// Package api provides the HTTP API server for agents_and_robots.
// It exposes REST endpoints for agent management and SSE streams for
// real-time status and log updates.
//
// Auth: every endpoint (except /health) requires:
//
//	Authorization: Bearer <AGENTS_API_KEY>
//
// with crypto/subtle constant-time comparison.
package api

import (
	"context"
	"crypto/subtle"
	"encoding/json"
	"log/slog"
	"net"
	"net/http"
	"strconv"
	"time"

	"github.com/enmanuel/agents/shell/process"
)

// Server is the HTTP API server.
type Server struct {
	mgr    *process.Manager
	apiKey string
	port   int
	logger *slog.Logger
	bus    *Bus
}

// New creates a new Server. apiKey is compared with subtle.ConstantTimeCompare.
// If apiKey is empty the server refuses to start.
func New(mgr *process.Manager, apiKey string, port int, logger *slog.Logger) *Server {
	if logger == nil {
		logger = slog.Default()
	}
	return &Server{
		mgr:    mgr,
		apiKey: apiKey,
		port:   port,
		logger: logger.With("component", "api"),
		bus:    NewBus(),
	}
}

// Run starts the HTTP server and blocks until ctx is done.
// It also starts the status-diff poller that feeds /sse/status.
func (s *Server) Run(ctx context.Context) error {
	mux := http.NewServeMux()

	// Public endpoints
	mux.HandleFunc("GET /health", s.handleHealth)

	// Auth-gated REST endpoints
	mux.Handle("GET /agents", s.auth(http.HandlerFunc(s.handleListAgents)))
	mux.Handle("GET /agents/{id}", s.auth(http.HandlerFunc(s.handleGetAgent)))
	mux.Handle("POST /agents/{id}/start", s.auth(http.HandlerFunc(s.handleStartAgent)))
	mux.Handle("POST /agents/{id}/stop", s.auth(http.HandlerFunc(s.handleStopAgent)))
	mux.Handle("POST /agents/{id}/restart", s.auth(http.HandlerFunc(s.handleRestartAgent)))
	mux.Handle("GET /agents/{id}/logs", s.auth(http.HandlerFunc(s.handleAgentLogs)))

	// SSE endpoints
	mux.Handle("GET /sse/status", s.auth(http.HandlerFunc(s.handleSSEStatus)))
	mux.Handle("GET /sse/agents/{id}/logs", s.auth(http.HandlerFunc(s.handleSSEAgentLogs)))

	addr := ":" + strconv.Itoa(s.port)
	ln, err := net.Listen("tcp", addr)
	if err != nil {
		return err
	}

	srv := &http.Server{
		Handler:     s.logMiddleware(mux),
		ReadTimeout: 10 * time.Second,
	}

	s.logger.Info("api server listening", "addr", addr)

	// Start the status poller
	go s.pollStatus(ctx)

	errCh := make(chan error, 1)
	go func() { errCh <- srv.Serve(ln) }()

	select {
	case <-ctx.Done():
		shutCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()
		return srv.Shutdown(shutCtx)
	case err := <-errCh:
		return err
	}
}

// --- Auth middleware ---

func (s *Server) auth(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		key := extractBearerToken(r)
		expected := []byte(s.apiKey)
		got := []byte(key)

		// Ensure equal-length comparison to avoid timing side-channel.
		// subtle.ConstantTimeCompare returns 0 if lengths differ too.
		if subtle.ConstantTimeCompare(got, expected) != 1 {
			writeJSON(w, http.StatusUnauthorized, map[string]string{"error": "unauthorized"})
			return
		}
		next.ServeHTTP(w, r)
	})
}

func extractBearerToken(r *http.Request) string {
	h := r.Header.Get("Authorization")
	if len(h) > 7 && h[:7] == "Bearer " {
		return h[7:]
	}
	return ""
}

// --- Log middleware ---

func (s *Server) logMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		rw := &statusWriter{ResponseWriter: w, code: http.StatusOK}
		next.ServeHTTP(rw, r)
		s.logger.Info("http",
			"method", r.Method,
			"path", r.URL.Path,
			"status", rw.code,
			"duration_ms", time.Since(start).Milliseconds(),
		)
	})
}

type statusWriter struct {
	http.ResponseWriter
	code int
}

func (sw *statusWriter) WriteHeader(code int) {
	sw.code = code
	sw.ResponseWriter.WriteHeader(code)
}

// --- Helpers ---

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

func writeError(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, map[string]string{"error": msg})
}