// Package api is the HTTP/WebSocket surface: auth, terminal CRUD, attach, static UI.
package api

import (
	"context"
	"encoding/json"
	"errors"
	"io"
	"io/fs"
	"log"
	"net/http"
	"os"
	"os/user"
	"strings"
	"time"

	"github.com/coder/websocket"

	"hamlab/internal/auth"
	"hamlab/internal/config"
	"hamlab/internal/metrics"
	"hamlab/internal/store"
	"hamlab/internal/term"
)

const cookieName = "hamlab_session"

type Server struct {
	cfg      *config.Config
	sessions *auth.Sessions
	limiter  auth.Limiter
	mgr      *term.Manager
	metrics  *metrics.Collector
	store    *store.Store
	version  string
	started  time.Time
	user     string
	host     string
	ui       fs.FS
	mux      *http.ServeMux
}

func New(cfg *config.Config, sessions *auth.Sessions, mgr *term.Manager, col *metrics.Collector, st *store.Store, ui fs.FS, version string) *Server {
	host, _ := os.Hostname()
	s := &Server{cfg: cfg, sessions: sessions, mgr: mgr, metrics: col, store: st, ui: ui, version: version,
		started: time.Now(), host: host, user: os.Getenv("USER")}
	if u, err := user.Current(); err == nil && u.Username != "" {
		s.user = u.Username
	}
	if s.user == "" {
		s.user = "?"
	}
	// The saved dashboard layout carries the sampling interval; apply it on boot.
	var raw json.RawMessage
	st.View(func(x *store.State) { raw = x.Dashboard })
	s.applyPrefs(raw)

	m := http.NewServeMux()
	m.HandleFunc("GET /healthz", func(w http.ResponseWriter, _ *http.Request) { w.WriteHeader(204) })
	m.HandleFunc("POST /api/login", s.login)
	m.HandleFunc("POST /api/logout", s.auth(s.logout))
	m.HandleFunc("GET /api/me", s.auth(s.me))
	m.HandleFunc("GET /api/terminals", s.auth(s.listTerminals))
	m.HandleFunc("POST /api/terminals", s.auth(s.createTerminal))
	m.HandleFunc("PATCH /api/terminals/{id}", s.auth(s.renameTerminal))
	m.HandleFunc("DELETE /api/terminals/{id}", s.auth(s.deleteTerminal))
	m.HandleFunc("GET /api/terminals/{id}/attach", s.auth(s.attach))
	m.HandleFunc("GET /api/metrics", s.auth(s.metricsLatest))
	m.HandleFunc("GET /api/metrics/history", s.auth(s.metricsHistory))
	m.HandleFunc("GET /api/prefs/dashboard", s.auth(s.getDashPrefs))
	m.HandleFunc("PUT /api/prefs/dashboard", s.auth(s.putDashPrefs))
	m.HandleFunc("/api/", func(w http.ResponseWriter, _ *http.Request) { jsonErr(w, 404, "not found") })
	m.HandleFunc("/", s.static)
	s.mux = m
	return s
}

func (s *Server) Handler() http.Handler { return s.mux }

// ---- helpers ----

func jsonOK(w http.ResponseWriter, code int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(code)
	_ = json.NewEncoder(w).Encode(v)
}

func jsonErr(w http.ResponseWriter, code int, msg string) {
	jsonOK(w, code, map[string]string{"error": msg})
}

func secure(r *http.Request) bool {
	return r.TLS != nil || strings.EqualFold(r.Header.Get("X-Forwarded-Proto"), "https")
}

func (s *Server) setCookie(w http.ResponseWriter, r *http.Request, tok string, maxAge int) {
	http.SetCookie(w, &http.Cookie{
		Name: cookieName, Value: tok, Path: "/", MaxAge: maxAge,
		HttpOnly: true, Secure: secure(r), SameSite: http.SameSiteStrictMode,
	})
}

func (s *Server) auth(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		c, err := r.Cookie(cookieName)
		if err != nil || !s.sessions.Valid(c.Value) {
			jsonErr(w, 401, "unauthenticated")
			return
		}
		next(w, r)
	}
}

// ---- auth ----

func (s *Server) login(w http.ResponseWriter, r *http.Request) {
	if err := s.limiter.Allow(); err != nil {
		jsonErr(w, 429, "too many attempts, try again later")
		return
	}
	var body struct {
		Password string `json:"password"`
	}
	if err := json.NewDecoder(io.LimitReader(r.Body, 4096)).Decode(&body); err != nil {
		jsonErr(w, 400, "bad request")
		return
	}
	if !auth.VerifyPassword(s.cfg.PasswordHash, body.Password) {
		s.limiter.Fail()
		log.Printf("login failed from %s", clientIP(r))
		jsonErr(w, 401, "wrong password")
		return
	}
	s.limiter.Reset()
	tok, err := s.sessions.Create()
	if err != nil {
		jsonErr(w, 500, "session error")
		return
	}
	s.setCookie(w, r, tok, int(auth.SessionTTL.Seconds()))
	log.Printf("login ok from %s", clientIP(r))
	w.WriteHeader(204)
}

func (s *Server) logout(w http.ResponseWriter, r *http.Request) {
	if c, err := r.Cookie(cookieName); err == nil {
		s.sessions.Delete(c.Value)
	}
	s.setCookie(w, r, "", -1)
	w.WriteHeader(204)
}

func clientIP(r *http.Request) string {
	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
		return strings.TrimSpace(strings.Split(xff, ",")[0]) + " via " + r.RemoteAddr
	}
	return r.RemoteAddr
}

// ---- me ----

func (s *Server) me(w http.ResponseWriter, _ *http.Request) {
	load := ""
	if b, err := os.ReadFile("/proc/loadavg"); err == nil {
		f := strings.Fields(string(b))
		if len(f) >= 3 {
			load = strings.Join(f[:3], " ")
		}
	}
	uptime := 0.0
	if b, err := os.ReadFile("/proc/uptime"); err == nil {
		if f := strings.Fields(string(b)); len(f) > 0 {
			uptime, _ = json.Number(f[0]).Float64()
		}
	}
	jsonOK(w, 200, map[string]any{
		"host": s.host, "user": s.user, "version": s.version,
		"load": load, "uptime": uptime, "service_started": s.started,
	})
}

// ---- metrics (Dashboard) ----

func (s *Server) metricsLatest(w http.ResponseWriter, _ *http.Request) {
	smp, ok := s.metrics.Latest()
	if !ok {
		jsonErr(w, 503, "no sample yet")
		return
	}
	jsonOK(w, 200, smp)
}

func (s *Server) metricsHistory(w http.ResponseWriter, _ *http.Request) {
	jsonOK(w, 200, s.metrics.History())
}

// ---- dashboard layout prefs (opaque JSON object, owned by the UI) ----

func (s *Server) getDashPrefs(w http.ResponseWriter, _ *http.Request) {
	var raw json.RawMessage
	s.store.View(func(st *store.State) { raw = st.Dashboard })
	if len(raw) == 0 {
		raw = json.RawMessage("{}")
	}
	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("Cache-Control", "no-store")
	_, _ = w.Write(raw)
}

func (s *Server) putDashPrefs(w http.ResponseWriter, r *http.Request) {
	b, err := io.ReadAll(io.LimitReader(r.Body, 64<<10))
	if err != nil || !json.Valid(b) || len(b) == 0 || b[0] != '{' {
		jsonErr(w, 400, "expected a JSON object")
		return
	}
	if err := s.store.Update(func(st *store.State) { st.Dashboard = json.RawMessage(b) }); err != nil {
		jsonErr(w, 500, err.Error())
		return
	}
	s.applyPrefs(b)
	w.WriteHeader(204)
}

// applyPrefs picks the few layout fields the server acts on (just the interval).
func (s *Server) applyPrefs(raw []byte) {
	var p struct {
		IntervalMs int `json:"intervalMs"`
	}
	if len(raw) == 0 || json.Unmarshal(raw, &p) != nil {
		return
	}
	if p.IntervalMs > 0 {
		s.metrics.SetInterval(time.Duration(p.IntervalMs) * time.Millisecond)
	} else {
		s.metrics.SetInterval(metrics.DefaultInterval)
	}
}

// ---- terminals ----

func (s *Server) listTerminals(w http.ResponseWriter, _ *http.Request) {
	jsonOK(w, 200, s.mgr.List())
}

func (s *Server) createTerminal(w http.ResponseWriter, r *http.Request) {
	var body struct {
		Name string `json:"name"`
	}
	_ = json.NewDecoder(io.LimitReader(r.Body, 4096)).Decode(&body)
	name := strings.TrimSpace(body.Name)
	if name == "" {
		name = "shell " + time.Now().Format("15:04")
	}
	sess, err := s.mgr.Create("", name)
	if err != nil {
		log.Printf("create terminal: %v", err)
		jsonErr(w, 500, err.Error())
		return
	}
	jsonOK(w, 201, map[string]string{"id": sess.ID, "name": sess.Name})
}

func (s *Server) renameTerminal(w http.ResponseWriter, r *http.Request) {
	var body struct {
		Name string `json:"name"`
	}
	if err := json.NewDecoder(io.LimitReader(r.Body, 4096)).Decode(&body); err != nil || strings.TrimSpace(body.Name) == "" {
		jsonErr(w, 400, "name required")
		return
	}
	if err := s.mgr.Rename(r.PathValue("id"), strings.TrimSpace(body.Name)); err != nil {
		jsonErr(w, 404, err.Error())
		return
	}
	w.WriteHeader(204)
}

func (s *Server) deleteTerminal(w http.ResponseWriter, r *http.Request) {
	if err := s.mgr.Close(r.PathValue("id")); err != nil {
		jsonErr(w, 404, err.Error())
		return
	}
	w.WriteHeader(204)
}

type resizeMsg struct {
	Type string `json:"type"`
	Cols uint16 `json:"cols"`
	Rows uint16 `json:"rows"`
}

func (s *Server) attach(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	client, snapshot, running, err := s.mgr.Attach(id)
	if err != nil {
		jsonErr(w, 404, err.Error())
		return
	}
	// Origin must match Host (coder/websocket default) — blocks cross-site attaches.
	conn, err := websocket.Accept(w, r, &websocket.AcceptOptions{CompressionMode: websocket.CompressionDisabled})
	if err != nil {
		s.mgr.Detach(client)
		return
	}
	defer s.mgr.Detach(client)
	defer conn.Close(websocket.StatusNormalClosure, "")
	conn.SetReadLimit(1 << 20)

	ctx, cancel := context.WithCancel(r.Context())
	defer cancel()

	if len(snapshot) > 0 {
		if err := conn.Write(ctx, websocket.MessageBinary, snapshot); err != nil {
			return
		}
	}
	if !running {
		_ = conn.Write(ctx, websocket.MessageText, []byte(`{"type":"exit"}`))
	}

	// writer: PTY → socket, plus keepalive pings so idle proxies don't cut us.
	go func() {
		defer cancel()
		ping := time.NewTicker(25 * time.Second)
		defer ping.Stop()
		for {
			select {
			case <-ctx.Done():
				return
			case <-ping.C:
				pctx, pc := context.WithTimeout(ctx, 10*time.Second)
				err := conn.Ping(pctx)
				pc()
				if err != nil {
					return
				}
			case msg, ok := <-client.Ch:
				if !ok {
					_ = conn.Write(ctx, websocket.MessageText, []byte(`{"type":"closed"}`))
					return
				}
				if msg.Data != nil {
					if err := conn.Write(ctx, websocket.MessageBinary, msg.Data); err != nil {
						return
					}
					continue
				}
				if msg.Event == "exit" {
					b, _ := json.Marshal(map[string]any{"type": "exit", "code": msg.Code})
					_ = conn.Write(ctx, websocket.MessageText, b)
				}
			}
		}
	}()

	// reader: socket → PTY (binary) or control (text JSON).
	for {
		typ, data, err := conn.Read(ctx)
		if err != nil {
			return
		}
		switch typ {
		case websocket.MessageBinary:
			if err := s.mgr.Write(id, data); err != nil && !errors.Is(err, term.ErrNotFound) {
				log.Printf("pty write %s: %v", id, err)
			}
		case websocket.MessageText:
			var m resizeMsg
			if json.Unmarshal(data, &m) == nil && m.Type == "resize" {
				_ = s.mgr.Resize(id, m.Cols, m.Rows)
			}
		}
	}
}

// ---- static UI with SPA fallback ----

func (s *Server) static(w http.ResponseWriter, r *http.Request) {
	p := strings.TrimPrefix(r.URL.Path, "/")
	if p == "" {
		p = "index.html"
	}
	f, err := s.ui.Open(p)
	if err == nil {
		st, _ := f.Stat()
		f.Close()
		if st != nil && !st.IsDir() {
			if strings.HasPrefix(p, "assets/") {
				w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
			} else {
				w.Header().Set("Cache-Control", "no-cache")
			}
			http.ServeFileFS(w, r, s.ui, p)
			return
		}
	}
	// SPA fallback
	w.Header().Set("Cache-Control", "no-cache")
	http.ServeFileFS(w, r, s.ui, "index.html")
}