using System;
using JD.Kernel.Classes;
using JD.Kernel.StaticHelpers;

namespace JD.PropertyService
{
    /// <summary>
    /// Properties that cache changes made to them until they are bulk written to
    /// the property object which is being cached.
    /// </summary>
    public class TransactionalProperties : Properties, IDisposable
    {
        #region Variables

        private readonly Scope m_isSyncing = new Scope();
        private IProperties m_internalProperties;
        private bool m_isDirty;

        #endregion

        #region Constructor

        /// <summary>
        /// Constructor
        /// </summary>        
        public TransactionalProperties()
            : this(new Properties())
        {}

        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="cachedProperties"></param>
        public TransactionalProperties(IProperties cachedProperties)
        {
            Throw.IfNull(cachedProperties, "cachedProperties");

            InternalProperties = cachedProperties;            
        }

        #endregion

        #region Properties

        /// <summary>
        /// Dirty flag
        /// </summary>
        public bool IsDirty
        {
            get { return m_isDirty; }
        }

        public override bool IsReadOnly
        {
            get
            {
                return m_internalProperties.IsReadOnly;
            }
        }

        /// <summary>
        /// Access to the cached properties
        /// </summary>
        public IProperties InternalProperties
        {
            get 
            {
                return m_internalProperties; 
            }
            set 
            {
                if (m_internalProperties != null)
                {
                    m_internalProperties.PropertyChanged -= InternalPropertiesPropertyChanged;
                }

                m_internalProperties = value;

                if (m_internalProperties != null)
                {
                    m_internalProperties.PropertyChanged += InternalPropertiesPropertyChanged;
                    Revert();
                }
            }
        }

        private bool Syncing
        {
            get { return m_isSyncing.InScope; }
        }

        #endregion

        #region Public Methods

        /// <summary>
        /// Write dirty cache entries to cached properties, then reload the cache.
        /// </summary>
        public void Commit()
        {
            if (!Syncing)
            {
                using (m_isSyncing.Begin())
                {
                    if (m_isDirty && OnPropertyChanging())
                    {
                        using (m_internalProperties.BeginScopedUpdate())
                        {
                            m_internalProperties.Clear();
                            CopyTo(m_internalProperties);
                        }
                        m_isDirty = false;
                        OnCommit();
                    }
                }
            }
        }

        /// <summary>
        /// Load the cache from the properties being cached, discarding any previous cache content.
        /// </summary>
        public void Revert()
        {
            if (!Syncing)
            {
                using (m_isSyncing.Begin())
                {
                    Clear();
                    m_internalProperties.CopyTo(this);
                    m_isDirty = false;

                    OnReverted();
                }
            }
        }

        #endregion

        #region Events

        private void OnCommit()
        {
            Commited?.Invoke(this, EventArgs.Empty);
        }

        private void OnReverted()
        {
            Reverted?.Invoke(this, EventArgs.Empty);
        }

        /// <summary>
        /// Raised when the cache has been reloaded from the cached item.
        /// </summary>                    
        public event EventHandler Reverted;

        /// <summary>
        /// Raised when a dirty cache was written.
        /// </summary>        
        public event EventHandler Commited;

        #endregion

        #region Event Handlers

        protected override void OnPropertyChanged(PropertyChangedEventArgs e)
        {
            m_isDirty = true;
            base.OnPropertyChanged(e);
        }

        private void InternalPropertiesPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            Revert();            
        }

        #endregion

        #region IDisposable Members

        /// <summary>
        /// Interface implementation
        /// </summary>
        public void Dispose()
        {
            // unbind event handlers
            InternalProperties = null;
        }

        #endregion
    }
}