package middleware_test

import (
	"net/http"
	"net/http/httptest"
	"strings"
	"testing"
	"time"

	"github.com/go-chi/chi/v5"
	"go.uber.org/fx/fxtest"

	"sneak.berlin/go/dnswatcher/internal/config"
	"sneak.berlin/go/dnswatcher/internal/globals"
	"sneak.berlin/go/dnswatcher/internal/handlers"
	"sneak.berlin/go/dnswatcher/internal/logger"
	"sneak.berlin/go/dnswatcher/internal/middleware"
	"sneak.berlin/go/dnswatcher/internal/notify"
	"sneak.berlin/go/dnswatcher/internal/state"
)

// Expected security header values, spelled out literally so that any
// change to the middleware has to be made deliberately here as well.
const (
	wantHSTS = "max-age=31536000; includeSubDomains"

	wantCSP = "default-src 'self'; " +
		"script-src 'none'; " +
		"style-src 'self'; " +
		"img-src 'self'; " +
		"font-src 'none'; " +
		"connect-src 'none'; " +
		"object-src 'none'; " +
		"base-uri 'none'; " +
		"form-action 'none'; " +
		"frame-ancestors 'none'"

	wantFrameOptions = "DENY"

	wantContentTypeOptions = "nosniff"

	wantReferrerPolicy = "no-referrer"

	wantPermissionsPolicy = "accelerometer=(), " +
		"autoplay=(), " +
		"camera=(), " +
		"display-capture=(), " +
		"encrypted-media=(), " +
		"fullscreen=(), " +
		"geolocation=(), " +
		"gyroscope=(), " +
		"magnetometer=(), " +
		"microphone=(), " +
		"midi=(), " +
		"payment=(), " +
		"picture-in-picture=(), " +
		"publickey-credentials-get=(), " +
		"screen-wake-lock=(), " +
		"usb=(), " +
		"xr-spatial-tracking=()"
)

// stylesheetPath is the only subresource the dashboard loads.
const stylesheetPath = "/s/css/tailwind.min.css"

// newTestLogger builds a logger for direct component construction.
func newTestLogger(t *testing.T) *logger.Logger {
	t.Helper()

	glob, err := globals.New(nil)
	if err != nil {
		t.Fatalf("globals.New: %v", err)
	}

	log, err := logger.New(nil, logger.Params{Globals: glob})
	if err != nil {
		t.Fatalf("logger.New: %v", err)
	}

	return log
}

// newTestMiddleware builds a Middleware without an fx application.
func newTestMiddleware(t *testing.T) *middleware.Middleware {
	t.Helper()

	glob, err := globals.New(nil)
	if err != nil {
		t.Fatalf("globals.New: %v", err)
	}

	mw, err := middleware.New(nil, middleware.Params{
		Logger:  newTestLogger(t),
		Globals: glob,
		Config:  &config.Config{},
	})
	if err != nil {
		t.Fatalf("middleware.New: %v", err)
	}

	return mw
}

// serveWithSecurityHeaders runs a GET through SecurityHeaders and
// returns the recorded response.
func serveWithSecurityHeaders(
	t *testing.T,
	target string,
	handler http.Handler,
) *httptest.ResponseRecorder {
	t.Helper()

	mw := newTestMiddleware(t)
	rec := httptest.NewRecorder()
	req := httptest.NewRequestWithContext(
		t.Context(), http.MethodGet, target, nil,
	)

	mw.SecurityHeaders()(handler).ServeHTTP(rec, req)

	return rec
}

// okHandler writes a trivial 200 response.
func okHandler() http.Handler {
	return http.HandlerFunc(func(
		writer http.ResponseWriter,
		_ *http.Request,
	) {
		writer.WriteHeader(http.StatusOK)
	})
}

func TestSecurityHeaders(t *testing.T) {
	t.Parallel()

	tests := []struct {
		name   string
		header string
		want   string
	}{
		{
			"hsts",
			"Strict-Transport-Security",
			wantHSTS,
		},
		{
			"csp",
			"Content-Security-Policy",
			wantCSP,
		},
		{
			"frame options",
			"X-Frame-Options",
			wantFrameOptions,
		},
		{
			"content type options",
			"X-Content-Type-Options",
			wantContentTypeOptions,
		},
		{
			"referrer policy",
			"Referrer-Policy",
			wantReferrerPolicy,
		},
		{
			"permissions policy",
			"Permissions-Policy",
			wantPermissionsPolicy,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			rec := serveWithSecurityHeaders(t, "/", okHandler())

			got := rec.Header().Get(tt.header)
			if got != tt.want {
				t.Errorf(
					"%s = %q, want %q",
					tt.header, got, tt.want,
				)
			}
		})
	}
}

// TestSecurityHeadersCSPDirectives guards the properties the repo
// policy requires of the content security policy itself.
func TestSecurityHeadersCSPDirectives(t *testing.T) {
	t.Parallel()

	rec := serveWithSecurityHeaders(t, "/", okHandler())
	csp := rec.Header().Get("Content-Security-Policy")

	forbidden := []string{"unsafe-inline", "unsafe-eval"}
	for _, directive := range forbidden {
		if strings.Contains(csp, directive) {
			t.Errorf("CSP must not contain %q: %q", directive, csp)
		}
	}

	required := []string{
		"default-src 'self'",
		"script-src 'none'",
		"style-src 'self'",
		"frame-ancestors 'none'",
	}
	for _, directive := range required {
		if !strings.Contains(csp, directive) {
			t.Errorf("CSP must contain %q: %q", directive, csp)
		}
	}
}

// TestSecurityHeadersOnErrorResponse verifies the headers are emitted
// even when the wrapped handler fails, since they are set before the
// handler runs.
func TestSecurityHeadersOnErrorResponse(t *testing.T) {
	t.Parallel()

	failing := http.HandlerFunc(func(
		writer http.ResponseWriter,
		_ *http.Request,
	) {
		http.Error(
			writer,
			"boom",
			http.StatusInternalServerError,
		)
	})

	rec := serveWithSecurityHeaders(t, "/api/v1/status", failing)

	if rec.Code != http.StatusInternalServerError {
		t.Fatalf("status = %d, want 500", rec.Code)
	}

	if got := rec.Header().Get(
		"X-Content-Type-Options",
	); got != wantContentTypeOptions {
		t.Errorf(
			"X-Content-Type-Options = %q, want %q",
			got, wantContentTypeOptions,
		)
	}

	if got := rec.Header().Get(
		"Strict-Transport-Security",
	); got != wantHSTS {
		t.Errorf(
			"Strict-Transport-Security = %q, want %q",
			got, wantHSTS,
		)
	}
}

// newTestHandlers builds real Handlers with empty monitoring state.
func newTestHandlers(t *testing.T) *handlers.Handlers {
	t.Helper()

	glob, err := globals.New(nil)
	if err != nil {
		t.Fatalf("globals.New: %v", err)
	}

	log := newTestLogger(t)

	notifier, err := notify.New(fxtest.NewLifecycle(t), notify.Params{
		Logger: log,
		Config: &config.Config{},
	})
	if err != nil {
		t.Fatalf("notify.New: %v", err)
	}

	st, err := state.New(fxtest.NewLifecycle(t), state.Params{
		Logger: log,
		Config: &config.Config{DataDir: t.TempDir()},
	})
	if err != nil {
		t.Fatalf("state.New: %v", err)
	}

	hnd, err := handlers.New(nil, handlers.Params{
		Logger:  log,
		Globals: glob,
		State:   st,
		Notify:  notifier,
	})
	if err != nil {
		t.Fatalf("handlers.New: %v", err)
	}

	return hnd
}

// TestDashboardRendersWithSecurityHeaders renders the real dashboard
// through the middleware and checks that the policy still permits the
// one stylesheet the page loads.
func TestDashboardRendersWithSecurityHeaders(t *testing.T) {
	t.Parallel()

	mw := newTestMiddleware(t)
	hnd := newTestHandlers(t)

	router := chi.NewRouter()
	router.Use(mw.SecurityHeaders())
	router.Get("/", hnd.HandleDashboard())

	rec := httptest.NewRecorder()
	req := httptest.NewRequestWithContext(
		t.Context(), http.MethodGet, "/", nil,
	)

	router.ServeHTTP(rec, req)

	if rec.Code != http.StatusOK {
		t.Fatalf("status = %d, want 200", rec.Code)
	}

	body := rec.Body.String()
	if !strings.Contains(body, stylesheetPath) {
		t.Errorf("dashboard does not reference %q", stylesheetPath)
	}

	if !strings.Contains(body, "dnswatcher") {
		t.Errorf("dashboard body looks empty: %d bytes", len(body))
	}

	csp := rec.Header().Get("Content-Security-Policy")
	if csp != wantCSP {
		t.Errorf("CSP = %q, want %q", csp, wantCSP)
	}

	// The stylesheet is same-origin, so style-src 'self' allows it.
	if !strings.Contains(csp, "style-src 'self'") {
		t.Errorf("CSP would block %q: %q", stylesheetPath, csp)
	}
}

// Addresses for the rate limit tests: a client connecting directly, a
// trusted proxy, and a client behind that proxy as its X-Real-IP
// header names it.
const (
	directClient  = "198.51.100.1:4000"
	trustedProxy  = "10.0.0.1:4000"
	proxiedClient = "203.0.113.1"
)

// statusFrom sends a GET through handler as if from remoteAddr, with
// an X-Real-IP header when xRealIP is not empty, and returns the
// response status.
func statusFrom(
	t *testing.T,
	handler http.Handler,
	remoteAddr string,
	xRealIP string,
) int {
	t.Helper()

	req := httptest.NewRequestWithContext(
		t.Context(), http.MethodGet, "/metrics", nil,
	)
	req.RemoteAddr = remoteAddr

	if xRealIP != "" {
		req.Header.Set("X-Real-IP", xRealIP)
	}

	rec := httptest.NewRecorder()
	handler.ServeHTTP(rec, req)

	return rec.Code
}

// TestMetricsRateLimitAllowsScraping checks that one address can send,
// within one window, what two Prometheus servers scraping every 5
// seconds send in that time, without being turned away.
func TestMetricsRateLimitAllowsScraping(t *testing.T) {
	t.Parallel()

	const scrapeInterval = 5 * time.Second

	scrapes := 2 * int(middleware.MetricsRequestWindow/scrapeInterval)
	limited := newTestMiddleware(t).MetricsRateLimit()(okHandler())

	for i := range scrapes {
		got := statusFrom(t, limited, directClient, "")
		if got != http.StatusOK {
			t.Fatalf(
				"scrape %d of %d: status = %d, want 200",
				i+1, scrapes, got,
			)
		}
	}
}

// TestMetricsRateLimitKeysOnClientAddress checks which requests share
// an allowance. Each case uses up the allowance of one client, then
// sends one more request.
func TestMetricsRateLimitKeysOnClientAddress(t *testing.T) {
	t.Parallel()

	tests := []struct {
		name           string
		usedRemoteAddr string
		usedXRealIP    string
		nextRemoteAddr string
		nextXRealIP    string
		want           int
	}{
		{
			"same address",
			directClient, "",
			directClient, "",
			http.StatusTooManyRequests,
		},
		{
			"another address",
			directClient, "",
			"198.51.100.2:4000", "",
			http.StatusOK,
		},
		{
			"own X-Real-IP from an untrusted address",
			directClient, "",
			directClient, "203.0.113.9",
			http.StatusTooManyRequests,
		},
		{
			"same client behind the proxy",
			trustedProxy, proxiedClient,
			trustedProxy, proxiedClient,
			http.StatusTooManyRequests,
		},
		{
			"another client behind the proxy",
			trustedProxy, proxiedClient,
			trustedProxy, "203.0.113.2",
			http.StatusOK,
		},
		{
			"another client behind the proxy, IPv6-mapped",
			trustedProxy, "::ffff:203.0.113.1",
			trustedProxy, "::ffff:203.0.113.2",
			http.StatusOK,
		},
		{
			"same IPv6 /64",
			"[2001:db8::1]:4000", "",
			"[2001:db8::2]:4000", "",
			http.StatusTooManyRequests,
		},
		{
			"another IPv6 /64",
			"[2001:db8::1]:4000", "",
			"[2001:db8:0:1::1]:4000", "",
			http.StatusOK,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			limited := newTestMiddleware(t).MetricsRateLimit()(okHandler())

			for range middleware.MetricsRequestLimit {
				statusFrom(t, limited, tt.usedRemoteAddr, tt.usedXRealIP)
			}

			got := statusFrom(
				t, limited, tt.nextRemoteAddr, tt.nextXRealIP,
			)
			if got != tt.want {
				t.Errorf("status = %d, want %d", got, tt.want)
			}
		})
	}
}