// Package ui provides the HTMX-based management web interface for MCIAS.
//
// Security design:
//   - Session tokens are stored as HttpOnly, Secure, SameSite=Strict cookies.
//     They are never accessible to JavaScript.
//   - CSRF protection uses the HMAC-signed Double-Submit Cookie pattern.
//     The mcias_csrf cookie is non-HttpOnly so HTMX can include it in the
//     X-CSRF-Token header on every mutating request. SameSite=Strict is the
//     primary browser-level CSRF defence.
//   - UI handlers call internal Go functions directly — no internal HTTP round-trips.
//   - All templates are parsed once at startup via embed.FS; no dynamic template
//     loading from disk at request time.
package ui

import (
	"bytes"
	"crypto/ed25519"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"html/template"
	"io/fs"
	"log/slog"
	"net/http"
	"strings"
	"sync"
	"time"

	"git.wntrmute.dev/kyle/mcias/internal/auth"
	"git.wntrmute.dev/kyle/mcias/internal/config"
	"git.wntrmute.dev/kyle/mcias/internal/db"
	"git.wntrmute.dev/kyle/mcias/internal/model"
	"git.wntrmute.dev/kyle/mcias/web"
)

const (
	sessionCookieName = "mcias_session"
	csrfCookieName    = "mcias_csrf"
	totpNonceTTL      = 90 * time.Second // single-use TOTP step nonce lifetime
	totpNonceBytes    = 16               // 128 bits of entropy
)

// pendingLogin is a short-lived record created after password verification
// succeeds but before TOTP confirmation. It holds the account ID so the
// TOTP step never needs to re-transmit the password.
//
// Security: the nonce is single-use (deleted on first lookup) and expires
// after totpNonceTTL to bound the window of a stolen nonce.
type pendingLogin struct {
	expiresAt time.Time
	accountID int64
}

// UIServer serves the HTMX-based management UI.
type UIServer struct {
	pendingLogins sync.Map                      // nonce (string) → *pendingLogin
	tmpls         map[string]*template.Template // page name → template set
	db            *db.DB
	cfg           *config.Config
	logger        *slog.Logger
	csrf          *CSRFManager
	pubKey        ed25519.PublicKey
	privKey       ed25519.PrivateKey
	masterKey     []byte
}

// issueTOTPNonce creates a random single-use nonce for the TOTP step and
// stores the account ID it corresponds to. Returns the hex-encoded nonce.
func (u *UIServer) issueTOTPNonce(accountID int64) (string, error) {
	raw := make([]byte, totpNonceBytes)
	if _, err := rand.Read(raw); err != nil {
		return "", fmt.Errorf("ui: generate TOTP nonce: %w", err)
	}
	nonce := hex.EncodeToString(raw)
	u.pendingLogins.Store(nonce, &pendingLogin{
		accountID: accountID,
		expiresAt: time.Now().Add(totpNonceTTL),
	})
	return nonce, nil
}

// consumeTOTPNonce looks up and deletes the nonce, returning the associated
// account ID. Returns (0, false) if the nonce is unknown or expired.
func (u *UIServer) consumeTOTPNonce(nonce string) (int64, bool) {
	v, ok := u.pendingLogins.LoadAndDelete(nonce)
	if !ok {
		return 0, false
	}
	pl, ok2 := v.(*pendingLogin)
	if !ok2 {
		return 0, false
	}
	if time.Now().After(pl.expiresAt) {
		return 0, false
	}
	return pl.accountID, true
}

// dummyHash returns the pre-computed Argon2id PHC hash for constant-time dummy
// verification when an account is unknown or inactive (F-07).
// Delegates to auth.DummyHash() which uses sync.Once for one-time computation.
func (u *UIServer) dummyHash() string {
	return auth.DummyHash()
}

// New constructs a UIServer, parses all templates, and returns it.
// Returns an error if template parsing fails.
func New(database *db.DB, cfg *config.Config, priv ed25519.PrivateKey, pub ed25519.PublicKey, masterKey []byte, logger *slog.Logger) (*UIServer, error) {
	csrf := newCSRFManager(masterKey)

	funcMap := template.FuncMap{
		"formatTime": func(t time.Time) string {
			if t.IsZero() {
				return ""
			}
			return t.UTC().Format("2006-01-02 15:04:05")
		},
		"truncateJTI": func(jti string) string {
			if len(jti) > 8 {
				return jti[:8]
			}
			return jti
		},
		"string": func(v interface{}) string {
			switch s := v.(type) {
			case model.AccountStatus:
				return string(s)
			case model.AccountType:
				return string(s)
			default:
				return fmt.Sprintf("%v", v)
			}
		},
		"hasRole": func(roles []string, role string) bool {
			for _, r := range roles {
				if r == role {
					return true
				}
			}
			return false
		},
		"not": func(b bool) bool { return !b },
		"add": func(a, b int) int { return a + b },
		"sub": func(a, b int) int { return a - b },
		"gt":  func(a, b int) bool { return a > b },
		"lt":  func(a, b int) bool { return a < b },
		"prettyJSON": func(s string) string {
			var v json.RawMessage
			if json.Unmarshal([]byte(s), &v) != nil {
				return s
			}
			pretty, err := json.MarshalIndent(v, "", "  ")
			if err != nil {
				return s
			}
			return string(pretty)
		},
	}

	// Parse shared templates (base layout + all fragments) into a base set.
	// Each page template is then parsed into a clone of this base set so that
	// competing "content"/"title" definitions do not collide.
	sharedFiles := []string{
		"templates/base.html",
		"templates/fragments/account_row.html",
		"templates/fragments/account_status.html",
		"templates/fragments/roles_editor.html",
		"templates/fragments/token_list.html",
		"templates/fragments/totp_step.html",
		"templates/fragments/error.html",
		"templates/fragments/audit_rows.html",
		"templates/fragments/pgcreds_form.html",
		"templates/fragments/tags_editor.html",
		"templates/fragments/policy_row.html",
		"templates/fragments/policy_form.html",
	}
	base, err := template.New("").Funcs(funcMap).ParseFS(web.TemplateFS, sharedFiles...)
	if err != nil {
		return nil, fmt.Errorf("ui: parse shared templates: %w", err)
	}

	// Each page template defines "content" and "title" blocks; parsing them
	// into separate clones prevents the last-defined block from winning.
	pageFiles := map[string]string{
		"login":          "templates/login.html",
		"dashboard":      "templates/dashboard.html",
		"accounts":       "templates/accounts.html",
		"account_detail": "templates/account_detail.html",
		"audit":          "templates/audit.html",
		"audit_detail":   "templates/audit_detail.html",
		"policies":       "templates/policies.html",
	}
	tmpls := make(map[string]*template.Template, len(pageFiles))
	for name, file := range pageFiles {
		clone, cloneErr := base.Clone()
		if cloneErr != nil {
			return nil, fmt.Errorf("ui: clone base templates for %s: %w", name, cloneErr)
		}
		if _, parseErr := clone.ParseFS(web.TemplateFS, file); parseErr != nil {
			return nil, fmt.Errorf("ui: parse page template %s: %w", name, parseErr)
		}
		tmpls[name] = clone
	}

	return &UIServer{
		db:        database,
		cfg:       cfg,
		pubKey:    pub,
		privKey:   priv,
		masterKey: masterKey,
		logger:    logger,
		csrf:      csrf,
		tmpls:     tmpls,
	}, nil
}

// Register attaches all UI routes to mux, wrapped with security headers.
// All UI responses (pages, fragments, redirects, static assets) carry the
// headers added by securityHeaders.
func (u *UIServer) Register(mux *http.ServeMux) {
	// Build a dedicated child mux for all UI routes so that securityHeaders
	// can be applied once as a wrapping middleware rather than per-route.
	uiMux := http.NewServeMux()

	// Static assets — serve from the web/static/ sub-directory of the embed.
	staticSubFS, err := fs.Sub(web.StaticFS, "static")
	if err != nil {
		panic(fmt.Sprintf("ui: static sub-FS: %v", err))
	}
	uiMux.Handle("GET /static/", http.StripPrefix("/static/", http.FileServerFS(staticSubFS)))

	// Redirect root to login.
	uiMux.HandleFunc("GET /", func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path == "/" {
			http.Redirect(w, r, "/login", http.StatusFound)
			return
		}
		http.NotFound(w, r)
	})

	// Auth routes (no session required).
	uiMux.HandleFunc("GET /login", u.handleLoginPage)
	uiMux.HandleFunc("POST /login", u.handleLoginPost)
	uiMux.HandleFunc("POST /logout", u.handleLogout)

	// Protected routes.
	auth := u.requireCookieAuth
	admin := func(h http.HandlerFunc) http.Handler {
		return auth(u.requireCSRF(http.HandlerFunc(h)))
	}
	adminGet := func(h http.HandlerFunc) http.Handler {
		return auth(http.HandlerFunc(h))
	}

	uiMux.Handle("GET /dashboard", adminGet(u.handleDashboard))
	uiMux.Handle("GET /accounts", adminGet(u.handleAccountsList))
	uiMux.Handle("POST /accounts", admin(u.handleCreateAccount))
	uiMux.Handle("GET /accounts/{id}", adminGet(u.handleAccountDetail))
	uiMux.Handle("PATCH /accounts/{id}/status", admin(u.handleUpdateAccountStatus))
	uiMux.Handle("DELETE /accounts/{id}", admin(u.handleDeleteAccount))
	uiMux.Handle("GET /accounts/{id}/roles/edit", adminGet(u.handleRolesEditForm))
	uiMux.Handle("PUT /accounts/{id}/roles", admin(u.handleSetRoles))
	uiMux.Handle("DELETE /token/{jti}", admin(u.handleRevokeToken))
	uiMux.Handle("POST /accounts/{id}/token", admin(u.handleIssueSystemToken))
	uiMux.Handle("PUT /accounts/{id}/pgcreds", admin(u.handleSetPGCreds))
	uiMux.Handle("GET /audit", adminGet(u.handleAuditPage))
	uiMux.Handle("GET /audit/rows", adminGet(u.handleAuditRows))
	uiMux.Handle("GET /audit/{id}", adminGet(u.handleAuditDetail))
	uiMux.Handle("GET /policies", adminGet(u.handlePoliciesPage))
	uiMux.Handle("POST /policies", admin(u.handleCreatePolicyRule))
	uiMux.Handle("PATCH /policies/{id}/enabled", admin(u.handleTogglePolicyRule))
	uiMux.Handle("DELETE /policies/{id}", admin(u.handleDeletePolicyRule))
	uiMux.Handle("PUT /accounts/{id}/tags", admin(u.handleSetAccountTags))

	// Mount the wrapped UI mux on the parent mux. The "/" pattern acts as a
	// catch-all for all UI paths; the more-specific /v1/ API patterns registered
	// on the parent mux continue to take precedence per Go's routing rules.
	mux.Handle("/", securityHeaders(uiMux))
}

// ---- Middleware ----

// requireCookieAuth validates the mcias_session cookie and injects claims.
// On failure, HTMX requests get HX-Redirect; browser requests get a redirect.
func (u *UIServer) requireCookieAuth(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		cookie, err := r.Cookie(sessionCookieName)
		if err != nil || cookie.Value == "" {
			u.redirectToLogin(w, r)
			return
		}

		claims, err := validateSessionToken(u.pubKey, cookie.Value, u.cfg.Tokens.Issuer)
		if err != nil {
			u.clearSessionCookie(w)
			u.redirectToLogin(w, r)
			return
		}

		// Check revocation.
		rec, err := u.db.GetTokenRecord(claims.JTI)
		if err != nil || rec.IsRevoked() {
			u.clearSessionCookie(w)
			u.redirectToLogin(w, r)
			return
		}

		ctx := contextWithClaims(r.Context(), claims)
		next.ServeHTTP(w, r.WithContext(ctx))
	})
}

// requireCSRF validates the CSRF token on mutating requests (POST/PUT/PATCH/DELETE).
// The token is read from X-CSRF-Token header (HTMX) or _csrf form field (fallback).
func (u *UIServer) requireCSRF(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		cookie, err := r.Cookie(csrfCookieName)
		if err != nil || cookie.Value == "" {
			http.Error(w, "CSRF cookie missing", http.StatusForbidden)
			return
		}

		// Header takes precedence (HTMX sets it automatically via hx-headers on body).
		formVal := r.Header.Get("X-CSRF-Token")
		if formVal == "" {
			// Fallback: parse form and read _csrf field.
			// Security: limit body size to prevent memory exhaustion (gosec G120).
			r.Body = http.MaxBytesReader(w, r.Body, maxFormBytes)
			if parseErr := r.ParseForm(); parseErr == nil {
				formVal = r.FormValue("_csrf")
			}
		}

		if !u.csrf.Validate(cookie.Value, formVal) {
			http.Error(w, "CSRF token invalid", http.StatusForbidden)
			return
		}
		next.ServeHTTP(w, r)
	})
}

// ---- Helpers ----

// isHTMX reports whether the request was initiated by HTMX.
func isHTMX(r *http.Request) bool {
	return r.Header.Get("HX-Request") == "true"
}

// redirectToLogin redirects to the login page, using HX-Redirect for HTMX.
func (u *UIServer) redirectToLogin(w http.ResponseWriter, r *http.Request) {
	if isHTMX(r) {
		w.Header().Set("HX-Redirect", "/login")
		w.WriteHeader(http.StatusUnauthorized)
		return
	}
	http.Redirect(w, r, "/login", http.StatusFound)
}

// clearSessionCookie expires the session cookie.
func (u *UIServer) clearSessionCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{
		Name:     sessionCookieName,
		Value:    "",
		Path:     "/",
		MaxAge:   -1,
		HttpOnly: true,
		Secure:   true,
		SameSite: http.SameSiteStrictMode,
	})
}

// setCSRFCookies sets the mcias_csrf cookie and returns the header value to
// embed in the page/form.
func (u *UIServer) setCSRFCookies(w http.ResponseWriter) (string, error) {
	cookieVal, headerVal, err := u.csrf.NewToken()
	if err != nil {
		return "", err
	}
	http.SetCookie(w, &http.Cookie{
		Name:  csrfCookieName,
		Value: cookieVal,
		Path:  "/",
		// Security: non-HttpOnly so that HTMX can embed it in hx-headers;
		// SameSite=Strict is the primary CSRF defence for browser requests.
		HttpOnly: false,
		Secure:   true,
		SameSite: http.SameSiteStrictMode,
	})
	return headerVal, nil
}

// render executes the named template, writing the result to w.
// Renders to a buffer first so partial template failures don't corrupt output.
// For page templates (dashboard, accounts, etc.) the page-specific template set
// is used; for fragment templates the name is looked up across all sets.
func (u *UIServer) render(w http.ResponseWriter, name string, data interface{}) {
	tmpl := u.templateFor(name)
	if tmpl == nil {
		u.logger.Error("template not found", "template", name)
		http.Error(w, "internal server error", http.StatusInternalServerError)
		return
	}
	var buf bytes.Buffer
	if err := tmpl.ExecuteTemplate(&buf, name, data); err != nil {
		u.logger.Error("template render error", "template", name, "error", err)
		http.Error(w, "internal server error", http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	_, _ = w.Write(buf.Bytes())
}

// templateFor returns the template set that contains the named template.
// Page templates have a dedicated set; fragment templates exist in every set.
func (u *UIServer) templateFor(name string) *template.Template {
	if t, ok := u.tmpls[name]; ok {
		return t
	}
	// Fragment — available in any page set; pick the first one.
	for _, t := range u.tmpls {
		if t.Lookup(name) != nil {
			return t
		}
	}
	return nil
}

// renderError returns an error response appropriate for the request type.
func (u *UIServer) renderError(w http.ResponseWriter, r *http.Request, status int, msg string) {
	if isHTMX(r) {
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		w.WriteHeader(status)
		_, _ = fmt.Fprintf(w, `<div class="alert alert-error" role="alert">%s</div>`, template.HTMLEscapeString(msg))
		return
	}
	http.Error(w, msg, status)
}

// maxFormBytes limits the size of UI form submissions (1 MiB).
// Security: prevents memory exhaustion from oversized POST bodies (gosec G120).
const maxFormBytes = 1 << 20

// securityHeaders returns middleware that adds defensive HTTP headers to every
// UI response.
//
// Security rationale for each header:
//   - Content-Security-Policy: restricts resource loading to same origin only,
//     mitigating XSS escalation even if an attacker injects HTML (e.g. via a
//     malicious stored username rendered in the admin panel).
//   - X-Content-Type-Options: prevents MIME-sniffing; browsers must honour the
//     declared Content-Type and not guess an executable type from body content.
//   - X-Frame-Options: blocks the admin panel from being framed by a third-party
//     origin, preventing clickjacking against admin actions.
//   - Strict-Transport-Security: instructs browsers to use HTTPS for all future
//     requests to this origin for two years, preventing TLS-strip on revisit.
//   - Referrer-Policy: suppresses the Referer header on outbound navigations so
//     JWTs or session identifiers embedded in URLs are not leaked to third parties.
func securityHeaders(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		h := w.Header()
		h.Set("Content-Security-Policy",
			"default-src 'self'; script-src 'self'; style-src 'self'; img-src 'self' data:; font-src 'self'")
		h.Set("X-Content-Type-Options", "nosniff")
		h.Set("X-Frame-Options", "DENY")
		h.Set("Strict-Transport-Security", "max-age=63072000; includeSubDomains")
		h.Set("Referrer-Policy", "no-referrer")
		next.ServeHTTP(w, r)
	})
}

// clientIP extracts the client IP from RemoteAddr (best effort).
func clientIP(r *http.Request) string {
	addr := r.RemoteAddr
	if idx := strings.LastIndex(addr, ":"); idx != -1 {
		return addr[:idx]
	}
	return addr
}

// ---- Page data types ----

// PageData is embedded in all page-level view structs.
type PageData struct {
	CSRFToken string
	Flash     string
	Error     string
}

// LoginData is the view model for the login page.
type LoginData struct {
	Error    string
	Username string // pre-filled on TOTP step
	// Security (F-02): Password is no longer carried in the HTML form. Instead
	// a short-lived server-side nonce is issued after successful password
	// verification, and only the nonce is embedded in the TOTP step form.
	Nonce string // single-use server-side nonce replacing the password hidden field
}

// DashboardData is the view model for the dashboard page.
type DashboardData struct {
	PageData
	RecentEvents   []*db.AuditEventView
	TotalAccounts  int
	ActiveAccounts int
}

// AccountsData is the view model for the accounts list page.
type AccountsData struct {
	PageData
	Accounts []*model.Account
}

// AccountDetailData is the view model for the account detail page.
type AccountDetailData struct {
	Account *model.Account
	PGCred  *model.PGCredential // nil if none stored or account is not a system account
	PageData
	Roles    []string
	AllRoles []string
	Tags     []string
	Tokens   []*model.TokenRecord
}

// AuditData is the view model for the audit log page.
type AuditData struct {
	PageData
	FilterType string
	Events     []*db.AuditEventView
	EventTypes []string
	Total      int64
	TotalPages int
	Page       int
}

// AuditDetailData is the view model for a single audit event detail page.
type AuditDetailData struct {
	Event *db.AuditEventView
	PageData
}

// PolicyRuleView is a single policy rule prepared for template rendering.
type PolicyRuleView struct {
	Description string
	RuleJSON    string
	CreatedAt   string
	UpdatedAt   string
	ID          int64
	Priority    int
	Enabled     bool
}

// PoliciesData is the view model for the policies list page.
type PoliciesData struct {
	PageData
	Rules      []*PolicyRuleView
	AllActions []string
}