package middleware_test

import (
	"context"
	"fmt"
	"sync"
	"sync/atomic"
	"testing"
	"time"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"sneak.berlin/go/webhooker/internal/database"
	"sneak.berlin/go/webhooker/internal/middleware"
)

// mib converts the Argon2id memory parameter, which is in KiB, to MB.
const mib = 1024

const (
	// guardInterval is the failure window these tests use. It is
	// long enough that nothing lapses mid-test on its own; tests
	// that need a lapse drive the clock instead.
	guardInterval = time.Minute

	// guardWait is the slot wait for tests that expect to get a
	// slot. Tests that expect to be refused set their own.
	guardWait = 2 * time.Second

	guardClient = "198.51.100.7"
	guardUser   = "admin"
)

// newGuard builds a guard with production-shaped defaults and the
// given key-set cap and verification concurrency.
func newGuard(maxKeys, concurrency int) *middleware.LoginGuard {
	return middleware.NewLoginGuardForTest(
		middleware.LoginRateLimitConst,
		guardInterval,
		maxKeys,
		concurrency,
		middleware.PasswordVerifyMaxWaitersConst,
		guardWait,
	)
}

// TestLoginGuard_ThrottlesRepeatedFailures is the brute-force half:
// wrong passwords for one username from one client key still run out
// of budget and are answered 429.
func TestLoginGuard_ThrottlesRepeatedFailures(t *testing.T) {
	t.Parallel()

	g := newGuard(middleware.LoginFailureMaxKeysConst, 1)

	for i := range middleware.LoginRateLimitConst - 1 {
		assert.False(
			t, g.FailForTest(guardClient, guardUser),
			"failure %d is still inside the budget", i,
		)
	}

	assert.True(
		t, g.FailForTest(guardClient, guardUser),
		"the last failure of the budget must throttle",
	)
	assert.True(
		t, g.FailForTest(guardClient, guardUser),
		"failures past the budget must stay throttled",
	)
}

// TestLoginGuard_SuccessForgivesFailures pins the forgiveness rule:
// an operator who mistypes several times and then gets it right must
// not be left throttled.
func TestLoginGuard_SuccessForgivesFailures(t *testing.T) {
	t.Parallel()

	g := newGuard(middleware.LoginFailureMaxKeysConst, 1)

	for range middleware.LoginRateLimitConst {
		g.FailForTest(guardClient, guardUser)
	}

	g.SucceedForTest(guardClient, guardUser)

	assert.False(
		t, g.FailForTest(guardClient, guardUser),
		"a success must reset the counter, so the next mistake "+
			"starts a fresh budget",
	)
}

// TestLoginGuard_FailuresAreKeyedPerUsername proves the second half
// of the keying: one username's spent budget does not throttle
// another's from the same client.
func TestLoginGuard_FailuresAreKeyedPerUsername(t *testing.T) {
	t.Parallel()

	g := newGuard(middleware.LoginFailureMaxKeysConst, 1)

	for range middleware.LoginRateLimitConst {
		g.FailForTest(guardClient, guardUser)
	}

	assert.True(t, g.FailForTest(guardClient, guardUser))
	assert.False(
		t, g.FailForTest(guardClient, "someone-else"),
		"a different submitted username must have its own budget",
	)
}

// TestLoginGuard_WindowLapses covers the interval: a counter that has
// gone quiet for the whole window starts again from zero.
func TestLoginGuard_WindowLapses(t *testing.T) {
	t.Parallel()

	g := newGuard(middleware.LoginFailureMaxKeysConst, 1)

	var now atomic.Int64

	now.Store(time.Now().UnixNano())
	g.SetNowForTest(func() time.Time {
		return time.Unix(0, now.Load())
	})

	for range middleware.LoginRateLimitConst {
		g.FailForTest(guardClient, guardUser)
	}

	assert.True(t, g.FailForTest(guardClient, guardUser))

	now.Add(int64(guardInterval) + 1)

	assert.False(
		t, g.FailForTest(guardClient, guardUser),
		"a lapsed window must start a fresh budget",
	)
}

// TestLoginGuard_UsernameKeySetIsBounded is the memory bound. The
// submitted username is attacker-controlled, so an attacker rotating
// usernames must not be able to grow the guard without limit: past
// the cap, tracking falls back to a counter keyed on the client
// address alone.
func TestLoginGuard_UsernameKeySetIsBounded(t *testing.T) {
	t.Parallel()

	const (
		maxKeys  = 8
		attempts = 500
	)

	g := newGuard(maxKeys, 1)

	for i := range attempts {
		g.FailForTest(guardClient, fmt.Sprintf("user-%d", i))
	}

	byUser, byAddr := g.TrackedKeysForTest()

	assert.LessOrEqual(
		t, byUser, maxKeys,
		"the per-username key set must not grow past its cap",
	)
	assert.LessOrEqual(
		t, byAddr, maxKeys,
		"the fallback key set must not grow past its cap either",
	)
	assert.Positive(
		t, byAddr,
		"past the cap, failures must fall back to the address "+
			"bucket rather than being dropped",
	)
	assert.Less(
		t, byUser+byAddr, attempts,
		"memory must not grow with the number of distinct "+
			"usernames submitted",
	)
}

// TestLoginGuard_BeyondBothCapsStaysThrottled covers the hard stop.
// When both key sets are full of live counters and the client is in
// neither, there is nothing to count without unbounded growth, so the
// failure is answered as throttled. That costs the operator nothing:
// a correct password never reaches this path.
func TestLoginGuard_BeyondBothCapsStaysThrottled(t *testing.T) {
	t.Parallel()

	const maxKeys = 4

	g := newGuard(maxKeys, 1)

	// Fill the per-username set from one client, then fill the
	// address set from distinct clients.
	for i := range maxKeys {
		g.FailForTest(guardClient, fmt.Sprintf("user-%d", i))
	}

	for i := range maxKeys {
		g.FailForTest(fmt.Sprintf("203.0.113.%d", i), "whoever")
	}

	assert.True(
		t, g.FailForTest("203.0.113.200", "brand-new"),
		"a client that fits in neither full key set must be "+
			"answered as throttled rather than tracked",
	)

	byUser, byAddr := g.TrackedKeysForTest()
	assert.LessOrEqual(t, byUser, maxKeys)
	assert.LessOrEqual(t, byAddr, maxKeys)
}

// TestLoginGuard_SemaphoreBoundsConcurrentVerifications is the memory
// bound on the hashing itself. Verifying credentials before spending
// limiter budget means an attacker can force one Argon2id hash per
// request, and each allocates 64 MB; without this bound the fix for
// an admin lockout would be a memory-exhaustion DoS instead.
func TestLoginGuard_SemaphoreBoundsConcurrentVerifications(
	t *testing.T,
) {
	t.Parallel()

	const (
		concurrency = 2
		workers     = 12
	)

	g := newGuard(middleware.LoginFailureMaxKeysConst, concurrency)

	var (
		mu      sync.Mutex
		inside  int
		highest int
		wg      sync.WaitGroup
	)

	for range workers {
		wg.Go(func() {
			release, ok := g.AcquireForTest(context.Background())
			if !ok {
				return
			}

			defer release()

			mu.Lock()

			inside++
			if inside > highest {
				highest = inside
			}

			mu.Unlock()

			// Hold the slot long enough that the other workers are
			// certainly contending for it.
			time.Sleep(10 * time.Millisecond)

			mu.Lock()
			inside--
			mu.Unlock()
		})
	}

	wg.Wait()

	mu.Lock()
	defer mu.Unlock()

	assert.Equal(
		t, concurrency, highest,
		"no more than %d verifications may run at once", concurrency,
	)
}

// TestLoginGuard_SaturatedSemaphoreRefusesRatherThanQueueing pins
// what happens when every slot is taken for longer than the wait: the
// request is refused, so the caller answers 503 without allocating
// another 64 MB hash.
func TestLoginGuard_SaturatedSemaphoreRefusesRatherThanQueueing(
	t *testing.T,
) {
	t.Parallel()

	g := middleware.NewLoginGuardForTest(
		middleware.LoginRateLimitConst,
		guardInterval,
		middleware.LoginFailureMaxKeysConst,
		1,
		middleware.PasswordVerifyMaxWaitersConst,
		10*time.Millisecond,
	)

	release, ok := g.AcquireForTest(context.Background())
	require.True(t, ok, "the first acquire must get the only slot")

	_, ok = g.AcquireForTest(context.Background())
	assert.False(
		t, ok,
		"with the only slot held, a second request must be refused "+
			"rather than wait indefinitely",
	)

	release()

	release, ok = g.AcquireForTest(context.Background())
	assert.True(
		t, ok, "the slot must be reusable once released",
	)

	release()
}

// TestLoginGuard_AcquireHonoursCancellation proves a client that
// disconnects while queued frees its place immediately instead of
// holding it for the full wait.
func TestLoginGuard_AcquireHonoursCancellation(t *testing.T) {
	t.Parallel()

	g := newGuard(middleware.LoginFailureMaxKeysConst, 1)

	release, ok := g.AcquireForTest(context.Background())
	require.True(t, ok)

	defer release()

	ctx, cancel := context.WithCancel(context.Background())
	cancel()

	_, ok = g.AcquireForTest(ctx)
	assert.False(
		t, ok, "a cancelled request must not wait for a slot",
	)
}

// TestPasswordVerifyConcurrency_MatchesMemoryBudget pins the
// concurrency constant to the arithmetic behind it: the number of
// slots is the hashing budget divided by what one Argon2id hash
// actually costs.
//
// The per-hash figure is read out of the shipped password
// parameters rather than copied here. A guard that asserts a literal
// against a literal cannot see the thing it guards: raising
// argon2Memory would leave it green while the real ceiling doubled.
func TestPasswordVerifyConcurrency_MatchesMemoryBudget(t *testing.T) {
	t.Parallel()

	// Memory is the real argon2Memory, in KiB.
	perHashMB := int(database.DefaultPasswordConfig().Memory) / mib

	require.Positive(
		t, perHashMB,
		"the Argon2id memory parameter must be readable in MB",
	)

	// The memory this service commits to password hashing.
	const budgetMB = 128

	assert.Equal(
		t,
		middleware.PasswordVerifyConcurrencyConst,
		budgetMB/perHashMB,
		"the verification concurrency must be the %d MB hashing "+
			"budget divided by the %d MB one Argon2id hash costs; "+
			"if the Argon2id parameters changed, the slot count "+
			"must change with them",
		budgetMB, perHashMB,
	)
}

// TestLoginGuard_ShedsPastTheQueueCap pins the memory bound on
// waiting, as distinct from the bound on hashing. A waiter arrives
// with its form already parsed, so an unbounded queue would hold up
// to maxFormBodySize per waiting request for the whole wait; past
// the cap the guard must refuse instantly rather than grow.
func TestLoginGuard_ShedsPastTheQueueCap(t *testing.T) {
	t.Parallel()

	const (
		maxWaiters = 2

		// Long enough that a queued waiter never times out on its
		// own, so anything the test observes leaving the queue left
		// because it was shed.
		neverElapses = time.Minute

		// The probe carries its own deadline, so a guard that queues
		// the probe instead of shedding it fails on the elapsed time
		// rather than hanging until the package test timeout.
		probeWait = 200 * time.Millisecond

		// Shedding takes no measurable time; queueing takes the whole
		// probeWait. Anything under half of it is unambiguous.
		shedFast = probeWait / 2
	)

	g := middleware.NewLoginGuardForTest(
		middleware.LoginRateLimitConst,
		guardInterval,
		middleware.LoginFailureMaxKeysConst,
		1,
		maxWaiters,
		neverElapses,
	)

	// Occupy the only slot, so everything after this queues.
	release, ok := g.AcquireForTest(context.Background())
	require.True(t, ok)

	defer release()
	defer fillQueue(t, g, maxWaiters)()

	got := probeQueueCap(g, probeWait)

	require.NotNil(
		t, got,
		"a request arriving past the queue cap is still waiting to "+
			"be queued; it must have been shed",
	)
	assert.False(
		t, got.ok,
		"a request arriving past the queue cap must be shed",
	)
	assert.Less(
		t, got.elapsed, shedFast,
		"shedding must be immediate; waiting for a place in the "+
			"queue is the memory growth this bounds",
	)
	assert.Equal(
		t, maxWaiters, g.QueuedWaitersForTest(),
		"a shed request must not have grown the queue",
	)
}

// fillQueue starts n waiters on g and returns once all of them are
// queued for a slot. The returned function releases them and waits
// for them to exit.
func fillQueue(
	t *testing.T,
	g *middleware.LoginGuard,
	n int,
) func() {
	t.Helper()

	ctx, cancel := context.WithCancel(context.Background())

	var wg sync.WaitGroup

	for range n {
		wg.Go(func() {
			done, got := g.AcquireForTest(ctx)
			if got {
				done()
			}
		})
	}

	require.Eventually(
		t,
		func() bool { return g.QueuedWaitersForTest() == n },
		time.Second, time.Millisecond,
		"the waiters must reach the queue before the cap is tested",
	)

	return func() {
		cancel()
		wg.Wait()
	}
}

// probeResult is what the queue-cap probe reports: whether it got a
// slot, and how long it took to find out.
type probeResult struct {
	ok      bool
	elapsed time.Duration
}

// probeQueueCap acquires from another goroutine and reports the
// result, or nil if the call was still blocked after wait.
//
// It runs off the test goroutine deliberately. Joining a full queue
// is not cancellable by context — refusing to join is the property
// under test — so a guard that fails this would otherwise hang the
// package until the test timeout instead of failing here.
func probeQueueCap(
	g *middleware.LoginGuard,
	wait time.Duration,
) *probeResult {
	probed := make(chan probeResult, 1)

	go func() {
		start := time.Now()

		release, ok := g.AcquireForTest(context.Background())
		if ok {
			release()
		}

		probed <- probeResult{ok: ok, elapsed: time.Since(start)}
	}()

	select {
	case result := <-probed:
		return &result
	case <-time.After(wait):
		return nil
	}
}