package display

// #cgo CFLAGS: --std=gnu99 -pedantic -Wall
// #cgo LDFLAGS: -lX11 -lXext
// #include "dpms.h"
// #include <stdlib.h>
// #include <stdbool.h>
import "C"
import (
	"unsafe"
	"errors"
	"os"
)


// Xset monitors/controls the display using the DPMS X extension
type Xset struct {}

// Suspend the display
func (Xset) Suspend() error {
	xDisplayName := C.CString(tryGetXDisplay())
	defer C.free(unsafe.Pointer(xDisplayName))

	err := C.turn_display_off(xDisplayName)
	if err != C.int(0) {
		return convertErrorIntToGoError(err)
	}

	return nil
}

func tryGetXDisplay() string {
	display := os.Getenv("DISPLAY")
	if display == "" {
		panic(errors.New("DISPLAY envvar not set"))
	}
	return display
}

func convertErrorIntToGoError(err C.int) error {
	errorMsg := ""
	switch err {
	case C.BADDISPLAY:
		errorMsg = "Failed to open X display"
	case C.NODPMSEXTENSION:
		errorMsg = "DPMS extension is not available"
	case C.NOTDPMSCAPABLE:
		errorMsg = "Display is not DPMS capable"
	case C.UNKNOWNDPMSMODE:
		errorMsg = "Reported DPMS state unknown"
	case C.DPMSDISABLED:
		errorMsg = "DPMS is disabled"
	default:
		errorMsg = "Unknown error from dpms.h"
	}
	return errors.New(errorMsg)
}

// IsOn determines if the display is on
func (Xset) IsOn() (bool, error) {
	xDisplayName := C.CString(tryGetXDisplay())
	defer C.free(unsafe.Pointer(xDisplayName))
	var isDisplayOn C.bool

	err := C.is_display_on(xDisplayName, &isDisplayOn)
	if err != C.int(0) {
		return false, convertErrorIntToGoError(err)
	}

	if isDisplayOn {
		return true, nil
	}
	return false, nil
}