﻿// ----------------------------------------------------------------------------------
// <copyright file="QueryExpressionHelper.cs" company="NMemory Team">
//     Copyright (C) NMemory Team
//
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//     of this software and associated documentation files (the "Software"), to deal
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//     copies of the Software, and to permit persons to whom the Software is
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//
//     The above copyright notice and this permission notice shall be included in
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// ----------------------------------------------------------------------------------

namespace NMemory.Common
{
    using System.Linq;
    using System.Linq.Expressions;

    internal static class QueryExpressionHelper
    {
        public static bool GetSelectManyCollectionSelector(
            Expression node,
            out LambdaExpression collectionSelector)
        {
            collectionSelector = null;
            MethodCallExpression method = node as MethodCallExpression;

            if (method == null)
            {
                return false;
            }

            // Check if SelectMany
            if (method.Method.DeclaringType != typeof(Queryable) ||
                !method.Method.IsGenericMethod ||
                method.Method.GetGenericMethodDefinition() != QueryMethods.SelectMany)
            {
                // Not SelectMany call
                return false;
            }

            collectionSelector =
                ExpressionHelper.SkipQuoteNode(method.Arguments[1]) as LambdaExpression;

            return (collectionSelector != null);
        }

        public static bool GetWherePredicate(
            Expression node,
            out LambdaExpression predicate)
        {
            predicate = null;
            MethodCallExpression method = node as MethodCallExpression;

            if (method == null)
            {
                return false;
            }

            if (method.Method.DeclaringType != typeof(Queryable) ||
               !method.Method.IsGenericMethod ||
               method.Method.GetGenericMethodDefinition() != QueryMethods.Where)
            {
                // Where method was not found
                return false;
            }

            predicate =
                ExpressionHelper.SkipQuoteNode(method.Arguments[1]) as LambdaExpression;

            return (predicate != null);
        }

        public static bool GetDefaultOrEmptySource(
            Expression node,
            out Expression source)
        {
            source = null;
            MethodCallExpression method = node as MethodCallExpression;

            if (method == null)
            {
                return false;
            }

            if (method.Method.DeclaringType != typeof(Queryable) ||
               !method.Method.IsGenericMethod ||
               method.Method.GetGenericMethodDefinition() != QueryMethods.DefaultIfEmpty)
            {
                // Where method was not found
                return false;
            }

            source = method.Arguments[0];

            return (source != null);
        }
    }
}
