package main

import (
	"context"
	"fmt"

	"cloud.google.com/go/datastore"
)

const (
	projectId = "SOME"
)

type T struct {
	Values []string `datastore:",noindex,omitempty" json:"values,omitempty"`
}

func test(client *datastore.Client, key string, want T) {
	k := datastore.NameKey("test", key, nil)

	fmt.Println("\nTEST", key)

	_, err := client.Put(context.TODO(), k, &want)
	if err != nil {
		fmt.Printf("datastore.Put(%s) %s\n", key, err)
		return
	}

	var got T
	err = client.Get(context.TODO(), k, &got)

	if err != nil {
		fmt.Printf("datastore.Get(%s) %s\n", key, err)
		return
	}

	fmt.Printf("want: %#v\n got: %#v\n", want, got)
}

func main() {
	client, err := datastore.NewClient(context.TODO(), projectId)
	if err != nil {
		panic(err)
	}

	test(client, "empty-strings", T{Values: []string{"", "", ""}})
	test(client, "non-empty-strings", T{Values: []string{"s0", "s1", "s2"}})
	test(client, "1st-item-is-empty-string", T{Values: []string{"", "s1", "s2"}})
	test(client, "2nd-item-is-empty-string", T{Values: []string{"s0", "", "s2"}})

	// Output:
	// TEST empty-strings
	// want: main.T{Values:[]string{"", "", ""}}
	// got: main.T{Values:[]string(nil)}
	//
	// TEST non-empty-strings
	// want: main.T{Values:[]string{"s0", "s1", "s2"}}
	// got: main.T{Values:[]string{"s0", "s1", "s2"}}
	//
	// TEST 1st-item-is-empty-string
	// datastore.Put(1st-item-is-empty-string) datastore: unexpected property "Values" in elem 1 of slice
	//
	// TEST 2nd-item-is-empty-string
	// want: main.T{Values:[]string{"s0", "", "s2"}}
	// got: main.T{Values:[]string{"s0", "s2"}}
}