package handlers_test

import (
	"bytes"
	"context"
	"io"
	"log"
	"net/http"
	"net/http/httptest"
	"net/url"
	"os"
	"strconv"
	"strings"
	"sync"
	"testing"
	"time"

	"github.com/go-chi/chi"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"gorm.io/gorm"
	gormlogger "gorm.io/gorm/logger"
	"sneak.berlin/go/webhooker/internal/database"
	"sneak.berlin/go/webhooker/internal/handlers"
	"sneak.berlin/go/webhooker/internal/middleware"
)

// gormBoundTailMarker sits at the far end of every client-chosen value
// this file sends. Its presence in the log means the whole value
// reached the log, so a value that merely happened to be short cannot
// pass for a truncated one.
const gormBoundTailMarker = "ENDOFCLIENTVALUE"

// gormBoundFills are the characters a client can drive through the
// receiver path segment and the login username, chosen for what a log
// handler charges for them.
//
// The bare C0 control is the one that matters: both handlers spell
// U+0001 as a six-byte escape for the one byte it costs to send, the
// widest multiplier available below U+10000 and the case a raw-byte
// budget breaks on first. GORM's default logger applies no budget at
// all, so under the mutation every one of these arrives whole.
func gormBoundFills() []struct {
	name string
	fill string
} {
	return []struct {
		name string
		fill string
	}{
		{"plain", "x"},
		{"quote", `"`},
		{"backslash", `\`},
		{"tab", "\t"},
		{"newline", "\n"},
		{"c0_control", "\x01"},
		{"astral_nonprintable", "\U0001000C"},
	}
}

// syncBuf collects captured output from the goroutine draining the
// pipe.
type syncBuf struct {
	mu sync.Mutex
	b  bytes.Buffer
}

func (s *syncBuf) Write(p []byte) (int, error) {
	s.mu.Lock()
	defer s.mu.Unlock()

	return s.b.Write(p)
}

func (s *syncBuf) String() string {
	s.mu.Lock()
	defer s.mu.Unlock()

	return s.b.String()
}

func (s *syncBuf) reset() {
	s.mu.Lock()
	defer s.mu.Unlock()

	s.b.Reset()
}

// stdoutCapture redirects os.Stdout for the duration of a test.
//
// internal/logger builds its handler over os.Stdout at construction
// time, so redirecting the variable before the application is built
// captures everything the service logger — and therefore the GORM
// adapter, which writes through it — emits.
type stdoutCapture struct {
	buf  *syncBuf
	r    *os.File
	w    *os.File
	orig *os.File
	done chan struct{}
	seq  int
}

func captureStdout(t *testing.T) *stdoutCapture {
	t.Helper()

	r, w, err := os.Pipe()
	require.NoError(t, err)

	c := &stdoutCapture{
		buf:  &syncBuf{},
		r:    r,
		w:    w,
		orig: os.Stdout,
		done: make(chan struct{}),
	}

	os.Stdout = w

	go func() {
		defer close(c.done)

		_, _ = io.Copy(c.buf, r)
	}()

	t.Cleanup(func() {
		os.Stdout = c.orig
		_ = w.Close()

		<-c.done

		_ = r.Close()
	})

	return c
}

// drain returns everything written since the previous drain and
// clears the buffer.
//
// A sentinel is pushed through the same pipe and waited for, so the
// draining goroutine is known to have caught up before the buffer is
// read. Without it the comparison below would race the reader rather
// than measure the writers.
func (c *stdoutCapture) drain(t *testing.T) string {
	t.Helper()

	c.seq++

	sentinel := "\n<<drain-" + strconv.Itoa(c.seq) + ">>\n"

	_, err := c.w.WriteString(sentinel)
	require.NoError(t, err)

	deadline := time.Now().Add(10 * time.Second)
	for !strings.Contains(c.buf.String(), sentinel) {
		require.False(
			t, time.Now().After(deadline),
			"timed out waiting for captured output",
		)
		time.Sleep(time.Millisecond)
	}

	out := strings.Replace(c.buf.String(), sentinel, "", 1)

	c.buf.reset()

	return out
}

// teeStdout writes to a buffer and to whatever os.Stdout is at the
// moment of the write.
//
// The second half is the point. GORM's package-level default logger
// resolves os.Stdout once, at package init, so a logger built over the
// variable would keep writing to the real terminal no matter what a
// test redirects. Resolving it per write puts the bytes a defaulted
// gorm.Config would cost in production into the same capture as
// everything else internal/logger emits, which is what lets the volume
// assertions below measure the whole writer set rather than one member
// of it.
type teeStdout struct {
	buf *syncBuf
}

func (w teeStdout) Write(p []byte) (int, error) {
	_, _ = os.Stdout.Write(p)

	return w.buf.Write(p)
}

// captureGORMDefault replaces GORM's package-level default logger with
// one configured exactly as GORM configures its own, writing to a
// buffer and to os.Stdout.
//
// This is the mutation detector. gormlogger.Default is what a bare
// &gorm.Config{} installs, and its config here is GORM's verbatim —
// Warn, IgnoreRecordNotFoundError false — so a reverted call site
// behaves as it would in production rather than as a test dialed it.
// With every gorm.Open in this service naming its own logger, nothing
// consults this value and the buffer stays empty; revert any one of
// the three and the interpolated SQL lands here.
func captureGORMDefault(t *testing.T) *syncBuf {
	t.Helper()

	buf := &syncBuf{}
	orig := gormlogger.Default

	gormlogger.Default = gormlogger.New(
		log.New(teeStdout{buf: buf}, "", log.LstdFlags),
		gormlogger.Config{
			SlowThreshold:             200 * time.Millisecond,
			LogLevel:                  gormlogger.Warn,
			IgnoreRecordNotFoundError: false,
			Colorful:                  false,
		},
	)

	t.Cleanup(func() { gormlogger.Default = orig })

	return buf
}

// floodUnauthenticated drives reps requests at each of the two
// unauthenticated lookups that miss by design, for every fill, with a
// client-chosen value of size raw bytes.
func floodUnauthenticated(
	t *testing.T, h *handlers.Handlers, size, reps int,
) int {
	t.Helper()

	requests := 0

	for _, f := range gormBoundFills() {
		var b strings.Builder

		for b.Len() < size {
			b.WriteString(f.fill)
		}

		b.WriteString(gormBoundTailMarker)

		value := b.String()

		for range reps {
			postWebhook(t, h, value)
			postLogin(t, h, value)

			requests += 2
		}
	}

	return requests
}

// floodPerWebhook drives the same client-chosen values at the second
// gorm.Open site, the per-webhook database internal/database's
// WebhookDBManager opens.
//
// That site is behind authentication in production, so this is not
// part of the unauthenticated flood above and is counted separately.
// It is here because the ceiling the README states covers every
// writer, and the manager is one of them: with nothing driving it, a
// bare &gorm.Config{} could be restored at
// internal/database/webhook_db_manager.go and the whole suite would
// stay green.
func floodPerWebhook(
	t *testing.T, mgr *database.WebhookDBManager, size, reps int,
) int {
	t.Helper()

	requests := 0

	for _, f := range gormBoundFills() {
		var b strings.Builder

		for b.Len() < size {
			b.WriteString(f.fill)
		}

		b.WriteString(gormBoundTailMarker)

		value := b.String()

		db, err := mgr.GetDB("pin-" + f.name)
		require.NoError(t, err)

		for range reps {
			var got database.Event

			err = db.Where("id = ?", value).First(&got).Error
			require.ErrorIs(t, err, gorm.ErrRecordNotFound)

			requests++
		}
	}

	return requests
}

// postWebhook drives the receiver with an invented entrypoint path.
// The route pattern matches any single segment, so every byte of the
// value is the client's, and the lookup behind it misses by design.
func postWebhook(
	t *testing.T, h *handlers.Handlers, entrypoint string,
) {
	t.Helper()

	req := httptest.NewRequestWithContext(
		context.Background(), http.MethodPost, "/webhook/x",
		strings.NewReader("{}"),
	)

	rctx := chi.NewRouteContext()
	rctx.URLParams.Add("uuid", entrypoint)

	req = req.WithContext(context.WithValue(
		req.Context(), chi.RouteCtxKey, rctx,
	))

	w := httptest.NewRecorder()
	h.HandleWebhook().ServeHTTP(w, req)

	require.Equal(t, http.StatusNotFound, w.Code)
}

// postLogin submits the login form with an unknown username. The
// field is bounded only by the 1 MB body cap, and the lookup behind
// it misses by design.
func postLogin(
	t *testing.T, h *handlers.Handlers, username string,
) {
	t.Helper()

	form := url.Values{}
	form.Set("username", username)
	form.Set("password", "not-the-password")

	req := httptest.NewRequestWithContext(
		context.Background(), http.MethodPost, "/pages/login",
		strings.NewReader(form.Encode()),
	)
	req.Header.Set(
		"Content-Type", "application/x-www-form-urlencoded",
	)

	w := httptest.NewRecorder()
	h.HandleLoginSubmit().ServeHTTP(w, req)

	// 401 while the client still has failure budget against this
	// username, 429 once the login guard has taken it away. Both
	// outcomes sit behind the user lookup, which is the query this
	// test is here to drive.
	require.Contains(
		t,
		[]int{http.StatusUnauthorized, http.StatusTooManyRequests},
		w.Code,
	)
}

// assertFloodBounded holds every captured line to the stated ceiling
// and proves nothing carried a whole client value.
func assertFloodBounded(t *testing.T, label, out string) {
	t.Helper()

	assert.NotContains(
		t, out, gormBoundTailMarker,
		"%s: the far end of a client-chosen value reached the "+
			"log, so nothing truncated it", label,
	)

	for line := range strings.SplitSeq(
		strings.TrimRight(out, "\n"), "\n",
	) {
		if line == "" {
			continue
		}

		assert.LessOrEqual(
			t, len(line), middleware.MaxAccessLogLineBytes,
			"%s: log line exceeded its bound: %s",
			label, line[:min(len(line), 300)],
		)
	}
}

// TestFlood_NoWriterGrowsWithTheInput is the definition of done for
// the GORM logger defect, stated over every writer at once, for two of
// this service's three gorm.Open sites: the main database behind the
// two unauthenticated lookups, and the per-webhook database the
// WebhookDBManager opens. The third, the archive writer, is pinned in
// internal/delivery, where its type lives.
//
// What each assertion is worth, since two of the three would pass
// against a service that had never been fixed if the capture were set
// up differently:
//
//   - The gormDefault check is the sharp one. It fires the moment any
//     gorm.Open in this service goes back to a bare &gorm.Config{}.
//   - The volume and per-line checks bite only because the replaced
//     default logger tees into os.Stdout, so a reverted call site
//     shows up in the same capture as everything internal/logger
//     writes — the way it would in production. Without that tee both
//     were vacuous: at INFO the two handler misses log at DEBUG and
//     the adapter drops the record-not-found, so the capture holds
//     nothing but fixed-string warnings.
//
// The level is left where newTestApp leaves it, at INFO, deliberately.
// At DEBUG the handlers' own miss lines log the client-chosen
// entrypoint and username untruncated — the first carve-out in the
// README's ceiling section, and https://git.eeqj.de/sneak/webhooker/issues/176's
// to fix, not this one's.
//
// It is deliberately not parallel: it redirects os.Stdout and replaces
// gormlogger.Default, both of which are process-global. Go runs every
// non-parallel top-level test to completion before it resumes the
// parallel ones, so nothing else in this package is running while the
// capture is installed.
//
//nolint:paralleltest // Deliberately sequential; see above.
func TestFlood_NoWriterGrowsWithTheInput(t *testing.T) {
	const (
		smallBytes = 128
		bigBytes   = 8 << 10
		reps       = 5
	)

	gormDefault := captureGORMDefault(t)
	capture := captureStdout(t)

	var (
		h   *handlers.Handlers
		mgr *database.WebhookDBManager
	)

	app := newTestApp(t, &h, &mgr)
	app.RequireStart()

	t.Cleanup(app.RequireStop)

	// Startup chatter is not what this test measures.
	capture.drain(t)

	floodUnauthenticated(t, h, smallBytes, reps)
	floodPerWebhook(t, mgr, smallBytes, reps)

	small := capture.drain(t)

	requests := floodUnauthenticated(t, h, bigBytes, reps)
	requests += floodPerWebhook(t, mgr, bigBytes, reps)
	big := capture.drain(t)

	assertFloodBounded(t, "small flood", small)
	assertFloodBounded(t, "big flood", big)

	// GORM's default logger is what the defect was. Nothing in this
	// service may reach it.
	got := gormDefault.String()
	assert.Empty(
		t, got,
		"GORM's default logger wrote %d bytes; the first of them: %s",
		len(got), got[:min(len(got), 300)],
	)

	// The same flood, with 64 times the client-chosen input, must not
	// buy 64 times the log. A few bytes of slack covers a latency
	// field changing width; the input grew by roughly half a megabyte.
	const slackPerRequest = 64

	assert.LessOrEqual(
		t, len(big), len(small)+slackPerRequest*requests,
		"log volume tracked the size of the client's input: "+
			"%d bytes at %d bytes of input per request, %d bytes "+
			"at %d",
		len(small), smallBytes, len(big), bigBytes,
	)
}