using System;
using System.Linq;
using System.Linq.Expressions;

namespace Ems.BusinessTracker.Common.Linq
{
    public static class LinqExtensions
    {
        /// <summary>Orders the sequence by specific column and direction.</summary>
        /// <param name="query">The query.</param>
        /// <param name="sortColumn">The sort column.</param>
        /// <param name="ascending">if set to true [ascending].</param>
        public static IQueryable<T> OrderBy<T>(this IQueryable<T> query, string sortColumn, string direction)
        {
            string methodName = string.Format("OrderBy{0}",
                direction.ToLower() == "asc" ? "" : "descending");

            ParameterExpression parameter = Expression.Parameter(query.ElementType, "p");

            MemberExpression memberAccess = null;
            foreach (var property in sortColumn.Split('.'))
                memberAccess = MemberExpression.Property
                   (memberAccess ?? (parameter as Expression), property);

            LambdaExpression orderByLambda = Expression.Lambda(memberAccess, parameter);

            MethodCallExpression result = Expression.Call(
                      typeof(Queryable),
                      methodName,
                      new[] { query.ElementType, memberAccess.Type },
                      query.Expression,
                      Expression.Quote(orderByLambda));

            return query.Provider.CreateQuery<T>(result);
        }


        public static IQueryable<T> Where<T>(this IQueryable<T> query,
            string column, object value, WhereOperation operation)
        {
            if (string.IsNullOrEmpty(column))
                return query;

            ParameterExpression parameter = Expression.Parameter(query.ElementType, "p");

            MemberExpression memberAccess = null;
            foreach (var property in column.Split('.'))
                memberAccess = MemberExpression.Property
                   (memberAccess ?? (parameter as Expression), property);

            //change param value type
            //necessary to getting bool from string
            ConstantExpression filter = Expression.Constant
                (
                    Convert.ChangeType(value, memberAccess.Type)
                );

            //switch operation
            Expression condition = null;
            LambdaExpression lambda = null;
            switch (operation)
            {
                //equal ==
                case WhereOperation.Equal:
                    condition = Expression.Equal(memberAccess, filter);
                    lambda = Expression.Lambda(condition, parameter);
                    break;
                //not equal !=
                case WhereOperation.NotEqual:
                    condition = Expression.NotEqual(memberAccess, filter);
                    lambda = Expression.Lambda(condition, parameter);
                    break;
                //string.Contains()
                case WhereOperation.Contains:
                    //condition = Expression.Call(memberAccess,
                    //    typeof(string).GetMethod("Contains"),
                    //    Expression.Constant(value));
                    //lambda = Expression.Lambda(condition, parameter);

                    var toLower = Expression.Call(memberAccess,
          typeof(string).GetMethod("ToLower", System.Type.EmptyTypes));
                    condition = Expression.Call(toLower,
                                                typeof(string).GetMethod("Contains"),
                                                Expression.Constant(value.ToString().ToLower()));
                    lambda = Expression.Lambda(condition, parameter);
                    break;
            }


            MethodCallExpression result = Expression.Call(
                   typeof(Queryable), "Where",
                   new[] { query.ElementType },
                   query.Expression,
                   lambda);

            return query.Provider.CreateQuery<T>(result);
        }
    }
}