package main

import (
	"sync"
)

type Fifo struct {
    slice []string
	mu sync.Mutex
	size int
}

func newfifo(size int) *Fifo {
    q := Fifo{}
    q.slice = make([]string, 0)
	q.size = size
    return &q
}
func (q *Fifo) Add(v string) int {
	q.mu.Lock()
	i := q.Contains(v)
	if i == -1 {
		if len(q.slice) >= q.size {
			q.DeleteFirst()
		}
		q.slice = append(q.slice, v)
	}
	q.mu.Unlock()
	return i
}

func (q *Fifo) Contains(v string) int {
	for i, val := range q.slice {
		if val == v {
			return i
		}
	}
	return -1
}

func (q *Fifo) DeleteFirst() string {
    a := q.slice[0]
    q.slice = q.slice[1:]
    return a
}