// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package google

import (
	"context"
	"log"
	"sync"

	"golang.org/x/oauth2"
)

var logOnce sync.Once // only spam about deprecation once

// AppEngineTokenSource returns a token source that fetches tokens from either
// the current application's service account or from the metadata server,
// depending on the App Engine environment. See below for environment-specific
// details. If you are implementing a 3-legged OAuth 2.0 flow on App Engine that
// involves user accounts, see oauth2.Config instead.
//
// The current version of this library requires at least Go 1.17 to build,
// so first generation App Engine runtimes (<= Go 1.9) are unsupported.
// Previously, on first generation App Engine runtimes, AppEngineTokenSource
// returned a token source that fetches tokens issued to the
// current App Engine application's service account. The provided context must have
// come from appengine.NewContext.
//
// Second generation App Engine runtimes (>= Go 1.11) and App Engine flexible:
// AppEngineTokenSource is DEPRECATED on second generation runtimes and on the
// flexible environment. It delegates to ComputeTokenSource, and the provided
// context and scopes are not used. Please use DefaultTokenSource (or ComputeTokenSource,
// which DefaultTokenSource will use in this case) instead.
func AppEngineTokenSource(ctx context.Context, scope ...string) oauth2.TokenSource {
	logOnce.Do(func() {
		log.Print("google: AppEngineTokenSource is deprecated on App Engine standard second generation runtimes (>= Go 1.11) and App Engine flexible. Please use DefaultTokenSource or ComputeTokenSource.")
	})
	return ComputeTokenSource("")
}