package getgr

import (
	"syscall"
	"unsafe"
)

//#define _POSIX_SOURCE // for getgrnam_r(3) in grp.h
//#include <stdlib.h>   // for free(3)
//#include <unistd.h>   // for sysconf(3)
//#include <grp.h>      // for getgrnam_r(3)
//static char *strary(char **ary, unsigned int n) { return ary[n]; }
import "C"

type Gid uint

type Group struct {
	Name   string
	Passwd string
	Gid    Gid
	Mem    []string
}

func strary(c **C.char) (g []string) {
	g = make([]string, 0)
	for i := C.uint(0); true; i++ {
		cstr := C.strary(c, i)
		if cstr == nil {
			return
		}
		g = append(g, C.GoString(cstr))
	}
	panic("not reached")
}

// A wrapper around C getgrnam_r
func ByName(name string) (*Group, error) {
	nameC := C.CString(name)
	defer C.free(unsafe.Pointer(nameC))

	buflen := C.sysconf(C._SC_GETGR_R_SIZE_MAX)
	if buflen < 1 {
		buflen = 1024
	}
	buf := make([]byte, buflen)
	var grp C.struct_group
	var ret *C.struct_group
	for {
		success, errno := C.getgrnam_r(nameC, &grp, (*C.char)(unsafe.Pointer(&buf[0])), C.size_t(buflen), &ret)
		if success >= 0 {
			break
		}
		if errno == syscall.ERANGE {
			buflen += 256
			buf = make([]byte, buflen)
		} else {
			return nil, errno
		}
	}
	if ret == nil {
		return nil, nil
	}
	return &Group{
		Name:   C.GoString(ret.gr_name),
		Passwd: C.GoString(ret.gr_passwd),
		Gid:    Gid(ret.gr_gid),
		Mem:    strary(ret.gr_mem),
	}, nil
}

// A wrapper around C getgrgid_r
func ByGid(gid int32) (*Group, error) {
	gidC := C.__gid_t(gid)

	buflen := C.sysconf(C._SC_GETGR_R_SIZE_MAX)
	if buflen < 1 {
		buflen = 1024
	}
	buf := make([]byte, buflen)
	var grp C.struct_group
	var ret *C.struct_group
	for {
		success, errno := C.getgrgid_r(gidC, &grp, (*C.char)(unsafe.Pointer(&buf[0])), C.size_t(buflen), &ret)
		if success >= 0 {
			break
		}
		if errno == syscall.ERANGE {
			buflen += 256
			buf = make([]byte, buflen)
		} else {
			return nil, errno
		}
	}
	if ret == nil {
		return nil, nil
	}
	return &Group{
		Name:   C.GoString(ret.gr_name),
		Passwd: C.GoString(ret.gr_passwd),
		Gid:    Gid(ret.gr_gid),
		Mem:    strary(ret.gr_mem),
	}, nil
}