// 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"
	"crypto/subtle"
	"errors"
	"fmt"
	"log/slog"
	"net/http"
	"strings"
	"sync"
	"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 API and template engine into HTTP handlers.
type Server struct {
	nb      netbox.API
	engine  *render.Engine
	metrics *metrics
	// fallback is the unknown-MAC iPXE behavior: "local" (safe default) or
	// "shell" (debug).
	fallback string
	// provisionToken guards POST /provisioned; empty disables the endpoint.
	provisionToken string

	// TLS listener (optional); the plain-HTTP listener is always on.
	tlsAddr string
	tlsCert string
	tlsKey  string
}

// Options configures a Server.
type Options struct {
	NetBox netbox.API
	Engine *render.Engine
	// Cache/GitStats, when non-nil, have their counters published as metrics.
	Cache              cacheStats
	GitStats           gitStats
	UnknownMACFallback string
	ProvisionToken     string
	TLSAddr            string
	TLSCertFile        string
	TLSKeyFile         string
}

// New builds a Server.
func New(o Options) *Server {
	fb := o.UnknownMACFallback
	if fb == "" {
		fb = "local"
	}
	return &Server{
		nb:             o.NetBox,
		engine:         o.Engine,
		metrics:        newMetrics(o.Cache, o.GitStats),
		fallback:       fb,
		provisionToken: o.ProvisionToken,
		tlsAddr:        o.TLSAddr,
		tlsCert:        o.TLSCertFile,
		tlsKey:         o.TLSKeyFile,
	}
}

// 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)

	// End-of-kickstart callback: flips pxe_enabled off in NetBox. Token-guarded.
	r.Post("/provisioned/{ident}", s.handleProvisioned)

	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
	}
	// Per-host PXE-enable gate (Cobbler's netboot_enabled): a KNOWN host whose
	// pxe_enabled is false must NOT re-install. Serve the safe local-boot script
	// so an already-provisioned machine just boots its disk.
	if !host.ShouldPXEInstall() {
		s.metrics.ipxeGated.Inc()
		slog.Info("ipxe gated: pxe_enabled=false; serving local boot", "host", host.Hostname)
		s.renderFallback(w, "ipxe", "pxe disabled for host")
		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")
}

// handleProvisioned is the end-of-kickstart callback. The %post posts here with
// the shared provision token when the install finishes; bootapi flips the host's
// pxe_enabled custom field to false in NetBox so the next PXE boots local disk
// instead of re-installing. This is bootapi's only NetBox write.
func (s *Server) handleProvisioned(w http.ResponseWriter, r *http.Request) {
	if s.provisionToken == "" {
		http.Error(w, "provisioned callback disabled: no token configured", http.StatusServiceUnavailable)
		s.metrics.provisioned.WithLabelValues("disabled").Inc()
		return
	}
	if subtle.ConstantTimeCompare([]byte(bearer(r)), []byte(s.provisionToken)) != 1 {
		http.Error(w, "invalid or missing provision token", http.StatusUnauthorized)
		s.metrics.provisioned.WithLabelValues("unauthorized").Inc()
		return
	}
	ident := chi.URLParam(r, "ident")
	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.provisioned.WithLabelValues("notfound").Inc()
			return
		}
		http.Error(w, "netbox lookup failed", http.StatusBadGateway)
		s.metrics.provisioned.WithLabelValues("error").Inc()
		return
	}
	if err := s.nb.SetPXEEnabled(r.Context(), host.DeviceID, false); err != nil {
		slog.Error("provisioned: failed to clear pxe_enabled", "host", host.Hostname, "err", err)
		http.Error(w, "failed to update NetBox", http.StatusBadGateway)
		s.metrics.provisioned.WithLabelValues("error").Inc()
		return
	}
	s.metrics.provisioned.WithLabelValues("ok").Inc()
	slog.Info("host provisioned; pxe_enabled cleared", "host", host.Hostname)
	w.WriteHeader(http.StatusNoContent)
}

// bearer extracts a token from "Authorization: Bearer <t>" or a bare "token"
// header.
func bearer(r *http.Request) string {
	if h := r.Header.Get("Authorization"); h != "" {
		if after, ok := strings.CutPrefix(h, "Bearer "); ok {
			return after
		}
	}
	return r.Header.Get("token")
}

// 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.nb.HostByMAC(ctx, value)
	} else {
		host, err = s.nb.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 plain-HTTP server (always) plus, when a TLS listener
// is configured, an HTTPS server sharing the same handler — both until ctx is
// cancelled. The boot path works over plain HTTP because PXE installers have no
// internal CA trust; HTTPS is offered in parallel for clients that do.
func (s *Server) ListenAndServe(ctx context.Context, addr string) error {
	h := s.Router()
	var wg sync.WaitGroup
	errc := make(chan error, 2)

	serve := func(name string, srv *http.Server, tls bool) {
		defer wg.Done()
		go func() {
			<-ctx.Done()
			shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
			defer cancel()
			_ = srv.Shutdown(shutdownCtx)
		}()
		slog.Info("bootapi listening", "listener", name, "addr", srv.Addr)
		var err error
		if tls {
			err = srv.ListenAndServeTLS(s.tlsCert, s.tlsKey)
		} else {
			err = srv.ListenAndServe()
		}
		if err != nil && !errors.Is(err, http.ErrServerClosed) {
			errc <- fmt.Errorf("%s listener: %w", name, err)
		}
	}

	wg.Add(1)
	go serve("http", &http.Server{Addr: addr, Handler: h, ReadHeaderTimeout: 10 * time.Second}, false)

	if s.tlsAddr != "" && s.tlsCert != "" && s.tlsKey != "" {
		wg.Add(1)
		go serve("https", &http.Server{Addr: s.tlsAddr, Handler: h, ReadHeaderTimeout: 10 * time.Second}, true)
	}

	wg.Wait()
	close(errc)
	return <-errc // first error, or nil (channel closed empty)
}

// 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)
	})
}