/// <summary>
/// Provided two composite types, determine if they "overlap". Two composite
/// types overlap when the Sets of possible concrete types for each intersect.
///
/// This is often used to determine if a fragment of a given type could possibly
/// be visited in a context of another type.
///
/// This function is commutative.
/// </summary>
public static bool DoTypesOverlap(this ISchema schema, GraphType typeA, GraphType typeB)
{
if (typeA.Equals(typeB))
{
return(true);
}
var a = typeA as GraphQLAbstractType;
var b = typeB as GraphQLAbstractType;
if (a != null)
{
if (b != null)
{
return(a.PossibleTypes.Any(type => b.IsPossibleType(type)));
}
return(a.IsPossibleType(typeB));
}
if (b != null)
{
return(b.IsPossibleType(typeA));
}
return(false);
}
/// <summary>
/// Provided a type and a super type, return true if the first type is either
/// equal or a subset of the second super type (covariant).
/// </summary>
public static bool IsSubtypeOf(this GraphType maybeSubType, GraphType superType, ISchema schema)
{
if (maybeSubType.Equals(superType))
{
return(true);
}
// If superType is non-null, maybeSubType must also be nullable.
if (superType is NonNullGraphType)
{
if (maybeSubType is NonNullGraphType)
{
var sub = (NonNullGraphType)maybeSubType;
var sup = (NonNullGraphType)superType;
return(IsSubtypeOf(schema.FindType(sub.Type), schema.FindType(sup.Type), schema));
}
return(false);
}
else if (maybeSubType is NonNullGraphType)
{
var sub = (NonNullGraphType)maybeSubType;
return(IsSubtypeOf(schema.FindType(sub.Type), superType, schema));
}
// If superType type is a list, maybeSubType type must also be a list.
if (superType is ListGraphType)
{
if (maybeSubType is ListGraphType)
{
var sub = (ListGraphType)maybeSubType;
var sup = (ListGraphType)superType;
return(IsSubtypeOf(schema.FindType(sub.Type), schema.FindType(sup.Type), schema));
}
return(false);
}
else if (maybeSubType is ListGraphType)
{
// If superType is not a list, maybeSubType must also be not a list.
return(false);
}
// If superType type is an abstract type, maybeSubType type may be a currently
// possible object type.
if (superType is GraphQLAbstractType &&
maybeSubType is ObjectGraphType)
{
return(((GraphQLAbstractType)superType).IsPossibleType(maybeSubType));
}
return(false);
}