using System;
using System.Collections.Generic;
using System.Linq;

namespace Salesforce.NET
{
    /// <summary>
    /// Allows for an object to track changes made
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public class Trackable<T>
    {
        private readonly Type type;

        private T value;
        private IDictionary<string, string> modified;

        private readonly IDictionary<string, string> originalPropertyValues = new Dictionary<string, string>();
        private readonly IDictionary<string, string> latestPropertyValues = new Dictionary<string, string>();

        public Trackable(T value)
        {
            this.value = value;

            type = value.GetType();

            SetPropertyValues(originalPropertyValues);
        }

        public T Value
        {
            get => value;
            protected set => this.value = value;
        }

        /// <summary>
        /// Gets a dictionary of modified fields since the <see cref="Trackable{T}"/> object was created
        /// </summary>
        public IDictionary<string, string> Modified
        {
            get
            {
                SetPropertyValues(latestPropertyValues);

                return originalPropertyValues
                    .Join(latestPropertyValues, o => o.Key, l => l.Key, (o, l) => new
                    {
                        Original = o,
                        Latest = l
                    })
                    .Where(p => !object.Equals(p.Original.Value, p.Latest.Value))
                    .Select(p => p.Latest)
                    .ToDictionary(t => t.Key, t => t.Value);
            }

            protected set => modified = value;
        }

        private void SetPropertyValues(IDictionary<string, string> propertyValues)
        {
            type
                .GetProperties()
                .ToList()
                .ForEach(p => propertyValues[p.Name] = p.GetValue(value)?.ToString());
        }
    }

    public static class Trackable
    {
        /// <summary>
        /// Allows an object to track changes for the Salesforce API update
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="value"></param>
        /// <returns></returns>
        public static Trackable<T> AsTrackable<T>(this T value)
        {
            return new Trackable<T>(value);
        }
    }
}