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package json2go |
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import ( |
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"encoding/json" |
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"errors" |
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"fmt" |
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"regexp" |
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"sort" |
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"strings" |
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) |
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var identRe = regexp.MustCompile(`^[A-Za-z_][A-Za-z0-9_]*$`) |
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var ( |
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ErrInvalidJSON = errors.New("invalid json") |
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ErrInvalidStructName = errors.New("invalid struct name") |
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) |
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type Transformer struct { |
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structName string |
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currentIndent int |
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} |
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func NewTransformer() *Transformer { |
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return &Transformer{} |
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} |
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// Transform transforms provided json string into go type annotation |
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func (t *Transformer) Transform(structName, jsonStr string) (string, error) { |
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if !identRe.MatchString(structName) { |
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return "", ErrInvalidStructName |
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} |
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t.structName = structName |
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t.currentIndent = 0 |
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var input any |
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if err := json.Unmarshal([]byte(jsonStr), &input); err != nil { |
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return "", errors.Join(ErrInvalidJSON, err) |
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} |
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type_ := t.getTypeAnnotation(structName, input) |
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return type_, nil |
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} |
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func (t *Transformer) getTypeAnnotation(typeName string, input any) string { |
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switch v := input.(type) { |
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case map[string]any: |
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return fmt.Sprintf("type %s %s", typeName, t.buildStruct(v)) |
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case []any: |
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if len(v) == 0 { |
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return fmt.Sprintf("type %s []any", typeName) |
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} |
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type_ := t.getGoType(typeName+"Item", v[0]) |
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return fmt.Sprintf("type %s []%s", typeName, type_) |
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case string: |
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return fmt.Sprintf("type %s string", typeName) |
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case float64: |
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if float64(int(v)) == v { |
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return fmt.Sprintf("type %s int", typeName) |
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} |
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return fmt.Sprintf("type %s float64", typeName) |
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case bool: |
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return fmt.Sprintf("type %s bool", typeName) |
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default: |
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return fmt.Sprintf("type %s any", typeName) |
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} |
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} |
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func (t *Transformer) buildStruct(input map[string]any) string { |
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var fields strings.Builder |
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for _, f := range mapToStructInput(input) { |
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fieldName := t.toGoFieldName(f.field) |
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if fieldName == "" { |
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fieldName = "NotNamedField" |
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f.field = "NotNamedField" |
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} |
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// increase indentation in case of building new struct |
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t.currentIndent++ |
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fieldType := t.getGoType(fieldName, f.type_) |
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t.currentIndent-- |
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jsonTag := fmt.Sprintf("`json:\"%s\"`", f.field) |
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indent := strings.Repeat("\t", t.currentIndent+1) |
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fields.WriteString(fmt.Sprintf( |
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"%s%s %s %s\n", |
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indent, |
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fieldName, |
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fieldType, |
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jsonTag, |
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)) |
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} |
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return fmt.Sprintf("struct {\n%s%s}", |
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fields.String(), |
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strings.Repeat("\t", t.currentIndent)) |
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} |
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func (t *Transformer) getGoType(fieldName string, value any) string { |
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switch v := value.(type) { |
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case map[string]any: |
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return t.buildStruct(v) |
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case []any: |
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if len(v) == 0 { |
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return "[]any" |
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} |
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type_ := t.getGoType(fieldName, v[0]) |
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return "[]" + type_ |
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case float64: |
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if float64(int(v)) == v { |
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return "int" |
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} |
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return "float64" |
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case string: |
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return "string" |
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case bool: |
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return "bool" |
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default: |
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return "any" |
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} |
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} |
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func (t *Transformer) toGoFieldName(jsonField string) string { |
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parts := strings.Split(jsonField, "_") |
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var result strings.Builder |
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for _, part := range parts { |
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if part != "" { |
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if len(part) > 0 { |
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result.WriteString(strings.ToUpper(part[:1]) + part[1:]) |
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} |
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} |
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} |
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return result.String() |
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} |
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type structInput struct { |
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field string |
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type_ any |
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} |
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func mapToStructInput(input map[string]any) []structInput { |
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res := make([]structInput, 0, len(input)) |
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for k, v := range input { |
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res = append(res, structInput{k, v}) |
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} |
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sort.Slice(res, func(i, j int) bool { |
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return res[i].field < res[j].field |
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}) |
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return res |
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} |