// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: PolyForm-Noncommercial-1.0.0

package admin

import (
	"fmt"
	"html"
	"log/slog"
	"net/http"
	"net/netip"
	"strconv"
	"strings"
	"time"

	"sourcedock.dev/petrbalvin/volumen/internal/audit"
	"sourcedock.dev/petrbalvin/volumen/internal/backup"
	"sourcedock.dev/petrbalvin/volumen/internal/config"
	"sourcedock.dev/petrbalvin/volumen/internal/i18n"
	"sourcedock.dev/petrbalvin/volumen/internal/post"
	"sourcedock.dev/petrbalvin/volumen/internal/ratelimit"
	"sourcedock.dev/petrbalvin/volumen/internal/session"
	"sourcedock.dev/petrbalvin/volumen/internal/store"
	"sourcedock.dev/petrbalvin/volumen/internal/templates"
	"sourcedock.dev/petrbalvin/volumen/internal/tokens"
	"sourcedock.dev/petrbalvin/volumen/internal/users"
	"sourcedock.dev/petrbalvin/volumen/internal/web"
	"sourcedock.dev/petrbalvin/volumen/internal/webhooks"
)

// Content is the content surface the admin uses: every post, one post by
// slug, the write and delete paths, the revision archive and the media
// library. It is an interface rather than *store.Store so the handlers can
// be tested against a fake and a second backend stays conceivable.
type Content interface {
	All() []*post.Post
	Find(slug, lang string) *post.Post
	Save(p *post.Post) (*post.Post, error)
	Delete(slug, lang string) (*post.Post, bool, error)
	Undelete(slug string) *post.Post
	Revisions(slug string) []store.Revision
	RevisionContent(slug, name string) string
	RestoreRevision(p *post.Post, name string) *post.Post
	InvalidateCache()
	StoreUpload(originalName string, data []byte) (string, error)
	MediaPath(name string) (string, error)
	DeleteMedia(url string) bool
	ListMedia() []store.Media
}

// Deps are the shared services the admin UI needs.
type Deps struct {
	Config    *config.Config
	Store     Content
	Users     *users.Users
	Templates *templates.Store
	Tokens    *tokens.Store
	Audit     *audit.Log
	LoginLim  *ratelimit.LoginLimiter
	Sessions  *session.Store
	Webhooks  *webhooks.Manager

	// PreviewKey signs the shareable preview links: the session secret
	// the app layer resolved, from [admin].session_key or from the
	// secret.key file it generated, so a default deployment offers
	// preview links the way the configuration documents it. Empty means
	// no link can be signed and none is offered.
	PreviewKey string

	// WebhooksFile is the admin-managed hook store the settings forms
	// rewrite, and StaticWebhooks the hooks that came from config.toml
	// and are read-only here. Together they are what the manager
	// delivers; every mutation re-saves the file and refreshes the
	// manager with the merge of the two.
	WebhooksFile   string
	StaticWebhooks []webhooks.Webhook

	Version string
	OnEvent func(event string, payload map[string]any)
	Backup  backup.Options

	// CheckUpdate returns the latest available version ("" when none),
	// and SelfUpdate replaces the running binary; both are wired by the
	// CLI layer and may be nil.
	CheckUpdate func() (string, error)
	SelfUpdate  func() (target string, err error)

	// UpdateInfo returns the newer version for the update banner, or ""
	// when the running version is current.
	UpdateInfo func() string
}

// Admin serves /admin routes.
type Admin struct {
	deps     Deps
	renderer *Renderer

	// trustedProxies are the peers whose X-Forwarded-For is believed.
	// The configuration is validated before the admin is built, so a
	// parse failure here cannot happen.
	trustedProxies []netip.Prefix
}

// New builds the admin handler.
func New(deps Deps) (*Admin, error) {
	renderer, err := NewRenderer()
	if err != nil {
		return nil, err
	}
	trusted, err := deps.Config.TrustedProxyPrefixes()
	if err != nil {
		return nil, err
	}
	if !deps.Config.Server.TrustProxy {
		trusted = nil
	}
	return &Admin{deps: deps, renderer: renderer, trustedProxies: trusted}, nil
}

// SetUpdateHooks wires the version-check callbacks after construction.
func (a *Admin) SetUpdateHooks(check func() (string, error), selfUpdate func() (string, error)) {
	a.deps.CheckUpdate = check
	a.deps.SelfUpdate = selfUpdate
	a.deps.UpdateInfo = func() string {
		latest, err := check()
		if err != nil || latest == "" || latest == a.deps.Version {
			return ""
		}
		return latest
	}
}

// Handler returns the admin route tree.
func (a *Admin) Handler() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /admin", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, "/admin/", http.StatusSeeOther)
	})
	// The interface sheets and fonts: public by design (the login page
	// needs them before any session), confined to the embedded set.
	mux.HandleFunc("GET /admin/assets/", web.AssetHandler)
	mux.HandleFunc("GET /admin/login", a.handleLoginForm)
	mux.HandleFunc("POST /admin/login", a.handleLogin)
	mux.HandleFunc("GET /admin/twofactor", a.handleTwofactorForm)
	mux.HandleFunc("POST /admin/twofactor", a.handleTwofactor)
	mux.HandleFunc("POST /admin/logout", a.handleLogout)
	a.registerSetupRoutes(mux)
	a.registerPostRoutes(mux)
	a.registerSettingsRoutes(mux)
	a.registerMediaRoutes(mux)
	// The subtree catch-all answers any /admin path no route above claims,
	// so a mistyped URL meets the shell's own 404 page rather than the
	// engine's bare text. It is the least specific pattern, so every
	// registered route still wins, and it sits behind requireLogin so an
	// anonymous visitor is sent to the sign-in screen first.
	mux.HandleFunc("/admin/", a.requireLogin(a.handleNotFound))
	return mux
}

// handleNotFound renders the admin 404 page inside the shell. Nothing
// about the request reaches the page beyond the interface strings, so the
// answer leaks nothing and carries the honest status.
func (a *Admin) handleNotFound(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet && r.Method != http.MethodHead {
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	}
	a.renderPage(w, r, "notfound.html", a.pageData(r), http.StatusNotFound)
}

// record appends an audit entry for one request, filling in the acting
// user and the client address so the log can answer "who, from where".
func (a *Admin) record(r *http.Request, action, resource string, detail map[string]any) {
	a.deps.Audit.Record(audit.Entry{
		User:     a.currentUser(r),
		Action:   action,
		Resource: resource,
		Detail:   detail,
		IP:       a.clientIP(r),
	})
}

// clientIP resolves the request origin with proxy awareness.
func (a *Admin) clientIP(r *http.Request) string {
	return web.ClientIP(r, a.trustedProxies)
}

// lang resolves the interface language for one request: the account's
// choice first, then the language cookie the choice set for the login
// screen, then the site language when it is one the UI ships, and
// English otherwise.
func (a *Admin) lang(r *http.Request, record *users.User) string {
	if record != nil && record.Language != "" {
		return record.Language
	}
	if c, err := r.Cookie(i18n.Cookie); err == nil {
		if lang := i18n.Normalize(c.Value); lang != "" {
			return lang
		}
	}
	if lang := i18n.Normalize(a.deps.Config.Site.Language); lang != "" {
		return lang
	}
	return "en"
}

// theme resolves the colour scheme for one request: the account's
// choice first, then the theme cookie the choice set for the login
// screen, then the default scheme.
func (a *Admin) theme(r *http.Request, record *users.User) string {
	if record != nil && record.Theme != "" {
		if web.ValidTheme(record.Theme) {
			return record.Theme
		}
	}
	if c, err := r.Cookie(web.ThemeCookie); err == nil && web.ValidTheme(c.Value) {
		return c.Value
	}
	return web.DefaultTheme
}

// langFor resolves the interface language from the request alone,
// without a page context: the signed-in account's choice, the language
// cookie, the site language, then English.
func (a *Admin) langFor(r *http.Request) string {
	return a.lang(r, a.deps.Users.Find(session.FromContext(r.Context()).Get("user")))
}

// tr translates an admin interface message in the request's language.
func (a *Admin) tr(r *http.Request, s string) string {
	return i18n.Admin.T(a.langFor(r), s)
}

// trf translates an admin interface message with one value.
func (a *Admin) trf(r *http.Request, s, arg string) string {
	return i18n.Admin.Tf(a.langFor(r), s, arg)
}

// trf2 translates an admin interface message with two values.
func (a *Admin) trf2(r *http.Request, s, first, second string) string {
	return i18n.Admin.Tf2(a.langFor(r), s, first, second)
}

// pageData builds the shared template context for one request.
func (a *Admin) pageData(r *http.Request) *PageData {
	sess := session.FromContext(r.Context())
	username := sess.Get("user")
	record := a.deps.Users.Find(username)
	data := &PageData{
		Config:            a.deps.Config,
		Path:              r.URL.Path,
		CSPNonce:          web.Nonce(r.Context()),
		Version:           a.deps.Version,
		Lang:              a.lang(r, record),
		Theme:             a.theme(r, record),
		CurrentUser:       username,
		CurrentUserRecord: record,
		UsersExist:        a.deps.Users.Any(),
		CSRFToken:         CSRFToken(sess),
		IsLogin:           strings.HasPrefix(r.URL.Path, "/admin/login") || r.URL.Path == "/admin/twofactor",
		IsSetup:           r.URL.Path == "/admin/setup",
		NavPosts:          r.URL.Path == "/admin/" || r.URL.Path == "/admin",
		NavNew:            r.URL.Path == "/admin/posts/new",
		NavImport:         r.URL.Path == "/admin/posts/import",
		NavMedia:          strings.HasPrefix(r.URL.Path, "/admin/media"),
		NavSettings:       strings.HasPrefix(r.URL.Path, "/admin/settings"),
	}
	if a.deps.UpdateInfo != nil {
		data.UpdateAvailable = a.deps.UpdateInfo()
	}
	if record != nil {
		data.IsAuthenticated = true
		data.CurrentRole = record.Role
		data.DisplayName = record.Name
		data.UserPhoto = record.Photo
		if data.DisplayName == "" {
			data.DisplayName = record.Username
		}
		data.UserInitial = firstUpper(data.DisplayName, "?")
	}
	return data
}

// templateEscape neutralises the characters that would end an HTML
// comment or open a tag inside one.
func templateEscape(s string) string {
	s = strings.ReplaceAll(s, "--", "- -")
	return html.EscapeString(s)
}

// renderPage executes an admin page with HTTP semantics.
func (a *Admin) renderPage(w http.ResponseWriter, r *http.Request, page string, data *PageData, status int) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(status)
	if err := a.renderer.Render(r.Context(), w, page, data); err != nil {
		// The status line is already sent, and the page is the user's
		// only signal, so it carries a note rather than nothing. The
		// text is escaped: an error message quoting content must not
		// close the comment and inject markup.
		fmt.Fprintf(w, "<!-- template error: %s -->", templateEscape(err.Error()))
	}
}

func (a *Admin) handleLoginForm(w http.ResponseWriter, r *http.Request) {
	sess := session.FromContext(r.Context())
	if sess.Get("user") != "" {
		http.Redirect(w, r, "/admin/", http.StatusSeeOther)
		return
	}
	// A session that already answered the password sits halfway in: the
	// second step is where it belongs, not the first one again.
	if sess.Get("totp_user") != "" {
		http.Redirect(w, r, "/admin/twofactor", http.StatusSeeOther)
		return
	}
	// A deployment with no accounts is one that has not been set up
	// yet: the login screen would only be a door with nothing behind
	// it, so the first visit goes to the wizard instead. It is a redirect,
	// not a rewrite, so the wizard has its own honest URL.
	if needed, broken := a.setupNeeded(); needed && broken == nil {
		http.Redirect(w, r, "/admin/setup", http.StatusSeeOther)
		return
	}
	a.renderPage(w, r, "login.html", a.pageData(r), http.StatusOK)
}

func (a *Admin) handleLogin(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseForm(); err != nil {
		http.Error(w, "bad form", http.StatusBadRequest)
		return
	}
	ip := a.clientIP(r)
	a.deps.LoginLim.Record(ip)
	if blocked, retryAfter := a.deps.LoginLim.Blocked(ip); blocked {
		data := a.pageData(r)
		data.Error = i18n.Admin.N(a.lang(r, nil), "login.seconds", retryAfter)
		data.RetryAfter = retryAfter
		a.renderPage(w, r, "login.html", data, http.StatusTooManyRequests)
		return
	}
	sess := session.FromContext(r.Context())
	if !ValidateCSRF(r, sess) {
		http.Error(w, "Invalid CSRF token", http.StatusForbidden)
		return
	}
	username := r.PostFormValue("username")
	password := r.PostFormValue("password")
	if user := a.deps.Users.Authenticate(username, password); user != nil {
		// An account with the second factor answers one more question
		// before it is in: the session holds the half-way name and no
		// user, so nothing behind requireLogin opens yet.
		if user.TotpSecret != "" {
			sess.Set("totp_user", user.Username)
			sess.Set("totp_at", strconv.FormatInt(time.Now().Unix(), 10))
			http.Redirect(w, r, "/admin/twofactor", http.StatusSeeOther)
			return
		}
		sess.Set("user", user.Username)
		sess.Set("pv", sessionFingerprint(user.PasswordHash))
		http.Redirect(w, r, "/admin/", http.StatusSeeOther)
		return
	}
	data := a.pageData(r)
	data.Error = data.Tr("Invalid username or password.")
	a.renderPage(w, r, "login.html", data, http.StatusUnauthorized)
}

// twofactorWindow bounds how long a password already answered may wait
// for its code before the whole sign-in starts over.
const twofactorWindow = 10 * time.Minute

// handleTwofactorForm shows the code prompt while a session holds a
// password-verified name; anything else goes back to the first step.
func (a *Admin) handleTwofactorForm(w http.ResponseWriter, r *http.Request) {
	sess := session.FromContext(r.Context())
	if sess.Get("user") != "" {
		http.Redirect(w, r, "/admin/", http.StatusSeeOther)
		return
	}
	if !a.twofactorPending(sess) {
		http.Redirect(w, r, "/admin/login", http.StatusSeeOther)
		return
	}
	a.renderPage(w, r, "twofactor.html", a.pageData(r), http.StatusOK)
}

func (a *Admin) twofactorPending(sess *session.Session) bool {
	name := sess.Get("totp_user")
	if name == "" {
		return false
	}
	started, err := strconv.ParseInt(sess.Get("totp_at"), 10, 64)
	if err != nil || time.Since(time.Unix(started, 0)) > twofactorWindow {
		sess.Delete("totp_user")
		sess.Delete("totp_at")
		return false
	}
	return true
}

// handleTwofactor answers the second question: a six-digit code from
// the account's application, or one of its recovery codes. The same
// limiter guards it as the password, so guessing a code costs the same
// lockout as guessing a password.
func (a *Admin) handleTwofactor(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseForm(); err != nil {
		http.Error(w, "bad form", http.StatusBadRequest)
		return
	}
	ip := a.clientIP(r)
	a.deps.LoginLim.Record(ip)
	if blocked, retryAfter := a.deps.LoginLim.Blocked(ip); blocked {
		data := a.pageData(r)
		data.Error = i18n.Admin.N(a.lang(r, nil), "login.seconds", retryAfter)
		data.RetryAfter = retryAfter
		a.renderPage(w, r, "twofactor.html", data, http.StatusTooManyRequests)
		return
	}
	sess := session.FromContext(r.Context())
	if !ValidateCSRF(r, sess) {
		http.Error(w, "Invalid CSRF token", http.StatusForbidden)
		return
	}
	if !a.twofactorPending(sess) {
		http.Redirect(w, r, "/admin/login", http.StatusSeeOther)
		return
	}
	name := sess.Get("totp_user")
	code := strings.TrimSpace(r.PostFormValue("code"))
	ok := false
	if isTotpShape(code) {
		ok = a.deps.Users.VerifyTotp(name, code, time.Now())
	} else {
		ok = a.deps.Users.ConsumeRecovery(name, code)
	}
	if !ok {
		slog.Warn("admin: second factor refused", "user", name)
		data := a.pageData(r)
		data.Error = data.Tr("Wrong or expired code.")
		a.renderPage(w, r, "twofactor.html", data, http.StatusUnauthorized)
		return
	}
	user := a.deps.Users.Find(name)
	if user == nil || user.TotpSecret == "" {
		sess.Delete("totp_user")
		sess.Delete("totp_at")
		http.Redirect(w, r, "/admin/login", http.StatusSeeOther)
		return
	}
	sess.Delete("totp_user")
	sess.Delete("totp_at")
	sess.Set("user", user.Username)
	sess.Set("pv", sessionFingerprint(user.PasswordHash))
	http.Redirect(w, r, "/admin/", http.StatusSeeOther)
}

// isTotpShape reports whether the answer looks like an application
// code; everything else is tried as a recovery code.
func isTotpShape(code string) bool {
	clean := strings.NewReplacer(" ", "", "-", "").Replace(code)
	return len(clean) == 6 && strings.Trim(clean, "0123456789") == ""
}

func (a *Admin) handleLogout(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseForm(); err != nil {
		http.Error(w, "bad form", http.StatusBadRequest)
		return
	}
	sess := session.FromContext(r.Context())
	if !ValidateCSRF(r, sess) {
		http.Error(w, "Invalid CSRF token", http.StatusForbidden)
		return
	}
	// Abandon rather than Clear: Clear would leave the session dirty, and
	// the middleware's Save would then append a fresh cookie after
	// Destroy's expiring one, which the browser applies last.
	sess.Abandon()
	a.deps.Sessions.Destroy(w)
	http.Redirect(w, r, "/admin/login", http.StatusSeeOther)
}