package handler

import (
	"encoding/json"
	"errors"
	"io"
	"net/http"

	"github.com/go-playground/validator/v10"

	"github.com/dbiz/cdp/data-layer/api/internal/apperr"
)

var validate = validator.New(validator.WithRequiredStructEnabled())

// decodeAndValidate reads JSON into `dst`, then runs validator tags. Returns
// a wrapped AppError so handlers can pass it straight to writeError.
func decodeAndValidate(r *http.Request, dst any) error {
	dec := json.NewDecoder(r.Body)
	dec.DisallowUnknownFields()
	if err := dec.Decode(dst); err != nil {
		if errors.Is(err, io.EOF) {
			return apperr.BadRequest("request body is empty", "", err)
		}
		return apperr.BadRequest("invalid JSON: "+err.Error(), "", err)
	}
	if err := validate.Struct(dst); err != nil {
		var verrs validator.ValidationErrors
		if errors.As(err, &verrs) && len(verrs) > 0 {
			ve := verrs[0]
			return apperr.BadRequest("validation failed on "+ve.Field()+": "+ve.Tag(), ve.Field(), err)
		}
		return apperr.BadRequest("validation failed: "+err.Error(), "", err)
	}
	return nil
}