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package main

import (
    "fmt"
    "log"
    "strings"

    "github.com/go-playground/validator/v10"
    "github.com/gofiber/fiber/v2"
)

type (
    User struct {
        Name string `validate:"required,min=5,max=20"` // Required field, min 5 char long max 20
        Age  int    `validate:"required,teener"`       // Required field, and client needs to implement our 'teener' tag format which we'll see later
    }

    ErrorResponse struct {
        Error       bool
        FailedField string
        Tag         string
        Value       interface{}
    }

    XValidator struct {
        validator *validator.Validate
    }

    GlobalErrorHandlerResp struct {
        Success bool   `json:"success"`
        Message string `json:"message"`
    }
)

// This is the validator instance
// for more information see: https://github.com/go-playground/validator
var validate = validator.New()

func (v XValidator) Validate(data interface{}) []ErrorResponse {
    validationErrors := []ErrorResponse{}

    errs := validate.Struct(data)
    if errs != nil {
        for _, err := range errs.(validator.ValidationErrors) {
            // In this case data object is actually holding the User struct
            var elem ErrorResponse

            elem.FailedField = err.Field() // Export struct field name
            elem.Tag = err.Tag()           // Export struct tag
            elem.Value = err.Value()       // Export field value
            elem.Error = true

            validationErrors = append(validationErrors, elem)
        }
    }

    return validationErrors
}

func main() {
    myValidator := &XValidator{
        validator: validate,
    }

    app := fiber.New(fiber.Config{
        // Global custom error handler
        ErrorHandler: func(c *fiber.Ctx, err error) error {
            return c.Status(fiber.StatusBadRequest).JSON(GlobalErrorHandlerResp{
                Success: false,
                Message: err.Error(),
            })
        },
    })

    // Custom struct validation tag format
    myValidator.validator.RegisterValidation("teener", func(fl validator.FieldLevel) bool {
        // User.Age needs to fit our needs, 12-18 years old.
        return fl.Field().Int() >= 12 && fl.Field().Int() <= 18
    })

    app.Get("/", func(c *fiber.Ctx) error {
        user := &User{
            Name: c.Query("name"),
            Age:  c.QueryInt("age"),
        }

        // Validation
        if errs := myValidator.Validate(user); len(errs) > 0 && errs[0].Error {
            errMsgs := make([]string, 0)

            for _, err := range errs {
                errMsgs = append(errMsgs, fmt.Sprintf(
                    "[%s]: '%v' | Needs to implement '%s'",
                    err.FailedField,
                    err.Value,
                    err.Tag,
                ))
            }

            return &fiber.Error{
                Code:    fiber.ErrBadRequest.Code,
                Message: strings.Join(errMsgs, " and "),
            }
        }

        // Logic, validated with success
        return c.SendString("Hello, World!")
    })

    log.Fatal(app.Listen(":3000"))
}

/**
OUTPUT

[1]
Request:

GET http://127.0.0.1:3000/

Response:

{"success":false,"message":"[Name]: '' | Needs to implement 'required' and [Age]: '0' | Needs to implement 'required'"}

[2]
Request:

GET http://127.0.0.1:3000/?name=efdal&age=9

Response:
{"success":false,"message":"[Age]: '9' | Needs to implement 'teener'"}

[3]
Request:

GET http://127.0.0.1:3000/?name=efdal&age=

Response:
{"success":false,"message":"[Age]: '0' | Needs to implement 'required'"}

[4]
Request:

GET http://127.0.0.1:3000/?name=efdal&age=18

Response:
Hello, World!

**/