// duo.go: co-op mode. Each player runs the program on their own PC,
// reading their own Elden Ring; one acts as the "hub" (serves the overlay
// to OBS) and the rest connect to it over WebSocket, pushing their count.
//
// The connection is ALWAYS opened by the peer toward the hub, which is
// what's convenient with Tailscale: it's enough for the hub to have a
// stable IP on the tailnet.
package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"strings"
	"sync"
	"sync/atomic"
	"time"
)

// If a peer sends nothing for this long, we consider it disconnected.
// The peer pushes once a second, so this is generous.
const peerTimeout = 6 * time.Second

// How long we keep showing the co-op layout after the partner disappears.
// See coopMode() for why.
const coopGrace = 2 * time.Minute

// --------------------------- peer registry ---------------------------

type playerView struct {
	Name         string `json:"name"`
	Deaths       int64  `json:"deaths"`
	BossFight    bool   `json:"bossFight"`
	PlayerLoaded bool   `json:"playerLoaded"`
	Connected    bool   `json:"connected"`
	Self         bool   `json:"self"`
}

// peerEntry: WATCH OUT for identity. The name does NOT work as a key:
// from the moment we read it off the character, it changes whenever the
// player loads a different save, and indexing by name would spawn a new
// player on every character switch while leaving the old one stuck on
// screen. Identity is the id each instance sends (see clientID), stable
// across reconnects and restarts; the name is only something we display.
type peerEntry struct {
	key          string // how we index it: the id, or "name:x" for an old client
	name         string
	deaths       int64
	bossFight    bool
	playerLoaded bool
	lastSeen     time.Time
	everSeen     bool
	reserved     bool // slot reserved by config, not yet claimed
}

type peerRegistry struct {
	mu    sync.Mutex
	peers map[string]*peerEntry
	order []string // order of appearance, so the overlay doesn't reshuffle

	forced   bool      // the config named a partner: co-op from startup
	latched  bool      // we've already seen a partner this run
	lastCoop time.Time // last time someone was connected
}

func newPeerRegistry() *peerRegistry {
	return &peerRegistry{peers: map[string]*peerEntry{}}
}

// declare reserves a partner's slot before they connect and locks in
// co-op mode from startup. Optional: useful when you want the overlay at
// its final size from minute zero instead of resizing once the other
// player shows up.
func (r *peerRegistry) declare(name string) {
	if name == "" {
		return
	}
	r.mu.Lock()
	defer r.mu.Unlock()
	key := "reserved:" + name
	if _, ok := r.peers[key]; !ok {
		r.peers[key] = &peerEntry{key: key, name: name, reserved: true}
		r.order = append(r.order, key)
	}
	r.forced = true
}

// coopMode decides whether the overlay shows one column or two.
//
// It latches on when a partner shows up and does NOT let go at the first
// hiccup: if it fell back to solo mode every time the network dropped for
// a second, the overlay would redraw live mid-stream. It only returns to
// single-player once the other player has been gone for a good while,
// which is the signal for "went to sleep", not "wifi hiccuped".
func (r *peerRegistry) coopMode() bool {
	r.mu.Lock()
	defer r.mu.Unlock()
	if r.forced {
		return true
	}
	now := time.Now()
	for _, p := range r.peers {
		if p.everSeen && now.Sub(p.lastSeen) < peerTimeout {
			if !r.latched {
				r.latched = true
				log.Printf("a partner is connected: switching the overlay to co-op mode")
			}
			r.lastCoop = now
			return true
		}
	}
	if r.latched {
		if now.Sub(r.lastCoop) < coopGrace {
			return true
		}
		r.latched = false
		log.Printf("no partner has shown up in %v: going back to the single-player overlay", coopGrace)
	}
	return false
}

// keyFor: the id wins. If it came in empty (an old version on the other
// end), fall back to the name, which is how it used to work.
func keyFor(m peerMessage) string {
	if id := strings.TrimSpace(m.ID); id != "" {
		return "id:" + id
	}
	return "name:" + strings.ToLower(strings.TrimSpace(m.Name))
}

// rekey moves an entry to another key while keeping its place in the
// order, so the overlay doesn't reshuffle columns underneath it.
func (r *peerRegistry) rekey(p *peerEntry, newKey string) {
	delete(r.peers, p.key)
	for i, k := range r.order {
		if k == p.key {
			r.order[i] = newKey
			break
		}
	}
	p.key = newKey
	r.peers[newKey] = p
}

func (r *peerRegistry) update(m peerMessage) {
	r.mu.Lock()
	defer r.mu.Unlock()

	key := keyFor(m)
	p := r.peers[key]

	// No entry of its own: if there's a slot reserved by config still
	// unclaimed, the first one to arrive takes it. Reserving it by exact
	// name wouldn't work, since the name sent is the character's.
	if p == nil {
		for _, k := range r.order {
			if e := r.peers[k]; e.reserved && !e.everSeen {
				e.reserved = false
				r.rekey(e, key)
				p = e
				break
			}
		}
	}
	if p == nil {
		p = &peerEntry{key: key}
		r.peers[key] = p
		r.order = append(r.order, key)
	}

	if n := strings.TrimSpace(m.Name); n != "" && n != p.name {
		if p.name != "" && p.everSeen {
			log.Printf("%s switched characters: now %s", p.name, n)
		}
		p.name = n
	}
	p.deaths = m.Deaths
	p.bossFight = m.BossFight
	p.playerLoaded = m.PlayerLoaded
	p.lastSeen = time.Now()
	p.everSeen = true
}

func (r *peerRegistry) views() []playerView {
	r.mu.Lock()
	defer r.mu.Unlock()
	now := time.Now()
	out := make([]playerView, 0, len(r.order))
	for _, k := range r.order {
		p := r.peers[k]
		// Anyone who hasn't shown up in a long while leaves the overlay:
		// same threshold we use to fall back to single-player mode.
		if p.everSeen && now.Sub(p.lastSeen) > coopGrace {
			continue
		}
		out = append(out, playerView{
			Name:         p.name,
			Deaths:       p.deaths,
			BossFight:    p.bossFight,
			PlayerLoaded: p.playerLoaded,
			Connected:    p.everSeen && now.Sub(p.lastSeen) < peerTimeout,
			Self:         false,
		})
	}
	return out
}

// ------------------------- message between the two -------------------------

// authChallenge is sent by the hub as soon as the connection opens.
type authChallenge struct {
	Type  string `json:"type"` // "challenge"
	Nonce string `json:"nonce"`
}

// authReply is the peer's response: proves it knows the token without
// sending it. See auth.go.
type authReply struct {
	Type  string `json:"type"` // "auth"
	ID    string `json:"id"`
	Proof string `json:"proof"`
}

type peerMessage struct {
	// ID identifies the installation, not the character: it's what lets a
	// character switch avoid spawning a new player in the overlay.
	ID           string `json:"id,omitempty"`
	Type         string `json:"type,omitempty"` // "state"
	Name         string `json:"name"`
	Deaths       int64  `json:"deaths"`
	BossFight    bool   `json:"bossFight"`
	PlayerLoaded bool   `json:"playerLoaded"`
}

// ------------------------------- hub side -------------------------------

func (r *peerRegistry) wsHandler(token string) http.HandlerFunc {
	var active atomic.Int32

	return func(w http.ResponseWriter, req *http.Request) {
		if n := active.Add(1); n > maxPeerConns {
			active.Add(-1)
			log.Printf("rejecting connection from %s: already %d connections open", req.RemoteAddr, maxPeerConns)
			http.Error(w, "too many connections", http.StatusServiceUnavailable)
			return
		}
		defer active.Add(-1)

		c, err := wsUpgrade(w, req)
		if err != nil {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		}
		defer c.Close()

		remote := c.RemoteAddr()

		// --- authentication: random challenge, the token never travels ---
		nonce, err := randomHex(nonceBytes)
		if err != nil {
			log.Printf("couldn't generate the challenge for %s: %v", remote, err)
			return
		}
		ch, _ := json.Marshal(authChallenge{Type: "challenge", Nonce: nonce})
		if err := c.WriteText(ch); err != nil {
			return
		}

		c.SetReadDeadline(time.Now().Add(authTimeoutSeconds * time.Second))
		raw, err := c.ReadMessage()
		if err != nil {
			log.Printf("%s left without authenticating: %v", remote, err)
			return
		}
		var reply authReply
		if err := json.Unmarshal(raw, &reply); err != nil || reply.Type != "auth" {
			log.Printf("rejecting %s: didn't send a valid authentication response", remote)
			return
		}
		if !proofValid(token, nonce, reply.Proof) {
			log.Printf("rejecting %s: token doesn't match", remote)
			return
		}
		log.Printf("a partner authenticated from %s", remote)

		var who string
		for {
			c.SetReadDeadline(time.Now().Add(15 * time.Second))
			raw, err := c.ReadMessage()
			if err != nil {
				if who != "" {
					log.Printf("%s disconnected (%s): %v", who, remote, err)
				} else {
					log.Printf("%s disconnected: %v", remote, err)
				}
				return
			}
			var m peerMessage
			if err := json.Unmarshal(raw, &m); err != nil {
				log.Printf("unreadable message from %s: %v", remote, err)
				continue
			}
			// The authenticated connection's id wins: a message declaring
			// a different id doesn't turn it into another player.
			if reply.ID != "" {
				m.ID = reply.ID
			}
			if strings.TrimSpace(m.Name) == "" {
				m.Name = "Player 2"
			}
			if who == "" {
				who = m.Name
				log.Printf("%s joined the shared counter", who)
			}
			r.update(m)
		}
	}
}

// ------------------------------ peer side ------------------------------

// resolvePeerConn decides which hub address, token, and certificate
// fingerprint to use for the peer connection — see invite.go/pin.go.
//
// ok=false, err=nil means peer mode has nothing configured yet (no
// invite, no manual hub/token/fingerprint): that's not an error, it's
// today's "not set up" state, and the caller should keep running as a
// local-only overlay instead of trying to connect anywhere.
//
// A non-nil err means something WAS configured but is broken: a bad
// invite code, or only some of hub/token/fingerprint set by hand. This
// never falls back to an unpinned connection — an incomplete
// configuration is meant to fail loudly at startup, not connect insecurely.
func resolvePeerConn(cfg config) (hub, token, fingerprint string, ok bool, err error) {
	if inv := strings.TrimSpace(cfg.Invite); inv != "" {
		code, derr := decodeInvite(inv)
		if derr != nil {
			return "", "", "", false, fmt.Errorf("invalid invite code: %w", derr)
		}
		hub = code.Host + ":" + code.Port
		if h := strings.TrimSpace(cfg.Hub); h != "" {
			hub = h // manual override of just the host:port, e.g. a wrong auto-detected host
		}
		return hub, code.Token, code.Fingerprint, true, nil
	}

	h := strings.TrimSpace(cfg.Hub)
	t := strings.TrimSpace(cfg.Token)
	f := strings.TrimSpace(cfg.Fingerprint)
	switch {
	case h == "" && t == "" && f == "":
		return "", "", "", false, nil
	case h == "" || t == "" || f == "":
		return "", "", "", false, fmt.Errorf("'hub', 'token', and 'fingerprint' all need to be set together in config.toml (or use 'invite' instead)")
	}
	return h, t, f, true, nil
}

// peerLoop keeps the connection to the hub alive and pushes local state
// once a second. Retries forever: if the hub restarts mid-stream, it
// reconnects without any intervention.
//
// hub/token/fingerprint come from resolvePeerConn, already validated as
// complete by the caller — see main.go.
func peerLoop(cfg config, hub, token, fingerprint string) {
	id := clientID()
	log.Printf("my client id is %s (switching characters doesn't create a new player on the other end)", id)
	cfg.clientID = id
	cfg.Token = token

	tlsCfg, err := pinnedClientTLSConfig(fingerprint)
	if err != nil {
		log.Fatalf("invalid peer fingerprint: %v", err)
	}

	for {
		c, err := wsDialTLS(hub, "/ws", 8*time.Second, tlsCfg)
		if err != nil {
			log.Printf("couldn't connect to the hub %s (%v) - retrying in 5s", hub, err)
			time.Sleep(5 * time.Second)
			continue
		}
		if err := authenticate(c, cfg); err != nil {
			c.Close()
			log.Printf("the hub didn't accept me (%v) - retrying in 5s", err)
			time.Sleep(5 * time.Second)
			continue
		}
		log.Printf("connected and authenticated with the hub %s", hub)

		err = pushLoop(c, cfg)
		c.Close()
		log.Printf("connection to the hub dropped (%v) - retrying in 5s", err)
		time.Sleep(5 * time.Second)
	}
}

// authenticate answers the hub's challenge. The token itself isn't sent:
// an HMAC of the challenge, keyed by the token, is sent instead.
func authenticate(c *wsConn, cfg config) error {
	c.SetReadDeadline(time.Now().Add(authTimeoutSeconds * time.Second))
	raw, err := c.ReadMessage()
	if err != nil {
		return fmt.Errorf("the challenge never arrived: %w", err)
	}
	var ch authChallenge
	if err := json.Unmarshal(raw, &ch); err != nil || ch.Type != "challenge" || ch.Nonce == "" {
		return fmt.Errorf("couldn't make sense of the hub's challenge")
	}
	if strings.TrimSpace(cfg.Token) == "" {
		return fmt.Errorf("you're missing the token in config.toml: ask whoever runs the hub for it")
	}
	reply, _ := json.Marshal(authReply{
		Type:  "auth",
		ID:    cfg.clientID,
		Proof: proofFor(cfg.Token, ch.Nonce),
	})
	if err := c.WriteText(reply); err != nil {
		return err
	}
	c.SetReadDeadline(time.Time{})
	return nil
}

func pushLoop(c *wsConn, cfg config) error {
	// A background reader: we don't expect messages from the hub, but we
	// still need to answer its pings and notice if it hangs up.
	readErr := make(chan error, 1)
	go func() {
		for {
			if _, err := c.ReadMessage(); err != nil {
				readErr <- err
				return
			}
		}
	}()

	tick := time.NewTicker(1 * time.Second)
	defer tick.Stop()

	for {
		select {
		case err := <-readErr:
			return err
		case <-tick.C:
			snap := st.snapshot()
			msg := peerMessage{
				Type:         "state",
				ID:           cfg.clientID,
				Name:         displayName(cfg),
				Deaths:       snap.Total,
				BossFight:    snap.BossFight,
				PlayerLoaded: snap.PlayerLoaded,
			}
			b, err := json.Marshal(msg)
			if err != nil {
				return err
			}
			if err := c.WriteText(b); err != nil {
				return err
			}
		}
	}
}