package main

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"flag"
	"io/fs"
	"log"
	"net/http"
	"strings"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"

	"gitea.parodia.dev/drwily/petal/internal/auth"
	"gitea.parodia.dev/drwily/petal/internal/config"
	"gitea.parodia.dev/drwily/petal/internal/db"
	"gitea.parodia.dev/drwily/petal/internal/docs"
	"gitea.parodia.dev/drwily/petal/internal/images"
	"gitea.parodia.dev/drwily/petal/internal/lexicon"
	"gitea.parodia.dev/drwily/petal/internal/llm"
	"gitea.parodia.dev/drwily/petal/internal/spell"
	"gitea.parodia.dev/drwily/petal/internal/suggestions"
	"gitea.parodia.dev/drwily/petal/internal/tts"
	"gitea.parodia.dev/drwily/petal/internal/vocab"
	"gitea.parodia.dev/drwily/petal/web"
)

func main() {
	backupTo := flag.String("backup", "",
		"write a consistent copy of the database to this path and exit (no server)")
	flag.Parse()

	cfg := config.Load()

	// Backup mode short-circuits before anything else starts: no migrations, no
	// seed, no listener. It runs against the live database safely (VACUUM INTO
	// takes only a read transaction), so the nightly job is
	//   docker compose exec petal /app/petal -backup /data/backups/<name>.db
	// against the running container rather than a copy of three WAL files.
	if *backupTo != "" {
		if err := db.Backup(cfg.DatabasePath, *backupTo); err != nil {
			log.Fatalf("backup: %v", err)
		}
		log.Printf("backup written to %s", *backupTo)
		return
	}

	database, err := db.Open(cfg.DatabasePath)
	if err != nil {
		log.Fatalf("database: %v", err)
	}
	defer database.Close()
	log.Printf("database ready at %s", cfg.DatabasePath)

	// Identity. With Authentik configured, Petal is an OIDC client in its own
	// right: /auth/login starts a real login and the session cookie it issues is
	// what every API request is resolved from. Without it — local development,
	// and every deployment before auth landed — StaticResolver hands out the
	// single hardcoded local user, so nothing about running Petal on a laptop
	// changes.
	sessions := auth.NewSessionStore(database.DB)
	users := auth.NewUserStore(database.DB)

	var resolver auth.Resolver = auth.StaticResolver(db.LocalUserID)
	var oidcClient *auth.OIDC
	if cfg.AuthEnabled() {
		oidcClient = auth.NewOIDC(context.Background(), auth.Options{
			IssuerURL:    cfg.AuthentikURL,
			ClientID:     cfg.AuthentikClientID,
			ClientSecret: cfg.AuthentikClientSecret,
			BaseURL:      cfg.BaseURL,
			Allowed:      auth.ParseAllowlist(cfg.AllowedSubs),
		}, sessions, users)
		resolver = sessions
		if n, err := sessions.Prune(); err == nil && n > 0 {
			log.Printf("auth: pruned %d expired session(s)", n)
		}
		log.Printf("auth: OIDC enabled (issuer=%s, redirect=%s)", cfg.AuthentikURL, oidcClient.RedirectURI())
	} else {
		log.Printf("auth: OIDC not configured — running as the single %q user", db.LocalUserID)
	}

	// The dictionary behind word lookups. dict.db is DreamDict's built database
	// — French, European Portuguese, Spanish and Mandarin in one read-only file
	// beside petal.db. It is optional on purpose: a laptop checkout has never
	// had one, and the Chinese pair doesn't need one, so its absence downgrades
	// lookups rather than stopping Petal. A file that is present but broken is
	// a different matter and gets said out loud.
	dict, err := lexicon.OpenDreamDict(cfg.DictPath)
	if err != nil {
		log.Printf("dictionary: %s unusable (%v) — falling back to the embedded datasets", cfg.DictPath, err)
	}
	defer dict.Close()
	lexSet := lexicon.NewSet(dict)
	if lexSet.HasDreamDict() {
		log.Printf("dictionary: DreamDict open at %s (%s)", cfg.DictPath, lexSet.Contents())
	} else {
		log.Printf("dictionary: no dict.db at %s — English/Chinese only", cfg.DictPath)
	}

	r := chi.NewRouter()
	r.Use(middleware.RequestID)
	r.Use(middleware.RealIP)
	r.Use(middleware.Logger)
	r.Use(middleware.Recoverer)

	// Build version: a hash of the embedded SPA shell. Vite rewrites index.html
	// with content-hashed asset names on every build, so this string changes
	// exactly when a new frontend is deployed — the client polls it to know when
	// to offer a refresh.
	version := buildVersion()
	log.Printf("frontend build version %s", version)

	r.Route("/api", func(api chi.Router) {
		// Cap request bodies so a runaway or hostile client can't stream an
		// unbounded payload into a JSON decoder. Image uploads carry their own
		// (larger) limit inside the images handler, so they're exempt here.
		api.Use(limitBody(maxAPIBodyBytes, "/api/images"))

		api.Get("/health", func(w http.ResponseWriter, _ *http.Request) {
			w.Header().Set("Content-Type", "application/json")
			_, _ = w.Write([]byte(`{"status":"ok"}`))
		})

		api.Get("/version", func(w http.ResponseWriter, _ *http.Request) {
			w.Header().Set("Content-Type", "application/json")
			// Never cache: a stale cached version would defeat the whole check.
			w.Header().Set("Cache-Control", "no-store")
			_, _ = w.Write([]byte(`{"version":"` + version + `"}`))
		})

		// Everything below serves or mutates a particular user's data, so it sits
		// behind the auth middleware. /health and /version deliberately stay
		// outside it: they carry no user data, and a monitoring probe (or the
		// client's update poll) must not need a session to reach them.
		//
		// The middleware resolves the caller once and hands handlers the answer via
		// auth.UserID(r.Context()). Which resolver it runs is the only thing that
		// changed when auth landed: the session store in a deployment with
		// Authentik configured, the static local user otherwise. No handler or
		// query moved for either.
		api.Group(func(pr chi.Router) {
			pr.Use(auth.Middleware(resolver))

			// Who am I? The frontend namespaces its per-account browser state by
			// this id and shows the signed-in writer.
			pr.Get("/me", users.MeHandler())

			llmClient := llm.NewLLMClient(cfg)
			sug := suggestions.New(database, llmClient)

			// Document CRUD plus the doc-scoped checkpoint/list suggestion routes,
			// both under /api/docs.
			docsHandler := docs.New(database)
			docsRouter := docsHandler.Routes()
			sug.RegisterDocRoutes(docsRouter)
			pr.Mount("/docs", docsRouter)

			// Tag management (the roster) and cross-document full-text search.
			pr.Mount("/tags", docsHandler.TagRoutes())
			pr.Mount("/search", docsHandler.SearchRoutes())

			// Per-suggestion actions (accept/dismiss) under /api/suggestions.
			pr.Mount("/suggestions", sug.Routes())

			// Offline lexicon: full word lookups (gloss + definition + synonyms) for
			// the right-click popover, and the lightweight gloss-only lookup for the
			// inline hover/select tooltip. One handler over one provider Set, so the
			// embedded datasets and dict.db are each opened once. Which of them
			// answers depends on the caller's language pair — so unlike before, the
			// response is no longer identical for everyone, and it stays behind auth
			// for that reason as much as for the API surface.
			lex := lexicon.NewHandler(database.DB, lexSet)
			pr.Mount("/word", lex.Routes())
			pr.Mount("/gloss", lex.GlossRoutes())

			// Vocabulary garden: words the writer looks up are captured here and
			// surfaced for gentle spaced-repetition review.
			pr.Mount("/vocab", vocab.New(database).Routes())

			// The personal spelling dictionary — the words she's told Petal to stop
			// flagging. Kept server-side (rather than in the browser) so it belongs
			// to her account and follows her between devices.
			pr.Mount("/spell", spell.New(database).Routes())

			// Editor image uploads, stored on disk and served back by content hash
			// to whoever owns them. Files already on disk from before ownership
			// existed are claimed for the local user at startup.
			imgHandler, err := images.New(cfg.ImageDir, database.DB, db.LocalUserID)
			if err != nil {
				log.Fatalf("image store: %v", err)
			}
			pr.Mount("/images", imgHandler.Routes())

			// Read-aloud: proxy short passages to a local Piper TTS server. Only
			// mounted when TTS_ENDPOINT is configured; otherwise the frontend falls
			// back to the browser's Web Speech API on its own.
			if ttsHandler, ok := tts.New(cfg); ok {
				pr.Mount("/tts", ttsHandler.Routes())
				log.Printf("read-aloud enabled (TTS endpoint=%s)", cfg.TTSEndpoint)
			}
		})
	})

	// Login lives outside /api: these are browser navigations, and they must be
	// reachable without a session — that is their entire job.
	if oidcClient != nil {
		r.Mount("/auth", oidcClient.Routes())
	}

	// Everything else: serve the embedded SPA (with index.html fallback for client routing).
	r.NotFound(spaHandler())

	addr := ":" + cfg.Port
	log.Printf("petal listening on %s (LLM backend=%s)", addr, cfg.LLMBackend)
	if err := http.ListenAndServe(addr, r); err != nil {
		log.Fatalf("server error: %v", err)
	}
}

// maxAPIBodyBytes caps a JSON API request body at 2 MiB. That's far above any
// real document save (the body is text plus lightweight marks; images upload
// separately by reference) while still bounding abuse. Exceeding it makes the
// handler's json.Decode fail, which surfaces as a 400.
const maxAPIBodyBytes = 2 << 20

// limitBody wraps each request body in an http.MaxBytesReader so handlers can't
// be made to read an unbounded payload. Paths under any of exemptPrefixes are
// left alone (e.g. image uploads, which set their own, larger limit).
func limitBody(max int64, exemptPrefixes ...string) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			for _, p := range exemptPrefixes {
				if strings.HasPrefix(r.URL.Path, p) {
					next.ServeHTTP(w, r)
					return
				}
			}
			if r.Body != nil {
				r.Body = http.MaxBytesReader(w, r.Body, max)
			}
			next.ServeHTTP(w, r)
		})
	}
}

// buildVersion derives a short, stable identifier for the currently embedded
// frontend by hashing dist/index.html. Vite stamps content-hashed asset names
// into that file each build, so the digest is a reliable "did the deploy
// change?" signal. Falls back to "dev" when the frontend hasn't been built.
func buildVersion() string {
	data, err := fs.ReadFile(web.DistFS, "dist/index.html")
	if err != nil {
		return "dev"
	}
	sum := sha256.Sum256(data)
	return hex.EncodeToString(sum[:])[:12]
}

// spaHandler serves the embedded web/dist as a single-page app: static files
// when they exist, falling back to index.html for unknown paths. If the
// frontend hasn't been built yet, it returns a friendly dev hint instead.
func spaHandler() http.HandlerFunc {
	sub, err := fs.Sub(web.DistFS, "dist")
	if err != nil {
		log.Fatalf("embed sub: %v", err)
	}

	if _, err := fs.Stat(sub, "index.html"); errors.Is(err, fs.ErrNotExist) {
		return func(w http.ResponseWriter, _ *http.Request) {
			w.Header().Set("Content-Type", "text/plain; charset=utf-8")
			w.WriteHeader(http.StatusOK)
			_, _ = w.Write([]byte("Petal backend is running, but the frontend isn't built yet.\n" +
				"Run `npm run build` in web/, or use `npm run dev` for the dev server on :5173.\n"))
		}
	}

	fileServer := http.FileServer(http.FS(sub))
	return func(w http.ResponseWriter, req *http.Request) {
		p := strings.TrimPrefix(req.URL.Path, "/")
		if p == "" {
			p = "index.html"
		}
		if _, err := fs.Stat(sub, p); errors.Is(err, fs.ErrNotExist) {
			// Unknown path → let the SPA router handle it.
			req2 := new(http.Request)
			*req2 = *req
			req2.URL.Path = "/"
			fileServer.ServeHTTP(w, req2)
			return
		}
		fileServer.ServeHTTP(w, req)
	}
}