camel_case.go

// "forked" from here, but fork button wasn't working, so copy/pated...
// https://gist.github.com/walm/e61b5e44b37a67c6eaa1e7c048ef7bf1
package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"regexp"
	"time"
)

// Regexp definitions
var keyMatchRegex = regexp.MustCompile(`\"(\w+)\":`)
var wordBarrierRegex = regexp.MustCompile(`(\w)([A-Z])`)

type conventionalMarshaller struct {
	Value interface{}
}

func (c conventionalMarshaller) MarshalJSON() ([]byte, error) {
	marshalled, err := json.Marshal(c.Value)

	converted := keyMatchRegex.ReplaceAllFunc(
		marshalled,
		func(match []byte) []byte {
			return bytes.ToLower(wordBarrierRegex.ReplaceAll(
				match,
				[]byte(`${1}_${2}`),
			))
		},
	)

	return converted, err
}

type exampleModel struct {
	Title       string
	ABVExample  string
	Description string
	CreatedAt   time.Time
	UpdatedAt   time.Time
	IsActive    bool
}

func main() {
	model := exampleModel{
		Title:       "Example Title",
    ABVExample:  "Example Title",
		Description: "whatever",
		CreatedAt:   time.Now(),
		UpdatedAt:   time.Now(),
		IsActive:    true,
	}

	encoded, _ := json.MarshalIndent(conventionalMarshaller{model}, "", "  ")

	fmt.Println(string(encoded))
}