// Copyright 2018 The Ebiten Authors
//
// 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.

// +build dragonfly freebsd linux netbsd openbsd solaris
// +build !js
// +build !android

package devicescale

import (
	"encoding/xml"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
)

type desktop int

const (
	desktopUnknown desktop = iota
	desktopGnome
	desktopCinnamon
	desktopUnity
	desktopKDE
	desktopXfce
)

func currentDesktop() desktop {
	tokens := strings.Split(os.Getenv("XDG_CURRENT_DESKTOP"), ":")
	switch tokens[len(tokens)-1] {
	case "GNOME":
		return desktopGnome
	case "X-Cinnamon":
		return desktopCinnamon
	case "Unity":
		return desktopUnity
	case "KDE":
		return desktopKDE
	case "XFCE":
		return desktopXfce
	default:
		return desktopUnknown
	}
}

var gsettingsRe = regexp.MustCompile(`\Auint32 (\d+)\s*\z`)

func gnomeScale() float64 {
	// TODO: Should 'monitors.xml' be loaded?

	out, err := exec.Command("gsettings", "get", "org.gnome.desktop.interface", "scaling-factor").Output()
	if err != nil {
		if err == exec.ErrNotFound {
			return 0
		}
		if _, ok := err.(*exec.ExitError); ok {
			return 0
		}
		panic(err)
	}
	m := gsettingsRe.FindStringSubmatch(string(out))
	s, err := strconv.Atoi(m[1])
	if err != nil {
		return 0
	}
	return float64(s)
}

type xmlBool bool

func (b *xmlBool) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
	var s string
	if err := d.DecodeElement(&s, &start); err != nil {
		return err
	}
	*b = xmlBool(s == "yes")
	return nil
}

func cinnamonScaleFromXML() (float64, error) {
	type cinnamonMonitors struct {
		XMLName       xml.Name `xml:"monitors"`
		Version       string   `xml:"version,attr"`
		Configuration struct {
			BaseScale float64 `xml:"base_scale"`
			Output    []struct {
				Scale   float64 `xml:"scale"`
				Primary xmlBool `xml:"primary"`
			} `xml:"output"`
		} `xml:"configuration"`
	}

	home, err := os.UserHomeDir()
	if err != nil {
		return 0, err
	}
	f, err := os.Open(filepath.Join(home, ".config", "cinnamon-monitors.xml"))
	if err != nil {
		return 0, err
	}
	defer f.Close()

	d := xml.NewDecoder(f)

	var monitors cinnamonMonitors
	if err = d.Decode(&monitors); err != nil {
		return 0, err
	}

	scale := monitors.Configuration.BaseScale
	for _, v := range monitors.Configuration.Output {
		// TODO: Get the monitor at the specified position.
		if v.Primary {
			if v.Scale != 0.0 {
				scale = v.Scale
			}
			break
		}
	}
	return scale, nil
}

func cinnamonScale() float64 {
	if s, err := cinnamonScaleFromXML(); err == nil && s > 0 {
		return s
	}

	out, err := exec.Command("gsettings", "get", "org.cinnamon.desktop.interface", "scaling-factor").Output()
	if err != nil {
		if err == exec.ErrNotFound {
			return 0
		}
		if _, ok := err.(*exec.ExitError); ok {
			return 0
		}
		panic(err)
	}
	m := gsettingsRe.FindStringSubmatch(string(out))
	s, err := strconv.Atoi(m[1])
	if err != nil {
		return 0
	}
	return float64(s)
}

func impl(x, y int) float64 {
	s := -1.0
	switch currentDesktop() {
	case desktopGnome:
		// TODO: Support wayland and per-monitor scaling https://wiki.gnome.org/HowDoI/HiDpi
		s = gnomeScale()
	case desktopCinnamon:
		s = cinnamonScale()
	case desktopUnity:
		// TODO: Implement, supports per-monitor scaling
	case desktopKDE:
		// TODO: Implement, appears to support per-monitor scaling
	case desktopXfce:
		// TODO: Implement
	}
	if s <= 0 {
		s = 1
	}

	return s
}