Complete package for generating ocds structs (with extensions) in golang

internal/generator/jsonobj.go

@@ -0,0 +1,149 @@
+package generator
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+)
+
+// Obj is a JSON object that remembers key order, so generated structs list
+// fields in the same order as the schema rather than alphabetically.
+type Obj struct {
+	Keys []string
+	M    map[string]any
+}
+
+func newObj() *Obj { return &Obj{M: map[string]any{}} }
+
+func (o *Obj) Get(k string) any { return o.M[k] }
+
+func (o *Obj) Set(k string, v any) {
+	if _, ok := o.M[k]; !ok {
+		o.Keys = append(o.Keys, k)
+	}
+	o.M[k] = v
+}
+
+func (o *Obj) Delete(k string) {
+	if _, ok := o.M[k]; !ok {
+		return
+	}
+	delete(o.M, k)
+	for i, key := range o.Keys {
+		if key == k {
+			o.Keys = append(o.Keys[:i], o.Keys[i+1:]...)
+			break
+		}
+	}
+}
+
+func (o *Obj) Obj(k string) *Obj {
+	v, _ := o.M[k].(*Obj)
+	return v
+}
+
+func (o *Obj) Str(k string) string {
+	v, _ := o.M[k].(string)
+	return v
+}
+
+// decodeOrdered parses JSON, returning *Obj for objects, []any for arrays,
+// and string / json.Number / bool / nil for scalars.
+func decodeOrdered(r io.Reader) (any, error) {
+	dec := json.NewDecoder(r)
+	dec.UseNumber()
+	return parseValue(dec)
+}
+
+func parseValue(dec *json.Decoder) (any, error) {
+	tok, err := dec.Token()
+	if err != nil {
+		return nil, err
+	}
+	switch t := tok.(type) {
+	case json.Delim:
+		switch t {
+		case '{':
+			o := newObj()
+			for dec.More() {
+				kt, err := dec.Token()
+				if err != nil {
+					return nil, err
+				}
+				k, ok := kt.(string)
+				if !ok {
+					return nil, fmt.Errorf("expected object key, got %v", kt)
+				}
+				v, err := parseValue(dec)
+				if err != nil {
+					return nil, err
+				}
+				o.Set(k, v)
+			}
+			_, err := dec.Token() // '}'
+			return o, err
+		case '[':
+			arr := []any{}
+			for dec.More() {
+				v, err := parseValue(dec)
+				if err != nil {
+					return nil, err
+				}
+				arr = append(arr, v)
+			}
+			_, err := dec.Token() // ']'
+			return arr, err
+		}
+		return nil, fmt.Errorf("unexpected delimiter %v", t)
+	default:
+		return t, nil
+	}
+}
+
+// mergePatch applies an RFC 7386 JSON Merge Patch, which is how OCDS
+// extensions are applied to the core schema. A null in the patch deletes
+// the key; objects merge recursively; anything else replaces.
+func mergePatch(target, patch any) any {
+	p, ok := patch.(*Obj)
+	if !ok {
+		return patch
+	}
+	t, ok := target.(*Obj)
+	if !ok {
+		t = newObj()
+	}
+	for _, k := range p.Keys {
+		v := p.M[k]
+		if v == nil {
+			t.Delete(k)
+			continue
+		}
+		t.Set(k, mergePatch(t.M[k], v))
+	}
+	return t
+}
+
+// MarshalJSON writes the object with its keys in their original order.
+func (o *Obj) MarshalJSON() ([]byte, error) {
+	var b bytes.Buffer
+	b.WriteByte('{')
+	for i, k := range o.Keys {
+		if i > 0 {
+			b.WriteByte(',')
+		}
+		kb, err := json.Marshal(k)
+		if err != nil {
+			return nil, err
+		}
+		vb, err := json.Marshal(o.M[k])
+		if err != nil {
+			return nil, err
+		}
+		b.Write(kb)
+		b.WriteByte(':')
+		b.Write(vb)
+	}
+	b.WriteByte('}')
+	return b.Bytes(), nil
+}