Fix panic on evaluate functions

pkg/pattern/template/point.go

@@ -19,6 +19,8 @@ var (
 
 	// ErrRelativePointRecursion is returned when a points are relative to itself.
 	ErrRelativePointRecursion = errors.New("point cannot be relative to itself")
+
+	ErrInvalidArguments = errors.New("invalid arguments to call function")
 )
 
 // Points contains a map with points.
@@ -40,52 +42,50 @@ var ErrInvalidPointID = errors.New("type cannot be converted to a PointID")
 func (p Points) Functions(pat *pattern.Pattern) map[string]govaluate.ExpressionFunction {
 	return map[string]govaluate.ExpressionFunction{
 		"DistanceBetween": func(args ...interface{}) (interface{}, error) {
-			id0, err := toPointID(args[0])
-			if err != nil {
-				return nil, fmt.Errorf("parsing args[0] to pointID: %w", err)
-			}
-
-			id1, err := toPointID(args[1])
-			if err != nil {
-				return nil, fmt.Errorf("parsing args[0] to pointID: %w", err)
-			}
-
-			p0, err := p.getOrCreate(id0, pat, 0)
-			if err != nil {
-				return nil, fmt.Errorf("get or create point %q: %w", id0, err)
+			if len(args) != 2 {
+				return nil, fmt.Errorf("function DistanceBetween() requires 2 arguments: %w",
+					ErrInvalidArguments)
 			}
 
-			p1, err := p.getOrCreate(id1, pat, 0)
+			points, err := p.getOrCreateFromArgs(pat, args...)
 			if err != nil {
-				return nil, fmt.Errorf("get or create point %q: %w", id1, err)
+				return nil, err
 			}
-
-			return p0.Position().Distance(p1.Position()), nil
+			return points[0].Position().Distance(points[1].Position()), nil
 		},
 		"AngleBetween": func(args ...interface{}) (interface{}, error) {
-			id0, err := toPointID(args[0])
-			if err != nil {
-				return nil, fmt.Errorf("parsing args[0] to pointID: %w", err)
+			if len(args) != 2 {
+				return nil, fmt.Errorf("function AngleBetween() requires 2 arguments: %w",
+					ErrInvalidArguments)
 			}
 
-			id1, err := toPointID(args[1])
+			points, err := p.getOrCreateFromArgs(pat, args...)
 			if err != nil {
-				return nil, fmt.Errorf("parsing args[0] to pointID: %w", err)
+				return nil, err
 			}
 
-			p0, err := p.getOrCreate(id0, pat, 0)
-			if err != nil {
-				return nil, fmt.Errorf("get or create point %q: %w", id0, err)
-			}
+			return points[0].Vector().AngleBetween(points[1].Vector()), nil
+		},
+	}
+}
 
-			p1, err := p.getOrCreate(id1, pat, 0)
-			if err != nil {
-				return nil, fmt.Errorf("get or create point %q: %w", id1, err)
-			}
+func (p Points) getOrCreateFromArgs(pat *pattern.Pattern, args ...interface{}) ([]point.Point, error) {
+	points := make([]point.Point, 0, len(args))
+	for i, arg := range args {
+		id, err := toPointID(arg)
+		if err != nil {
+			return nil, fmt.Errorf("parsing args[%d] to pointID: %w", i, err)
+		}
 
-			return p0.Vector().AngleBetween(p1.Vector()), nil
-		},
+		newPoint, err := p.getOrCreate(id, pat, 0)
+		if err != nil {
+			return nil, fmt.Errorf("get or create point %q: %w", id, err)
+		}
+
+		points = append(points, newPoint)
 	}
+
+	return points, nil
 }
 
 func toPointID(arg interface{}) (point.ID, error) {
@@ -111,9 +111,19 @@ type BetweenPoint struct {
 func (p Points) evaluationFunctions() map[string]govaluate.ExpressionFunction {
 	return map[string]govaluate.ExpressionFunction{
 		"acos": func(args ...interface{}) (interface{}, error) {
+			if len(args) != 1 {
+				return nil, fmt.Errorf("function acos() requires 1 argument: %w",
+					ErrInvalidArguments)
+			}
+
 			return math.Acos(args[0].(float64)), nil
 		},
 		"atan2": func(args ...interface{}) (interface{}, error) {
+			if len(args) != 2 {
+				return nil, fmt.Errorf("function atan2() requires 2 arguments: %w",
+					ErrInvalidArguments)
+			}
+
 			return math.Atan2(args[0].(float64), args[1].(float64)), nil
 		},
 	}