// Copyright 2017 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package internal

import (
	"fmt"
	"io/ioutil"

	"golang.org/x/net/context"
	"golang.org/x/oauth2"
	"golang.org/x/oauth2/google"
)

// ServiceAcctTokenSource reads a JWT config from filename and returns
// a TokenSource constructed from the config.
func ServiceAcctTokenSource(ctx context.Context, filename string, scope ...string) (oauth2.TokenSource, error) {
	data, err := ioutil.ReadFile(filename)
	if err != nil {
		return nil, fmt.Errorf("cannot read service account file: %v", err)
	}
	cfg, err := google.JWTConfigFromJSON(data, scope...)
	if err != nil {
		return nil, fmt.Errorf("google.JWTConfigFromJSON: %v", err)
	}
	return cfg.TokenSource(ctx), nil
}