package main

import (
	"fmt"
	"log"
	"net"
	"sync"
	"time"
)

type DiscardedHost struct {
	Host  string
	Tries int
}

type DiscardedHostHandler struct {
	mu           sync.RWMutex
	port         int
	hosts        []*DiscardedHost
	onConnection *func(string)
}

func (d *DiscardedHostHandler) run() {
	for range time.Tick(time.Second) {
		d.mu.RLock()
		lst := make([]*DiscardedHost, 0, len(d.hosts))
		for _, host := range d.hosts {
			if host.Tries >= 0 && host.Tries < 5 {
				go d.testConnection(host)
				lst = append(lst, host)
			} else {
				if host.Tries > 0 {
					log.Printf("Host %s discarded after %d tries", host.Host, host.Tries)
				}
			}
		}
		d.mu.RUnlock()
		d.mu.Lock()
		d.hosts = lst
		d.mu.Unlock()
	}

}

func (d *DiscardedHostHandler) testConnection(host *DiscardedHost) {
	addr := fmt.Sprintf("%s:%d", host.Host, d.port)
	conn, err := net.Dial("tcp", addr)

	if err != nil {
		host.Tries++
		if host.Tries >= 5 {
			// Exceeded retry threshold; will be dropped by run loop.
		}
	} else {
		conn.Close()
		if d.onConnection != nil {
			fn := *d.onConnection
			fn(host.Host)
		}
	}
}

func NewDiscardedHostHandler(port int) *DiscardedHostHandler {
	ret := &DiscardedHostHandler{
		hosts: make([]*DiscardedHost, 0),
		port:  port,
	}
	go ret.run()
	return ret
}

func (d *DiscardedHostHandler) SetReconnectHandler(fn func(string)) {
	d.onConnection = &fn
}

func (d *DiscardedHostHandler) AppendHost(host string) {
	d.mu.Lock()
	defer d.mu.Unlock()
	log.Printf("Adding host %s to retry list", host)
	d.hosts = append(d.hosts, &DiscardedHost{
		Host:  host,
		Tries: 0,
	})
}