package handler

import (
  "context"
  "time"

  "github.com/ya5u/fsevent"
)

// FsData is defined type for firestore as you like
type FsData struct {
  Name     string     `firestore:"name"`
  Age      int64      `firestore:"age"`
  Birthday *time.Time `firestore:"birthday"`
}

// Handler is the entry point of Cloud Functions triggered by firestore event
func Handler(ctx context.Context, e fsevent.FirestoreEvent) error {
  // get event type
  eventType := e.Type()

  // reflect updated value to struct you defined
  var updated FsData
  err := e.Value.DataTo(&updated)
  if err != nil {
    // error handling
  }

  // reflect old value to struct you defined
  var old FsData
  err = e.OldValue.DataTo(&old)
  if err != nil {
    // error handling
  }
}