package pipeline

import (
	mathrand "math/rand/v2"
	"sync"
)

// stringSample is a memory-bounded queue that keeps a random sample of recent
// hostnames instead of a FIFO. A FIFO fills with the first N hostnames seen at
// startup and drops everything after, so DNS enrichment only ever sees stale
// hostnames and CNAME discovery stalls. Random replacement makes coverage
// representative at bounded memory. Not on the certificate hot path.
type stringSample struct {
	mu     sync.Mutex
	items  []string
	cap    int
	notify chan struct{}
	stop   chan struct{}
	once   sync.Once
}

func newStringSample(capacity int) *stringSample {
	return &stringSample{
		cap:    capacity,
		notify: make(chan struct{}, 1),
		stop:   make(chan struct{}),
	}
}

func (q *stringSample) push(s string) {
	q.mu.Lock()
	if len(q.items) < q.cap {
		q.items = append(q.items, s)
	} else {
		q.items[mathrand.IntN(len(q.items))] = s
	}
	q.mu.Unlock()
	select {
	case q.notify <- struct{}{}:
	default:
	}
}

func (q *stringSample) pop() (string, bool) {
	q.mu.Lock()
	n := len(q.items)
	if n == 0 {
		q.mu.Unlock()
		return "", false
	}
	i := mathrand.IntN(n)
	s := q.items[i]
	q.items[i] = q.items[n-1]
	q.items = q.items[:n-1]
	q.mu.Unlock()
	return s, true
}

func (q *stringSample) len() int {
	q.mu.Lock()
	defer q.mu.Unlock()
	return len(q.items)
}

func (q *stringSample) close() {
	q.once.Do(func() { close(q.stop) })
	select {
	case q.notify <- struct{}{}:
	default:
	}
}