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main.go
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main.go
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package main
import (
"crypto/sha256"
"encoding/hex"
"encoding/json"
"fmt"
"go/format"
"io/ioutil"
"log"
"net/http"
"os"
"sort"
"strings"
)
func main() {
contents, err := readFile("example.json")
if err != nil {
log.Fatal(err)
}
errorDefinitions, err := parseErrorDefinitions(contents)
if err != nil {
log.Fatal(err)
}
errorCodeDefinitions, err := generateErrorDefinitions(errorDefinitions)
if err != nil {
log.Fatal(err)
}
errorIDs, err := generateErrorIDs(errorDefinitions)
if err != nil {
log.Fatal(err)
}
o := &outFile{
errorIDs: errorIDs,
imports: imports,
predefined: predefined,
errorDefinitions: errorCodeDefinitions,
}
result := o.compose("test")
formattedResult, err := formatCode(result)
if err != nil {
log.Fatal(err)
}
if err := writeGenerated("test/test.go", formattedResult); err != nil {
log.Fatal(err)
}
}
type errorDefinition struct {
HTTPCode int
Payload map[string]string
}
type errID struct {
ErrName string
ID string
}
func (e *errID) String() string {
return fmt.Sprintf("%s = \"%s\"", e.ErrName, e.ID)
}
type outFile struct {
errorIDs []*errID
imports string
predefined string
errorDefinitions []*errorCodeDefinition
}
func (f *outFile) compose(packageName string) string {
parts := make([]string, 0, 4+len(f.errorDefinitions))
errIDConstants := make([]string, len(f.errorIDs))
for i, id := range f.errorIDs {
errIDConstants[i] = id.String()
}
parts = append(parts, []string{
fmt.Sprintf("package %s", packageName),
f.imports,
f.predefined,
fmt.Sprintf("const (\n%s\n)", strings.Join(errIDConstants, "\n")),
}...)
for _, def := range f.errorDefinitions {
parts = append(parts, def.String())
}
result := strings.Join(parts, "\n")
return result
}
func parseErrorDefinitions(defs []byte) (map[string]errorDefinition, error) {
var jsonDefs map[string]errorDefinition
if err := json.Unmarshal(defs, &jsonDefs); err != nil {
return nil, fmt.Errorf("failed to unmarshal errors definitions: %v", err)
}
return jsonDefs, nil
}
func generateErrorDefinitions(defs map[string]errorDefinition) ([]*errorCodeDefinition, error) {
errorDefinitions := make([]*errorCodeDefinition, 0, len(defs))
for errName, d := range defs {
errDef, err := generateErrorDefinition(errName, &d)
if err != nil {
return nil, fmt.Errorf("failed to generate code for the error %s: %v", errName, err)
}
errorDefinitions = append(errorDefinitions, errDef)
}
return errorDefinitions, nil
}
func generateErrorIDs(defs map[string]errorDefinition) ([]*errID, error) {
errorIDs := make([]*errID, 0, len(defs)+2)
for errName, d := range defs {
id := generateErrorID(errName, &d)
constName, err := generateFromTemplate(tmplErrorIDConstName, &tmplErrorIDConstNameIn{
errorNameIn: errorNameIn{
ErrorName: errName,
},
})
if err != nil {
return nil, fmt.Errorf("failed to generate an ID for the error %s from a template: %v", errName, err)
}
errID := &errID{
ErrName: constName,
ID: id,
}
errorIDs = append(errorIDs, errID)
}
return errorIDs, nil
}
func readFile(path string) ([]byte, error) {
f, err := os.Open(path)
if err != nil {
return nil, fmt.Errorf("failed to open the file %s: %v", path, err)
}
defer f.Close()
data, err := ioutil.ReadAll(f)
if err != nil {
return nil, fmt.Errorf("failed to read the file %s: %v", path, err)
}
return data, nil
}
func writeGenerated(path string, result string) error {
f, err := os.Create(path)
if err != nil {
return fmt.Errorf("failed to open the file %s: %v", path, err)
}
defer f.Close()
if _, err := f.Write([]byte(result)); err != nil {
return fmt.Errorf("failed to write the result to the file %s: %v", path, err)
}
return nil
}
type errorCodeDefinition struct {
Payload string
ErrorType string
Constructor string
}
func (d *errorCodeDefinition) String() string {
result := fmt.Sprintf("%s\n%s\n%s", d.Payload, d.ErrorType, d.Constructor)
return result
}
func generateErrorDefinition(name string, def *errorDefinition) (*errorCodeDefinition, error) {
codeDef := &errorCodeDefinition{}
var err error
hasPayload := len(def.Payload) != 0
if hasPayload {
codeDef.Payload, err = generateErrorPayloadDefinition(name, def.Payload)
if err != nil {
return nil, fmt.Errorf("failed to generate a payload structure for the error %s: %v", name, err)
}
}
codeDef.ErrorType, err = generateErrorTypeDefinition(name, hasPayload)
if err != nil {
return nil, fmt.Errorf("failed to generate the error type definition for the error %s: %v", name, err)
}
if def.HTTPCode == 0 {
def.HTTPCode = http.StatusInternalServerError
}
codeDef.Constructor, err = generateErrorConstructor(&tmplErrorConstructorIn{
tmplErrorTypeIn: tmplErrorTypeIn{
tmplErrorPayloadNameIn: tmplErrorPayloadNameIn{
ErrorName: name,
},
HasPayload: hasPayload,
},
HTTPCode: def.HTTPCode,
})
return codeDef, nil
}
func generateErrorPayloadDefinition(errorName string, payload map[string]string) (string, error) {
def, err := generateFromTemplate(tmplErrorPayload, &tmplErrorPayloadIn{
errorNameIn: errorNameIn{
ErrorName: errorName,
},
Fields: payload,
})
if err != nil {
return "", fmt.Errorf("failed to generate the definition from template: %v", err)
}
return def, nil
}
func generateErrorTypeDefinition(errorName string, hasPayload bool) (string, error) {
def, err := generateFromTemplate(tmplErrorType, &tmplErrorTypeIn{
tmplErrorPayloadNameIn: tmplErrorPayloadNameIn{
ErrorName: errorName,
},
HasPayload: hasPayload,
})
if err != nil {
return "", fmt.Errorf("failed to generate the definition from template: %v", err)
}
return def, nil
}
func generateErrorConstructor(in *tmplErrorConstructorIn) (string, error) {
def, err := generateFromTemplate(tmplErrorConstructor, in)
if err != nil {
return "", fmt.Errorf("template generation failed: %v", err)
}
return def, nil
}
func generateErrorID(errName string, d *errorDefinition) string {
toHash := make([]string, len(d.Payload)+1)
for field := range d.Payload {
toHash = append(toHash, field)
}
sort.Slice(toHash, func(i int, j int) bool {
return toHash[i] < toHash[j]
})
toHash = append(toHash, errName)
toHashString := strings.Join(toHash, ",")
h := sha256.New()
h.Write([]byte(toHashString))
hash := h.Sum(nil)
id := hex.EncodeToString(hash)
return id
}
func formatCode(code string) (string, error) {
formattedCode, err := format.Source([]byte(code))
if err != nil {
return "", fmt.Errorf("code formatting failed: %v", err)
}
return string(formattedCode), nil
}