package main

import (
	"bufio"
	"context"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strconv"
	"strings"

	"adwaita/internal/desktop"
)

type adwaita struct {
	d          desktop.Desk
	home       string
	iconDirs   []string
	portalDirs []string
	uid        int
}

const iface = "org.gnome.desktop.interface"

// ParseINI reads a key file (GTK's settings.ini, qt6ct.conf, a .portal, index.theme): sections of
// key=value, `#` and `;` comments.
func ParseINI(text string) map[string]map[string]string {
	out := map[string]map[string]string{}
	section := ""
	sc := bufio.NewScanner(strings.NewReader(text))
	for sc.Scan() {
		l := strings.TrimSpace(sc.Text())
		if l == "" || strings.HasPrefix(l, "#") || strings.HasPrefix(l, ";") {
			continue
		}
		if strings.HasPrefix(l, "[") && strings.HasSuffix(l, "]") {
			section = l[1 : len(l)-1]
			continue
		}
		if k, v, ok := strings.Cut(l, "="); ok {
			if out[section] == nil {
				out[section] = map[string]string{}
			}
			out[section][strings.TrimSpace(k)] = strings.TrimSpace(v)
		}
	}
	return out
}

func readINI(path string) map[string]map[string]string {
	b, err := os.ReadFile(path)
	if err != nil {
		return nil
	}
	return ParseINI(string(b))
}

// gsetting is one GSettings value, unquoted.
func (a adwaita) gsetting(ctx context.Context, schema, key string) (string, error) {
	r := a.d.AsUser(ctx, "gsettings", "get", schema, key)
	if !r.OK() {
		return "", r.Err()
	}
	return strings.Trim(strings.TrimSpace(r.Stdout), "'"), nil
}

// themeWords are the words of the user manager's environment the theme is about; nothing else of it
// is read back.
var themeWords = []string{"GTK_THEME", "GTK2_RC_FILES", "QT_QPA_PLATFORMTHEME", "QT_STYLE_OVERRIDE", "QT_SELECT",
	"XCURSOR_THEME", "XCURSOR_SIZE", "XDG_CURRENT_DESKTOP"}

func (a adwaita) userEnvironment(ctx context.Context) map[string]string {
	r := a.d.AsUser(ctx, "systemctl", "--user", "show-environment")
	all := desktop.ParseProperties(r.Stdout)
	out := map[string]string{}
	for _, w := range themeWords {
		if v, ok := all[w]; ok {
			out[w] = v
		}
	}
	return out
}

var portalScheme = regexp.MustCompile(`^v u (\d)`)

// portalColourScheme asks the portal what it tells applications: 0 no preference, 1 dark, 2 light.
func (a adwaita) portalColourScheme(ctx context.Context) string {
	r := a.d.AsUser(ctx, "busctl", "--user", "call", "org.freedesktop.portal.Desktop", "/org/freedesktop/portal/desktop",
		"org.freedesktop.portal.Settings", "ReadOne", "ss", "org.freedesktop.appearance", "color-scheme")
	m := portalScheme.FindStringSubmatch(strings.TrimSpace(r.Stdout))
	if !r.OK() || m == nil {
		return "unanswered"
	}
	return map[string]string{"0": "no-preference", "1": "dark", "2": "light"}[m[1]]
}

func (a adwaita) appearance(ctx context.Context, args desktop.Args) (any, error) {
	mode := args.Opt("mode", "")
	if mode != "" && mode != "dark" && mode != "light" {
		return nil, fmt.Errorf("mode is dark or light")
	}
	if mode != "" {
		scheme := map[string]string{"dark": "prefer-dark", "light": "prefer-light"}[mode]
		if r := a.d.AsUser(ctx, "gsettings", "set", iface, "color-scheme", scheme); !r.OK() {
			return nil, r.Err()
		}
	}
	scheme, err := a.gsetting(ctx, iface, "color-scheme")
	if err != nil {
		return nil, fmt.Errorf("GSettings does not answer on the account's bus: %w", err)
	}
	gtkTheme, _ := a.gsetting(ctx, iface, "gtk-theme")
	gtk3 := readINI(filepath.Join(a.home, ".config", "gtk-3.0", "settings.ini"))["Settings"]
	gtk4 := readINI(filepath.Join(a.home, ".config", "gtk-4.0", "settings.ini"))["Settings"]
	qt := readINI(filepath.Join(a.home, ".config", "qt6ct", "qt6ct.conf"))["Appearance"]
	env := a.userEnvironment(ctx)
	answer := map[string]any{
		"gsettings":   map[string]string{"color-scheme": scheme, "gtk-theme": gtkTheme},
		"portal":      a.portalColourScheme(ctx),
		"gtk3":        map[string]string{"theme": gtk3["gtk-theme-name"], "prefer-dark": gtk3["gtk-application-prefer-dark-theme"]},
		"gtk4":        map[string]string{"theme": gtk4["gtk-theme-name"], "prefer-dark": gtk4["gtk-application-prefer-dark-theme"]},
		"qt":          map[string]string{"style": qt["style"], "palette": filepath.Base(qt["color_scheme_path"])},
		"environment": env,
	}
	if mode != "" {
		var stays []string
		if strings.HasSuffix(env["GTK_THEME"], ":dark") && mode == "light" {
			stays = append(stays, "GTK 3 programs: GTK_THEME="+env["GTK_THEME"]+" in the environment pins them dark")
		}
		if mode == "light" {
			stays = append(stays, "the GTK settings files and Qt's palette, which the module declares dark")
		}
		answer["switched"] = mode
		answer["follows_live"] = "programs asking the portal: Electron, Chromium, Firefox, libadwaita and flatpaks"
		if len(stays) > 0 {
			answer["stays"] = stays
		}
		answer["lasts"] = "until the next login, which sets the module's default (dark) again; a persistent choice waits for settings (hq issue 168)"
	}
	return answer, nil
}

// Theme is one installed icon or cursor theme.
type Theme struct {
	Name     string   `json:"name"`
	Dir      string   `json:"dir"`
	Title    string   `json:"title,omitempty"`
	Inherits []string `json:"inherits,omitempty"`
	Cursors  bool     `json:"cursors"`
	Icons    bool     `json:"icons"`
}

// Themes lists the themes in dirs; a name found earlier hides the same name later, as lookups do.
func Themes(dirs []string) []Theme {
	seen := map[string]bool{}
	var out []Theme
	for _, d := range dirs {
		entries, _ := os.ReadDir(d)
		for _, e := range entries {
			if !e.IsDir() && e.Type()&os.ModeSymlink == 0 || seen[e.Name()] {
				continue
			}
			dir := filepath.Join(d, e.Name())
			t := Theme{Name: e.Name(), Dir: dir}
			if info, err := os.Stat(filepath.Join(dir, "cursors")); err == nil && info.IsDir() {
				t.Cursors = true
			}
			if ini := readINI(filepath.Join(dir, "index.theme")); ini != nil {
				th := ini["Icon Theme"]
				t.Title = th["Name"]
				if th["Directories"] != "" {
					t.Icons = true
				}
				for _, i := range strings.Split(th["Inherits"], ",") {
					if i = strings.TrimSpace(i); i != "" {
						t.Inherits = append(t.Inherits, i)
					}
				}
			}
			if !t.Cursors && !t.Icons && t.Title == "" {
				continue
			}
			seen[e.Name()] = true
			out = append(out, t)
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
	return out
}

var cursorName = regexp.MustCompile(`^[A-Za-z0-9._ -]{1,64}$`)

func (a adwaita) cursor(ctx context.Context, args desktop.Args) (any, error) {
	theme := args.Opt("theme", "")
	size, err := args.Whole("size", 0, 8, 256)
	if err != nil {
		return nil, err
	}
	var cursors []string
	installed := map[string]bool{}
	for _, t := range Themes(a.iconDirs) {
		if t.Cursors {
			cursors = append(cursors, t.Name)
			installed[t.Name] = true
		}
	}
	changed := theme != "" || size != 0
	if theme != "" && (!cursorName.MatchString(theme) || !installed[theme]) {
		return nil, fmt.Errorf("%q is not an installed cursor theme; installed: %s", theme, strings.Join(cursors, ", "))
	}
	var resources []string
	if theme != "" {
		if r := a.d.AsUser(ctx, "gsettings", "set", iface, "cursor-theme", theme); !r.OK() {
			return nil, r.Err()
		}
		resources = append(resources, "Xcursor.theme: "+theme)
	}
	if size != 0 {
		if r := a.d.AsUser(ctx, "gsettings", "set", iface, "cursor-size", strconv.Itoa(size)); !r.OK() {
			return nil, r.Err()
		}
		resources = append(resources, "Xcursor.size: "+strconv.Itoa(size))
	}
	answer := map[string]any{"installed": cursors}
	gTheme, _ := a.gsetting(ctx, iface, "cursor-theme")
	gSize, _ := a.gsetting(ctx, iface, "cursor-size")
	answer["gsettings"] = map[string]string{"cursor-theme": gTheme, "cursor-size": gSize}
	env := a.userEnvironment(ctx)
	answer["environment"] = map[string]string{"XCURSOR_THEME": env["XCURSOR_THEME"], "XCURSOR_SIZE": env["XCURSOR_SIZE"]}
	if s, err := a.d.Find(); err == nil {
		senv := s.Env(a.d.Base)
		if len(resources) > 0 {
			if r := a.d.Run(ctx, senv, []byte(strings.Join(resources, "\n")+"\n"), "xrdb", "-nocpp", "-merge", "-"); !r.OK() {
				return nil, r.Err()
			}
		}
		q := a.d.Run(ctx, senv, nil, "xrdb", "-query")
		x := map[string]string{}
		for _, l := range strings.Split(q.Stdout, "\n") {
			if k, v, ok := strings.Cut(l, ":"); ok && strings.HasPrefix(k, "Xcursor.") {
				x[k] = strings.TrimSpace(v)
			}
		}
		answer["x_resources"] = x
	} else {
		answer["x_resources"] = nil
		if changed {
			answer["note"] = "no graphical session: GSettings changed, the X resources not"
		}
	}
	if changed {
		answer["lasts"] = "for windows opened from now on, until the next login"
	}
	return answer, nil
}

func (a adwaita) icons(ctx context.Context, args desktop.Args) (any, error) {
	var themes []Theme
	for _, t := range Themes(a.iconDirs) {
		if t.Icons {
			themes = append(themes, t)
		}
	}
	gtk3 := readINI(filepath.Join(a.home, ".config", "gtk-3.0", "settings.ini"))["Settings"]
	qt := readINI(filepath.Join(a.home, ".config", "qt6ct", "qt6ct.conf"))["Appearance"]
	g, _ := a.gsetting(ctx, iface, "icon-theme")
	return map[string]any{
		"installed": themes,
		"in_use":    map[string]string{"gsettings": g, "gtk": gtk3["gtk-icon-theme-name"], "qt": qt["icon_theme"]},
	}, nil
}

// Backend is one installed portal backend.
type Backend struct {
	Name       string   `json:"name"`
	DBusName   string   `json:"dbus_name"`
	Interfaces []string `json:"interfaces"`
	UseIn      []string `json:"use_in,omitempty"`
	Running    bool     `json:"running"`
}

func splitList(v string) []string {
	var out []string
	for _, x := range strings.Split(v, ";") {
		if x = strings.TrimSpace(x); x != "" {
			out = append(out, x)
		}
	}
	return out
}

// Backends reads the installed `.portal` files.
func Backends(dirs []string) []Backend {
	var out []Backend
	for _, d := range dirs {
		files, _ := filepath.Glob(filepath.Join(d, "*.portal"))
		sort.Strings(files)
		for _, f := range files {
			p := readINI(f)["portal"]
			out = append(out, Backend{Name: strings.TrimSuffix(filepath.Base(f), ".portal"), DBusName: p["DBusName"],
				Interfaces: splitList(p["Interfaces"]), UseIn: splitList(p["UseIn"])})
		}
	}
	return out
}

// PortalConfigs are the files xdg-desktop-portal looks for, in its order (portals.conf(5)): for each
// directory, `<desktop>-portals.conf` for each of the desktops named, then `portals.conf`. The first
// that exists decides everything.
func PortalConfigs(home string, desktops []string) []string {
	dirs := []string{
		filepath.Join(home, ".config", "xdg-desktop-portal"), "/etc/xdg/xdg-desktop-portal", "/etc/xdg-desktop-portal",
		filepath.Join(home, ".local", "share", "xdg-desktop-portal"), "/usr/local/share/xdg-desktop-portal", "/usr/share/xdg-desktop-portal",
	}
	var out []string
	for _, d := range dirs {
		for _, desk := range desktops {
			out = append(out, filepath.Join(d, strings.ToLower(desk)+"-portals.conf"))
		}
		out = append(out, filepath.Join(d, "portals.conf"))
	}
	return out
}

// Resolve says which backend answers each interface the backends implement, given the deciding
// file's [preferred] section: an interface's own key first, else `default`; each a list of backend
// names, the first one that implements the interface wins; `none` answers nothing, `*` any.
// With no file, a backend whose UseIn names the desktop answers.
func Resolve(backends []Backend, preferred map[string]string, desktops []string) map[string]string {
	out := map[string]string{}
	implements := func(b Backend, i string) bool {
		for _, x := range b.Interfaces {
			if x == i {
				return true
			}
		}
		return false
	}
	var all []string
	seen := map[string]bool{}
	for _, b := range backends {
		for _, i := range b.Interfaces {
			if !seen[i] {
				seen[i] = true
				all = append(all, i)
			}
		}
	}
	sort.Strings(all)
	for _, i := range all {
		var want []string
		if preferred != nil {
			if v, ok := preferred[i]; ok {
				want = splitList(v)
			} else {
				want = splitList(preferred["default"])
			}
		} else {
			for _, b := range backends {
				for _, u := range b.UseIn {
					for _, d := range desktops {
						if strings.EqualFold(u, d) {
							want = append(want, b.Name)
						}
					}
				}
			}
		}
		out[i] = "(none)"
	pick:
		for _, w := range want {
			if w == "none" {
				break
			}
			for _, b := range backends {
				if (w == "*" || w == b.Name) && implements(b, i) {
					out[i] = b.Name
					break pick
				}
			}
		}
	}
	return out
}

func (a adwaita) portalCheck(ctx context.Context, args desktop.Args) (any, error) {
	env := a.userEnvironment(ctx)
	desktops := splitColon(env["XDG_CURRENT_DESKTOP"])
	backends := Backends(a.portalDirs)
	names := map[string]bool{}
	if r := a.d.AsUser(ctx, "busctl", "--user", "list", "--no-legend", "--no-pager"); r.OK() {
		for _, l := range strings.Split(r.Stdout, "\n") {
			if f := strings.Fields(l); len(f) > 1 && f[1] != "-" {
				names[f[0]] = true
			}
		}
	}
	for i := range backends {
		backends[i].Running = names[backends[i].DBusName]
	}
	var decided string
	var preferred map[string]string
	looked := PortalConfigs(a.home, desktops)
	for _, f := range looked {
		if ini := readINI(f); ini != nil {
			decided, preferred = f, ini["preferred"]
			if preferred == nil {
				preferred = map[string]string{}
			}
			break
		}
	}
	return map[string]any{
		"desktop":       env["XDG_CURRENT_DESKTOP"],
		"portal":        map[string]bool{"running": names["org.freedesktop.portal.Desktop"]},
		"backends":      backends,
		"decided_by":    decided,
		"preferred":     preferred,
		"answers":       Resolve(backends, preferred, desktops),
		"colour_scheme": a.portalColourScheme(ctx),
	}, nil
}

func splitColon(v string) []string {
	var out []string
	for _, x := range strings.Split(v, ":") {
		if x = strings.TrimSpace(x); x != "" {
			out = append(out, x)
		}
	}
	return out
}