Connected.Framework/Connected.Expressions/Translation/Binder.cs

using Connected.Expressions.Evaluation;
using Connected.Expressions.Expressions;
using Connected.Expressions.Mappings;
using Connected.Expressions.Reflection;
using Connected.Expressions.Translation.Projections;
using Connected.Expressions.Visitors;
using Connected.Interop;
using System.Collections;
using System.Linq.Expressions;
using System.Reflection;

namespace Connected.Expressions.Translation;

public sealed class Binder : DatabaseVisitor
{
    private Binder(ExpressionCompilationContext context, Expression expression)
    {
        Context = context;
        Expression = expression;

        ParameterMapping = new();
        GroupByMap = new();
    }

    private ExpressionCompilationContext Context { get; }
    private Dictionary<ParameterExpression, Expression> ParameterMapping { get; }
    private Dictionary<Expression, GroupByDescriptor> GroupByMap { get; }
    private List<OrderExpression>? ThenBys { get; set; }
    private Expression CurrentGroupElement { get; set; }
    private Expression Expression { get; set; }
    public static Expression? Bind(ExpressionCompilationContext context, Expression expression)
    {
        return new Binder(context, expression).Visit(expression);
    }

    public static Expression Bind(Expression source, MemberInfo member)
    {
        switch (source.NodeType)
        {
            case (ExpressionType)DatabaseExpressionType.Entity:
                var ex = (EntityExpression)source;
                var result = Bind(ex.Expression, member);
                var mex = result as MemberExpression;

                if (mex is not null && mex.Expression == ex.Expression && mex.Member == member)
                    return Expression.MakeMemberAccess(source, member);

                return result;
            case ExpressionType.Convert:
                var ux = (UnaryExpression)source;

                return Bind(ux.Operand, member);
            case ExpressionType.MemberInit:
                var min = (MemberInitExpression)source;

                for (var i = 0; i < min.Bindings.Count; i++)
                {
                    var assign = min.Bindings[i] as MemberAssignment;

                    if (assign is not null && MembersMatch(assign.Member, member))
                        return assign.Expression;
                }

                break;
            case ExpressionType.New:
                var nex = (NewExpression)source;

                if (nex.Members is not null)
                {
                    for (var i = 0; i < nex.Members.Count; i++)
                    {
                        if (MembersMatch(nex.Members[i], member))
                            return nex.Arguments[i];
                    }
                }
                else if (nex.Type.GetTypeInfo().IsGenericType && nex.Type.GetGenericTypeDefinition() == typeof(Grouping<,>))
                {
                    if (string.Equals(member.Name, "Key", StringComparison.Ordinal))
                        return nex.Arguments[0];
                }

                break;
            case (ExpressionType)DatabaseExpressionType.Projection:
                var proj = (ProjectionExpression)source;
                var newProjector = Bind(proj.Projector, member);
                var mt = Members.GetMemberType(member);

                return new ProjectionExpression(proj.Select, newProjector, Aggregator.GetAggregator(mt, typeof(IEnumerable<>).MakeGenericType(mt)));

            case (ExpressionType)DatabaseExpressionType.OuterJoined:
                var oj = (OuterJoinedExpression)source;
                var em = Bind(oj.Expression, member);

                if (em is ColumnExpression)
                    return em;

                return new OuterJoinedExpression(oj.Test, em);
            case ExpressionType.Conditional:
                var cex = (ConditionalExpression)source;

                return Expression.Condition(cex.Test, Bind(cex.IfTrue, member), Bind(cex.IfFalse, member));
            case ExpressionType.Constant:
                var con = (ConstantExpression)source;
                var memberType = Members.GetMemberType(member);

                if (con.Value is null)
                    return Expression.Constant(GetDefault(memberType), memberType);
                else
                    return Expression.Constant(GetValue(con.Value, member), memberType);
        }

        return Expression.MakeMemberAccess(source, member);
    }

    protected override Expression? VisitMethodCall(MethodCallExpression expression)
    {
        if (expression.Method.IsInQueryable())
        {
            switch (expression.Method.Name)
            {
                case "Where":
                    return BindWhere(expression.Arguments[0], GetLambda(expression.Arguments[1]));
                case "Select":
                    return BindSelect(expression.Arguments[0], GetLambda(expression.Arguments[1]));
                case "SelectMany":

                    if (expression.Arguments.Count == 2)
                        return BindSelectMany(expression.Arguments[0], GetLambda(expression.Arguments[1]), null);
                    else if (expression.Arguments.Count == 3)
                        return BindSelectMany(expression.Arguments[0], GetLambda(expression.Arguments[1]), GetLambda(expression.Arguments[2]));

                    break;
                case "Join":

                    return BindJoin(expression.Arguments[0], expression.Arguments[1], GetLambda(expression.Arguments[2]),
                        GetLambda(expression.Arguments[3]), GetLambda(expression.Arguments[4]));

                case "GroupJoin":

                    if (expression.Arguments.Count == 5)
                    {
                        return BindGroupJoin(expression.Method, expression.Arguments[0], expression.Arguments[1], GetLambda(expression.Arguments[2]),
                            GetLambda(expression.Arguments[3]), GetLambda(expression.Arguments[4]));
                    }

                    break;
                case "OrderBy":
                    return BindOrderBy(expression.Arguments[0], GetLambda(expression.Arguments[1]), OrderType.Ascending);
                case "OrderByDescending":
                    return BindOrderBy(expression.Arguments[0], GetLambda(expression.Arguments[1]), OrderType.Descending);
                case "ThenBy":
                    return BindThenBy(expression.Arguments[0], GetLambda(expression.Arguments[1]), OrderType.Ascending);
                case "ThenByDescending":
                    return BindThenBy(expression.Arguments[0], GetLambda(expression.Arguments[1]), OrderType.Descending);
                case "GroupBy":

                    if (expression.Arguments.Count == 2)
                        return BindGroupBy(expression.Arguments[0], GetLambda(expression.Arguments[1]), null, null);
                    else if (expression.Arguments.Count == 3)
                    {
                        var lambda1 = GetLambda(expression.Arguments[1]);
                        var lambda2 = GetLambda(expression.Arguments[2]);

                        if (lambda2.Parameters.Count == 1)
                            return BindGroupBy(expression.Arguments[0], lambda1, lambda2, null);
                        else if (lambda2.Parameters.Count == 2)
                            return BindGroupBy(expression.Arguments[0], lambda1, null, lambda2);
                    }
                    else if (expression.Arguments.Count == 4)
                        return BindGroupBy(expression.Arguments[0], GetLambda(expression.Arguments[1]), GetLambda(expression.Arguments[2]), GetLambda(expression.Arguments[3]));

                    break;
                case "Distinct":

                    if (expression.Arguments.Count == 1)
                        return BindDistinct(expression.Arguments[0]);

                    break;
                case "Skip":

                    if (expression.Arguments.Count == 2)
                        return BindSkip(expression.Arguments[0], expression.Arguments[1]);

                    break;
                case "Take":

                    if (expression.Arguments.Count == 2)
                        return BindTake(expression.Arguments[0], expression.Arguments[1]);

                    break;
                case "First":
                case "FirstOrDefault":
                case "Single":
                case "SingleOrDefault":
                case "Last":
                case "LastOrDefault":

                    if (expression.Arguments.Count == 1)
                        return BindFirst(expression.Arguments[0], null, expression.Method.Name, expression == Expression);
                    else if (expression.Arguments.Count == 2)
                        return BindFirst(expression.Arguments[0], GetLambda(expression.Arguments[1]), expression.Method.Name, expression == Expression);

                    break;
                case "Any":

                    if (expression.Arguments.Count == 1)
                        return BindAnyAll(expression.Arguments[0], expression.Method, null, expression == Expression);
                    else if (expression.Arguments.Count == 2)
                        return BindAnyAll(expression.Arguments[0], expression.Method, GetLambda(expression.Arguments[1]), expression == Expression);

                    break;
                case "All":
                    if (expression.Arguments.Count == 2)
                        return BindAnyAll(expression.Arguments[0], expression.Method, GetLambda(expression.Arguments[1]), expression == Expression);
                    break;
                case "Contains":
                    if (expression.Arguments.Count == 2)
                        return BindContains(expression.Arguments[0], expression.Arguments[1], expression == Expression);
                    break;
                case "Cast":
                    if (expression.Arguments.Count == 1)
                        return BindCast(expression.Arguments[0], expression.Method.GetGenericArguments()[0]);
                    break;
                case "Reverse":
                    return BindReverse(expression.Arguments[0]);
                case "Intersect":
                case "Except":
                    if (expression.Arguments.Count == 2)
                        return BindIntersect(expression.Arguments[0], expression.Arguments[1], expression.Method.Name == "Except");
                    break;
            }
        }

        if (Context.Language.IsAggregate(expression.Method))
        {
            var lambda = expression.Arguments.Count > 1 ? GetLambda(expression.Arguments[1]) : null;
            return BindAggregate(expression.Arguments[0], expression.Method.Name, expression.Method.ReturnType, lambda, expression == Expression);
        }

        return base.VisitMethodCall(expression);
    }

    private Expression BindAggregate(Expression expression, string aggregateName, Type returnType, LambdaExpression? argument, bool isRoot)
    {
        var hasPredicateArg = Context.Language.IsAggregateArgumentPredicate(aggregateName);
        var isDistinct = false;
        var argumentWasPredicate = false;
        var useAlternateArg = false;
        var methodCall = expression as MethodCallExpression;

        if (methodCall is not null && !hasPredicateArg && argument is null)
        {
            if (string.Equals(methodCall.Method.Name, "Distinct", StringComparison.Ordinal) && methodCall.Arguments.Count == 1 &&
                methodCall.Method.IsInQueryable() && Context.Language.AllowDistinctInAggregates)
            {
                expression = methodCall.Arguments[0];
                isDistinct = true;
            }
        }

        if (argument is not null && hasPredicateArg)
        {
            var enType = expression.Type.GetEnumerableElementType();
            expression = Expression.Call(typeof(Queryable), "Where", enType is null ? null : new[] { enType }, expression, argument);
            argument = null;
            argumentWasPredicate = true;
        }

        var projection = VisitSequence(expression);
        Expression? argExpr = null;

        if (argument is not null)
        {
            ParameterMapping[argument.Parameters[0]] = projection.Projector;
            argExpr = Visit(argument.Body);
        }
        else if (!hasPredicateArg || useAlternateArg)
            argExpr = projection.Projector;

        var alias = Alias.New();

        ProjectColumns(projection.Projector, alias, projection.Select.Alias);

        var aggExpr = new AggregateExpression(returnType, aggregateName, argExpr, isDistinct);
        var colType = Context.Language.TypeSystem.ResolveColumnType(returnType);
        var select = new SelectExpression(alias, new ColumnDeclaration[] { new ColumnDeclaration(string.Empty, aggExpr, colType) }, projection.Select, null);

        if (isRoot)
        {
            var p = Expression.Parameter(typeof(IEnumerable<>).MakeGenericType(aggExpr.Type), "p");
            var gator = Expression.Lambda(Expression.Call(typeof(Enumerable), "Single", new Type[] { returnType }, p), p);

            return new ProjectionExpression(select, new ColumnExpression(returnType, Context.Language.TypeSystem.ResolveColumnType(returnType), alias, ""), gator);
        }

        var subquery = new ScalarExpression(returnType, select);

        if (!argumentWasPredicate && GroupByMap.TryGetValue(projection, out GroupByDescriptor? info))
        {
            if (argument is not null)
            {
                ParameterMapping[argument.Parameters[0]] = info.Element;
                argExpr = Visit(argument.Body);
            }
            else if (!hasPredicateArg || useAlternateArg)
                argExpr = info.Element;

            if (aggExpr is not null)
                aggExpr = new AggregateExpression(returnType, aggregateName, argExpr, isDistinct);

            if (projection == CurrentGroupElement)
                return aggExpr;

            return new AggregateSubqueryExpression(info.Alias, aggExpr, subquery);
        }

        return subquery;
    }

    private static LambdaExpression GetLambda(Expression expression)
    {
        while (expression.NodeType == ExpressionType.Quote)
            expression = ((UnaryExpression)expression).Operand;

        if (expression.NodeType == ExpressionType.Constant)
        {
            if (expression is not ConstantExpression constantExpression)
                throw new InvalidCastException(nameof(ConstantExpression));

            if (constantExpression.Value is not LambdaExpression lambdaExpression)
                throw new InvalidCastException(nameof(LambdaExpression));

            return lambdaExpression;
        }

        if (expression is not LambdaExpression lambda)
            throw new InvalidCastException(nameof(LambdaExpression));

        return lambda;
    }

    private Expression BindWhere(Expression source, LambdaExpression predicate)
    {
        var projection = VisitSequence(source);

        ParameterMapping[predicate.Parameters[0]] = projection.Projector;

        var where = Visit(predicate.Body);
        var alias = Alias.New();
        var pc = ProjectColumns(projection.Projector, alias, projection.Select.Alias);

        return new ProjectionExpression(new SelectExpression(alias, pc.Columns, projection.Select, where), pc.Projector);
    }

    private ProjectionExpression VisitSequence(Expression source) => ConvertToSequence(Visit(source));

    private static ProjectionExpression ConvertToSequence(Expression expression)
    {
        switch (expression.NodeType)
        {
            case (ExpressionType)DatabaseExpressionType.Projection:
                return (ProjectionExpression)expression;
            case ExpressionType.New:
                var nex = (NewExpression)expression;

                if (expression.Type.GetTypeInfo().IsGenericType && expression.Type.GetGenericTypeDefinition() == typeof(Grouping<,>))
                    return (ProjectionExpression)nex.Arguments[1];

                goto default;
            case ExpressionType.MemberAccess:

                if (expression.NodeType != ExpressionType.MemberAccess)
                    return ConvertToSequence(expression);

                goto default;
            default:

                if (GetNewExpression(expression) is Expression newExpression)
                {
                    expression = newExpression;

                    goto case ExpressionType.New;
                }

                throw new NotSupportedException($"The expression of type '{expression.Type}' is not a sequence");
        }
    }

    private static NewExpression? GetNewExpression(Expression expression)
    {
        while (expression.NodeType == ExpressionType.Convert || expression.NodeType == ExpressionType.ConvertChecked)
            expression = ((UnaryExpression)expression).Operand;

        return expression as NewExpression;
    }

    private Expression BindSelect(Expression source, LambdaExpression selector)
    {
        var projection = VisitSequence(source);

        ParameterMapping[selector.Parameters[0]] = projection.Projector;

        var expression = Visit(selector.Body);
        var alias = Alias.New();
        var pc = ProjectColumns(expression, alias, projection.Select.Alias);

        return new ProjectionExpression(new SelectExpression(alias, pc.Columns, projection.Select, null), pc.Projector);
    }

    private ProjectedColumns ProjectColumns(Expression expression, Alias alias, params Alias[] existingAliases)
    {
        return ColumnProjector.ProjectColumns(Context.Language, expression, null, alias, existingAliases);
    }

    private Expression BindSelectMany(Expression source, LambdaExpression collectionSelector, LambdaExpression resultSelector)
    {
        var projection = VisitSequence(source);

        ParameterMapping[collectionSelector.Parameters[0]] = projection.Projector;

        var collection = collectionSelector.Body;
        var defaultIfEmpty = false;
        var mcs = collection as MethodCallExpression;

        if (mcs is not null && string.Equals(mcs.Method.Name, "DefaultIfEmpty", StringComparison.Ordinal) && mcs.Arguments.Count == 1 && mcs.Method.IsInQueryable())
        {
            collection = mcs.Arguments[0];
            defaultIfEmpty = true;
        }

        var collectionProjection = VisitSequence(collection);
        var isTable = collectionProjection.Select.From is TableExpression;
        var joinType = isTable ? JoinType.CrossJoin : defaultIfEmpty ? JoinType.OuterApply : JoinType.CrossApply;

        if (joinType == JoinType.OuterApply)
            collectionProjection = Context.Language.AddOuterJoinTest(collectionProjection);

        var join = new JoinExpression(joinType, projection.Select, collectionProjection.Select, null);
        var alias = Alias.New();
        ProjectedColumns pc;

        if (resultSelector is null)
            pc = ProjectColumns(collectionProjection.Projector, alias, projection.Select.Alias, collectionProjection.Select.Alias);
        else
        {
            ParameterMapping[resultSelector.Parameters[0]] = projection.Projector;
            ParameterMapping[resultSelector.Parameters[1]] = collectionProjection.Projector;

            var result = Visit(resultSelector.Body);

            pc = ProjectColumns(result, alias, projection.Select.Alias, collectionProjection.Select.Alias);
        }

        return new ProjectionExpression(new SelectExpression(alias, pc.Columns, join, null), pc.Projector);
    }

    private Expression BindJoin(Expression outerSource, Expression innerSource, LambdaExpression outerKey, LambdaExpression innerKey, LambdaExpression resultSelector)
    {
        if (VisitSequence(outerSource) is not ProjectionExpression outerProjection)
            throw new NullReferenceException(nameof(outerProjection));

        if (VisitSequence(innerSource) is not ProjectionExpression innerProjection)
            throw new NullReferenceException(nameof(innerProjection));

        ParameterMapping[outerKey.Parameters[0]] = outerProjection.Projector;

        var outerKeyExpr = Visit(outerKey.Body);

        ParameterMapping[innerKey.Parameters[0]] = innerProjection.Projector;

        var innerKeyExpr = Visit(innerKey.Body);

        ParameterMapping[resultSelector.Parameters[0]] = outerProjection.Projector;
        ParameterMapping[resultSelector.Parameters[1]] = innerProjection.Projector;

        if (Visit(resultSelector.Body) is not Expression resultExpression)
            throw new NullReferenceException(nameof(resultExpression));

        var join = new JoinExpression(JoinType.InnerJoin, outerProjection.Select, innerProjection.Select, outerKeyExpr.Equal(innerKeyExpr));
        var alias = Alias.New();
        var pc = ProjectColumns(resultExpression, alias, outerProjection.Select.Alias, innerProjection.Select.Alias);

        return new ProjectionExpression(new SelectExpression(alias, pc.Columns, join, null), pc.Projector);
    }

    private Expression BindGroupJoin(MethodInfo groupJoinMethod, Expression outerSource, Expression innerSource, LambdaExpression outerKey,
        LambdaExpression innerKey, LambdaExpression resultSelector)
    {
        /*
		 * A database will treat this no differently than a SelectMany w/ result selector, so just use that translation instead
		 */
        var args = groupJoinMethod.GetGenericArguments();
        var outerProjection = VisitSequence(outerSource);

        ParameterMapping[outerKey.Parameters[0]] = outerProjection.Projector;

        var predicateLambda = Expression.Lambda(innerKey.Body.Equal(outerKey.Body), innerKey.Parameters[0]);
        var callToWhere = Expression.Call(typeof(Enumerable), "Where", new Type[] { args[1] }, innerSource, predicateLambda);
        var group = Visit(callToWhere);

        ParameterMapping[resultSelector.Parameters[0]] = outerProjection.Projector;

        if (group is not null)
            ParameterMapping[resultSelector.Parameters[1]] = group;

        var resultExpr = Visit(resultSelector.Body);
        var alias = Alias.New();
        var pc = ProjectColumns(resultExpr, alias, outerProjection.Select.Alias);

        return new ProjectionExpression(new SelectExpression(alias, pc.Columns, outerProjection.Select, null), pc.Projector);
    }

    private Expression BindOrderBy(Expression source, LambdaExpression orderSelector, OrderType orderType)
    {
        var myThenBys = ThenBys;

        ThenBys = null;

        var projection = VisitSequence(source);

        ParameterMapping[orderSelector.Parameters[0]] = projection.Projector;

        var orderings = new List<OrderExpression> { new OrderExpression(orderType, Visit(orderSelector.Body)) };

        if (myThenBys is not null)
        {
            for (var i = myThenBys.Count - 1; i >= 0; i--)
            {
                var tb = myThenBys[i];
                var lambda = (LambdaExpression)tb.Expression;

                ParameterMapping[lambda.Parameters[0]] = projection.Projector;

                orderings.Add(new OrderExpression(tb.OrderType, Visit(lambda.Body)));
            }
        }

        var alias = Alias.New();
        var pc = ProjectColumns(projection.Projector, alias, projection.Select.Alias);

        return new ProjectionExpression(new SelectExpression(alias, pc.Columns, projection.Select, null, orderings.AsReadOnly(), null), pc.Projector);
    }

    private Expression BindThenBy(Expression source, LambdaExpression orderSelector, OrderType orderType)
    {
        ThenBys ??= new List<OrderExpression>();

        ThenBys.Add(new OrderExpression(orderType, orderSelector));

        return Visit(source);
    }

    private Expression BindGroupBy(Expression source, LambdaExpression keySelector, LambdaExpression elementSelector, LambdaExpression resultSelector)
    {
        var projection = VisitSequence(source);

        ParameterMapping[keySelector.Parameters[0]] = projection.Projector;

        var keyExpr = Visit(keySelector.Body);
        var elemExpr = projection.Projector;

        if (elementSelector is not null)
        {
            ParameterMapping[elementSelector.Parameters[0]] = projection.Projector;

            elemExpr = Visit(elementSelector.Body);
        }

        var keyProjection = ProjectColumns(keyExpr, projection.Select.Alias, projection.Select.Alias);
        var groupExprs = keyProjection.Columns.Select(c => c.Expression).ToArray();
        var subqueryBasis = VisitSequence(source);

        ParameterMapping[keySelector.Parameters[0]] = subqueryBasis.Projector;

        var subqueryKey = Visit(keySelector.Body);
        var subqueryKeyPC = ProjectColumns(subqueryKey, subqueryBasis.Select.Alias, subqueryBasis.Select.Alias);
        var subqueryGroupExprs = subqueryKeyPC.Columns.Select(c => c.Expression).ToArray();
        var subqueryCorrelation = BuildPredicateWithNullsEqual(subqueryGroupExprs, groupExprs);
        var subqueryElemExpr = subqueryBasis.Projector;

        if (elementSelector is not null)
        {
            ParameterMapping[elementSelector.Parameters[0]] = subqueryBasis.Projector;

            subqueryElemExpr = Visit(elementSelector.Body);
        }

        var elementAlias = Alias.New();
        var elementPC = ProjectColumns(subqueryElemExpr, elementAlias, subqueryBasis.Select.Alias);
        var elementSubquery = new ProjectionExpression(new SelectExpression(elementAlias, elementPC.Columns, subqueryBasis.Select, subqueryCorrelation), elementPC.Projector);
        var alias = Alias.New();
        var info = new GroupByDescriptor(alias, elemExpr);

        GroupByMap.Add(elementSubquery, info);

        Expression resultExpr;

        if (resultSelector is not null)
        {
            var saveGroupElement = CurrentGroupElement;

            CurrentGroupElement = elementSubquery;

            ParameterMapping[resultSelector.Parameters[0]] = keyProjection.Projector;
            ParameterMapping[resultSelector.Parameters[1]] = elementSubquery;

            resultExpr = Visit(resultSelector.Body);

            CurrentGroupElement = saveGroupElement;
        }
        else
        {
            resultExpr = Expression.New(typeof(Grouping<,>).MakeGenericType(keyExpr.Type, subqueryElemExpr.Type).GetTypeInfo().DeclaredConstructors.First(),
                    new Expression[] { keyExpr, elementSubquery });

            resultExpr = Expression.Convert(resultExpr, typeof(IGrouping<,>).MakeGenericType(keyExpr.Type, subqueryElemExpr.Type));
        }

        var pc = ProjectColumns(resultExpr, alias, projection.Select.Alias);

        var newResult = GetNewExpression(pc.Projector);

        if (newResult is not null && newResult.Type.GetTypeInfo().IsGenericType && newResult.Type.GetGenericTypeDefinition() == typeof(Grouping<,>))
        {
            var projectedElementSubquery = newResult.Arguments[1];

            GroupByMap.Add(projectedElementSubquery, info);
        }

        return new ProjectionExpression(new SelectExpression(alias, pc.Columns, projection.Select, null, null, groupExprs), pc.Projector);
    }

    private Expression BindDistinct(Expression source)
    {
        var projection = VisitSequence(source);
        var alias = Alias.New();
        var pc = ColumnProjector.ProjectColumns(Context.Language, ProjectionAffinity.Server, projection.Projector, null, alias, projection.Select.Alias);

        return new ProjectionExpression(new SelectExpression(alias, pc.Columns, projection.Select, null, null, null, true, null, null, false), pc.Projector);
    }

    private Expression BindTake(Expression source, Expression take)
    {
        var projection = VisitSequence(source);

        take = Visit(take);

        var alias = Alias.New();
        var pc = ProjectColumns(projection.Projector, alias, projection.Select.Alias);

        return new ProjectionExpression(new SelectExpression(alias, pc.Columns, projection.Select, null, null, null, false, null, take, false), pc.Projector);
    }

    private Expression BindSkip(Expression source, Expression skip)
    {
        var projection = VisitSequence(source);

        skip = Visit(skip);

        var alias = Alias.New();
        var pc = ProjectColumns(projection.Projector, alias, projection.Select.Alias);

        return new ProjectionExpression(new SelectExpression(alias, pc.Columns, projection.Select, null, null, null, false, skip, null, false), pc.Projector);
    }

    private Expression BindFirst(Expression source, LambdaExpression predicate, string kind, bool isRoot)
    {
        var projection = VisitSequence(source);
        Expression? where = null;

        if (predicate is not null)
        {
            ParameterMapping[predicate.Parameters[0]] = projection.Projector;
            where = Visit(predicate.Body);
        }

        var isFirst = kind.StartsWith("First");
        var isLast = kind.StartsWith("Last");
        var take = (isFirst || isLast) ? Expression.Constant(1) : null;

        if (take is not null || where is not null)
        {
            var alias = Alias.New();
            var pc = ProjectColumns(projection.Projector, alias, projection.Select.Alias);
            projection = new ProjectionExpression(new SelectExpression(alias, pc.Columns, projection.Select, where, null, null, false, null, take, isLast), pc.Projector);
        }

        if (isRoot)
        {
            var elementType = projection.Projector.Type;
            var p = Expression.Parameter(typeof(IEnumerable<>).MakeGenericType(elementType), "p");
            var gator = Expression.Lambda(Expression.Call(typeof(Enumerable), kind, new Type[] { elementType }, p), p);

            return new ProjectionExpression(projection.Select, projection.Projector, gator);
        }

        return projection;
    }

    private Expression BindAnyAll(Expression source, MethodInfo method, LambdaExpression predicate, bool isRoot)
    {
        var isAll = string.Equals(method.Name, "All", StringComparison.Ordinal);
        var constSource = source as ConstantExpression;

        if (constSource is not null && !IsQuery(constSource))
        {
            System.Diagnostics.Debug.Assert(!isRoot);
            Expression where = null;

            foreach (object value in (IEnumerable)constSource.Value)
            {
                var expr = Expression.Invoke(predicate, Expression.Constant(value, predicate.Parameters[0].Type));

                if (where is null)
                    where = expr;
                else if (isAll)
                    where = where.And(expr);
                else
                    where = where.Or(expr);
            }

            return Visit(where);
        }
        else
        {
            if (isAll)
                predicate = Expression.Lambda(Expression.Not(predicate.Body), predicate.Parameters.ToArray());

            if (predicate is not null)
                source = Expression.Call(typeof(Enumerable), "Where", method.GetGenericArguments(), source, predicate);

            var projection = VisitSequence(source);
            Expression result = new ExistsExpression(projection.Select);

            if (isAll)
                result = Expression.Not(result);

            if (isRoot)
            {
                if (Context.Language.AllowSubqueryInSelectWithoutFrom)
                    return GetSingletonSequence(result, "SingleOrDefault");
                else
                {
                    var colType = Context.Language.TypeSystem.ResolveColumnType(typeof(int));
                    var newSelect = projection.Select.SetColumns(new[] { new ColumnDeclaration("value", new AggregateExpression(typeof(int), "Count", null, false), colType) });
                    var colx = new ColumnExpression(typeof(int), colType, newSelect.Alias, "value");
                    var exp = isAll ? colx.Equal(Expression.Constant(0)) : colx.GreaterThan(Expression.Constant(0));

                    return new ProjectionExpression(newSelect, exp, Aggregator.GetAggregator(typeof(bool), typeof(IEnumerable<bool>)));
                }
            }

            return result;
        }
    }

    private Expression BindContains(Expression source, Expression match, bool isRoot)
    {
        var constSource = source as ConstantExpression;

        if (constSource is not null && !IsQuery(constSource))
        {
            System.Diagnostics.Debug.Assert(!isRoot);
            var values = new List<Expression>();

            foreach (object value in (IEnumerable)constSource.Value)
                values.Add(Expression.Constant(Convert.ChangeType(value, match.Type), match.Type));

            match = Visit(match);

            return new InExpression(match, values);
        }
        else if (isRoot && !Context.Language.AllowSubqueryInSelectWithoutFrom)
        {
            var p = Expression.Parameter(Enumerables.GetEnumerableElementType(source.Type), "x");
            var predicate = Expression.Lambda(p.Equal(match), p);
            var exp = Expression.Call(typeof(Queryable), "Any", new Type[] { p.Type }, source, predicate);

            Expression = exp;

            return Visit(exp);
        }
        else
        {
            var projection = VisitSequence(source);

            match = Visit(match);

            var result = new InExpression(match, projection.Select);

            if (isRoot)
                return GetSingletonSequence(result, "SingleOrDefault");

            return result;
        }
    }

    private Expression BindCast(Expression source, Type targetElementType)
    {
        var projection = VisitSequence(source);
        var elementType = GetTrueUnderlyingType(projection.Projector);

        if (!targetElementType.IsAssignableFrom(elementType))
            throw new InvalidOperationException($"Cannot cast elements from type '{elementType}' to type '{targetElementType}'");

        return projection;
    }

    private Expression BindIntersect(Expression outerSource, Expression innerSource, bool negate)
    {
        /*
		 * SELECT * FROM outer WHERE EXISTS(SELECT * FROM inner WHERE inner = outer))
		 */
        var outerProjection = VisitSequence(outerSource);
        var innerProjection = VisitSequence(innerSource);

        Expression exists = new ExistsExpression(new SelectExpression(Alias.New(), null, innerProjection.Select, innerProjection.Projector.Equal(outerProjection.Projector)));

        if (negate)
            exists = Expression.Not(exists);

        var alias = Alias.New();
        var pc = ProjectColumns(outerProjection.Projector, alias, outerProjection.Select.Alias);

        return new ProjectionExpression(new SelectExpression(alias, pc.Columns, outerProjection.Select, exists), pc.Projector, outerProjection.Aggregator);
    }

    private Expression BindReverse(Expression expression)
    {
        var projection = VisitSequence(expression);
        var alias = Alias.New();
        var pc = ProjectColumns(projection.Projector, alias, projection.Select.Alias);

        return new ProjectionExpression(new SelectExpression(alias, pc.Columns, projection.Select, null).SetReverse(true), pc.Projector);
    }

    private static Expression? BuildPredicateWithNullsEqual(IEnumerable<Expression> source1, IEnumerable<Expression> source2)
    {
        var en1 = source1.GetEnumerator();
        var en2 = source2.GetEnumerator();
        Expression? result = null;

        while (en1.MoveNext() && en2.MoveNext())
        {
            var compare = Expression.Or(new IsNullExpression(en1.Current).And(new IsNullExpression(en2.Current)), en1.Current.Equal(en2.Current));

            result = (result is null) ? compare : result.And(compare);
        }

        return result;
    }

    private static bool IsQuery(Expression expression)
    {
        var elementType = Enumerables.GetEnumerableElementType(expression.Type);

        return elementType is not null && typeof(IQueryable<>).MakeGenericType(elementType).IsAssignableFrom(expression.Type);
    }

    private Expression GetSingletonSequence(Expression expr, string aggregator)
    {
        var p = Expression.Parameter(typeof(IEnumerable<>).MakeGenericType(expr.Type), "p");
        LambdaExpression gator = null;

        if (aggregator is not null)
            gator = Expression.Lambda(Expression.Call(typeof(Enumerable), aggregator, new Type[] { expr.Type }, p), p);

        var alias = Alias.New();
        var colType = Context.Language.TypeSystem.ResolveColumnType(expr.Type);
        var select = new SelectExpression(alias, new[] { new ColumnDeclaration("value", expr, colType) }, null, null);

        return new ProjectionExpression(select, new ColumnExpression(expr.Type, colType, alias, "value"), gator);
    }

    private static Type GetTrueUnderlyingType(Expression expression)
    {
        while (expression.NodeType == ExpressionType.Convert)
            expression = ((UnaryExpression)expression).Operand;

        return expression.Type;
    }

    private static bool MembersMatch(MemberInfo a, MemberInfo b)
    {
        if (a.Name == b.Name)
            return true;

        if (a is MethodInfo && b is PropertyInfo info)
            return a.Name == info.GetMethod.Name;
        else if (a is PropertyInfo info1 && b is MethodInfo)
            return info1.GetMethod.Name == b.Name;

        return false;
    }

    private static object? GetValue(object instance, MemberInfo member)
    {
        var fi = member as FieldInfo;

        if (fi is not null)
            return fi.GetValue(instance);

        var pi = member as PropertyInfo;

        if (pi is not null)
            return pi.GetValue(instance, null);

        return null;
    }

    private static object? GetDefault(Type type)
    {
        if (!type.GetTypeInfo().IsValueType || Nullables.IsNullableType(type))
            return null;
        else
            return Activator.CreateInstance(type);
    }

    protected override Expression VisitConstant(ConstantExpression expression)
    {
        if (IsQuery(expression))
        {
            var q = (IQueryable)expression.Value;

            if (q.Expression.NodeType == ExpressionType.Constant)
            {
                var mapping = MappingsCache.Get(q.ElementType);

                return VisitSequence(mapping.CreateExpression(Context));
            }
            else
            {
                var pev = PartialEvaluator.Eval(Context, q.Expression);

                return Visit(pev);
            }
        }

        return expression;
    }

    protected override Expression VisitParameter(ParameterExpression expression)
    {
        if (ParameterMapping.TryGetValue(expression, out Expression? e))
            return e;

        return expression;
    }

    protected override Expression VisitInvocation(InvocationExpression expression)
    {
        if (expression.Expression is LambdaExpression lambda)
        {
            for (var i = 0; i < lambda.Parameters.Count; i++)
                ParameterMapping[lambda.Parameters[i]] = expression.Arguments[i];

            return Visit(lambda.Body);
        }

        return base.VisitInvocation(expression);
    }

    protected override Expression VisitMemberAccess(MemberExpression expression)
    {
        if (expression.Expression is not null
            && expression.Expression.NodeType == ExpressionType.Parameter
            && !ParameterMapping.ContainsKey((ParameterExpression)expression.Expression)
            && IsQuery(expression))
        {
            //var mapping = MappingsCache.Get();


            //  return this.VisitSequence(MappingsCache.Mapper.GetQueryExpression(Mapper.Mapping.GetMapping(expression.Member)));
        }

        var source = Visit(expression.Expression);

        if (Context.Language.IsAggregate(expression.Member) && IsRemoteQuery(source))
            return BindAggregate(expression.Expression, expression.Member.Name, Members.GetMemberType(expression.Member), null, expression == Expression);

        var result = Bind(source, expression.Member);
        var mex = result as MemberExpression;

        if (mex is not null && mex.Member == expression.Member && mex.Expression == expression.Expression)
            return expression;

        return result;
    }

    private bool IsRemoteQuery(Expression expression)
    {
        if (expression.NodeType.IsDatabaseExpression())
            return true;

        switch (expression.NodeType)
        {
            case ExpressionType.MemberAccess:
                return IsRemoteQuery(((MemberExpression)expression).Expression);
            case ExpressionType.Call:
                var mc = (MethodCallExpression)expression;

                if (mc.Object is not null)
                    return IsRemoteQuery(mc.Object);
                else if (mc.Arguments.Count > 0)
                    return IsRemoteQuery(mc.Arguments[0]);
                break;
        }

        return false;
    }
}