// Copyright 2013 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 cgo

import (
	"errors"
	"fmt"
	"go/build"
	"os/exec"
	"strings"
)

// pkgConfig runs pkg-config with the specified arguments and returns the flags it prints.
func pkgConfig(mode string, pkgs []string) (flags []string, err error) {
	cmd := exec.Command("pkg-config", append([]string{mode}, pkgs...)...)
	out, err := cmd.Output()
	if err != nil {
		s := fmt.Sprintf("%s failed: %v", strings.Join(cmd.Args, " "), err)
		if len(out) > 0 {
			s = fmt.Sprintf("%s: %s", s, out)
		}
		if err, ok := err.(*exec.ExitError); ok && len(err.Stderr) > 0 {
			s = fmt.Sprintf("%s\nstderr:\n%s", s, err.Stderr)
		}
		return nil, errors.New(s)
	}
	if len(out) > 0 {
		flags = strings.Fields(string(out))
	}
	return
}

// pkgConfigFlags calls pkg-config if needed and returns the cflags
// needed to build the package.
func pkgConfigFlags(p *build.Package) (cflags []string, err error) {
	if len(p.CgoPkgConfig) == 0 {
		return nil, nil
	}
	return pkgConfig("--cflags", p.CgoPkgConfig)
}