Add merge operation

README.md

@@ -39,6 +39,7 @@ Available operations:
 | ------------- | ------------- |
 | set(path, value)  | assign field to a particular value  |
 | del(path)  | delete a key  |
+| merge(path, value)  | merge json value into the path. Only JSON values are allowed  |
 
 ## Examples:
 

pkg/operations/merge.go

@@ -0,0 +1,70 @@
+package operations
+
+import (
+	"github.com/can3p/sackmesser/pkg/traverse/types"
+	"github.com/pkg/errors"
+)
+
+func Merge(root types.Node, path []string, args ...any) error {
+	if len(args) != 1 {
+		return errors.Errorf("set operation expects one argument")
+	}
+
+	value, ok := args[0].(map[string]any)
+	if !ok {
+		return errors.Errorf("Merge expects a json as an argument")
+	}
+
+	if len(path) == 1 {
+		fieldName := path[0]
+		fieldVal, err := root.GetField(fieldName)
+
+		if err == types.ErrFieldMissing {
+			return root.SetField(fieldName, value)
+		}
+
+		if err != nil {
+			return err
+		}
+
+		fieldVal = mergeObject(fieldVal, value)
+		return root.SetField(fieldName, fieldVal)
+	}
+
+	node, err := root.Visit(path[0])
+
+	if err != nil {
+		return err
+	}
+
+	return Merge(node, path[1:], value)
+}
+
+func mergeObject(existingValue any, value map[string]any) any {
+	typed, ok := existingValue.(map[string]any)
+
+	if !ok {
+		return value
+	}
+
+	for fieldName, value := range value {
+		subfieldValue, exists := typed[fieldName]
+
+		if !exists {
+			typed[fieldName] = value
+			continue
+		}
+
+		typedSubfieldValue, subfieldIsMap := subfieldValue.(map[string]any)
+		typedNewValue, newValueIsMap := value.(map[string]any)
+
+		if !subfieldIsMap || !newValueIsMap {
+			typed[fieldName] = value
+			continue
+		}
+
+		typed[fieldName] = mergeObject(typedSubfieldValue, typedNewValue)
+	}
+
+	return typed
+}

pkg/operations/merge_test.go

@@ -0,0 +1,68 @@
+package operations
+
+import (
+	"testing"
+
+	"github.com/alecthomas/assert/v2"
+	"github.com/can3p/sackmesser/pkg/traverse/simplejson"
+)
+
+func TestMergeOperation(t *testing.T) {
+	jstr := `{ "abc": { "def": { "cfa": [1, 2, 3] } } }`
+
+	examples := []struct {
+		description string
+		path        []string
+		arg         any
+		initial     string
+		expected    string
+		isErr       bool
+	}{
+		{
+			description: "add new field to the object",
+			path:        []string{"abc", "def"},
+			arg:         map[string]any{"added": true},
+			initial:     jstr,
+			expected:    `{ "abc": { "def": { "cfa": [ 1, 2, 3 ], "added": true } } }`,
+		},
+		{
+			description: "scalar value should produce an error",
+			path:        []string{"abc", "def"},
+			arg:         true,
+			initial:     jstr,
+			isErr:       true,
+		},
+		{
+			description: "non existant field is just set",
+			path:        []string{"abc", "new field"},
+			arg:         map[string]any{"added": true},
+			initial:     jstr,
+			expected:    `{ "abc": { "def": { "cfa": [ 1, 2, 3 ] },  "new field": { "added": true } } }`,
+		},
+		{
+			description: "non object target field means set",
+			path:        []string{"abc", "def"},
+			arg:         map[string]any{"added": true},
+			initial:     `{ "abc": { "def": true } }`,
+			expected:    `{ "abc": { "def": { "added": true } } }`,
+		},
+	}
+
+	for idx, ex := range examples {
+		node := simplejson.MustParse([]byte(ex.initial))
+
+		err := Merge(node, ex.path, ex.arg)
+
+		if ex.isErr {
+			assert.Error(t, err, "[Ex %d - %s]", idx+1, ex.description)
+			continue
+		} else {
+			assert.NoError(t, err, "[Ex %d - %s]", idx+1, ex.description)
+		}
+
+		expected := simplejson.MustParse([]byte(ex.expected))
+
+		assert.Equal(t, expected.Value(), node.Value(), "[Ex %d - %s]", idx+1, ex.description)
+	}
+
+}

pkg/operations/parse.go

@@ -29,8 +29,9 @@ func (op *OpInstance) Apply(root types.Node) error {
 }
 
 var operations = map[string]Operation{
-	"set": Set,
-	"del": Delete,
+	"set":   Set,
+	"del":   Delete,
+	"merge": Merge,
 }
 
 //nolint:govet

pkg/traverse/simplejson/simplejson.go

@@ -70,6 +70,20 @@ func (n *jnode) Visit(field string) (types.Node, error) {
 	panic("unreachable")
 }
 
+func (n *jnode) GetField(field string) (any, error) {
+	typed, ok := n.v.(map[string]any)
+
+	if !ok {
+		return nil, types.ErrWrongVisit
+	}
+
+	if value, ok := typed[field]; ok {
+		return value, nil
+	}
+
+	return nil, types.ErrFieldMissing
+}
+
 func (n *jnode) SetField(field string, value any) error {
 	switch n.NodeType() {
 	case types.NodeTypeNull:

pkg/traverse/simpleyaml/simpleyaml.go

@@ -71,6 +71,20 @@ func (n *jnode) Visit(field string) (types.Node, error) {
 	panic("unreachable")
 }
 
+func (n *jnode) GetField(field string) (any, error) {
+	typed, ok := n.v.(map[string]any)
+
+	if !ok {
+		return nil, types.ErrWrongVisit
+	}
+
+	if value, ok := typed[field]; ok {
+		return value, nil
+	}
+
+	return nil, types.ErrFieldMissing
+}
+
 func (n *jnode) SetField(field string, value any) error {
 	switch n.NodeType() {
 	case types.NodeTypeNull:

pkg/traverse/types/types.go

@@ -21,6 +21,7 @@ type Node interface {
 	Visit(field string) (Node, error)
 	NodeType() NodeType
 	Value() any
+	GetField(field string) (any, error)
 	SetField(field string, value any) error
 	DeleteField(field string) error
 	Serialize() ([]byte, error)