// Package app wires the application together: configuration, store, auth,
// HTTP, and the lifecycle that starts and stops them.
//
// Keeping the wiring in one place means main() is a dozen lines, the whole
// object graph can be constructed in a test, and there is exactly one place to
// look to answer "what actually runs in production".
package app

import (
	"context"
	"errors"
	"fmt"
	"net"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/urpi/go-bananas/internal/auth"
	"github.com/urpi/go-bananas/internal/config"
	"github.com/urpi/go-bananas/internal/domain"
	"github.com/urpi/go-bananas/internal/httpapi"
	"github.com/urpi/go-bananas/internal/logging"
	"github.com/urpi/go-bananas/internal/seed"
	"github.com/urpi/go-bananas/internal/store"
)

// Build information, stamped at link time with -ldflags -X.
//
// Every value has a usable default so that `go run ./cmd/go-bananas` and a plain
// `go build` both work without ceremony, and so that a binary built by hand still
// reports something meaningful rather than an empty string in a log line.
var (
	// Version is the release version, e.g. 1.4.2.
	Version = "dev"
	// Commit is the source revision.
	Commit = "unknown"
	// BuildDate is the RFC 3339 build timestamp.
	BuildDate = "unknown"
)

// App is the assembled application.
type App struct {
	Config config.Config
	Log    logging.Logger
	Store  *store.Store
	Cache  *httpapi.ThemeCache
	Auth   *auth.Authenticator
	Router http.Handler
	Server *http.Server

	metrics *httpapi.Metrics
	// listener is bound before Serve so that the ready log line can report the
	// real address, which matters when the configured port is 0.
	listener net.Listener
}

// Options are the inputs needed to build an App.
type Options struct {
	// Config is the resolved configuration.
	Config config.Config
	// Version is the build version.
	Version string
	// Logger overrides the constructed logger, for tests.
	Logger logging.Logger
}

// New builds the application without starting it.
//
// Construction validates the whole object graph and reconciles the built-in
// themes, so a misconfigured deployment or a broken migration fails here rather
// than on the first request.
func New(ctx context.Context, opts Options) (*App, error) {
	cfg := opts.Config
	if cfg.StaticDir == "" && cfg.SDKDir == "" {
		return nil, errors.New("neither STATIC_DIR nor SDK_DIR is set")
	}

	log := opts.Logger
	if cfg.EphemeralSessionSecret() {
		// Worth a warning: an operator debugging a session that "keeps logging
		// me out" in local development needs to know why.
		if log == nil {
			log = logging.New(logging.Options{
				Level: cfg.LogLevel, Format: cfg.LogFormat,
				Service: "Go Bananas!!", Environment: cfg.Environment, Version: opts.Version,
			})
		}
		log.Warn("SESSION_SECRET was not set; an ephemeral one was generated. " +
			"Sessions will not survive a restart. Set SESSION_SECRET to at least 32 bytes.")
	}
	if log == nil {
		log = logging.New(logging.Options{
			Level:       cfg.LogLevel,
			Format:      cfg.LogFormat,
			Service:     "Go Bananas!!",
			Environment: cfg.Environment,
			Version:     opts.Version,
		})
	}

	st, err := store.Open(ctx, store.Options{
		Path:        cfg.DatabasePath,
		BusyTimeout: cfg.DatabaseBusyTimeout,
		MaxConns:    cfg.DatabaseMaxConns,
	})
	if err != nil {
		return nil, fmt.Errorf("open store: %w", err)
	}

	cache := httpapi.NewThemeCache()

	if cfg.SeedOnStart {
		inserted, refreshed, err := st.Seed(ctx, seed.Themes())
		if err != nil {
			st.Close()
			return nil, fmt.Errorf("seed built-in themes: %w", err)
		}
		if inserted > 0 || refreshed > 0 {
			log.Info("built-in themes reconciled",
				"inserted", inserted, "refreshed", refreshed, "total", len(seed.Slugs()))
		}
	}

	authenticator, err := buildAuthenticator(ctx, cfg, st, log)
	if err != nil {
		st.Close()
		return nil, err
	}

	// Warming the render cache at start-up means the first request after a deploy
	// is already fast. Failure is not fatal: the cache is an optimisation.
	warmed := 0
	if themes, err := st.ListRuntime(ctx); err == nil {
		for _, theme := range themes {
			warmed += cache.Prefetch(theme, nil)
		}
	}
	if warmed > 0 {
		log.Debug("render cache warmed", "artefacts", warmed)
	}

	metrics := httpapi.NewMetrics().WithCache(cache)
	metrics.RegisterCounter("bananas_theme_publishes_total", "Themes moved to the published status.")
	metrics.RegisterCounter("bananas_theme_updates_total", "Theme documents written.")
	metrics.RegisterCounter("bananas_auth_failures_total", "Requests rejected for want of a usable credential.")

	app := &App{
		Config:  cfg,
		Log:     log,
		Store:   st,
		Cache:   cache,
		Auth:    authenticator,
		metrics: metrics,
	}

	app.Router = httpapi.NewRouter(httpapi.Deps{
		Config:        cfg,
		Store:         st,
		Cache:         cache,
		Authenticator: authenticator,
		Log:           log,
		Version:       opts.Version,
		Metrics:       metrics,
		StaticHandler: staticHandler(cfg.StaticDir),
		SDKHandler:    sdkHandler(cfg.SDKDir),
		// Resolved per request rather than captured at start-up, so that changing the
		// default theme in the admin UI takes effect without a restart.
		//
		// A missing setting yields the supplied default, which is the normal case.
		// A database error is different: it would otherwise look like "no default
		// configured" and every runtime request would fall through to asking the
		// consumer for a theme. It is logged rather than propagated because this runs
		// inside a request handler whose job is to serve a theme, and failing the
		// whole request over a settings lookup would be a worse outcome than serving
		// the fallback.
		RuntimeDefaults: func() (string, domain.Appearance) {
			slug, err := st.Setting(ctx, domain.SettingDefaultTheme, "")
			if err != nil {
				log.Warn("could not read the default theme setting", "error", err)
			}
			appearance, err := st.Setting(ctx, domain.SettingDefaultAppearance, string(domain.AppearanceLight))
			if err != nil {
				log.Warn("could not read the default appearance setting", "error", err)
			}
			return slug, domain.Appearance(appearance)
		},
	})

	app.Server = &http.Server{
		Addr:              cfg.HTTPAddr,
		Handler:           app.Router,
		ReadTimeout:       cfg.ReadTimeout,
		ReadHeaderTimeout: 10 * time.Second,
		WriteTimeout:      cfg.WriteTimeout,
		IdleTimeout:       cfg.IdleTimeout,
		MaxHeaderBytes:    1 << 20,
		ErrorLog:          nil,
		BaseContext:       func(_ net.Listener) context.Context { return context.WithoutCancel(ctx) },
	}

	return app, nil
}

// buildAuthenticator constructs the auth stack for the configured mode.
func buildAuthenticator(ctx context.Context, cfg config.Config, st *store.Store, log logging.Logger) (*auth.Authenticator, error) {
	switch cfg.AuthMode {
	case config.AuthModeOIDC:
		state := auth.NewStateStore(
			cfg.SessionSecret,
			"go-bananas-oidc-state",
			cfg.SessionSecure,
			sameSiteFrom(cfg.SessionSameSite),
			10*time.Minute,
		)
		provider, err := auth.NewOIDCProvider(ctx, cfg, state)
		if err != nil {
			return nil, fmt.Errorf("identity provider: %w", err)
		}
		log.Info("identity provider configured",
			"issuer", cfg.OIDCIssuer,
			"clientId", cfg.OIDCClientID,
			"redirectUrl", cfg.RedirectURL(),
			"adminGroups", cfg.OIDCAdminGroups,
			"editorGroups", cfg.OIDCEditorGroups,
		)
		return auth.New(cfg, provider, st)

	case config.AuthModeDev:
		log.Warn("AUTH MODE IS DEV: every request is authenticated as a local administrator. " +
			"This mode is refused outside a development environment.")
		return auth.New(cfg, nil, st)

	case config.AuthModeNone:
		log.Warn("AUTH MODE IS NONE: every request is granted administrator access. " +
			"This mode is refused outside a development environment.")
		return auth.New(cfg, nil, st)

	default:
		return nil, fmt.Errorf("unknown AUTH_MODE %q", cfg.AuthMode)
	}
}

// sameSiteFrom maps a configuration value onto an http.SameSite.
func sameSiteFrom(raw string) (result sameSite) {
	switch strings.ToLower(raw) {
	case "strict":
		return sameSiteStrict
	case "none":
		return sameSiteNone
	default:
		return sameSiteLax
	}
}

// Run starts the server and blocks until ctx is cancelled.
//
// The shutdown sequence is the part worth reading: on cancellation the listener
// is closed first so no new connection is accepted, then in-flight requests get
// ShutdownTimeout to finish, and only then is the store closed. Closing the store
// while a request is still reading would surface as a confusing 500 to a user
// who did nothing wrong.
func (a *App) Run(ctx context.Context) error {
	listenCfg := net.ListenConfig{}
	listener, err := listenCfg.Listen(ctx, "tcp", a.Config.HTTPAddr)
	if err != nil {
		return fmt.Errorf("listen on %s: %w", a.Config.HTTPAddr, err)
	}
	a.listener = listener

	a.Log.Info("starting Go Bananas!!",
		"address", listener.Addr().String(),
		"publicUrl", a.Config.Origin(),
		"authMode", a.Config.AuthMode,
		"database", a.Config.DatabasePath,
		"environment", a.Config.Environment,
		"version", Version,
		"commit", Commit,
		"built", BuildDate,
	)

	serverErrors := make(chan error, 1)
	go func() {
		err := a.Server.Serve(listener)
		if errors.Is(err, http.ErrServerClosed) {
			err = nil
		}
		serverErrors <- err
	}()

	select {
	case err := <-serverErrors:
		if err != nil {
			return fmt.Errorf("serve: %w", err)
		}
		return nil

	case <-ctx.Done():
		a.Log.Info("shutdown signal received", "graceful", true)
	}

	shutdownCtx, cancel := context.WithTimeout(context.WithoutCancel(ctx), a.Config.ShutdownTimeout)
	defer cancel()

	if err := a.Server.Shutdown(shutdownCtx); err != nil {
		// A timeout here means a request outlived the grace period. Closing hard
		// is better than hanging, and the error is logged so it is visible.
		a.Log.Error("graceful shutdown timed out; closing connections", "error", err)
		if closeErr := a.Server.Close(); closeErr != nil {
			a.Log.Error("force close failed", "error", closeErr)
		}
	}

	if err := <-serverErrors; err != nil {
		return fmt.Errorf("serve: %w", err)
	}
	a.Log.Info("stopped cleanly")
	return nil
}

// Addr returns the bound address, useful when the configured port is 0.
func (a *App) Addr() string {
	if a.listener == nil {
		return a.Config.HTTPAddr
	}
	return a.listener.Addr().String()
}

// Close releases the application's resources.
func (a *App) Close() error {
	if a.Store == nil {
		return nil
	}
	return a.Store.Close()
}

// Run is the top-level entrypoint: load configuration, build, run, shut down.
func Run(ctx context.Context) error {
	cfg, err := config.Load()
	if err != nil {
		// Configuration errors are reported plainly rather than through the logger,
		// because the logger's own configuration may be part of what is wrong.
		return fmt.Errorf("%w", err)
	}

	application, err := New(ctx, Options{Config: cfg, Version: Version})
	if err != nil {
		return err
	}
	defer application.Close()

	return application.Run(ctx)
}

// staticHandler serves the built admin UI, or nil when no build is present.
//
// A missing UI is not fatal: the API is independently useful, and a deployment
// that only serves the runtime endpoints has no reason to carry the SPA.
func staticHandler(dir string) http.Handler {
	if dir == "" {
		return nil
	}
	index := filepath.Join(dir, "index.html")
	if _, err := os.Stat(index); err != nil {
		return nil
	}
	fileServer := spaHandler{root: dir, files: http.FileServer(http.Dir(dir))}
	return fileServer
}

// spaHandler serves the admin single-page application.
//
// Any GET that does not resolve to a real file falls through to index.html so
// that client-side routes survive a page reload. An unknown /api or /rt path must
// still 404 as JSON rather than returning HTML, which is handled by the router
// before this handler is reached.
type spaHandler struct {
	root  string
	files http.Handler
}

// withinRoot reports whether path is root or lives beneath it.
//
// It compares path components rather than string prefixes, because a prefix test
// cannot tell "/srv/web" from "/srv/web-secrets": the first contains the second as
// a leading substring, and a request for the second would pass a HasPrefix check
// against the first.
func withinRoot(root, path string) bool {
	absRoot, err := filepath.Abs(root)
	if err != nil {
		return false
	}
	// The root is resolved when it exists. When it does not, Abs still gives an
	// absolute path to compare against, which is the best available answer.
	if resolvedRoot, resolveErr := filepath.EvalSymlinks(absRoot); resolveErr == nil {
		absRoot = resolvedRoot
	}

	absPath, err := filepath.Abs(path)
	if err != nil {
		return false
	}

	rel, err := filepath.Rel(absRoot, absPath)
	if err != nil {
		return false
	}
	// ".." is the only relative path that leaves the root. "." is the root itself,
	// which is allowed; a path equal to the root is not a file but reaching it is
	// not an escape.
	return rel == "." || (rel != ".." && !strings.HasPrefix(rel, ".."+string(filepath.Separator)))
}

// ServeHTTP implements http.Handler.
func (h spaHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet && r.Method != http.MethodHead {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}

	// Anchoring the path with a leading slash and cleaning it removes every ".."
	// segment, so Join below cannot escape the root. The check after it is a
	// belt-and-braces assertion that the result really is inside, rather than a
	// prefix test: a plain HasPrefix against the root would accept a sibling
	// directory whose name merely starts with the root's.
	cleaned := filepath.Clean("/" + strings.TrimPrefix(r.URL.Path, "/"))
	candidate := filepath.Join(h.root, cleaned)

	if !withinRoot(h.root, candidate) {
		http.Error(w, "not found", http.StatusNotFound)
		return
	}

	// The static file server resolves symlinks, so a symlink inside the web
	// directory pointing at /etc would otherwise be served. Resolving the real
	// path and re-checking it is what actually closes that: the root itself is
	// resolved too, so a root reached through a symlink does not trip the check.
	resolved, err := filepath.EvalSymlinks(candidate)
	if err != nil {
		// A path that does not exist is not an error here: the SPA fallback below
		// serves the shell for it. Only a real failure is reported.
		resolved = candidate
	}
	if !withinRoot(h.root, resolved) {
		http.Error(w, "not found", http.StatusNotFound)
		return
	}

	//nolint:gosec // G703: as on the ServeFile call below; the taint source is
	// r.URL.Path and both paths it reaches are checked by withinRoot.
	if info, err := os.Stat(resolved); err == nil && !info.IsDir() {
		setStaticCacheHeaders(w, resolved)
		// ServeFile rather than the file server, because the request URL is the
		// uncleaned path and the file to serve is the resolved one. The directory
		// case cannot reach here, which is the only case in which ServeFile
		// redirects.
		//
		//nolint:gosec // G703: gosec's taint analysis cannot see withinRoot. The
		// containment predicate compares path components rather than prefixes, so a
		// sibling directory named "web-secrets" beside "web" is rejected, and
		// resolved above is the symlink-resolved path that was re-checked against it.
		// TestSPARejectsTraversal, TestSPARejectsSymlinkEscape and TestWithinRoot are
		// what hold this in place.
		http.ServeFile(w, r, resolved)
		return
	}

	// Serve the shell for a client-side route. The request path is rewritten to
	// the directory root rather than to index.html: http.FileServer answers a
	// request for /index.html with a 301 to /, which would turn every deep link
	// into a redirect loop against the SPA router.
	w.Header().Set("Cache-Control", "no-cache")
	h.files.ServeHTTP(w, indexRequest(r))
}

// indexRequest rewrites a request onto the SPA entry point.
func indexRequest(r *http.Request) *http.Request {
	clone := r.Clone(r.Context())
	clone.URL.Path = "/"
	return clone
}

// staticAssetSuffixes are the file extensions that may be cached indefinitely,
// because Vite emits content-hashed names for them.
var staticAssetSuffixes = []string{".js", ".css", ".woff", ".woff2", ".svg", ".png", ".jpg", ".webp", ".avif"}

// setStaticCacheHeaders chooses a cache policy for a static asset.
func setStaticCacheHeaders(w http.ResponseWriter, path string) {
	for _, suffix := range staticAssetSuffixes {
		if strings.HasSuffix(path, suffix) {
			w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
			return
		}
	}
	w.Header().Set("Cache-Control", "public, max-age=300")
}

// sameSite aliases keep the http.SameSite constants out of this file's imports,
// which keeps the mapping in one readable block.
type sameSite = http.SameSite

// Cookie SameSite modes, re-exported for the configuration mapping above.
const (
	sameSiteLax    = http.SameSiteLaxMode
	sameSiteStrict = http.SameSiteStrictMode
	sameSiteNone   = http.SameSiteNoneMode
)

// sdkHandler serves the built runtime SDK bundles, or nil when no build is
// present.
//
// The SDK is served from the same origin as the runtime API so that a consuming
// application can load it with a plain URL and no build step, which is the whole
// point of delivering themes at runtime rather than through a package registry.
func sdkHandler(dir string) http.Handler {
	if dir == "" {
		return nil
	}
	if _, err := os.Stat(filepath.Join(dir, "runtime.js")); err != nil {
		return nil
	}
	return http.StripPrefix("/rt/v1/", http.FileServer(http.Dir(dir)))
}