package main

import (
	"time"
)

const (
	addAction    = 0
	removeAction = 1
)
type Update struct {
	Song *Song
	Action uint8
	Timestamp int64
	Next *Update
}
var headUpdates map[int]*Update
var tailUpdates map[int]*Update

func init() {
	headUpdates = make(map[int]*Update)
	tailUpdates = make(map[int]*Update)
}

func addUpdate(pid int, action uint8, song *Song) {
	update := new(Update)
	update.Song = song
	update.Action = action
	update.Timestamp = time.Nanoseconds()
	pup, ok := tailUpdates[pid]
	if ok {
		pup.Next = update
	} else {
		headUpdates[pid] = update
	}
	tailUpdates[pid] = update
}

func getUpdates(pid int, timestamp int64) *Update {
	pup, ok := headUpdates[pid]
	if !ok {
		return nil
	}
	for pup != nil {
		if pup.Timestamp > timestamp {
			return pup
		}
		pup = pup.Next
	}
	return nil
}