Add not func

Author: TomWright

func.go

@@ -58,6 +58,7 @@ func standardFunctions() *FunctionCollection {
 		LessThanFunc,
 		AndFunc,
 		OrFunc,
+		NotFunc,
 
 		// Metadata
 		MetadataFunc,

func_not.go

@@ -0,0 +1,48 @@
+package dasel
+
+import (
+	"fmt"
+	"reflect"
+)
+
+var NotFunc = BasicFunction{
+	name: "not",
+	runFn: func(c *Context, s *Step, args []string) (Values, error) {
+		if err := requireXOrMoreArgs("filter", args, 1); err != nil {
+			return nil, err
+		}
+
+		input := c.inputValue(s)
+
+		runComparison := func(value Value, selector string) (bool, error) {
+			gotValues, err := performSubQuery(c, value, selector)
+			if err != nil {
+				return false, err
+			}
+
+			if len(gotValues) > 1 {
+				return false, fmt.Errorf("not expects selector to return a single value")
+			}
+
+			if len(gotValues) == 0 {
+				return false, nil
+			}
+
+			return IsTruthy(gotValues[0].Interface()), nil
+		}
+
+		res := make(Values, 0)
+
+		for _, val := range input {
+			for _, selector := range args {
+				truthy, err := runComparison(val, selector)
+				if err != nil {
+					return nil, err
+				}
+				res = append(res, Value{Value: reflect.ValueOf(!truthy)})
+			}
+		}
+
+		return res, nil
+	},
+}

func_not_test.go

@@ -0,0 +1,45 @@
+package dasel
+
+import (
+	"testing"
+)
+
+func TestNotFunc(t *testing.T) {
+
+	t.Run(
+		"Single Equal",
+		selectTest(
+			"name.all().not(equal(key(),first))",
+			map[string]interface{}{
+				"name": map[string]interface{}{
+					"first": "Tom",
+					"last":  "Wright",
+				},
+			},
+			[]interface{}{
+				false,
+				true,
+			},
+		),
+	)
+
+	t.Run(
+		"Not Banned",
+		selectTest(
+			"all().filter(not(equal(banned,true))).name",
+			[]map[string]interface{}{
+				{
+					"name":   "Tom",
+					"banned": true,
+				},
+				{
+					"name":   "Jess",
+					"banned": false,
+				},
+			},
+			[]interface{}{
+				"Jess",
+			},
+		),
+	)
+}