// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>

package main

import (
	"encoding/json"
	"fmt"
	"testing"
	"time"
)

func mkEvent(i int) BrowserEvent {
	p, _ := json.Marshal(map[string]int{"i": i})
	return BrowserEvent{
		Maglevd:  "lb",
		Type:     "backend",
		AtUnixNs: time.Now().UnixNano(),
		Payload:  p,
	}
}

func TestBrokerSubscribeNoHeaderResync(t *testing.T) {
	b := NewBroker()
	b.Publish(mkEvent(1))

	res := b.Subscribe("")
	defer b.Unsubscribe(res.Channel)
	if !res.NeedResync {
		t.Errorf("expected NeedResync=true when Last-Event-ID is empty")
	}
	if len(res.ReplayEvents) != 0 {
		t.Errorf("expected no replay events, got %d", len(res.ReplayEvents))
	}
}

func TestBrokerReplayMatchingEpoch(t *testing.T) {
	b := NewBroker()
	b.Publish(mkEvent(1))
	b.Publish(mkEvent(2))
	b.Publish(mkEvent(3))

	// Publishes used seqs 0,1,2. Client last saw seq 0, so we expect
	// replay of seqs 1 and 2.
	lastID := fmt.Sprintf("%d-0", b.Epoch())
	res := b.Subscribe(lastID)
	defer b.Unsubscribe(res.Channel)
	if res.NeedResync {
		t.Errorf("expected no resync when seqs are in buffer")
	}
	if len(res.ReplayEvents) != 2 {
		t.Fatalf("expected 2 replay events (seqs 1,2), got %d", len(res.ReplayEvents))
	}
	if res.ReplayEvents[0].ID != fmt.Sprintf("%d-1", b.Epoch()) {
		t.Errorf("replay[0] ID = %q, want epoch-1", res.ReplayEvents[0].ID)
	}
}

func TestBrokerEpochMismatchResyncs(t *testing.T) {
	b := NewBroker()
	b.Publish(mkEvent(1))

	res := b.Subscribe("9999-0")
	defer b.Unsubscribe(res.Channel)
	if !res.NeedResync {
		t.Errorf("expected resync on epoch mismatch")
	}
}

func TestBrokerLiveDelivery(t *testing.T) {
	b := NewBroker()
	res := b.Subscribe("")
	defer b.Unsubscribe(res.Channel)
	b.Publish(mkEvent(42))
	select {
	case ev := <-res.Channel:
		if ev.ID == "" {
			t.Errorf("live event should have an ID")
		}
	case <-time.After(500 * time.Millisecond):
		t.Fatalf("timed out waiting for live event delivery")
	}
}

func TestBrokerExactlyOnceOverSubscribeBoundary(t *testing.T) {
	// Invariant: an event published while a subscriber is mid-subscribe
	// should be delivered exactly once — either via replay or via the
	// live channel. We approximate by publishing, subscribing with the
	// previous event ID, and checking that exactly one delivery happens.
	b := NewBroker()
	b.Publish(mkEvent(1)) // seq 0
	b.Publish(mkEvent(2)) // seq 1
	lastID := fmt.Sprintf("%d-0", b.Epoch())
	res := b.Subscribe(lastID)
	defer b.Unsubscribe(res.Channel)

	// Expect seq 1 in replay, nothing on the live channel yet.
	if len(res.ReplayEvents) != 1 {
		t.Fatalf("expected 1 replay event, got %d", len(res.ReplayEvents))
	}
	select {
	case <-res.Channel:
		t.Fatalf("unexpected live event without any publish")
	case <-time.After(50 * time.Millisecond):
	}

	// New publish should arrive live.
	b.Publish(mkEvent(3))
	select {
	case <-res.Channel:
	case <-time.After(500 * time.Millisecond):
		t.Fatalf("new publish not delivered live")
	}
}