package subscriptions

import (
	"context"
	"fmt"
	"io"
	"log/slog"
	"sync"
	"testing"
	"time"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

type ping struct {
	ID string
}

func quiet() Option {
	return WithLogger(slog.New(slog.NewTextHandler(io.Discard, nil)))
}

// recordObserver records the metric callbacks; safe for concurrent use.
type recordObserver struct {
	mu          sync.Mutex
	pushed      []string
	skipped     []string
	dropped     []string
	channelFull []string
}

func (o *recordObserver) Pushed(k string)      { o.add(&o.pushed, k) }
func (o *recordObserver) PushSkipped(k string) { o.add(&o.skipped, k) }
func (o *recordObserver) Dropped(k string)     { o.add(&o.dropped, k) }
func (o *recordObserver) ChannelFull(k string) { o.add(&o.channelFull, k) }

func (o *recordObserver) add(dst *[]string, k string) {
	o.mu.Lock()
	defer o.mu.Unlock()
	*dst = append(*dst, k)
}

func (o *recordObserver) count(get func(*recordObserver) []string) int {
	o.mu.Lock()
	defer o.mu.Unlock()
	return len(get(o))
}

func (o *recordObserver) pushedCount() int {
	return o.count(func(r *recordObserver) []string { return r.pushed })
}

func (o *recordObserver) skippedCount() int {
	return o.count(func(r *recordObserver) []string { return r.skipped })
}

func (o *recordObserver) droppedCount() int {
	return o.count(func(r *recordObserver) []string { return r.dropped })
}

func (o *recordObserver) channelFullCount() int {
	return o.count(func(r *recordObserver) []string { return r.channelFull })
}

func ready(p *ping) Producer[ping] {
	return func(context.Context) (*ping, bool) { return p, true }
}

func never() Producer[ping] {
	return func(context.Context) (*ping, bool) { return nil, false }
}

func recv(t *testing.T, ch <-chan *ping) *ping {
	t.Helper()
	select {
	case v := <-ch:
		return v
	case <-time.After(2 * time.Second):
		t.Fatal("timed out waiting for a push")
		return nil
	}
}

func assertNoPush(t *testing.T, ch <-chan *ping) {
	t.Helper()
	select {
	case v := <-ch:
		t.Fatalf("unexpected push: %+v", v)
	case <-time.After(100 * time.Millisecond):
	}
}

func TestSubmit_pushesWhenReady(t *testing.T) {
	r := New[ping](quiet())
	defer r.Close()

	ch, cleanup, err := r.AddReceiver("c1")
	require.NoError(t, err)
	defer cleanup()

	r.Submit("c1", ready(&ping{ID: "eb1"}))

	assert.Equal(t, &ping{ID: "eb1"}, recv(t, ch))
}

func TestSubmit_noSubscribers_doesNotEnqueue(t *testing.T) {
	r := New[ping](quiet())
	defer r.Close()

	var calls int
	r.Submit("c1", func(context.Context) (*ping, bool) {
		calls++
		return &ping{ID: "x"}, true
	})

	// No subscribers → Submit returns on the fast path without enqueuing, so the
	// producer is never invoked.
	assert.Equal(t, 0, calls)
}

func TestSubmit_emptyKey_isNoop(t *testing.T) {
	r := New[ping](quiet())
	defer r.Close()

	var calls int
	r.Submit("", func(context.Context) (*ping, bool) {
		calls++
		return nil, true
	})
	assert.Equal(t, 0, calls)
}

func TestSubmit_lagThenReady(t *testing.T) {
	r := New[ping](quiet(), WithReadRetry(50, time.Millisecond))
	defer r.Close()

	ch, cleanup, _ := r.AddReceiver("c1")
	defer cleanup()

	var mu sync.Mutex
	calls := 0
	r.Submit("c1", func(context.Context) (*ping, bool) {
		mu.Lock()
		defer mu.Unlock()
		calls++
		// Not visible on the first read; visible thereafter.
		return &ping{ID: "eb1"}, calls > 1
	})

	assert.Equal(t, &ping{ID: "eb1"}, recv(t, ch))
}

func TestSubmit_neverReady_skipsAndReports(t *testing.T) {
	obs := &recordObserver{}
	r := New[ping](quiet(), WithObserver(obs), WithReadRetry(2, time.Millisecond))
	defer r.Close()

	ch, cleanup, _ := r.AddReceiver("c1")
	defer cleanup()

	r.Submit("c1", never())

	assert.Eventually(t, func() bool { return obs.skippedCount() == 1 }, time.Second, 5*time.Millisecond)
	assert.Equal(t, 0, obs.pushedCount())
	assertNoPush(t, ch)
}

func TestObserver_pushedOnDelivery(t *testing.T) {
	obs := &recordObserver{}
	r := New[ping](quiet(), WithObserver(obs))
	defer r.Close()

	ch, cleanup, _ := r.AddReceiver("c1")
	defer cleanup()

	r.Submit("c1", ready(&ping{ID: "eb1"}))
	recv(t, ch)

	assert.Eventually(t, func() bool { return obs.pushedCount() == 1 }, time.Second, 5*time.Millisecond)
}

func TestPush_allSubscribersOfKey(t *testing.T) {
	r := New[ping](quiet())
	defer r.Close()

	chA, cleanupA, _ := r.AddReceiver("c1")
	defer cleanupA()
	chB, cleanupB, _ := r.AddReceiver("c1")
	defer cleanupB()

	r.Submit("c1", ready(&ping{ID: "eb1"}))

	assert.Equal(t, "eb1", recv(t, chA).ID)
	assert.Equal(t, "eb1", recv(t, chB).ID)
}

func TestSubmit_keysIsolated(t *testing.T) {
	r := New[ping](quiet())
	defer r.Close()

	chA, cleanupA, _ := r.AddReceiver("c1")
	defer cleanupA()
	chB, cleanupB, _ := r.AddReceiver("c2")
	defer cleanupB()

	r.Submit("c1", ready(&ping{ID: "eb1"}))

	assert.Equal(t, "eb1", recv(t, chA).ID)
	assertNoPush(t, chB)
}

// TestPerKeyOrdering asserts that events for one key are delivered FIFO even
// across the worker pool (same key → same shard → one worker). This guards the
// ordering guarantee a payload the client consumes directly relies on.
func TestPerKeyOrdering(t *testing.T) {
	r := New[ping](quiet(), WithWorkers(4))
	defer r.Close()

	ch, cleanup, _ := r.AddReceiver("c1")
	defer cleanup()

	const n = 10
	for i := range n {
		r.Submit("c1", ready(&ping{ID: fmt.Sprintf("e%02d", i)}))
	}
	for i := range n {
		assert.Equal(t, fmt.Sprintf("e%02d", i), recv(t, ch).ID)
	}
}

func TestAddReceiver_emptyKeyErrors(t *testing.T) {
	r := New[ping](quiet())
	defer r.Close()

	ch, cleanup, err := r.AddReceiver("")
	assert.ErrorIs(t, err, ErrEmptyKey)
	assert.Nil(t, ch)
	assert.Nil(t, cleanup)
}

func TestRemoveReceiver_closesChannel(t *testing.T) {
	r := New[ping](quiet())
	defer r.Close()

	ch, cleanup, _ := r.AddReceiver("c1")
	cleanup()

	// Draining a closed channel terminates the range/returns ok=false.
	_, ok := <-ch
	assert.False(t, ok)
}

func TestRemoveReceiver_idempotent(t *testing.T) {
	r := New[ping](quiet())
	defer r.Close()

	_, cleanup, _ := r.AddReceiver("c1")
	cleanup()
	assert.NotPanics(t, cleanup) // second call is a no-op
}

func TestChannelFull_dropsAndReports(t *testing.T) {
	obs := &recordObserver{}
	// One worker so the two pushes are serialized; buffer 1 so the second drops.
	r := New[ping](quiet(), WithObserver(obs), WithBufferSize(1), WithWorkers(1))
	defer r.Close()

	_, cleanup, _ := r.AddReceiver("c1") // never read from the channel
	defer cleanup()

	r.Submit("c1", ready(&ping{ID: "first"}))
	r.Submit("c1", ready(&ping{ID: "second"}))

	assert.Eventually(t, func() bool { return obs.channelFullCount() == 1 }, time.Second, 5*time.Millisecond)
}

func TestSubmit_queueFull_dropsAndReports(t *testing.T) {
	obs := &recordObserver{}
	started := make(chan struct{})
	release := make(chan struct{})

	r := New[ping](quiet(), WithObserver(obs), WithWorkers(1), WithQueueSize(1), WithReadRetry(0, time.Millisecond))
	defer r.Close()      // runs last
	defer close(release) // runs before Close, unblocking the worker

	_, cleanup, _ := r.AddReceiver("c1")
	defer cleanup()

	var once sync.Once
	r.Submit("c1", func(context.Context) (*ping, bool) {
		once.Do(func() { close(started) })
		<-release
		return &ping{ID: "blocking"}, true
	})
	<-started // the single worker is now blocked in produce; its shard queue is empty

	r.Submit("c1", ready(&ping{ID: "fills-queue"})) // occupies the cap-1 shard queue
	r.Submit("c1", ready(&ping{ID: "dropped"}))     // queue full → dropped

	assert.Eventually(t, func() bool { return obs.droppedCount() >= 1 }, time.Second, 5*time.Millisecond)
}

func TestClose_isIdempotentAndSubmitAfterCloseIsNoop(t *testing.T) {
	r := New[ping](quiet())
	r.Close()
	r.Close() // idempotent

	assert.NotPanics(t, func() {
		r.Submit("c1", ready(&ping{ID: "x"}))
	})
}

// TestClose_cancelsInFlightGate asserts Close returns promptly even while a
// worker is mid-gate, rather than blocking for the full retry budget (~5s by
// default). Guards the registry-level context cancellation.
func TestClose_cancelsInFlightGate(t *testing.T) {
	started := make(chan struct{})
	r := New[ping](quiet()) // default retry budget ≈ 5s

	_, cleanup, _ := r.AddReceiver("c1")
	defer cleanup()

	var once sync.Once
	r.Submit("c1", func(context.Context) (*ping, bool) {
		once.Do(func() { close(started) })
		return nil, false // never ready → worker stays in the gate loop
	})
	<-started // worker is now in the gate loop

	done := make(chan struct{})
	go func() { r.Close(); close(done) }()

	select {
	case <-done:
	case <-time.After(2 * time.Second):
		t.Fatal("Close did not return promptly while a worker was gating")
	}
}

// TestConcurrentChurn stresses the race between removeReceiver (which closes a
// subscriber channel under the write lock) and a worker push (which sends under
// the read lock). Before sends were moved under the read lock this panicked
// with "send on closed channel". Run with -race.
func TestConcurrentChurn(t *testing.T) {
	r := New[ping](quiet(), WithReadRetry(0, time.Millisecond), WithWorkers(8))
	defer r.Close()

	// A long-lived reader so there is always at least one subscriber being
	// pushed to while others churn.
	_, steadyCleanup, _ := r.AddReceiver("c1")
	defer steadyCleanup()
	go func() {
		ch, _, _ := r.AddReceiver("c1")
		for range ch { //nolint:revive // drain
		}
	}()

	var wg sync.WaitGroup

	wg.Add(1)
	go func() {
		defer wg.Done()
		for range 2000 {
			_, cleanup, err := r.AddReceiver("c1")
			if err != nil {
				t.Errorf("AddReceiver: %v", err)
				return
			}
			cleanup()
		}
	}()

	wg.Add(1)
	go func() {
		defer wg.Done()
		for range 2000 {
			r.Submit("c1", ready(&ping{ID: "x"}))
		}
	}()

	wg.Wait()
}