package dl

import (
	"errors"
	"unsafe"
)

//#cgo LDFLAGS: -ldl
//#include <stdlib.h>
//#include <dlfcn.h>
import "C"

type Flag int

const (
	RTLD_LAZY   Flag = C.RTLD_LAZY   // Relocations are performed at an
					 // implementation-defined time.
	RTLD_NOW    Flag = C.RTLD_NOW    // Relocations are performed when the
				         // object is loaded.
	RTLD_GLOBAL Flag = C.RTLD_GLOBAL // All symbols are available for
					 // relocation processing of other
					 // modules.
	RTLD_LOCAL  Flag = C.RTLD_LOCAL  // All symbols are not made available
					 // for relocation processing by other
					 // modules.
)

type Handle struct {
	c unsafe.Pointer
}

func Open(name string, flags Flag) (Handle, error) {
	nameC := C.CString(name)
	defer C.free(unsafe.Pointer(nameC))

	dlerror()
	ptr := C.dlopen(nameC, C.int(flags))
	if ptr == nil {
		return Handle{}, dlerror()
	}
	return Handle{ptr}, nil
}

// This returns uintptr instead of unsafe.Pointer so that code using
// reflect cannot obtain unsafe.Pointers without importing the unsafe
// package explicitly.
func (h Handle) Sym(symbol string) (uintptr, error) {
	symbolC := C.CString(symbol)
	defer C.free(unsafe.Pointer(symbolC))

	dlerror()
	ptr := C.dlsym(h.c, symbolC)
	if ptr == nil {
		return 0, dlerror()
	}
	return uintptr(ptr), nil
}

func (h Handle) Close() error {
	dlerror()
	r := C.dlclose(h.c)
	if r != 0 {
		return dlerror()
	}
	return nil
}

func dlerror() error {
	strC := C.dlerror()
	if strC == nil {
		return nil
	}
	return errors.New(C.GoString(strC))
}