package main

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

	"lemurs/internal/desktop"
)

type lemurs struct {
	d      desktop.Desk
	config string
	log    string
	uid    int
}

// Config is the part of lemurs's configuration the tools read, with lemurs 0.4's defaults.
type Config struct {
	Cache          string `json:"cache_path"`
	X11Scripts     string `json:"x11_scripts"`
	X11Sessions    string `json:"x11_desktop_entries"`
	WaylandScripts string `json:"wayland_scripts"`
	WaylandEntries string `json:"wayland_desktop_entries"`
	Display        string `json:"x11_display"`
	TTY            int    `json:"tty"`
}

// ParseConfig reads the keys it needs from lemurs's TOML: `[section]` headers and `key = value`
// lines, a quoted value unquoted. Enough for this file, which holds no nested values it needs.
func ParseConfig(text string) Config {
	c := Config{
		Cache: "/var/cache/lemurs", X11Scripts: "/etc/lemurs/wms", X11Sessions: "/usr/share/xsessions",
		WaylandScripts: "/etc/lemurs/wayland", WaylandEntries: "/usr/share/wayland-sessions", Display: ":1", TTY: 2,
	}
	section := ""
	sc := bufio.NewScanner(strings.NewReader(text))
	for sc.Scan() {
		line := strings.TrimSpace(sc.Text())
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		if strings.HasPrefix(line, "[") {
			section = strings.Trim(line, "[] ")
			continue
		}
		k, v, ok := strings.Cut(line, "=")
		if !ok {
			continue
		}
		k, v = strings.TrimSpace(k), strings.TrimSpace(v)
		if uq, err := strconv.Unquote(v); err == nil {
			v = uq
		}
		switch section + "." + k {
		case ".cache_path":
			c.Cache = v
		case ".tty":
			if n, err := strconv.Atoi(v); err == nil {
				c.TTY = n
			}
		case "x11.scripts_path":
			c.X11Scripts = v
		case "x11.xsessions_path":
			c.X11Sessions = v
		case "x11.x11_display":
			c.Display = v
		case "wayland.scripts_path":
			c.WaylandScripts = v
		case "wayland.wayland_sessions_path":
			c.WaylandEntries = v
		}
	}
	return c
}

// Session is one entry of the login screen.
type Session struct {
	Name       string `json:"name"`
	Kind       string `json:"kind"`   // x11 or wayland
	Source     string `json:"source"` // script or desktop-entry
	Path       string `json:"path"`
	Exec       string `json:"exec,omitempty"`
	Executable bool   `json:"executable"`
	Offered    bool   `json:"offered"`
}

// ListSessions is every entry lemurs offers, in its order: X desktop entries, Wayland desktop
// entries, X scripts, Wayland scripts (lemurs's get_envs). A script that is not executable is listed
// as not offered, because lemurs skips it with only a warning in its log.
func ListSessions(c Config) []Session {
	var out []Session
	entries := func(dir, kind string) {
		files, _ := os.ReadDir(dir)
		for _, f := range files {
			p := filepath.Join(dir, f.Name())
			name, exec, ok := desktopEntry(p)
			if !ok {
				continue
			}
			out = append(out, Session{Name: name, Kind: kind, Source: "desktop-entry", Path: p, Exec: exec, Executable: true, Offered: true})
		}
	}
	scripts := func(dir, kind string) {
		files, _ := os.ReadDir(dir)
		for _, f := range files {
			p := filepath.Join(dir, f.Name())
			info, err := os.Stat(p)
			if err != nil || info.IsDir() {
				continue
			}
			x := info.Mode()&0o111 != 0
			out = append(out, Session{Name: f.Name(), Kind: kind, Source: "script", Path: p, Exec: firstCommand(p), Executable: x, Offered: x})
		}
	}
	entries(c.X11Sessions, "x11")
	entries(c.WaylandEntries, "wayland")
	scripts(c.X11Scripts, "x11")
	scripts(c.WaylandScripts, "wayland")
	return out
}

// desktopEntry reads Name and Exec from a session's desktop entry, as lemurs does.
func desktopEntry(path string) (string, string, bool) {
	b, err := os.ReadFile(path)
	if err != nil {
		return "", "", false
	}
	in, name, exec := false, "", ""
	for _, l := range strings.Split(string(b), "\n") {
		l = strings.TrimSpace(l)
		if strings.HasPrefix(l, "[") {
			in = l == "[Desktop Entry]"
			continue
		}
		if !in {
			continue
		}
		if v, ok := strings.CutPrefix(l, "Name="); ok && name == "" {
			name = v
		}
		if v, ok := strings.CutPrefix(l, "Exec="); ok && exec == "" {
			exec = v
		}
	}
	if exec == "" {
		return "", "", false
	}
	if name == "" {
		name = exec
	}
	return name, exec, true
}

// firstCommand is a script's first line that is neither blank nor a comment: what it runs.
func firstCommand(path string) string {
	b, err := os.ReadFile(path)
	if err != nil {
		return ""
	}
	for _, l := range strings.Split(string(b), "\n") {
		if l = strings.TrimSpace(l); l != "" && !strings.HasPrefix(l, "#") {
			return l
		}
	}
	return ""
}

// Cached is lemurs's cache file: the session on its first line, the account on its second.
type Cached struct {
	Session string `json:"session"`
	Account string `json:"account"`
}

func readCache(path string) (Cached, error) {
	b, err := os.ReadFile(path)
	if err != nil {
		return Cached{}, err
	}
	lines := strings.Split(strings.TrimSpace(string(b)), "\n")
	c := Cached{Session: strings.TrimSpace(lines[0])}
	if len(lines) > 1 {
		c.Account = strings.TrimSpace(lines[1])
	}
	return c, nil
}

func (l lemurs) readConfig() (Config, error) {
	b, err := os.ReadFile(l.config)
	if err != nil {
		return Config{}, fmt.Errorf("lemurs's configuration cannot be read (%v): is the lemurs module's package installed?", err)
	}
	return ParseConfig(string(b)), nil
}

func (l lemurs) sessions(ctx context.Context, a desktop.Args) (any, error) {
	c, err := l.readConfig()
	if err != nil {
		return nil, err
	}
	answer := map[string]any{"config": l.config, "sessions": ListSessions(c), "directories": c}
	if cached, err := readCache(c.Cache); err == nil {
		answer["default"] = cached
	} else {
		answer["default"] = nil
	}
	return answer, nil
}

var accountName = regexp.MustCompile(`^[a-z_][a-z0-9_-]{0,31}$`)

func (l lemurs) defaultSession(ctx context.Context, a desktop.Args) (any, error) {
	c, err := l.readConfig()
	if err != nil {
		return nil, err
	}
	cached, _ := readCache(c.Cache)
	want := a.Opt("session", "")
	if want == "" {
		return map[string]any{"default": cached, "cache": c.Cache}, nil
	}
	known := false
	var names []string
	for _, s := range ListSessions(c) {
		if s.Offered {
			names = append(names, s.Name)
			known = known || s.Name == want
		}
	}
	if !known {
		sort.Strings(names)
		return nil, fmt.Errorf("%q is not a session lemurs offers; it offers %s", want, strings.Join(names, ", "))
	}
	account := a.Opt("account", cached.Account)
	if account == "" {
		account = os.Getenv("MESH_OPERATOR_ACCOUNT")
	}
	if !accountName.MatchString(account) {
		return nil, fmt.Errorf("%q is not an account name", account)
	}
	content := []byte(want + "\n" + account + "\n")
	var res desktop.Result
	if l.uid == 0 {
		res = l.d.Run(ctx, l.d.Base, content, "tee", c.Cache)
	} else {
		res = l.d.Run(ctx, l.d.Base, content, "sudo", "-n", "tee", c.Cache)
	}
	if !res.OK() {
		return nil, fmt.Errorf("writing %s: %w", c.Cache, res.Err())
	}
	return map[string]any{
		"default": Cached{Session: want, Account: account}, "was": cached, "cache": c.Cache,
		"shown": "when lemurs next starts (a reboot, or the login manager restarted); lemurs rewrites it after each login when remember is on",
	}, nil
}

// Login is one event of the login screen.
type Login struct {
	Time    string `json:"time"`
	Event   string `json:"event"` // opened, closed or failed
	Account string `json:"account,omitempty"`
}

var (
	opened  = regexp.MustCompile(`pam_unix\(lemurs:session\): session opened for user ([^(\s]+)`)
	closed  = regexp.MustCompile(`pam_unix\(lemurs:session\): session closed for user ([^(\s]+)`)
	failed  = regexp.MustCompile(`pam_unix\(lemurs:auth\): authentication failure;.*?user=(\S+)`)
	started = regexp.MustCompile(`^\[(\S+) INFO\s+lemurs\] Starting new session for '([^']*)' in environment '(.*)'$`)
)

// ParseJournal reads `journalctl -o short-iso` lines of lemurs into login events.
func ParseJournal(text string) []Login {
	var out []Login
	for _, line := range strings.Split(text, "\n") {
		f := strings.Fields(line)
		if len(f) < 3 || strings.HasPrefix(line, "--") {
			continue
		}
		for _, p := range []struct {
			re    *regexp.Regexp
			event string
		}{{opened, "opened"}, {closed, "closed"}, {failed, "failed"}} {
			if m := p.re.FindStringSubmatch(line); m != nil {
				out = append(out, Login{Time: f[0], Event: p.event, Account: m[1]})
			}
		}
	}
	return out
}

// Started is one session lemurs started, from its own log.
type Started struct {
	Time        string `json:"time"`
	Account     string `json:"account"`
	Environment string `json:"environment"`
}

// ParseStarts reads lemurs's own log for the sessions it started and which entry each ran.
func ParseStarts(text string) []Started {
	var out []Started
	for _, line := range strings.Split(text, "\n") {
		if m := started.FindStringSubmatch(line); m != nil {
			out = append(out, Started{Time: m[1], Account: m[2], Environment: m[3]})
		}
	}
	return out
}

var since = regexp.MustCompile(`^[-+]?[0-9A-Za-z :.]{1,40}$`)

func (l lemurs) logins(ctx context.Context, a desktop.Args) (any, error) {
	from := a.Opt("since", "-7d")
	if !since.MatchString(from) {
		return nil, fmt.Errorf("since is a time journalctl reads, e.g. -7d or 2026-10-01")
	}
	limit, err := a.Whole("limit", 50, 1, 500)
	if err != nil {
		return nil, err
	}
	res := l.d.Plain(ctx, "journalctl", "_COMM=lemurs", "--since", from, "-o", "short-iso", "--no-pager", "-q")
	if !res.OK() {
		return nil, res.Err()
	}
	events := ParseJournal(res.Stdout)
	cut := false
	if len(events) > limit {
		events, cut = events[len(events)-limit:], true
	}
	answer := map[string]any{"since": from, "events": events}
	if cut {
		answer["cut"] = true
	}
	if b, err := os.ReadFile(l.log); err == nil {
		answer["started"] = ParseStarts(string(b))
	}
	return answer, nil
}