// Copyright (C) 2026 Danilo M. <danix@danix.xyz>
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License version 2 as
// published by the Free Software Foundation.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

package notify

import (
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
)

// IconThemeName reads the desktop's current icon theme: qt6ct is the truth on
// this desktop, then the GTK3 setting, then hicolor. A missing or empty value
// falls through.
func IconThemeName() string {
	if v := iniValue(filepath.Join(homeDir(), ".config", "qt6ct", "qt6ct.conf"), "icon_theme"); v != "" {
		return v
	}
	if v := iniValue(filepath.Join(homeDir(), ".config", "gtk-3.0", "settings.ini"), "gtk-icon-theme-name"); v != "" {
		return v
	}
	return "hicolor"
}

// ResolveIcon turns an app_icon or image-path value into a file path. A URI is
// trimmed, a path is returned unchanged, and a bare name is looked up in the
// icon theme. Nothing found is an empty string, which renders no image.
func ResolveIcon(value string) string {
	if value == "" {
		return ""
	}
	if strings.HasPrefix(value, "file://") {
		return strings.TrimPrefix(value, "file://")
	}
	if strings.Contains(value, "/") {
		return value
	}
	return lookupThemeIcon(value, IconThemeName())
}

// XDGIconDirs is the icon search path: the user's dir then each data dir.
func XDGIconDirs() []string {
	home := os.Getenv("XDG_DATA_HOME")
	if home == "" {
		home = filepath.Join(homeDir(), ".local", "share")
	}
	dirs := []string{filepath.Join(home, "icons")}
	for _, d := range filepath.SplitList(os.Getenv("XDG_DATA_DIRS")) {
		if d != "" {
			dirs = append(dirs, filepath.Join(d, "icons"))
		}
	}
	if len(dirs) == 1 {
		dirs = append(dirs, "/usr/local/share/icons", "/usr/share/icons")
	}
	return dirs
}

// lookupThemeIcon searches the theme, then its Inherits chain, then hicolor.
func lookupThemeIcon(name, theme string) string {
	seen := map[string]bool{}
	for theme != "" && !seen[theme] {
		seen[theme] = true
		found, next := "", ""
		for _, root := range XDGIconDirs() {
			base := filepath.Join(root, theme)
			if p := findInTheme(base, name); p != "" {
				found = p
				break
			}
			if next == "" {
				next = inheritsOf(base)
			}
		}
		if found != "" {
			return found
		}
		theme = next
	}
	for _, root := range XDGIconDirs() {
		if p := findInTheme(filepath.Join(root, "hicolor"), name); p != "" {
			return p
		}
	}
	return ""
}

// findInTheme prefers scalable, then the largest raster. It searches both the
// KDE/Papirus apps/<size> layout and the freedesktop <size>/apps layout.
func findInTheme(base, name string) string {
	for _, dir := range themeSizeDirs(base) {
		for _, ext := range []string{"svg", "png", "xpm"} {
			p := filepath.Join(dir, name+"."+ext)
			if fileExists(p) {
				return p
			}
		}
	}
	return ""
}

// sizeDir is one candidate icon directory inside a theme.
type sizeDir struct {
	path     string
	scalable bool
	size     int
	name     string
}

// themeSizeDirs lists a theme's candidate directories, scalable first, then
// rasters by effective pixel size descending, name as a deterministic
// tie-break. Both icon layouts are covered.
func themeSizeDirs(base string) []string {
	var found []sizeDir
	add := func(name, path string) {
		if name == "scalable" {
			found = append(found, sizeDir{path: path, scalable: true, name: name})
			return
		}
		if n, ok := pixelSize(name); ok {
			found = append(found, sizeDir{path: path, size: n, name: name})
		}
	}
	// KDE/Papirus: apps/<size>/
	if entries, err := os.ReadDir(filepath.Join(base, "apps")); err == nil {
		for _, e := range entries {
			if e.IsDir() {
				add(e.Name(), filepath.Join(base, "apps", e.Name()))
			}
		}
	}
	// freedesktop: <size>/apps/
	if entries, err := os.ReadDir(base); err == nil {
		for _, e := range entries {
			if !e.IsDir() {
				continue
			}
			apps := filepath.Join(base, e.Name(), "apps")
			if info, err := os.Stat(apps); err == nil && info.IsDir() {
				add(e.Name(), apps)
			}
		}
	}
	sort.Slice(found, func(i, j int) bool {
		a, b := found[i], found[j]
		if a.scalable != b.scalable {
			return a.scalable
		}
		if a.size != b.size {
			return a.size > b.size
		}
		return a.name < b.name
	})
	dirs := make([]string, len(found))
	for i, d := range found {
		dirs[i] = d.path
	}
	return dirs
}

// pixelSize turns a size directory name into its effective pixel size. "48"
// and "48x48" styles are recognised, and a trailing @2x doubles the size.
func pixelSize(name string) (int, bool) {
	s := name
	mult := 1
	if strings.HasSuffix(s, "@2x") {
		s = strings.TrimSuffix(s, "@2x")
		mult = 2
	}
	if i := strings.IndexByte(s, 'x'); i >= 0 {
		s = s[:i]
	}
	n, err := strconv.Atoi(s)
	if err != nil {
		return 0, false
	}
	return n * mult, true
}

func inheritsOf(base string) string {
	v := iniValue(filepath.Join(base, "index.theme"), "Inherits")
	if i := strings.IndexByte(v, ','); i >= 0 {
		v = v[:i]
	}
	return strings.TrimSpace(v)
}

func iniValue(path, key string) string {
	data, err := os.ReadFile(path)
	if err != nil {
		return ""
	}
	for _, line := range strings.Split(string(data), "\n") {
		line = strings.TrimSpace(line)
		if strings.HasPrefix(line, "#") || !strings.Contains(line, "=") {
			continue
		}
		k, v, _ := strings.Cut(line, "=")
		if strings.TrimSpace(k) == key {
			return strings.TrimSpace(v)
		}
	}
	return ""
}

func homeDir() string {
	if h := os.Getenv("HOME"); h != "" {
		return h
	}
	return os.TempDir()
}

func fileExists(path string) bool {
	info, err := os.Stat(path)
	return err == nil && !info.IsDir()
}