// Command pages-server serves static sites deployed through the pages CLI and
// exposes the management API used to drive those deployments.
//
// It binds two listeners: a public one that only ever serves site content, and a
// management one (loopback by default) that only ever serves the API. Keeping
// them apart means the management surface never shares an origin with content
// that projects control.
package main

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"os"
	"os/signal"
	"sync"
	"sync/atomic"
	"syscall"
	"time"

	"github.com/iceBear67/simplepages/internal/adminapi"
	"github.com/iceBear67/simplepages/internal/auth"
	"github.com/iceBear67/simplepages/internal/cas"
	"github.com/iceBear67/simplepages/internal/config"
	"github.com/iceBear67/simplepages/internal/deploy"
	"github.com/iceBear67/simplepages/internal/httpx"
	"github.com/iceBear67/simplepages/internal/site"
	"github.com/iceBear67/simplepages/internal/store"
	"github.com/iceBear67/simplepages/internal/version"
	"github.com/iceBear67/simplepages/internal/webroot"
)

// Background worker cadences. The auth flusher batches last_used_at updates;
// writing one per request would funnel every authenticated read through the
// single write connection.
const (
	touchFlushInterval = 60 * time.Second

	// failedAuthBurst is how many failed authentications one client address may
	// make before it is throttled, and failedAuthPeriod is how long a full
	// budget takes to refill. Successful requests cost nothing, so a busy CI
	// fleet never meets these numbers.
	failedAuthBurst   = 10
	failedAuthPeriod  = time.Minute
	failedAuthClients = 10000
)

func main() {
	if err := run(os.Args[1:], os.Stdout, os.Stderr); err != nil {
		if errors.Is(err, flag.ErrHelp) {
			os.Exit(2)
		}
		fmt.Fprintf(os.Stderr, "pages-server: %v\n", err)
		os.Exit(1)
	}
}

func run(args []string, stdout, stderr io.Writer) error {
	opts, err := config.Load(args, stderr)
	if err != nil {
		return err
	}
	if opts.ShowVersion {
		fmt.Fprintf(stdout, "pages-server %s\n", version.String())
		return nil
	}
	if opts.CheckOnly {
		fmt.Fprintln(stdout, "configuration ok")
		return nil
	}

	cfg := opts.Config
	log := cfg.Logger(stderr)
	log.Info("starting", "version", version.Short(),
		"data_dir", cfg.DataDir, "webroot", cfg.Webroot,
		"assemble_mode", string(cfg.AssembleMode))

	if err := cfg.EnsureDirs(); err != nil {
		return err
	}

	// The first signal starts a graceful shutdown; a second one gives up on the
	// in-flight requests, which is what an operator means by pressing Ctrl-C
	// twice.
	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	defer stop()
	go func() {
		<-ctx.Done()
		hard := make(chan os.Signal, 1)
		signal.Notify(hard, os.Interrupt, syscall.SIGTERM)
		<-hard
		fmt.Fprintln(stderr, "pages-server: second signal, exiting immediately")
		os.Exit(130)
	}()

	app, err := newApp(ctx, cfg, log)
	if err != nil {
		return err
	}
	defer app.close()

	// Background workers get their own cancellable context so they are stopped
	// *after* the listeners have drained: the auth flusher's final write should
	// include the last requests the server handled.
	workerCtx, stopWorkers := context.WithCancel(context.Background())
	var workers sync.WaitGroup
	// Registered after the app's own cleanup so it runs before it: the workers
	// must be finished with the database before anything closes it.
	defer func() {
		stopWorkers()
		workers.Wait()
	}()
	for _, worker := range []func(context.Context){
		func(ctx context.Context) { app.verifier.RunFlusher(ctx, touchFlushInterval) },
		func(ctx context.Context) { app.deploy.RunReconciler(ctx, cfg.ReconcileInterval.D()) },
		func(ctx context.Context) { app.deploy.RunCollector(ctx, cfg.GCInterval.D()) },
	} {
		workers.Add(1)
		go func() {
			defer workers.Done()
			worker(workerCtx)
		}()
	}

	siteSrv, err := httpx.Listen("site", cfg.Listen, app.siteHandler(), httpx.Timeouts{
		ReadHeader: cfg.ReadHeaderTimeout.D(),
		Read:       cfg.ReadTimeout.D(),
		Idle:       cfg.IdleTimeout.D(),
		// No Write timeout: see httpx.Timeouts.
	}, log)
	if err != nil {
		return fmt.Errorf("listen %s: %w", cfg.Listen, err)
	}
	apiSrv, err := httpx.Listen("api", cfg.APIListen, app.apiHandler(), httpx.Timeouts{
		ReadHeader: cfg.ReadHeaderTimeout.D(),
		Read:       cfg.ReadTimeout.D(),
		Idle:       cfg.IdleTimeout.D(),
	}, log)
	if err != nil {
		return fmt.Errorf("listen %s: %w", cfg.APIListen, err)
	}

	app.ready.Store(true)

	g := &httpx.Group{
		Servers: []*httpx.Server{siteSrv, apiSrv},
		Grace:   cfg.ShutdownGrace.D(),
		Log:     log,
	}
	if err := g.Run(ctx); err != nil {
		return err
	}
	log.Info("stopped")
	return nil
}

// app holds the process-wide state shared by both listeners.
type app struct {
	cfg     config.Config
	log     *slog.Logger
	started time.Time

	db       *store.DB
	cas      *cas.Store
	sites    *site.Registry
	webroot  *webroot.Webroot
	deploy   *deploy.Service
	verifier *auth.Verifier
	authmw   *auth.Middleware
	admin    *adminapi.Server

	// ready gates /readyz: the process may be accepting connections before it
	// can actually answer for content, and a load balancer needs to know.
	ready atomic.Bool
}

func newApp(ctx context.Context, cfg config.Config, log *slog.Logger) (*app, error) {
	db, err := store.Open(ctx, cfg.DBPath(), log)
	if err != nil {
		return nil, fmt.Errorf("open store: %w", err)
	}

	if _, err := auth.EnsureAdminKey(ctx, db, cfg.BootstrapTokenPath(), log); err != nil {
		db.Close()
		return nil, err
	}

	// The probe directory must be the one trees are assembled in: hardlinks
	// cannot cross filesystems, so probing anywhere else answers a different
	// question. With assemble_mode=none nothing is assembled and the mode is
	// irrelevant, so ask for copy rather than probe for something unused.
	casOpts := cas.Options{ProbeDir: cfg.DeploymentsDir(), Log: log}
	switch cfg.AssembleMode {
	case config.AssembleHardlink:
		casOpts.Mode = cas.LinkHard
	case config.AssembleCopy, config.AssembleNone:
		casOpts.Mode = cas.LinkCopy
	}
	cs, err := cas.Open(cfg.CASDir(), casOpts)
	if err != nil {
		db.Close()
		return nil, err
	}

	verifier := auth.NewVerifier(db, log, auth.DefaultCacheTTL)
	// An empty Dir is how the service is told to skip on-disk assembly.
	deployDir := cfg.DeploymentsDir()
	if cfg.AssembleMode == config.AssembleNone {
		deployDir = ""
	}

	// With nothing assembled on disk there is nothing for a symlink to point at,
	// so assemble_mode=none leaves the webroot unmanaged. Failing to open it
	// otherwise is a permissions or layout problem the operator asked for and
	// should hear about now, rather than as a warning on every activation.
	var wr *webroot.Webroot
	if deployDir != "" && cfg.Webroot != "" {
		wr, err = webroot.Open(cfg.Webroot, deployDir)
		if err != nil {
			cs.Close()
			db.Close()
			return nil, err
		}
	}

	a := &app{
		cfg:      cfg,
		log:      log,
		started:  time.Now(),
		db:       db,
		cas:      cs,
		sites:    site.NewRegistry(),
		webroot:  wr,
		verifier: verifier,
		authmw: &auth.Middleware{
			V:       verifier,
			Limiter: auth.NewLimiter(failedAuthBurst, failedAuthPeriod, failedAuthClients),
			Trusted: cfg.TrustedProxies(),
			Log:     log,
		},
	}
	a.deploy = &deploy.Service{
		DB: db, CAS: cs, Log: log, Dir: deployDir,
		Sites: a.sites, Webroot: wr,
	}
	a.admin = &adminapi.Server{
		DB:     db,
		Auth:   a.authmw,
		Deploy: a.deploy,
		Log:    log,
		Limits: cfg.Limits,
		// The registry answers ownership checks and "what is this project
		// serving" from memory. Both are only correct once LoadSites below has
		// finished, which is why it runs before any listener exists.
		Resolver: a.sites,
		Sites:    a.sites,
		BaseURL:  cfg.SiteURL,
		LinkMode: string(cs.LinkMode()),
		Started:  a.started,
	}
	a.admin.Hooks = adminapi.Hooks{
		ProjectChanged: func(_ context.Context, p *store.Project) {
			// A new project starts with nothing activated, so it resolves and
			// then answers 503 until something is deployed to it. A changed one
			// keeps serving what it was serving, with new settings.
			a.sites.Put(p)
		},
		ProjectDeleted: func(ctx context.Context, p *store.Project) {
			a.sites.Delete(p.Name)
			if wr != nil {
				if err := wr.Unpoint(p.Name); err != nil {
					log.WarnContext(ctx, "could not remove the webroot symlink",
						"project", p.Name, "err", err)
				}
			}
			// The rows are already gone and their blobs are already
			// unreferenced; this is only the assembled trees, which nothing
			// would otherwise account for. A failure here is not worth failing
			// the request over — the startup sweep removes them as orphans.
			if err := a.deploy.RemoveProjectTrees(p.ID); err != nil {
				log.WarnContext(ctx, "could not remove the project's deployment trees",
					"project", p.Name, "err", err)
			}
		},
	}

	// Recovery runs before the registry is built, and both run before any
	// listener exists. That order is what lets recovery assume it is alone with
	// the data directory, and it means the first request is answered from state
	// that has already been reconciled rather than from whatever the last crash
	// left behind.
	if err := a.deploy.Recover(ctx); err != nil {
		a.close()
		return nil, fmt.Errorf("recover: %w", err)
	}
	if err := a.deploy.LoadSites(ctx); err != nil {
		a.close()
		return nil, fmt.Errorf("load sites: %w", err)
	}
	return a, nil
}

// pingDB checks that the read pool can still reach the database, with a
// deadline of its own so a wedged store cannot hold a probe open indefinitely.
func (a *app) pingDB(ctx context.Context) error {
	if a.db == nil {
		return errors.New("store not open")
	}
	ctx, cancel := context.WithTimeout(ctx, 2*time.Second)
	defer cancel()
	return a.db.Reader().PingContext(ctx)
}

func (a *app) close() {
	if a.cas != nil {
		if err := a.cas.Close(); err != nil {
			a.log.Error("closing content store", "err", err)
		}
	}
	if a.db != nil {
		if err := a.db.Close(); err != nil {
			a.log.Error("closing store", "err", err)
		}
	}
}

// middleware is the chain shared by both listeners, outermost first.
//
// The order is load-bearing. Recover must sit *inside* AccessLog: a panic that
// unwound past AccessLog would skip its logging entirely, so the one request
// that most needs a log line would be the one without one. With Recover
// innermost the panic becomes an ordinary 500 return that AccessLog then records
// normally, and Recover can see the shared request id and the recorder that
// tells it whether a response has already begun. Panics in the middleware
// itself are left to net/http, which closes the connection.
func (a *app) middleware() []httpx.Middleware {
	return []httpx.Middleware{
		httpx.WithRequestID(a.cfg.TrustedProxies()),
		httpx.AccessLog(a.log, a.cfg.TrustedProxies()),
		httpx.Recover(a.log),
	}
}

func (a *app) siteHandler() http.Handler {
	mux := http.NewServeMux()
	a.registerHealth(mux)

	// Site routing is hand-parsed rather than expressed as a ServeMux pattern:
	// "/~{project}/{path...}" is rejected by net/http, whose wildcards must start
	// at the beginning of a path segment. Registering "/" still gets us the mux's
	// built-in ".."/"//" normalisation redirects.
	//
	// Those redirects are a convenience, not a defence: a percent-encoded
	// "/~a/%2e%2e/%2e%2e/etc/passwd" reaches the handler with r.URL.Path already
	// decoded to "/~a/../../etc/passwd" and no redirect issued (verified against
	// this server). The resolver therefore does its own path.Clean and validation
	// rather than assume the mux normalised anything.
	mux.Handle("/", &site.Handler{Registry: a.sites, CAS: a.cas, Log: a.log})
	return httpx.Chain(mux, a.middleware()...)
}

func (a *app) apiHandler() http.Handler {
	mux := http.NewServeMux()
	a.registerHealth(mux)
	a.admin.Register(mux)
	return httpx.Chain(mux, a.middleware()...)
}

// registerHealth adds the probe endpoints to a mux. They live on both listeners
// so a probe can target whichever one the deployment exposes.
func (a *app) registerHealth(mux *http.ServeMux) {
	// Liveness: answers as long as the process can schedule a goroutine. It must
	// never touch the database, or a slow query would get the process killed.
	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
		w.Header().Set("Cache-Control", "no-store")
		fmt.Fprintln(w, "ok")
	})

	// Readiness: reports whether this process can serve real traffic yet.
	mux.HandleFunc("GET /readyz", func(w http.ResponseWriter, r *http.Request) {
		status := http.StatusOK
		body := map[string]any{
			"status":   "ready",
			"version":  version.Short(),
			"uptime_s": int64(time.Since(a.started).Seconds()),
		}
		if !a.ready.Load() {
			status = http.StatusServiceUnavailable
			body["status"] = "starting"
		} else if err := a.pingDB(r.Context()); err != nil {
			// Unlike /healthz this may touch the database: a process that
			// cannot read its own store should be taken out of rotation, not
			// restarted.
			a.log.WarnContext(r.Context(), "readiness probe: store unreachable", "err", err)
			status = http.StatusServiceUnavailable
			body["status"] = "degraded"
		}
		w.Header().Set("Cache-Control", "no-store")
		httpx.WriteJSON(w, status, body)
	})
}