// Package server exposes bootapi over HTTP: iPXE boot scripts and rendered
// kickstarts for PXE-booting hosts, plus health and metrics endpoints.
package server

import (
	"context"
	"errors"
	"log/slog"
	"net/http"
	"strings"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
	"github.com/prometheus/client_golang/prometheus/promhttp"

	"git.unkin.net/unkin/bootapi/internal/model"
	"git.unkin.net/unkin/bootapi/internal/netbox"
	"git.unkin.net/unkin/bootapi/internal/render"
)

// Server wires the NetBox resolver and template engine into HTTP handlers.
type Server struct {
	resolver netbox.Resolver
	engine   *render.Engine
	metrics  *metrics
	// fallback is the unknown-MAC iPXE behavior: "local" (safe default) or
	// "shell" (debug).
	fallback string
}

// Options configures a Server.
type Options struct {
	Resolver netbox.Resolver
	Engine   *render.Engine
	// Cache, when non-nil, has its hit/miss counters published as metrics.
	Cache              cacheStats
	UnknownMACFallback string
}

// New builds a Server.
func New(o Options) *Server {
	fb := o.UnknownMACFallback
	if fb == "" {
		fb = "local"
	}
	return &Server{
		resolver: o.Resolver,
		engine:   o.Engine,
		metrics:  newMetrics(o.Cache),
		fallback: fb,
	}
}

// Router returns the fully-wired HTTP handler.
func (s *Server) Router() http.Handler {
	r := chi.NewRouter()
	r.Use(middleware.RequestID)
	r.Use(middleware.Recoverer)
	r.Use(s.logRequests)

	r.Get("/healthz", s.handleHealthz)
	r.Get("/readyz", s.handleReadyz)
	r.Handle("/metrics", promhttp.HandlerFor(s.metrics.reg, promhttp.HandlerOpts{}))

	// iPXE boot script: primary path-style, plus a query-style alias.
	r.Get("/ipxe/{mac}", s.handleIPXE)
	r.Get("/boot/ipxe", s.handleIPXEQuery)

	// Rendered kickstart, keyed by MAC or hostname.
	r.Get("/ks/{ident}", s.handleKickstart)

	return r
}

func (s *Server) handleHealthz(w http.ResponseWriter, _ *http.Request) {
	s.ok(w, http.StatusOK, "text/plain", []byte("ok\n"), "healthz")
}

// handleReadyz is ready once templates parsed (engine present). NetBox is a
// soft dependency — the iPXE fallback works without it — so readiness does not
// probe NetBox.
func (s *Server) handleReadyz(w http.ResponseWriter, _ *http.Request) {
	if s.engine == nil {
		s.ok(w, http.StatusServiceUnavailable, "text/plain", []byte("no template engine\n"), "readyz")
		return
	}
	s.ok(w, http.StatusOK, "text/plain", []byte("ready\n"), "readyz")
}

// handleIPXE serves the per-MAC iPXE script. An unknown MAC (or a NetBox error)
// yields a SAFE fallback script with HTTP 200 — never a 404 — so the booting
// firmware always receives a valid iPXE script instead of failing the chain.
func (s *Server) handleIPXE(w http.ResponseWriter, r *http.Request) {
	s.serveIPXE(w, r, chi.URLParam(r, "mac"))
}

func (s *Server) handleIPXEQuery(w http.ResponseWriter, r *http.Request) {
	s.serveIPXE(w, r, r.URL.Query().Get("mac"))
}

func (s *Server) serveIPXE(w http.ResponseWriter, r *http.Request, mac string) {
	const ct = "text/plain" // iPXE scripts are served as text/plain
	mac = strings.TrimSuffix(mac, ".ipxe")
	if mac == "" {
		s.renderFallback(w, "ipxe", "missing MAC")
		return
	}
	host, err := s.lookup(r.Context(), "mac", mac)
	if err != nil {
		if errors.Is(err, netbox.ErrNotFound) {
			slog.Info("ipxe unknown MAC; serving fallback", "mac", mac, "fallback", s.fallback)
		} else {
			slog.Error("ipxe netbox lookup failed; serving safe fallback", "mac", mac, "err", err)
		}
		s.renderFallback(w, "ipxe", "unknown or unresolvable MAC")
		return
	}
	body, err := s.engine.RenderIPXE(host)
	if err != nil {
		s.metrics.renders.WithLabelValues("ipxe", "error").Inc()
		slog.Error("render ipxe", "host", host.Hostname, "err", err)
		s.renderFallback(w, "ipxe", "render error")
		return
	}
	s.metrics.renders.WithLabelValues("ipxe", "ok").Inc()
	s.ok(w, http.StatusOK, ct, body, "ipxe")
}

// renderFallback emits the configured unknown-MAC iPXE script (still HTTP 200).
func (s *Server) renderFallback(w http.ResponseWriter, endpoint, _ string) {
	body, err := s.engine.RenderFallback(s.fallback)
	if err != nil {
		// Last-resort inline script so the firmware still gets something valid.
		body = []byte("#!ipxe\necho bootapi: fallback render failed; booting local disk\nsanboot --no-describe --drive 0x80 || exit\n")
	}
	s.ok(w, http.StatusOK, "text/plain", body, endpoint)
}

// handleKickstart serves the rendered kickstart for a host identified by MAC or
// hostname. Unlike iPXE, an unknown host here is a hard 404: the installer has
// already committed to installing and a wrong/empty kickstart is worse than a
// clear failure.
func (s *Server) handleKickstart(w http.ResponseWriter, r *http.Request) {
	ident := chi.URLParam(r, "ident")
	for _, suf := range []string{".ks", ".cfg"} {
		ident = strings.TrimSuffix(ident, suf)
	}
	if ident == "" {
		http.Error(w, "missing host identifier", http.StatusBadRequest)
		s.metrics.httpRequests.WithLabelValues("ks", "4xx").Inc()
		return
	}

	field := "name"
	if looksLikeMAC(ident) {
		field = "mac"
	}
	host, err := s.lookup(r.Context(), field, ident)
	if err != nil {
		if errors.Is(err, netbox.ErrNotFound) {
			http.Error(w, "no host in NetBox for "+ident, http.StatusNotFound)
			s.metrics.httpRequests.WithLabelValues("ks", "4xx").Inc()
			return
		}
		http.Error(w, "netbox lookup failed", http.StatusBadGateway)
		s.metrics.httpRequests.WithLabelValues("ks", "5xx").Inc()
		return
	}
	body, name, err := s.engine.RenderKickstart(host)
	if err != nil {
		s.metrics.renders.WithLabelValues("kickstart", "error").Inc()
		slog.Error("render kickstart", "host", host.Hostname, "err", err)
		http.Error(w, "kickstart render failed", http.StatusInternalServerError)
		s.metrics.httpRequests.WithLabelValues("ks", "5xx").Inc()
		return
	}
	s.metrics.renders.WithLabelValues("kickstart", "ok").Inc()
	slog.Info("served kickstart", "host", host.Hostname, "template", name)
	s.ok(w, http.StatusOK, "text/plain", body, "ks")
}

// lookup resolves a host by field ("mac" or "name"), recording metrics.
func (s *Server) lookup(ctx context.Context, field, value string) (*model.Host, error) {
	start := time.Now()
	var host *model.Host
	var err error
	if field == "mac" {
		host, err = s.resolver.HostByMAC(ctx, value)
	} else {
		host, err = s.resolver.HostByName(ctx, value)
	}
	s.metrics.netboxDuration.WithLabelValues(field).Observe(time.Since(start).Seconds())
	switch {
	case err == nil:
		s.metrics.netboxLookups.WithLabelValues(field, "ok").Inc()
	case errors.Is(err, netbox.ErrNotFound):
		s.metrics.netboxLookups.WithLabelValues(field, "notfound").Inc()
	default:
		s.metrics.netboxLookups.WithLabelValues(field, "error").Inc()
	}
	return host, err
}

func (s *Server) ok(w http.ResponseWriter, status int, contentType string, body []byte, endpoint string) {
	w.Header().Set("Content-Type", contentType)
	w.WriteHeader(status)
	_, _ = w.Write(body)
	s.metrics.httpRequests.WithLabelValues(endpoint, statusClass(status)).Inc()
}

// ListenAndServe runs the HTTP server until ctx is cancelled.
func (s *Server) ListenAndServe(ctx context.Context, addr string) error {
	srv := &http.Server{
		Addr:              addr,
		Handler:           s.Router(),
		ReadHeaderTimeout: 10 * time.Second,
	}
	go func() {
		<-ctx.Done()
		shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
		defer cancel()
		_ = srv.Shutdown(shutdownCtx)
	}()
	slog.Info("bootapi listening", "addr", addr)
	if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
		return err
	}
	return nil
}

// looksLikeMAC reports whether s is plausibly a MAC (12 hex nibbles, ignoring
// common separators). Used to pick the NetBox lookup field for /ks/{ident}.
func looksLikeMAC(s string) bool {
	n := 0
	for _, r := range strings.ToLower(s) {
		switch {
		case r >= '0' && r <= '9', r >= 'a' && r <= 'f':
			n++
		case r == ':' || r == '-' || r == '.':
			// separator, ignore
		default:
			return false
		}
	}
	return n == 12
}

func statusClass(code int) string {
	switch {
	case code < 300:
		return "2xx"
	case code < 400:
		return "3xx"
	case code < 500:
		return "4xx"
	default:
		return "5xx"
	}
}

func (s *Server) logRequests(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		ww := middleware.NewWrapResponseWriter(w, r.ProtoMajor)
		defer func() {
			slog.Info("request",
				"method", r.Method,
				"path", r.URL.Path,
				"status", ww.Status(),
				"duration_ms", time.Since(start).Milliseconds(),
				"remote", r.RemoteAddr,
				"request_id", middleware.GetReqID(r.Context()),
			)
		}()
		next.ServeHTTP(ww, r)
	})
}