feat: add merge errors for incompatible values (#9)

mergevalues.go

@@ -0,0 +1,123 @@
+package astjson
+
+import (
+	"bytes"
+	"errors"
+)
+
+var (
+	ErrMergeDifferentTypes        = errors.New("cannot merge different types")
+	ErrMergeDifferingArrayLengths = errors.New("cannot merge arrays of differing lengths")
+	ErrMergeUnknownType           = errors.New("cannot merge unknown type")
+)
+
+func MergeValues(a, b *Value) (v *Value, changed bool, err error) {
+	if a == nil {
+		return b, true, nil
+	}
+	if b == nil {
+		return a, false, nil
+	}
+	aBool, bBool := a.Type() == TypeTrue || a.Type() == TypeFalse, b.Type() == TypeTrue || b.Type() == TypeFalse
+	booleans := aBool && bBool
+	oneIsNull := a.Type() == TypeNull || b.Type() == TypeNull
+	if a.Type() != b.Type() && !booleans && !oneIsNull {
+		return nil, false, ErrMergeDifferentTypes
+	}
+	if b.Type() == TypeNull && a.Type() != TypeNull {
+		return b, true, nil
+	}
+	switch a.Type() {
+	case TypeObject:
+		ao, _ := a.Object()
+		bo, _ := b.Object()
+		ao.unescapeKeys()
+		bo.unescapeKeys()
+		for i := range bo.kvs {
+			k := bo.kvs[i].k
+			r := bo.kvs[i].v
+			l := ao.Get(k)
+			if l == nil {
+				ao.Set(k, r)
+				continue
+			}
+			n, changed, err := MergeValues(l, r)
+			if err != nil {
+				return nil, false, err
+			}
+			if changed {
+				ao.Set(k, n)
+			}
+		}
+		return a, false, nil
+	case TypeArray:
+		aa, _ := a.Array()
+		ba, _ := b.Array()
+		if len(aa) == 0 {
+			return b, true, nil
+		}
+		if len(ba) == 0 {
+			return a, false, nil
+		}
+		if len(aa) != len(ba) {
+			return nil, false, ErrMergeDifferingArrayLengths
+		}
+		for i := range aa {
+			n, changed, err := MergeValues(aa[i], ba[i])
+			if err != nil {
+				return nil, false, err
+			}
+			if changed {
+				aa[i] = n
+			}
+		}
+		return a, false, nil
+	case TypeFalse:
+		if b.Type() == TypeTrue {
+			return b, true, nil
+		}
+		return a, false, nil
+	case TypeTrue:
+		if b.Type() == TypeFalse {
+			return b, true, nil
+		}
+		return a, false, nil
+	case TypeNull:
+		if b.Type() != TypeNull {
+			return b, true, nil
+		}
+		return a, false, nil
+	case TypeNumber:
+		af, _ := a.Float64()
+		bf, _ := b.Float64()
+		if af != bf {
+			return b, true, nil
+		}
+		return a, false, nil
+	case TypeString:
+		as, _ := a.StringBytes()
+		bs, _ := b.StringBytes()
+		if !bytes.Equal(as, bs) {
+			return b, true, nil
+		}
+		return a, false, nil
+	default:
+		return nil, false, ErrMergeUnknownType
+	}
+}
+
+func MergeValuesWithPath(a, b *Value, path ...string) (v *Value, changed bool, err error) {
+	if len(path) == 0 {
+		return MergeValues(a, b)
+	}
+	root := &Value{
+		t: TypeObject,
+	}
+	current := root
+	for i := 0; i < len(path)-1; i++ {
+		current.Set(path[i], &Value{t: TypeObject})
+		current = current.Get(path[i])
+	}
+	current.Set(path[len(path)-1], b)
+	return MergeValues(a, root)
+}