package ws

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

	"github.com/gorilla/websocket"

	"drmdecryption/apps/streamd/internal/db"
)

const (
	agentHeartbeatEvery = 20 * time.Second
	agentStaleAfter     = 45 * time.Second
	claimRenewTTL       = 90 * time.Second
	writeWait           = 10 * time.Second
	pongWait            = 60 * time.Second
)

var upgrader = websocket.Upgrader{
	CheckOrigin: func(r *http.Request) bool { return true },
}

// Hub tracks agent WebSocket sessions and UI listeners.
type Hub struct {
	Store *db.Store
	Token string
	Log   *log.Logger

	mu     sync.Mutex
	agents map[string]*agentConn // agent_id -> conn
	uis    map[*websocket.Conn]struct{}
}

type agentConn struct {
	conn     *websocket.Conn
	agentID  string
	lastSeen time.Time
	send     chan []byte
}

type inbound struct {
	Type    string `json:"type"`
	AgentID string `json:"agent_id,omitempty"`
}

type outbound struct {
	Type    string `json:"type"`
	AgentID string `json:"agent_id,omitempty"`
	OK      bool   `json:"ok,omitempty"`
	Error   string `json:"error,omitempty"`
	Agents  []any  `json:"agents,omitempty"`
	Message string `json:"message,omitempty"`
}

func NewHub(store *db.Store, token string, lg *log.Logger) *Hub {
	if lg == nil {
		lg = log.Default()
	}
	return &Hub{
		Store:  store,
		Token:  token,
		Log:    lg,
		agents: map[string]*agentConn{},
		uis:    map[*websocket.Conn]struct{}{},
	}
}

func (h *Hub) Mount(mux *http.ServeMux) {
	mux.HandleFunc("/ws/agent", h.handleAgent)
	mux.HandleFunc("/ws/ui", h.handleUI)
	mux.HandleFunc("/api/agents", h.handleAgentsAPI)
}

// RunExpireLoop periodically drops expired claims and dead agent sessions.
func (h *Hub) RunExpireLoop(stop <-chan struct{}) {
	t := time.NewTicker(10 * time.Second)
	defer t.Stop()
	for {
		select {
		case <-stop:
			return
		case <-t.C:
			h.tick()
		}
	}
}

func (h *Hub) tick() {
	n, err := h.Store.ExpireClaims()
	if err != nil {
		h.Log.Printf("ws: expire claims: %v", err)
	} else if n > 0 {
		h.Log.Printf("ws: expired %d stale claim(s)", n)
		h.broadcastUI(outbound{Type: "claims_changed", Message: "expired"})
	}

	now := time.Now().UTC()
	var stale []string
	h.mu.Lock()
	for id, a := range h.agents {
		if now.Sub(a.lastSeen) > agentStaleAfter {
			stale = append(stale, id)
		}
	}
	h.mu.Unlock()
	for _, id := range stale {
		h.Log.Printf("ws: agent %s heartbeat stale — releasing claims", id)
		h.dropAgent(id, true)
	}
}

func (h *Hub) authToken(r *http.Request) bool {
	if h.Token == "" {
		return true
	}
	tok := r.URL.Query().Get("token")
	if tok == "" {
		auth := r.Header.Get("Authorization")
		tok = strings.TrimPrefix(auth, "Bearer ")
	}
	if tok == "" {
		tok = r.Header.Get("X-Streamd-Token")
	}
	return tok == h.Token
}

func (h *Hub) handleAgentsAPI(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		http.Error(w, `{"error":"method not allowed"}`, http.StatusMethodNotAllowed)
		return
	}
	writeJSON(w, map[string]any{"agents": h.snapshotAgents()})
}

func (h *Hub) handleUI(w http.ResponseWriter, r *http.Request) {
	conn, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		return
	}
	h.mu.Lock()
	h.uis[conn] = struct{}{}
	h.mu.Unlock()
	defer func() {
		h.mu.Lock()
		delete(h.uis, conn)
		h.mu.Unlock()
		_ = conn.Close()
	}()

	_ = conn.SetReadDeadline(time.Now().Add(pongWait))
	conn.SetPongHandler(func(string) error {
		_ = conn.SetReadDeadline(time.Now().Add(pongWait))
		return nil
	})
	// Push initial agent list.
	h.sendJSON(conn, outbound{Type: "agents", Agents: h.snapshotAgents()})
	for {
		if _, _, err := conn.ReadMessage(); err != nil {
			return
		}
	}
}

func (h *Hub) handleAgent(w http.ResponseWriter, r *http.Request) {
	if !h.authToken(r) {
		http.Error(w, `{"error":"unauthorized"}`, http.StatusUnauthorized)
		return
	}
	agentID := strings.TrimSpace(r.URL.Query().Get("agent_id"))
	if agentID == "" {
		http.Error(w, `{"error":"agent_id required"}`, http.StatusBadRequest)
		return
	}
	conn, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		return
	}
	ac := &agentConn{
		conn:     conn,
		agentID:  agentID,
		lastSeen: time.Now().UTC(),
		send:     make(chan []byte, 8),
	}
	h.mu.Lock()
	if old, ok := h.agents[agentID]; ok {
		close(old.send)
		_ = old.conn.Close()
	}
	h.agents[agentID] = ac
	h.mu.Unlock()
	h.Log.Printf("ws: agent connected id=%s", agentID)
	h.broadcastUI(outbound{Type: "agent_online", AgentID: agentID, Agents: h.snapshotAgents()})

	go h.agentWriter(ac)

	defer h.dropAgent(agentID, true)

	_ = conn.SetReadDeadline(time.Now().Add(pongWait))
	conn.SetPongHandler(func(string) error {
		_ = conn.SetReadDeadline(time.Now().Add(pongWait))
		return nil
	})

	// Greeting + first renew.
	h.renew(agentID)
	h.queue(ac, outbound{Type: "hello", AgentID: agentID, OK: true})

	for {
		_, data, err := conn.ReadMessage()
		if err != nil {
			return
		}
		_ = conn.SetReadDeadline(time.Now().Add(pongWait))
		var msg inbound
		if err := json.Unmarshal(data, &msg); err != nil {
			continue
		}
		switch strings.ToLower(msg.Type) {
		case "heartbeat", "ping", "hello":
			h.mu.Lock()
			if cur, ok := h.agents[agentID]; ok {
				cur.lastSeen = time.Now().UTC()
			}
			h.mu.Unlock()
			n, err := h.renew(agentID)
			if err != nil {
				h.queue(ac, outbound{Type: "heartbeat_ack", OK: false, Error: err.Error()})
				continue
			}
			h.queue(ac, outbound{Type: "heartbeat_ack", OK: true, Message: "renewed", AgentID: agentID})
			if n > 0 {
				h.broadcastUI(outbound{Type: "claims_changed", AgentID: agentID, Message: "renewed"})
			}
		case "release_all":
			_, _ = h.Store.ReleaseAgentClaims(agentID)
			h.broadcastUI(outbound{Type: "claims_changed", AgentID: agentID, Message: "released"})
			h.queue(ac, outbound{Type: "release_ack", OK: true})
		}
	}
}

func (h *Hub) renew(agentID string) (int64, error) {
	return h.Store.RenewAgentClaims(agentID, claimRenewTTL)
}

func (h *Hub) dropAgent(agentID string, releaseClaims bool) {
	h.mu.Lock()
	ac, ok := h.agents[agentID]
	if ok {
		delete(h.agents, agentID)
	}
	h.mu.Unlock()
	if !ok {
		return
	}
	close(ac.send)
	_ = ac.conn.Close()
	if releaseClaims {
		n, err := h.Store.ReleaseAgentClaims(agentID)
		if err != nil {
			h.Log.Printf("ws: release claims for %s: %v", agentID, err)
		} else if n > 0 {
			h.Log.Printf("ws: released %d claim(s) for disconnected agent %s", n, agentID)
		}
	}
	h.Log.Printf("ws: agent disconnected id=%s", agentID)
	h.broadcastUI(outbound{Type: "agent_offline", AgentID: agentID, Agents: h.snapshotAgents()})
}

func (h *Hub) agentWriter(ac *agentConn) {
	ticker := time.NewTicker(agentHeartbeatEvery)
	defer ticker.Stop()
	for {
		select {
		case msg, ok := <-ac.send:
			if !ok {
				return
			}
			_ = ac.conn.SetWriteDeadline(time.Now().Add(writeWait))
			if err := ac.conn.WriteMessage(websocket.TextMessage, msg); err != nil {
				return
			}
		case <-ticker.C:
			_ = ac.conn.SetWriteDeadline(time.Now().Add(writeWait))
			if err := ac.conn.WriteControl(websocket.PingMessage, []byte("ping"), time.Now().Add(writeWait)); err != nil {
				return
			}
		}
	}
}

func (h *Hub) queue(ac *agentConn, msg outbound) {
	b, err := json.Marshal(msg)
	if err != nil {
		return
	}
	select {
	case ac.send <- b:
	default:
	}
}

func (h *Hub) sendJSON(conn *websocket.Conn, msg outbound) {
	b, _ := json.Marshal(msg)
	_ = conn.SetWriteDeadline(time.Now().Add(writeWait))
	_ = conn.WriteMessage(websocket.TextMessage, b)
}

func (h *Hub) broadcastUI(msg outbound) {
	b, err := json.Marshal(msg)
	if err != nil {
		return
	}
	h.mu.Lock()
	defer h.mu.Unlock()
	for conn := range h.uis {
		_ = conn.SetWriteDeadline(time.Now().Add(writeWait))
		if err := conn.WriteMessage(websocket.TextMessage, b); err != nil {
			_ = conn.Close()
			delete(h.uis, conn)
		}
	}
}

func (h *Hub) snapshotAgents() []any {
	h.mu.Lock()
	defer h.mu.Unlock()
	out := make([]any, 0, len(h.agents))
	now := time.Now().UTC()
	for id, a := range h.agents {
		out = append(out, map[string]any{
			"agent_id":    id,
			"last_seen_s": now.Sub(a.lastSeen).Seconds(),
			"connected":   true,
		})
	}
	return out
}

func writeJSON(w http.ResponseWriter, v any) {
	w.Header().Set("Content-Type", "application/json")
	enc := json.NewEncoder(w)
	enc.SetIndent("", "  ")
	_ = enc.Encode(v)
}