// 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 cmd

import (
	"errors"
	"flag"
	"io/ioutil"
	"os"

	"bitbucket.org/creachadair/shell"
)

func parseFlags(file string) error {
	args, valid := shell.Split(file)
	if !valid {
		return errors.New("flag file contains unclosed quotations")
	}
	// Expand any environment variables in the args
	for i := range args {
		args[i] = os.ExpandEnv(args[i])
	}

	if err := flag.CommandLine.Parse(args); err != nil {
		return err
	}

	// Call flag.Parse() again so that command line flags
	// can override flags provided in the provided flag file.
	flag.Parse()
	return nil
}

// ParseFlagFile parses a set of flags from a file at the provided
// path. Re-calls flag.Parse() after parsing the flags in the file
// so that flags provided on the command line take precedence over
// flags provided in the file.
func ParseFlagFile(path string) error {
	file, err := ioutil.ReadFile(path)
	if err != nil {
		return err
	}
	return parseFlags(string(file))
}
