package eventsbus

import (
	"sync"
	"time"
)

type Event struct {
	ID   int64
	Kind string
	Ts   string
	Data any
}

type Bus struct {
	mu   sync.Mutex
	cond *sync.Cond
	buf  []Event
	cap  int
	next int64
}

func New(capacity int) *Bus {
	if capacity < 16 {
		capacity = 16
	}
	b := &Bus{
		cap: capacity,
		buf: make([]Event, 0, capacity),
	}
	b.cond = sync.NewCond(&b.mu)
	return b
}

func (b *Bus) Push(kind string, data any) Event {
	b.mu.Lock()
	defer b.mu.Unlock()

	b.next++
	evt := Event{
		ID:   b.next,
		Kind: kind,
		Ts:   time.Now().UTC().Format(time.RFC3339Nano),
		Data: data,
	}

	if len(b.buf) >= b.cap {
		b.buf = b.buf[1:]
	}
	b.buf = append(b.buf, evt)
	b.cond.Broadcast()
	return evt
}

func (b *Bus) Since(id int64) []Event {
	b.mu.Lock()
	defer b.mu.Unlock()
	if len(b.buf) == 0 {
		return nil
	}
	out := make([]Event, 0, len(b.buf))
	for _, ev := range b.buf {
		if ev.ID > id {
			out = append(out, ev)
		}
	}
	return out
}