package relay

// Pool manages connections to multiple relays.
type Pool struct {
	conns map[string]*Conn
}

// NewPool creates a relay pool.
func NewPool() (p *Pool) {
	return &Pool{
		conns: map[string]*Conn{},
	}
}

// Connect gets or creates a connection to a relay.
//
// An existing Conn is reused even when it is currently closed: Conn.maybeReconnect
// redials the SAME object, and its flushSubs re-establishes every subscription
// held in c.subs. Replacing it instead orphaned those subscriptions - the new
// Conn started with an empty registry, nothing re-subscribed the entries the
// consumer still had registered, and that relay went silently dead for them.
func (p *Pool) Connect(url string) (c *Conn) {
	if existing, ok := p.conns[url]; ok {
		return existing
	}
	c = Dial(url)
	p.conns[url] = c
	return c
}

// Get returns an existing connection, or nil.
func (p *Pool) Get(url string) (c *Conn) {
	got, ok := p.conns[url]
	if !ok || !got.IsOpen() {
		return nil
	}
	return got
}

// Disconnect closes and removes a connection.
func (p *Pool) Disconnect(url string) {
	if c, ok2 := p.conns[url]; ok2 {
		c.Close()
		delete(p.conns, url)
	}
}

// CloseAll closes all connections.
func (p *Pool) CloseAll() {
	for url, c := range p.conns {
		c.Close()
		delete(p.conns, url)
	}
}

// URLs returns all connected relay URLs.
func (p *Pool) URLs() (ss []string) {
	var out []string
	for url, c := range p.conns {
		if c.IsOpen() {
			out = push(out, url)
		}
	}
	return out
}

// AllConns returns all connections regardless of state.
func (p *Pool) AllConns() (cs []*Conn) {
	p.evictClosed()
	var out []*Conn
	for _, c := range p.conns {
		out = push(out, c)
	}
	return out
}

// evictClosed removes closed connections that hold no subscriptions. A closed
// Conn that still holds them is mid-reconnect: it redials itself and flushes
// them again, so dropping it here would lose them for good.
func (p *Pool) evictClosed() {
	for url, c := range p.conns {
		if c.state == StateClosed && len(c.subs) == 0 {
			delete(p.conns, url)
		}
	}
}