package lua

import (
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"sort"
	"strings"
	"sync"
	"time"
)

// Package lua — 登录会话抽象（R4-e）
//
// 用户需求：把"同类插件"做出来 —— 插件自己**驱动外部平台的链接认证**，拿到
// 凭据后把平台接进网关当源用；配独立标签页做登录/认证/配置。
//
// 用户原提议：服务端通过 VNC 穿透一个无头浏览器，用户在自己浏览器里操作。
// 实测参考插件（dsh-our-free-model，13 个账号渠道）后的结论是：
//
//	puppeteer / playwright / chromium / headless / vnc / selenium  →  0 处
//
// 它的登录是**把 URL 交给用户自己的浏览器**，插件轮询凭据是否就绪：
//
//	loginUrl 113 次 · cookie 133 次 · oauth 43 次 · deviceCode 8 次 · qrcode 7 次
//
// 所以本文件实现**多流程**抽象，VNC 是其中一条默认关闭的逃生舱：
//
//	link-poll  给 URL，插件轮询结果        ← 首选，覆盖设备码/OAuth
//	callback   OAuth 重定向回来带 code     ← 复用已有的自定义挂载点
//	paste      用户把 cookie/token 粘回来  ← 兜住 cookie 类渠道
//	vnc        服务端出浏览器              ← 逃生舱，默认关闭
//
// 为什么不以 VNC 为主路径（四条具体理由，非偏好）：
//
//  1. Passkey/WebAuthn 基本不可用：凭据绑在用户设备，VNC 里是另一台机器，
//     跨设备流程要蓝牙/扫码，而 VNC 延迟让这体验很差。
//  2. 无头浏览器更容易被判为机器人，不是更少 —— 登录场景最不能踩这个。
//  3. 安全面：llmsproxy 以 root 运行（master.key 是 0600 root），systemd 已加
//     ProtectHome=yes。从 root 服务开一条 VNC 通道到一个"即将登录用户各平台
//     账号"的浏览器，等于把提权面与高价值目标绑在一起。
//  4. 最关键：**它不解决取凭据**。VNC 登录后凭据活在浏览器 profile 的 cookie
//     里，不在插件里；还是要提取 profile，而那正是最脆弱的一环。轮询流程是
//     直接产出 token 的。
//
// VNC 唯一不可替代的场景：服务端与用户不同网，且平台要求登录 IP 与调用 IP
// 一致（区域限制）。所以它作为可选项存在，而不是地基。

// LoginFlow names one way a plugin can obtain credentials for a platform.
type LoginFlow string

const (
	// FlowLinkPoll: the plugin mints a URL (device code / OAuth authorize), the
	// operator opens it in their OWN browser, and the plugin polls until the
	// platform reports the credential. This is the reference implementation's
	// dominant pattern and needs no browser on the server.
	FlowLinkPoll LoginFlow = "link-poll"
	// FlowCallback: a standard OAuth redirect. The plugin claims a route (the
	// custom mount points from Phase 6 already allow /plugins/<name>/...) and the
	// platform's redirect lands there with the code. The session carries the
	// state nonce so a callback cannot be replayed into the wrong session.
	FlowCallback LoginFlow = "callback"
	// FlowPaste: the operator pastes a cookie or token into the settings page.
	// Covers the cookie-based channels (133 hits in the reference plugin) where
	// no OAuth exists at all.
	FlowPaste LoginFlow = "paste"
	// FlowVNC: a server-side browser exposed over VNC. Opt-in escape hatch, off
	// by default (see the header note).
	FlowVNC LoginFlow = "vnc"
)

// LoginSessionState is the lifecycle of one attempt.
type LoginSessionState string

const (
	LoginPending   LoginSessionState = "pending"
	LoginCompleted LoginSessionState = "completed"
	LoginFailed    LoginSessionState = "failed"
	LoginExpired   LoginSessionState = "expired"
	LoginCancelled LoginSessionState = "cancelled"
)

// LoginSession is one in-flight authentication attempt.
//
// It is created by a plugin (or the settings page) and polled until it reaches a
// terminal state. The credential itself is never stored here — the plugin stores
// it in its own vault (__llmsproxy_secrets) and reports bare completion. Keeping
// tokens out of the session record means a session listing, which IS exposed to
// the UI, can never leak one.
type LoginSession struct {
	ID       string            `json:"id"`
	Plugin   string            `json:"plugin"`
	Platform string            `json:"platform"`
	Flow     LoginFlow         `json:"flow"`
	State    LoginSessionState `json:"state"`
	// URL is what the operator must open (link-poll) or the VNC entry point.
	URL string `json:"url,omitempty"`
	// UserCode is the short code a device flow shows (e.g. "WDJB-MJHT").
	UserCode string `json:"user_code,omitempty"`
	// State nonce for the callback flow. A callback whose state does not match is
	// refused, so an attacker cannot inject a code into someone else's session.
	Nonce string `json:"-"`
	// Message explains a non-pending state in the operator's terms.
	Message string `json:"message,omitempty"`
	// Account is a display label the plugin reports on success (a login name),
	// never a secret.
	Account   string    `json:"account,omitempty"`
	CreatedAt time.Time `json:"created_at"`
	ExpiresAt time.Time `json:"expires_at"`
}

// loginSessionTTL bounds how long a pending attempt lives. A login the operator
// abandoned must not leave a pollable session (and a browser tab prompt) forever;
// the reference implementation uses the same 15 minute idea.
const loginSessionTTL = 15 * time.Minute

// loginSessions owns all in-flight attempts.
type loginSessions struct {
	mu   sync.Mutex
	byID map[string]*LoginSession
}

func newLoginSessions() *loginSessions {
	return &loginSessions{byID: map[string]*LoginSession{}}
}

// newLoginID returns an unguessable session id.
//
// Unguessable matters: the id is the handle the settings page polls, and the
// callback route carries its nonce. A sequential id would let a caller enumerate
// other plugins' pending logins.
func newLoginID() string {
	var b [12]byte
	if _, err := rand.Read(b[:]); err != nil {
		// crypto/rand failing is not a condition this process can serve around;
		// fall back to a time-based id rather than returning empty.
		return fmt.Sprintf("ls-%d", time.Now().UnixNano())
	}
	return "ls-" + hex.EncodeToString(b[:])
}

// newLoginNonce returns the callback state nonce.
func newLoginNonce() string {
	var b [16]byte
	if _, err := rand.Read(b[:]); err != nil {
		return fmt.Sprintf("n-%d", time.Now().UnixNano())
	}
	return hex.EncodeToString(b[:])
}

// BeginLogin starts a session. The plugin decides the flow and supplies what
// that flow needs; the kernel only owns the lifecycle.
func (ps *Plugins) BeginLogin(s LoginSession) (*LoginSession, error) {
	if s.Plugin == "" {
		return nil, fmt.Errorf("login session requires a plugin")
	}
	if ps.find(s.Plugin) == nil {
		return nil, fmt.Errorf("plugin %s not found", s.Plugin)
	}
	switch s.Flow {
	case FlowLinkPoll, FlowCallback, FlowPaste, FlowVNC:
	default:
		return nil, fmt.Errorf("unknown login flow %q", s.Flow)
	}
	if s.Flow == FlowVNC && !ps.VNCEnabled() {
		return nil, fmt.Errorf("the VNC login flow is disabled; enable it in settings if the platform " +
			"requires a server-side browser (it is off by default for security)")
	}
	now := time.Now()
	out := &LoginSession{
		ID:        newLoginID(),
		Plugin:    s.Plugin,
		Platform:  s.Platform,
		Flow:      s.Flow,
		State:     LoginPending,
		URL:       s.URL,
		UserCode:  s.UserCode,
		Nonce:     newLoginNonce(),
		CreatedAt: now,
		ExpiresAt: now.Add(loginSessionTTL),
	}
	ps.logins().mu.Lock()
	ps.logins().sweepLocked(now)
	ps.logins().byID[out.ID] = out
	ps.logins().mu.Unlock()
	cp := out.clone()
	return &cp, nil
}

// GetLogin returns one session, expiring it if its TTL has passed.
//
// Expiry is applied on READ rather than by a background timer: a gateway with no
// logins in flight pays nothing, and a session can never be observed as pending
// after its deadline even if no goroutine happens to have run.
func (ps *Plugins) GetLogin(id string) (*LoginSession, bool) {
	now := time.Now()
	ls := ps.logins()
	ls.mu.Lock()
	defer ls.mu.Unlock()
	ls.sweepLocked(now)
	s, ok := ls.byID[id]
	if !ok {
		return nil, false
	}
	cp := s.clone()
	return &cp, true
}

// ResolveLogin moves a session to a terminal state. It is the only way a session
// ends successfully, so the credential handling stays in one place.
//
// `account` is a display label only — never a token. The plugin has already
// stored the credential in its vault by the time it calls this; passing it
// through here would put it in a UI-visible record.
func (ps *Plugins) ResolveLogin(id string, state LoginSessionState, account, message string) error {
	switch state {
	case LoginCompleted, LoginFailed, LoginExpired, LoginCancelled:
	default:
		return fmt.Errorf("resolveLogin needs a terminal state, got %q", state)
	}
	ls := ps.logins()
	ls.mu.Lock()
	defer ls.mu.Unlock()
	s, ok := ls.byID[id]
	if !ok {
		return fmt.Errorf("no such login session")
	}
	if s.isTerminal() {
		// Already finished. Reporting success again would let a plugin turn a
		// cancelled session into a completed one.
		return fmt.Errorf("login session is already %s", s.State)
	}
	s.State = state
	s.Account = account
	s.Message = message
	return nil
}

// MatchCallbackNonce finds the pending callback session for a nonce.
//
// The nonce is the CSRF defence for the callback flow: a redirect that does not
// carry the nonce of a live session is not answered, so a code delivered to an
// attacker-controlled session cannot be replayed into this gateway's login.
func (ps *Plugins) MatchCallbackNonce(nonce string) (*LoginSession, bool) {
	if nonce == "" {
		return nil, false
	}
	now := time.Now()
	ls := ps.logins()
	ls.mu.Lock()
	defer ls.mu.Unlock()
	ls.sweepLocked(now)
	for _, s := range ls.byID {
		if s.Nonce == nonce && s.Flow == FlowCallback && !s.isTerminal() {
			cp := s.clone()
			return &cp, true
		}
	}
	return nil, false
}

// ListLogins returns a plugin's sessions, newest first, for its settings page.
func (ps *Plugins) ListLogins(plugin string) []LoginSession {
	now := time.Now()
	ls := ps.logins()
	ls.mu.Lock()
	defer ls.mu.Unlock()
	ls.sweepLocked(now)
	out := make([]LoginSession, 0, 4)
	for _, s := range ls.byID {
		if s.Plugin != plugin {
			continue
		}
		cp := s.clone()
		cp.Nonce = "" // never expose the nonce to the UI
		out = append(out, cp)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].CreatedAt.After(out[j].CreatedAt) })
	return out
}

// CancelLogins drops a plugin's pending sessions. Used on plugin unload so an
// uninstalled plugin leaves no pollable login behind.
func (ps *Plugins) CancelLogins(plugin string) int {
	ls := ps.logins()
	ls.mu.Lock()
	defer ls.mu.Unlock()
	n := 0
	for _, s := range ls.byID {
		if s.Plugin == plugin && !s.isTerminal() {
			s.State = LoginCancelled
			n++
		}
	}
	return n
}

// sweepLocked expires overdue sessions and reaps terminal ones. Caller holds mu.
func (ls *loginSessions) sweepLocked(now time.Time) {
	for id, s := range ls.byID {
		if !s.isTerminal() && now.After(s.ExpiresAt) {
			s.State = LoginExpired
			s.Message = "the login attempt timed out; start it again"
		}
		// Terminal sessions are reaped after a grace period so the UI can show
		// the outcome. Deleting immediately would make a completed login look
		// like it never happened.
		if s.isTerminal() && now.After(s.ExpiresAt.Add(loginSessionTTL)) {
			delete(ls.byID, id)
		}
	}
}

func (s *LoginSession) isTerminal() bool {
	switch s.State {
	case LoginCompleted, LoginFailed, LoginExpired, LoginCancelled:
		return true
	}
	return false
}

// clone returns a copy so callers cannot mutate the stored session, and so a
// data race cannot expose a half-updated struct to the UI.
func (s *LoginSession) clone() LoginSession {
	cp := *s
	return cp
}

// loginSessions lazily creates the store so a Plugins value built in a test
// without construction still works.
func (ps *Plugins) logins() *loginSessions {
	ps.loginOnce.Do(func() {
		if ps.loginStore == nil {
			ps.loginStore = newLoginSessions()
		}
	})
	return ps.loginStore
}

// VNCEnabled reports whether the VNC escape hatch is on. Off by default: a
// server-side browser is the highest-risk login path and must be a deliberate
// operator choice.
func (ps *Plugins) VNCEnabled() bool {
	ps.mu.RLock()
	defer ps.mu.RUnlock()
	return ps.vncPermitted
}

// SetVNCEnabled turns the VNC login flow on or off.
func (ps *Plugins) SetVNCEnabled(on bool) {
	ps.mu.Lock()
	ps.vncPermitted = on
	ps.mu.Unlock()
}

// ---- 登录主机授权 ----
//
// 登录流程要访问的 host（auth.huaweicloud.com、accounts.google.com…）不是源，
// 所以出站白名单默认会掐断整个流程（已实测确认）。这是**正确**的默认：白名单
// 的意义就是"插件只能去它该去的地方"。
//
// 解法与内核权限同一个姿态：插件在源码里**声明**它需要哪些登录 host
// （plugin.auth_hosts），运维在设置页批准后才放行。声明是请求，批准才是授权。
//
// 为什么要声明而不是给个通用开关：一个能访问任意 host 的插件等于没有白名单，
// 而"登录"这个理由足够正当，正当到很容易被用来把整张名单打开。要求逐个列出，
// 运维才有机会看出"这个插件为什么要访问一个我没听说过的域名"。

// PluginAuthHosts returns the login hosts a plugin declared.
func (ps *Plugins) PluginAuthHosts(plugin string) []string {
	ps.mu.RLock()
	defer ps.mu.RUnlock()
	for _, p := range ps.plugins {
		if p.Info.Name == plugin {
			return append([]string(nil), p.AuthHosts...)
		}
	}
	return nil
}

// GrantAuthHosts approves a set of login hosts for a plugin.
//
// Only hosts the plugin DECLARED may be granted: accepting an arbitrary host from
// the settings page would make the declaration decorative, and the point of the
// declaration is that the operator reviews a list the plugin itself committed to
// in source that is on disk and reviewable.
func (ps *Plugins) GrantAuthHosts(plugin string, hosts []string) error {
	if ps.find(plugin) == nil {
		return fmt.Errorf("plugin %s not found", plugin)
	}
	declared := map[string]bool{}
	for _, h := range ps.PluginAuthHosts(plugin) {
		declared[normalizeHost(h)] = true
	}
	clean := make([]string, 0, len(hosts))
	for _, h := range hosts {
		hn := normalizeHost(h)
		if hn == "" {
			continue
		}
		if !declared[hn] {
			return fmt.Errorf("plugin %s did not declare auth host %q", plugin, hn)
		}
		clean = append(clean, hn)
	}
	sort.Strings(clean)
	ps.mu.Lock()
	if ps.authHosts == nil {
		ps.authHosts = map[string][]string{}
	}
	if len(clean) == 0 {
		delete(ps.authHosts, plugin)
	} else {
		ps.authHosts[plugin] = clean
	}
	ps.rebuildOutboundAllowlistLocked()
	ps.saveKernelPermissionsLocked()
	ps.mu.Unlock()
	return nil
}

// AuthHostsGranted returns the approved hosts for each plugin (for the UI).
func (ps *Plugins) AuthHostsGranted() map[string][]string {
	ps.mu.RLock()
	defer ps.mu.RUnlock()
	out := make(map[string][]string, len(ps.authHosts))
	for k, v := range ps.authHosts {
		out[k] = append([]string(nil), v...)
	}
	return out
}

// normalizeHost lowercases a host and strips a port, so "Auth.Example.com:443"
// and "auth.example.com" cannot both be granted under different names.
func normalizeHost(h string) string {
	h = strings.ToLower(strings.TrimSpace(h))
	if i := strings.LastIndex(h, ":"); i > 0 && !strings.Contains(h[i:], "]") {
		// Leave IPv6 literals ("[::1]:443") alone apart from the port.
		h = h[:i]
	}
	h = strings.Trim(h, "[]")
	return h
}

// rebuildOutboundAllowlistLocked folds the SOURCE hosts and every GRANTED auth
// host into the allowlist the HTTP bridge consults. Caller holds ps.mu.
//
// Declared-but-not-granted hosts are deliberately excluded: that exclusion is the
// whole security property, so it is the one thing this function must not be
// tempted to "helpfully" relax.
func (ps *Plugins) rebuildOutboundAllowlistLocked() {
	hosts := append([]string(nil), ps.sourceHosts...)
	for _, granted := range ps.authHosts {
		hosts = append(hosts, granted...)
	}
	ps.allowHTTP = newHTTPAllowlist(hosts)
}