, "Timed out after {0} seconds.", timeOut.TotalSeconds);
                throw new TimeoutException(timeoutMessage);
            }
        }

        ///<summary>
        /// Check for well known error cases, which would mean that loading has finished, but an error
        /// condition was seen. If an error has occured throw any exception other than LoadableComponentException
        /// </summary>
        protected virtual void IsError()
        {
            // no-op by default
        }

        protected virtual int SleepFor
        {
            get
            {
                return 200;
            }
        }

        private void WaitFor()
        {
            Thread.Sleep(SleepFor);
        }
    }
}