// Package web serves the Bootstrap management interface, the observability
// endpoints and the static assets. The REST API is mounted underneath it.
package web

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"net/http"
	"runtime/debug"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/owen/vibedns/internal/app"
	"github.com/owen/vibedns/internal/auditlog"
	"github.com/owen/vibedns/internal/auth"
	"github.com/owen/vibedns/internal/netutil"
	webui "github.com/owen/vibedns/web"
)

// Server is the HTTP management interface.
type Server struct {
	app  *app.App
	log  *slog.Logger
	tmpl *templates

	http     *http.Server
	apiMount http.Handler

	limiter *httpLimiter
	mu      sync.Mutex
	addr    string
}

// Options configures the HTTP server.
type Options struct {
	App *app.App
	Log *slog.Logger
	// API is mounted at /api/v1 when non-nil.
	API http.Handler
}

// New creates the HTTP server and parses the embedded templates.
func New(opts Options) (*Server, error) {
	tmpl, err := loadTemplates(templateFuncs())
	if err != nil {
		return nil, err
	}
	s := &Server{
		app:      opts.App,
		log:      opts.Log,
		tmpl:     tmpl,
		apiMount: opts.API,
		limiter:  newHTTPLimiter(),
	}
	return s, nil
}

// Handler builds the fully wrapped HTTP handler.
func (s *Server) Handler() http.Handler {
	mux := http.NewServeMux()
	s.routes(mux)

	var h http.Handler = mux
	h = s.withBodyLimit(h)
	h = s.withRateLimit(h)
	h = s.withRequestLog(h)
	h = s.withSecurityHeaders(h)
	h = s.withRecover(h)
	return h
}

// Start binds the management listener.
func (s *Server) Start(addr string) error {
	h := s.Handler()
	s.mu.Lock()
	s.addr = addr
	s.http = &http.Server{
		Addr:              addr,
		Handler:           h,
		ReadHeaderTimeout: 10 * time.Second,
		ReadTimeout:       2 * time.Minute, // large blocklist uploads
		WriteTimeout:      5 * time.Minute, // large exports
		IdleTimeout:       120 * time.Second,
		ErrorLog:          slog.NewLogLogger(s.log.Handler(), slog.LevelDebug),
	}
	srv := s.http
	s.mu.Unlock()

	ln, err := listen(addr)
	if err != nil {
		return err
	}
	go func() {
		if err := srv.Serve(ln); err != nil && !errors.Is(err, http.ErrServerClosed) {
			s.log.Error("management HTTP server stopped", "error", err)
		}
	}()
	s.log.Info("management interface started", "address", addr)
	return nil
}

// Shutdown stops the management listener.
func (s *Server) Shutdown(ctx context.Context) error {
	s.mu.Lock()
	srv := s.http
	s.mu.Unlock()
	if srv == nil {
		return nil
	}
	return srv.Shutdown(ctx)
}

// routes registers every endpoint.
func (s *Server) routes(mux *http.ServeMux) {
	// Public endpoints. Static assets are unauthenticated because they are
	// Bootstrap and our own CSS: requiring credentials for them would force an
	// Argon2 verification on every asset request for no benefit.
	static := http.FileServer(http.FS(webui.Static()))
	mux.Handle("GET /static/", http.StripPrefix("/static/", cacheStatic(static)))
	mux.HandleFunc("GET /favicon.ico", s.handleFavicon)
	mux.HandleFunc("GET /healthz", s.handleHealthz)
	mux.HandleFunc("GET /readyz", s.handleReadyz)
	mux.HandleFunc("GET /metrics", s.handleMetrics)

	if s.apiMount != nil {
		mux.Handle("/api/v1/", s.apiMount)
	}

	// Everything below requires the administrator.
	page := s.protect

	mux.Handle("GET /{$}", page(s.handleDashboard))
	mux.Handle("GET /dashboard", page(s.handleDashboard))

	// Zones.
	mux.Handle("GET /zones", page(s.handleZones))
	mux.Handle("GET /zones/reverse", page(s.handleZonesReverse))
	mux.Handle("GET /zones/new", page(s.handleZoneNew))
	mux.Handle("POST /zones/new", page(s.handleZoneCreate))
	mux.Handle("GET /zones/{id}", page(s.handleZoneRecords))
	mux.Handle("GET /zones/{id}/edit", page(s.handleZoneEdit))
	mux.Handle("POST /zones/{id}/edit", page(s.handleZoneUpdate))
	mux.Handle("POST /zones/{id}/delete", page(s.handleZoneDelete))
	mux.Handle("POST /zones/{id}/toggle", page(s.handleZoneToggle))
	mux.Handle("POST /zones/{id}/clone", page(s.handleZoneClone))
	mux.Handle("GET /zones/{id}/export", page(s.handleZoneExport))
	mux.Handle("POST /zones/{id}/import", page(s.handleZoneImport))

	// Records.
	mux.Handle("GET /records", page(s.handleRecordsAll))
	mux.Handle("POST /zones/{id}/records", page(s.handleRecordCreate))
	mux.Handle("POST /zones/{id}/records/bulk", page(s.handleRecordBulk))
	mux.Handle("POST /records/{id}/edit", page(s.handleRecordUpdate))
	mux.Handle("POST /records/{id}/delete", page(s.handleRecordDelete))
	mux.Handle("POST /records/{id}/toggle", page(s.handleRecordToggle))

	// Resolver and cache.
	mux.Handle("GET /resolver", page(s.handleResolver))
	mux.Handle("POST /resolver/test", page(s.handleResolverTest))
	mux.Handle("GET /cache", page(s.handleCache))
	mux.Handle("POST /cache/flush", page(s.handleCacheFlush))
	mux.Handle("POST /cache/delete", page(s.handleCacheDelete))

	// Policies.
	mux.Handle("GET /policies", page(s.handlePolicies))
	mux.Handle("GET /policies/networks", page(s.handleNetworks))
	mux.Handle("GET /policies/networks/new", page(s.handleNetworkNew))
	mux.Handle("POST /policies/networks/new", page(s.handleNetworkCreate))
	mux.Handle("GET /policies/networks/{id}", page(s.handleNetworkEdit))
	mux.Handle("POST /policies/networks/{id}", page(s.handleNetworkUpdate))
	mux.Handle("POST /policies/networks/{id}/delete", page(s.handleNetworkDelete))
	mux.Handle("POST /policies/networks/{id}/toggle", page(s.handleNetworkToggle))

	mux.Handle("GET /policies/rules/new", page(s.handlePolicyNew))
	mux.Handle("POST /policies/rules/new", page(s.handlePolicyCreate))
	mux.Handle("GET /policies/rules/{id}", page(s.handlePolicyEdit))
	mux.Handle("POST /policies/rules/{id}", page(s.handlePolicyUpdate))
	mux.Handle("POST /policies/rules/{id}/delete", page(s.handlePolicyDelete))
	mux.Handle("POST /policies/rules/{id}/toggle", page(s.handlePolicyToggle))

	mux.Handle("GET /policies/blacklists", page(s.handleBlacklists))
	mux.Handle("GET /policies/allowlists", page(s.handleAllowlists))
	mux.Handle("POST /policies/lists/new", page(s.handleListCreate))
	mux.Handle("GET /policies/lists/{id}", page(s.handleListDetail))
	mux.Handle("POST /policies/lists/{id}", page(s.handleListUpdate))
	mux.Handle("POST /policies/lists/{id}/delete", page(s.handleListDelete))
	mux.Handle("POST /policies/lists/{id}/toggle", page(s.handleListToggle))
	mux.Handle("POST /policies/lists/{id}/clear", page(s.handleListClear))
	mux.Handle("POST /policies/lists/{id}/import", page(s.handleListImport))
	mux.Handle("GET /policies/lists/{id}/export", page(s.handleListExport))
	mux.Handle("POST /policies/lists/{id}/domains", page(s.handleDomainAdd))
	mux.Handle("POST /policies/domains/{id}/delete", page(s.handleDomainDelete))

	// Logs.
	mux.Handle("GET /querylog", page(s.handleQueryLog))
	mux.Handle("POST /querylog/clear", page(s.handleQueryLogClear))
	mux.Handle("GET /audit", page(s.handleAuditLog))

	// Tools.
	mux.Handle("GET /tools", page(s.handleTools))
	mux.Handle("POST /tools/lookup", page(s.handleToolsLookup))

	// Settings.
	mux.Handle("GET /settings", page(s.redirectTo("/settings/dns")))
	mux.Handle("GET /settings/dns", page(s.handleSettingsDNS))
	mux.Handle("POST /settings/dns", page(s.handleSettingsDNSSave))
	mux.Handle("GET /settings/resolver", page(s.handleSettingsResolver))
	mux.Handle("POST /settings/resolver", page(s.handleSettingsResolverSave))
	mux.Handle("GET /settings/cache", page(s.handleSettingsCache))
	mux.Handle("POST /settings/cache", page(s.handleSettingsCacheSave))
	mux.Handle("GET /settings/logging", page(s.handleSettingsLogging))
	mux.Handle("POST /settings/logging", page(s.handleSettingsLoggingSave))
	mux.Handle("GET /settings/http", page(s.handleSettingsHTTP))
	mux.Handle("POST /settings/http", page(s.handleSettingsHTTPSave))
	mux.Handle("GET /settings/database", page(s.handleSettingsDatabase))
	mux.Handle("POST /settings/database", page(s.handleSettingsDatabaseSave))
	mux.Handle("POST /settings/database/backup", page(s.handleBackupNow))
	mux.Handle("GET /settings/database/backup/{name}", page(s.handleBackupDownload))
	mux.Handle("POST /settings/database/backup/{name}/delete", page(s.handleBackupDelete))
	mux.Handle("POST /settings/database/backup/{name}/restore", page(s.handleBackupRestore))
	mux.Handle("POST /settings/database/restore/cancel", page(s.handleRestoreCancel))
	mux.Handle("GET /settings/blockpage", page(s.handleSettingsBlockPage))
	mux.Handle("POST /settings/blockpage", page(s.handleSettingsBlockPageSave))
	mux.Handle("POST /settings/blockpage/preview", page(s.handleSettingsBlockPagePreview))
	mux.Handle("GET /settings/api", page(s.handleSettingsAPI))
	mux.Handle("POST /settings/api/tokens", page(s.handleTokenCreate))
	mux.Handle("POST /settings/api/tokens/{id}/delete", page(s.handleTokenDelete))
	mux.Handle("POST /settings/api/tokens/{id}/toggle", page(s.handleTokenToggle))
	mux.Handle("GET /settings/config/export", page(s.handleConfigExport))
	mux.Handle("POST /settings/config/import", page(s.handleConfigImport))

	// Account.
	mux.Handle("GET /account", page(s.handleAccount))
	mux.Handle("POST /account", page(s.handleAccountSave))

	// Anything unmatched. Registered without a method so it does not conflict
	// with the "/api/v1/" prefix pattern: ServeMux rejects a method-specific
	// catch-all that is more general in path than an existing prefix route.
	mux.Handle("/", page(s.handleNotFound))
}

// handlerFunc is a page handler that may return an error for central handling.
type handlerFunc func(http.ResponseWriter, *http.Request) error

// protect wraps a page handler with authentication and CSRF enforcement.
func (s *Server) protect(fn handlerFunc) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		p, err := s.app.Auth.Authenticate(r, false)
		if err != nil {
			s.challenge(w, r, err)
			return
		}
		ctx := auth.WithPrincipal(r.Context(), p)
		r = r.WithContext(ctx)

		// The CSRF cookie is refreshed on every page view so it never expires
		// out from under an open tab.
		token := s.app.Auth.IssueCSRFToken(p.Name)
		if r.Method == http.MethodGet {
			auth.SetCSRFCookie(w, r, token)
		} else if err := s.app.Auth.CheckCSRF(r, p); err != nil {
			s.log.Warn("rejected a request that failed the CSRF check",
				"path", r.URL.Path, "client", p.ClientIP)
			s.renderError(w, r, http.StatusForbidden, err.Error())
			return
		}

		if err := fn(w, r); err != nil {
			s.handleError(w, r, err)
		}
	})
}

// challenge sends the Basic authentication challenge, or a lockout message.
func (s *Server) challenge(w http.ResponseWriter, r *http.Request, err error) {
	switch {
	case errors.Is(err, auth.ErrLockedOut):
		w.Header().Set("Retry-After", "300")
		s.renderError(w, r, http.StatusTooManyRequests,
			"Too many failed sign-in attempts from this address. Try again in a few minutes.")
	case errors.Is(err, auth.ErrNoAdmin):
		s.renderError(w, r, http.StatusServiceUnavailable,
			"No administrator account exists yet. Restart the server to create one.")
	default:
		w.Header().Set("WWW-Authenticate", fmt.Sprintf("Basic realm=%q, charset=\"UTF-8\"", auth.Realm))
		s.renderError(w, r, http.StatusUnauthorized, "Sign in to continue.")
	}
}

// handleError turns a service error into a flash or an error page.
func (s *Server) handleError(w http.ResponseWriter, r *http.Request, err error) {
	if app.IsInternal(err) {
		s.log.Error("request failed", "path", r.URL.Path, "method", r.Method, "error", err)
	}
	status := app.StatusOf(err)
	message := app.MessageOf(err)

	// A failed form submission returns the operator to the page they were on
	// with the reason shown, rather than dumping them on an error page.
	if r.Method == http.MethodPost && status < 500 {
		setFlash(w, r, "danger", message)
		s.redirectBack(w, r)
		return
	}
	s.renderError(w, r, status, message)
}

// redirectBack returns to the referring page, or a supplied fallback.
func (s *Server) redirectBack(w http.ResponseWriter, r *http.Request) {
	target := r.FormValue("return_to")
	if target == "" {
		target = safeReferer(r)
	}
	if target == "" {
		target = "/"
	}
	http.Redirect(w, r, target, http.StatusSeeOther)
}

// safeReferer only accepts a same-origin path, so a crafted Referer cannot
// turn an error into an open redirect.
func safeReferer(r *http.Request) string {
	ref := r.Header.Get("Referer")
	if ref == "" {
		return ""
	}
	if strings.HasPrefix(ref, "/") && !strings.HasPrefix(ref, "//") {
		return ref
	}
	if u, err := parseURL(ref); err == nil && u.Host == r.Host {
		return u.RequestURI()
	}
	return ""
}

func (s *Server) redirectTo(target string) handlerFunc {
	return func(w http.ResponseWriter, r *http.Request) error {
		http.Redirect(w, r, target, http.StatusSeeOther)
		return nil
	}
}

// redirect issues a see-other redirect after a successful mutation.
func (s *Server) redirect(w http.ResponseWriter, r *http.Request, target string) error {
	http.Redirect(w, r, target, http.StatusSeeOther)
	return nil
}

// actor builds the audit actor for the current request.
func (s *Server) actor(r *http.Request) auditlog.Actor {
	p, _ := auth.PrincipalFrom(r.Context())
	source := auditlog.SourceWeb
	if p.Kind == auth.KindToken {
		source = auditlog.SourceAPI
	}
	return auditlog.Actor{Name: p.Name, Source: source, ClientIP: p.ClientIP}
}

// base builds the common page envelope.
func (s *Server) base(r *http.Request, title, nav string) PageData {
	p, _ := auth.PrincipalFrom(r.Context())
	return PageData{
		Title: title,
		Nav:   nav,
		User:  p,
		CSRF:  s.app.Auth.IssueCSRFToken(p.Name),
		Query: r.URL.Query(),
	}
}

// pathID reads an {id} path parameter.
func pathID(r *http.Request, name string) (int64, error) {
	raw := r.PathValue(name)
	id, err := strconv.ParseInt(raw, 10, 64)
	if err != nil || id <= 0 {
		return 0, app.Invalid("%q is not a valid identifier.", raw)
	}
	return id, nil
}

// --- middleware ---------------------------------------------------------

func (s *Server) withRecover(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if rec := recover(); rec != nil {
				s.log.Error("panic while handling request",
					"path", r.URL.Path, "panic", rec, "stack", string(debug.Stack()))
				// The stack trace goes to the log, never to the browser.
				s.renderError(w, r, http.StatusInternalServerError,
					"An unexpected error occurred. Check the server log for details.")
			}
		}()
		next.ServeHTTP(w, r)
	})
}

func (s *Server) withSecurityHeaders(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		h := w.Header()
		h.Set("X-Content-Type-Options", "nosniff")
		h.Set("X-Frame-Options", "DENY")
		h.Set("Referrer-Policy", "same-origin")
		h.Set("Cross-Origin-Opener-Policy", "same-origin")
		h.Set("Permissions-Policy", "geolocation=(), microphone=(), camera=(), interest-cohort=()")
		// Everything is served from this origin: no CDN, no inline event
		// handlers, no eval. 'unsafe-inline' is allowed for style attributes
		// only, which Bootstrap components set programmatically.
		h.Set("Content-Security-Policy",
			"default-src 'self'; "+
				"script-src 'self'; "+
				"style-src 'self' 'unsafe-inline'; "+
				"img-src 'self' data:; "+
				"font-src 'self'; "+
				"connect-src 'self'; "+
				"form-action 'self'; "+
				"frame-src 'self'; "+
				"frame-ancestors 'none'; "+
				"base-uri 'none'; "+
				"object-src 'none'")
		if r.TLS != nil {
			h.Set("Strict-Transport-Security", "max-age=31536000; includeSubDomains")
		}
		next.ServeHTTP(w, r)
	})
}

// statusRecorder captures the response status for logging.
type statusRecorder struct {
	http.ResponseWriter
	status int
	bytes  int
}

func (w *statusRecorder) WriteHeader(code int) {
	w.status = code
	w.ResponseWriter.WriteHeader(code)
}

func (w *statusRecorder) Write(b []byte) (int, error) {
	if w.status == 0 {
		w.status = http.StatusOK
	}
	n, err := w.ResponseWriter.Write(b)
	w.bytes += n
	return n, err
}

func (s *Server) withRequestLog(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		rec := &statusRecorder{ResponseWriter: w}
		next.ServeHTTP(rec, r)

		if strings.HasPrefix(r.URL.Path, "/static/") {
			return // asset noise
		}
		level := slog.LevelDebug
		if rec.status >= 500 {
			level = slog.LevelError
		} else if rec.status >= 400 {
			level = slog.LevelWarn
		}
		s.log.Log(r.Context(), level, "http request",
			"method", r.Method, "path", r.URL.Path, "status", rec.status,
			"bytes", rec.bytes, "duration_ms", time.Since(start).Milliseconds(),
			"client", s.app.Auth.ClientIP(r))
	})
}

// withBodyLimit caps request bodies so an oversized upload cannot exhaust
// memory. The limit follows the configured upload size.
func (s *Server) withBodyLimit(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.Body != nil && r.Method != http.MethodGet && r.Method != http.MethodHead {
			limit := int64(s.app.Settings().HTTP.MaxUploadMB) * 1024 * 1024
			if limit <= 0 {
				limit = 64 * 1024 * 1024
			}
			r.Body = http.MaxBytesReader(w, r.Body, limit)
		}
		next.ServeHTTP(w, r)
	})
}

// withRateLimit applies a coarse per-address request limit to the management
// interface. It is a brute-force and runaway-script guard, not a DoS defence.
func (s *Server) withRateLimit(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if strings.HasPrefix(r.URL.Path, "/static/") || r.URL.Path == "/healthz" {
			next.ServeHTTP(w, r)
			return
		}
		perMin := s.app.Settings().HTTP.RateLimitPerMin
		addr, ok := netutil.AddrFromHostPort(s.app.Auth.ClientIP(r))
		if ok && !s.limiter.allow(addr.String(), perMin) {
			w.Header().Set("Retry-After", "60")
			http.Error(w, "Too many requests. Slow down and try again shortly.", http.StatusTooManyRequests)
			return
		}
		next.ServeHTTP(w, r)
	})
}

// cacheStatic marks embedded assets as immutable. They only change when the
// binary changes, and the binary is what serves them.
func cacheStatic(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Cache-Control", "public, max-age=86400")
		next.ServeHTTP(w, r)
	})
}