Silly command to add db tags to pb.go

inject.go

package main

import (
	"bytes"
	"go/ast"
	"go/format"
	"go/parser"
	"go/token"
	"io/ioutil"
	"log"
	"os"
	"strings"

	"github.com/azer/snakecase"
	"github.com/fatih/structtag"
)

func main() {
	path := os.Args[len(os.Args)-1]
	err := transform(path)
	if err != nil {
		log.Fatal(err)
	}
}

func transform(path string) error {
	log.Printf("parsing file %q for inject tag comments", path)
	fset := token.NewFileSet()
	f, err := parser.ParseFile(fset, path, nil, parser.ParseComments)
	if err != nil {
		return err
	}

	for _, decl := range f.Decls {
		genDecl, ok := decl.(*ast.GenDecl)
		if !ok {
			continue
		}

		var typeSpec *ast.TypeSpec
		for _, spec := range genDecl.Specs {
			if ts, tsOK := spec.(*ast.TypeSpec); tsOK {
				typeSpec = ts
				break
			}
		}

		if typeSpec == nil {
			continue
		}

		structDecl, ok := typeSpec.Type.(*ast.StructType)
		if !ok {
			continue
		}
		// log.Printf("found a struct! %+v", typeSpec)

		for _, field := range structDecl.Fields.List {
			if len(field.Names) > 0 && field.Tag != nil {
				// log.Printf("found a field with a tag! %s (%s)", field.Names[0].Name, field.Tag.Value)

				tags, err := structtag.Parse(strings.Trim(field.Tag.Value, "`"))
				if err != nil {
					log.Printf("failed to parse field tag: %v", err)
					continue
				}

				json, err := tags.Get("json")
				if err != nil {
					// log.Printf("failed to get json tag: %v", err)
					continue
				}

				db := &structtag.Tag{
					Key:  "db",
					Name: snakecase.SnakeCase(json.Name),
				}
				if db.Name == "id" {
					db.Name = snakecase.SnakeCase(typeSpec.Name.Name) + "_id"
				}
				tags.Set(db)

				field.Tag.Value = "`" + tags.String() + "`"
			}
		}
	}

	buf := &bytes.Buffer{}
	err = format.Node(buf, fset, f)
	if err != nil {
		return err
	}
	out := buf.Bytes()

	return ioutil.WriteFile(path, out, 0644)
}