package main

import (
	"bytes"
	"crypto/sha256"
	"database/sql"
	"encoding/hex"
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"io"
	"io/fs"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"sync"
	"time"

	_ "modernc.org/sqlite"
)

type Event struct {
	ID         string  `json:"id"`
	Type       string  `json:"type"`
	At         int64   `json:"at"`
	Note       string  `json:"note"`
	PhotoID    string  `json:"photoId,omitempty"`
	Weight     float64 `json:"weight,omitempty"` // kilograms, for "weight" events
	ExerciseID string  `json:"exerciseId,omitempty"` // for "training" events
	UpdatedAt  int64   `json:"updatedAt"`
	Deleted    bool    `json:"deleted,omitempty"`
}

// Exercise is a user-defined training exercise (e.g. "Sit", "Leash walking"):
// a name plus optional instruction text. Training sessions reference one by
// ExerciseID on the event. Exercises sync exactly like events: UUID ids,
// last-write-wins on UpdatedAt, tombstoned deletes.
type Exercise struct {
	ID        string `json:"id"`
	Name      string `json:"name"`
	Note      string `json:"note"` // instructions / reminder how to do it
	UpdatedAt int64  `json:"updatedAt"`
	Deleted   bool   `json:"deleted,omitempty"`
}

var uuidRE = regexp.MustCompile(`^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$`)

func validUUID(s string) bool { return uuidRE.MatchString(s) }

var birthdayRE = regexp.MustCompile(`^\d{4}-\d{2}-\d{2}$`)

func validBirthday(s string) bool { return s == "" || birthdayRE.MatchString(s) }

// Config is the shared puppy profile (name + birthday). It lives on the host so
// every client sees the same values without configuring each device. UpdatedAt
// drives last-write-wins, mirroring how events sync.
type Config struct {
	Name      string `json:"name"`
	Birthday  string `json:"birthday"`
	UpdatedAt int64  `json:"updatedAt"`
}

type ConfigStore struct {
	db *sql.DB
}

func newConfigStore(db *sql.DB) *ConfigStore {
	return &ConfigStore{db: db}
}

func (cs *ConfigStore) get(userID string) Config {
	var c Config
	// One profile row per user. A missing row is the pre-configuration state,
	// so a zero-value Config is the right answer.
	err := cs.db.QueryRow(
		`SELECT name, birthday, updated FROM config WHERE user_id = ?`, userID,
	).Scan(&c.Name, &c.Birthday, &c.UpdatedAt)
	if err != nil && !errors.Is(err, sql.ErrNoRows) {
		log.Printf("config get: %v", err)
	}
	return c
}

// merge applies an incoming config for one user with last-write-wins by
// UpdatedAt and returns the resulting stored config (which the caller sends back).
func (cs *ConfigStore) merge(userID string, in Config) (Config, error) {
	// The upsert's WHERE clause enforces last-write-wins: the incoming row only
	// replaces the stored one when it is strictly newer.
	_, err := cs.db.Exec(`
		INSERT INTO config (user_id, name, birthday, updated)
		VALUES (?, ?, ?, ?)
		ON CONFLICT(user_id) DO UPDATE SET
			name = excluded.name, birthday = excluded.birthday, updated = excluded.updated
		WHERE excluded.updated > config.updated`,
		userID, in.Name, in.Birthday, in.UpdatedAt)
	if err != nil {
		return Config{}, err
	}
	return cs.get(userID), nil
}

type Store struct {
	db *sql.DB
}

func newStore(db *sql.DB) *Store {
	return &Store{db: db}
}

// sync merges one user's client events into the store using last-write-wins by
// UpdatedAt, then returns that user's full merged set (tombstones included, as
// they must propagate).
func (s *Store) sync(userID string, client []Event) ([]Event, error) {
	tx, err := s.db.Begin()
	if err != nil {
		return nil, err
	}
	defer tx.Rollback()

	// The WHERE clause on the upsert is the last-write-wins rule: an incoming
	// event only overwrites the stored one when its updatedAt is strictly newer.
	// The `events.user_id = excluded.user_id` guard means one user can never
	// clobber another's row even if a client forges a colliding event ID —
	// the row stays put and, because reads are scoped, stays invisible to them.
	stmt, err := tx.Prepare(`
		INSERT INTO events (id, type, at, note, photo_id, weight, exercise_id, updated, deleted, user_id)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
		ON CONFLICT(id) DO UPDATE SET
			type = excluded.type, at = excluded.at, note = excluded.note,
			photo_id = excluded.photo_id, weight = excluded.weight,
			exercise_id = excluded.exercise_id,
			updated = excluded.updated, deleted = excluded.deleted
		WHERE excluded.updated > events.updated
		  AND events.user_id = excluded.user_id`)
	if err != nil {
		return nil, err
	}
	defer stmt.Close()

	for _, ce := range client {
		if ce.ID == "" {
			continue
		}
		if _, err := stmt.Exec(
			ce.ID, ce.Type, ce.At, ce.Note, ce.PhotoID, ce.Weight, ce.ExerciseID, ce.UpdatedAt, ce.Deleted, userID,
		); err != nil {
			return nil, err
		}
	}
	if err := tx.Commit(); err != nil {
		return nil, err
	}
	return s.all(userID)
}

// all returns one user's events, tombstones included.
func (s *Store) all(userID string) ([]Event, error) {
	rows, err := s.db.Query(
		`SELECT id, type, at, note, photo_id, weight, exercise_id, updated, deleted
		   FROM events WHERE user_id = ?`, userID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := make([]Event, 0)
	for rows.Next() {
		var e Event
		if err := rows.Scan(
			&e.ID, &e.Type, &e.At, &e.Note, &e.PhotoID, &e.Weight, &e.ExerciseID, &e.UpdatedAt, &e.Deleted,
		); err != nil {
			return nil, err
		}
		out = append(out, e)
	}
	return out, rows.Err()
}

// ExerciseStore mirrors Store for the exercises collection: same LWW sync by
// UpdatedAt, same user_id guard against cross-user id collisions, same
// tombstone propagation.
type ExerciseStore struct {
	db *sql.DB
}

func newExerciseStore(db *sql.DB) *ExerciseStore {
	return &ExerciseStore{db: db}
}

func (s *ExerciseStore) sync(userID string, client []Exercise) ([]Exercise, error) {
	tx, err := s.db.Begin()
	if err != nil {
		return nil, err
	}
	defer tx.Rollback()

	stmt, err := tx.Prepare(`
		INSERT INTO exercises (id, name, note, updated, deleted, user_id)
		VALUES (?, ?, ?, ?, ?, ?)
		ON CONFLICT(id) DO UPDATE SET
			name = excluded.name, note = excluded.note,
			updated = excluded.updated, deleted = excluded.deleted
		WHERE excluded.updated > exercises.updated
		  AND exercises.user_id = excluded.user_id`)
	if err != nil {
		return nil, err
	}
	defer stmt.Close()

	for _, ce := range client {
		if ce.ID == "" {
			continue
		}
		if _, err := stmt.Exec(
			ce.ID, ce.Name, ce.Note, ce.UpdatedAt, ce.Deleted, userID,
		); err != nil {
			return nil, err
		}
	}
	if err := tx.Commit(); err != nil {
		return nil, err
	}
	return s.all(userID)
}

func (s *ExerciseStore) all(userID string) ([]Exercise, error) {
	rows, err := s.db.Query(
		`SELECT id, name, note, updated, deleted
		   FROM exercises WHERE user_id = ?`, userID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := make([]Exercise, 0)
	for rows.Next() {
		var e Exercise
		if err := rows.Scan(&e.ID, &e.Name, &e.Note, &e.UpdatedAt, &e.Deleted); err != nil {
			return nil, err
		}
		out = append(out, e)
	}
	return out, rows.Err()
}

// openDB opens (creating if needed) the SQLite database and ensures the schema
// exists. WAL mode plays nicely with concurrent readers during a sync write;
// busy_timeout avoids spurious "database is locked" errors under contention.
func openDB(path string) (*sql.DB, error) {
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return nil, err
	}
	db, err := sql.Open("sqlite", path)
	if err != nil {
		return nil, err
	}
	for _, pragma := range []string{
		`PRAGMA journal_mode = WAL`,
		`PRAGMA busy_timeout = 5000`,
		`PRAGMA synchronous = NORMAL`,
	} {
		if _, err := db.Exec(pragma); err != nil {
			db.Close()
			return nil, err
		}
	}
	// Fresh-install schema. Every row is scoped to a user_id; the empty string
	// is the "ownerless" bucket that legacy single-tenant data lands in until
	// the first account adopts it (see Auth.adopt).
	schema := `
		CREATE TABLE IF NOT EXISTS events (
			id          TEXT PRIMARY KEY,
			type        TEXT NOT NULL DEFAULT '',
			at          INTEGER NOT NULL DEFAULT 0,
			note        TEXT NOT NULL DEFAULT '',
			photo_id    TEXT NOT NULL DEFAULT '',
			weight      REAL NOT NULL DEFAULT 0,
			exercise_id TEXT NOT NULL DEFAULT '',
			updated     INTEGER NOT NULL DEFAULT 0,
			deleted     INTEGER NOT NULL DEFAULT 0,
			user_id     TEXT NOT NULL DEFAULT ''
		);
		CREATE INDEX IF NOT EXISTS idx_events_user ON events(user_id);
		CREATE TABLE IF NOT EXISTS exercises (
			id      TEXT PRIMARY KEY,
			name    TEXT NOT NULL DEFAULT '',
			note    TEXT NOT NULL DEFAULT '',
			updated INTEGER NOT NULL DEFAULT 0,
			deleted INTEGER NOT NULL DEFAULT 0,
			user_id TEXT NOT NULL DEFAULT ''
		);
		CREATE INDEX IF NOT EXISTS idx_exercises_user ON exercises(user_id);
		CREATE TABLE IF NOT EXISTS config (
			user_id  TEXT PRIMARY KEY,
			name     TEXT NOT NULL DEFAULT '',
			birthday TEXT NOT NULL DEFAULT '',
			updated  INTEGER NOT NULL DEFAULT 0
		);
		CREATE TABLE IF NOT EXISTS users (
			id       TEXT PRIMARY KEY,
			email    TEXT NOT NULL UNIQUE COLLATE NOCASE,
			password TEXT NOT NULL,
			created  INTEGER NOT NULL
		);
		CREATE TABLE IF NOT EXISTS sessions (
			token   TEXT PRIMARY KEY,
			user_id TEXT NOT NULL,
			created INTEGER NOT NULL,
			expires INTEGER NOT NULL
		);`
	if _, err := db.Exec(schema); err != nil {
		db.Close()
		return nil, err
	}
	if err := migrateSchema(db); err != nil {
		db.Close()
		return nil, err
	}
	return db, nil
}

// migrateSchema upgrades a single-tenant database (from before accounts existed)
// in place: it adds events.user_id and rewrites the config table from its
// old single-row (id = 1) shape to one keyed by user_id. Pre-accounts data ends
// up ownerless (user_id = ”), ready for the first account to adopt. It is a
// no-op on a fresh DB, where openDB already created the current schema.
func migrateSchema(db *sql.DB) error {
	has, err := columnExists(db, "events", "user_id")
	if err != nil {
		return err
	}
	if !has {
		if _, err := db.Exec(`ALTER TABLE events ADD COLUMN user_id TEXT NOT NULL DEFAULT ''`); err != nil {
			return err
		}
		if _, err := db.Exec(`CREATE INDEX IF NOT EXISTS idx_events_user ON events(user_id)`); err != nil {
			return err
		}
	}
	hasExercise, err := columnExists(db, "events", "exercise_id")
	if err != nil {
		return err
	}
	if !hasExercise {
		if _, err := db.Exec(`ALTER TABLE events ADD COLUMN exercise_id TEXT NOT NULL DEFAULT ''`); err != nil {
			return err
		}
	}
	oldConfig, err := columnExists(db, "config", "id")
	if err != nil {
		return err
	}
	if oldConfig {
		// Rebuild config keyed by user_id, moving the lone id=1 row into the
		// ownerless bucket.
		stmts := []string{
			`ALTER TABLE config RENAME TO config_old`,
			`CREATE TABLE config (
				user_id  TEXT PRIMARY KEY,
				name     TEXT NOT NULL DEFAULT '',
				birthday TEXT NOT NULL DEFAULT '',
				updated  INTEGER NOT NULL DEFAULT 0
			)`,
			`INSERT INTO config (user_id, name, birthday, updated)
				SELECT '', name, birthday, updated FROM config_old WHERE id = 1`,
			`DROP TABLE config_old`,
		}
		for _, s := range stmts {
			if _, err := db.Exec(s); err != nil {
				return err
			}
		}
	}
	return nil
}

// columnExists reports whether the given table has a column of the given name.
// A missing table reports false (no error), which is what fresh installs want.
func columnExists(db *sql.DB, table, col string) (bool, error) {
	rows, err := db.Query(`SELECT name FROM pragma_table_info(?)`, table)
	if err != nil {
		return false, err
	}
	defer rows.Close()
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			return false, err
		}
		if name == col {
			return true, nil
		}
	}
	return false, rows.Err()
}

// migrateJSON imports a pre-SQLite events.json / config.json sitting in dataDir
// into an otherwise-empty database, then renames each file to *.imported so the
// import runs exactly once. It is a no-op when the DB already holds data or the
// legacy files are absent.
func migrateJSON(db *sql.DB, dataDir string) error {
	if err := importEvents(db, filepath.Join(dataDir, "events.json")); err != nil {
		return err
	}
	return importConfig(db, filepath.Join(dataDir, "config.json"))
}

func importEvents(db *sql.DB, path string) error {
	var n int
	if err := db.QueryRow(`SELECT COUNT(*) FROM events`).Scan(&n); err != nil {
		return err
	}
	if n > 0 {
		return nil // DB already has data; never clobber it
	}
	f, err := os.Open(path)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			return nil
		}
		return err
	}
	var evs []Event
	dec := json.NewDecoder(f)
	err = dec.Decode(&evs)
	f.Close()
	if err != nil && !errors.Is(err, io.EOF) {
		return err
	}
	// Imported as ownerless (user_id = ""); the first account to register adopts
	// them. Mirrors how in-place schema migration parks legacy rows.
	store := newStore(db)
	if _, err := store.sync("", evs); err != nil {
		return err
	}
	log.Printf("migrated %d events from %s", len(evs), path)
	return os.Rename(path, path+".imported")
}

func importConfig(db *sql.DB, path string) error {
	var n int
	if err := db.QueryRow(`SELECT COUNT(*) FROM config`).Scan(&n); err != nil {
		return err
	}
	if n > 0 {
		return nil
	}
	f, err := os.Open(path)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			return nil
		}
		return err
	}
	var c Config
	dec := json.NewDecoder(f)
	err = dec.Decode(&c)
	f.Close()
	if err != nil && !errors.Is(err, io.EOF) {
		return err
	}
	if c.UpdatedAt == 0 {
		// Nothing meaningful to import; leave config empty.
		return os.Rename(path, path+".imported")
	}
	// Ownerless until the first account adopts it (see importEvents).
	if _, err := newConfigStore(db).merge("", c); err != nil {
		return err
	}
	log.Printf("migrated config from %s", path)
	return os.Rename(path, path+".imported")
}

type syncRequest struct {
	Events []Event `json:"events"`
}

type syncResponse struct {
	Events    []Event `json:"events"`
	ServerNow int64   `json:"serverNow"`
}

type exerciseSyncRequest struct {
	Exercises []Exercise `json:"exercises"`
}

type exerciseSyncResponse struct {
	Exercises []Exercise `json:"exercises"`
}

type cacheControlFS struct {
	root http.FileSystem
}

func (c cacheControlFS) Open(name string) (http.File, error) { return c.root.Open(name) }

// swVersion computes a short content hash over the static assets the service
// worker caches. The hash is substituted into sw.js at serve time (see
// serveSW), so the served worker changes whenever any asset changes — that byte
// difference is what makes the browser install a new worker and prompt to
// reload. Results are memoised and only recomputed when a file's size or modtime
// changes, so the steady state is a handful of cheap stats.
type swVersion struct {
	dir   string
	files []string

	mu   sync.Mutex
	sig  string // signature of (name,size,modtime) across files
	hash string
}

func newSWVersion(dir string) *swVersion {
	// The assets the SW caches and that actually change between builds. sw.js
	// itself is excluded: it carries the placeholder, so hashing it would be
	// circular and it never changes except when we edit it here.
	return &swVersion{
		dir:   dir,
		files: []string{"index.html", "style.css", "app.js", "manifest.json", "icon.svg"},
	}
}

func (v *swVersion) hashHex() string {
	v.mu.Lock()
	defer v.mu.Unlock()

	var sb strings.Builder
	for _, name := range v.files {
		if info, err := os.Stat(filepath.Join(v.dir, name)); err == nil {
			fmt.Fprintf(&sb, "%s:%d:%d;", name, info.Size(), info.ModTime().UnixNano())
		}
	}
	sig := sb.String()
	if sig == v.sig && v.hash != "" {
		return v.hash
	}

	h := sha256.New()
	for _, name := range v.files {
		f, err := os.Open(filepath.Join(v.dir, name))
		if err != nil {
			continue
		}
		_, _ = io.Copy(h, f)
		f.Close()
	}
	v.sig = sig
	v.hash = hex.EncodeToString(h.Sum(nil))[:12]
	return v.hash
}

// serveSW renders sw.js with the current build hash substituted for its
// placeholder. no-cache lets the browser refetch and byte-compare on each
// update check; the substituted hash is what actually differs between builds.
func serveSW(w http.ResponseWriter, staticDir string, ver *swVersion) {
	data, err := os.ReadFile(filepath.Join(staticDir, "sw.js"))
	if err != nil {
		http.Error(w, "not found", http.StatusNotFound)
		return
	}
	out := bytes.ReplaceAll(data, []byte("__BUILD_HASH__"), []byte(ver.hashHex()))
	w.Header().Set("Content-Type", "text/javascript; charset=utf-8")
	w.Header().Set("Cache-Control", "no-cache")
	_, _ = w.Write(out)
}

func main() {
	addr := flag.String("addr", ":8080", "listen address (e.g. :8080 or 0.0.0.0:8080)")
	dataPath := flag.String("data", "puppy.db", "path to SQLite database file")
	staticDir := flag.String("static", "", "directory of static files to serve")
	inviteCode := flag.String("invite-code", os.Getenv("PUPPY_INVITE_CODE"),
		"shared secret required to register (env PUPPY_INVITE_CODE); empty disables registration")
	secureCookies := flag.Bool("secure-cookies", false,
		"mark session cookies Secure (enable when served over HTTPS / behind a TLS proxy)")
	flag.Parse()

	db, err := openDB(*dataPath)
	if err != nil {
		log.Fatalf("open db: %v", err)
	}
	defer db.Close()

	// One-time import of any pre-SQLite JSON data sitting next to the DB.
	if err := migrateJSON(db, filepath.Dir(*dataPath)); err != nil {
		log.Fatalf("migrate json: %v", err)
	}

	store := newStore(db)
	configStore := newConfigStore(db)
	exerciseStore := newExerciseStore(db)

	photosDir := filepath.Join(filepath.Dir(*dataPath), "photos")
	if err := os.MkdirAll(photosDir, 0o755); err != nil {
		log.Fatalf("mkdir photos: %v", err)
	}

	auth := newAuth(db, *inviteCode, *secureCookies, photosDir)
	if *inviteCode == "" {
		log.Print("WARNING: no invite code set — registration is disabled (set -invite-code / PUPPY_INVITE_CODE)")
	}

	mux := http.NewServeMux()

	mux.HandleFunc("/api/register", auth.handleRegister)
	mux.HandleFunc("/api/login", auth.handleLogin)
	mux.HandleFunc("/api/logout", auth.handleLogout)
	mux.HandleFunc("/api/me", auth.requireUser(func(w http.ResponseWriter, r *http.Request) {
		switch r.Method {
		case http.MethodGet:
			auth.handleMe(w, r)
		case http.MethodDelete:
			auth.handleDeleteAccount(w, r)
		default:
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		}
	}))

	mux.HandleFunc("/api/events/sync", auth.requireUser(func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}
		var req syncRequest
		if err := json.NewDecoder(io.LimitReader(r.Body, 8<<20)).Decode(&req); err != nil {
			http.Error(w, "bad json: "+err.Error(), http.StatusBadRequest)
			return
		}
		merged, err := store.sync(userID(r), req.Events)
		if err != nil {
			log.Printf("sync: %v", err)
			http.Error(w, "server error", http.StatusInternalServerError)
			return
		}
		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("Cache-Control", "no-store")
		_ = json.NewEncoder(w).Encode(syncResponse{
			Events:    merged,
			ServerNow: time.Now().UnixMilli(),
		})
	}))

	// POST /api/exercises/sync — merge the caller's training exercises, same
	// LWW contract as /api/events/sync.
	mux.HandleFunc("/api/exercises/sync", auth.requireUser(func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}
		var req exerciseSyncRequest
		if err := json.NewDecoder(io.LimitReader(r.Body, 8<<20)).Decode(&req); err != nil {
			http.Error(w, "bad json: "+err.Error(), http.StatusBadRequest)
			return
		}
		merged, err := exerciseStore.sync(userID(r), req.Exercises)
		if err != nil {
			log.Printf("exercises sync: %v", err)
			http.Error(w, "server error", http.StatusInternalServerError)
			return
		}
		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("Cache-Control", "no-store")
		_ = json.NewEncoder(w).Encode(exerciseSyncResponse{Exercises: merged})
	}))

	// GET  /api/config — return the caller's puppy profile.
	// PUT  /api/config — update it (last-write-wins by updatedAt).
	mux.HandleFunc("/api/config", auth.requireUser(func(w http.ResponseWriter, r *http.Request) {
		writeConfig := func(c Config) {
			w.Header().Set("Content-Type", "application/json")
			w.Header().Set("Cache-Control", "no-store")
			_ = json.NewEncoder(w).Encode(c)
		}
		switch r.Method {
		case http.MethodGet:
			writeConfig(configStore.get(userID(r)))
		case http.MethodPut, http.MethodPost:
			var in Config
			if err := json.NewDecoder(io.LimitReader(r.Body, 1<<16)).Decode(&in); err != nil {
				http.Error(w, "bad json: "+err.Error(), http.StatusBadRequest)
				return
			}
			in.Name = strings.TrimSpace(in.Name)
			if len(in.Name) > 100 {
				in.Name = in.Name[:100]
			}
			if !validBirthday(in.Birthday) {
				http.Error(w, "invalid birthday (want YYYY-MM-DD)", http.StatusBadRequest)
				return
			}
			merged, err := configStore.merge(userID(r), in)
			if err != nil {
				log.Printf("config save: %v", err)
				http.Error(w, "server error", http.StatusInternalServerError)
				return
			}
			writeConfig(merged)
		default:
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		}
	}))

	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("ok"))
	})

	// POST /api/photos — multipart upload with form fields `id` (UUID) and
	// `file` (JPEG). The client generates the ID so the event referencing
	// the photo can be written before the upload round-trips.
	mux.HandleFunc("/api/photos", auth.requireUser(func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}
		r.Body = http.MaxBytesReader(w, r.Body, 15<<20)
		if err := r.ParseMultipartForm(15 << 20); err != nil {
			http.Error(w, "parse: "+err.Error(), http.StatusBadRequest)
			return
		}
		id := r.FormValue("id")
		if !validUUID(id) {
			http.Error(w, "invalid id", http.StatusBadRequest)
			return
		}
		file, _, err := r.FormFile("file")
		if err != nil {
			http.Error(w, "no file: "+err.Error(), http.StatusBadRequest)
			return
		}
		defer file.Close()

		// Photos live under the owner's directory so a photo can only ever be
		// read back by the account that uploaded it.
		userDir := filepath.Join(photosDir, userID(r))
		if err := os.MkdirAll(userDir, 0o755); err != nil {
			http.Error(w, "mkdir: "+err.Error(), http.StatusInternalServerError)
			return
		}
		dstPath := filepath.Join(userDir, id+".jpg")
		tmp := dstPath + ".tmp"
		dst, err := os.Create(tmp)
		if err != nil {
			http.Error(w, "create: "+err.Error(), http.StatusInternalServerError)
			return
		}
		if _, err := io.Copy(dst, file); err != nil {
			dst.Close()
			os.Remove(tmp)
			http.Error(w, "copy: "+err.Error(), http.StatusInternalServerError)
			return
		}
		if err := dst.Close(); err != nil {
			os.Remove(tmp)
			http.Error(w, "close: "+err.Error(), http.StatusInternalServerError)
			return
		}
		if err := os.Rename(tmp, dstPath); err != nil {
			os.Remove(tmp)
			http.Error(w, "rename: "+err.Error(), http.StatusInternalServerError)
			return
		}

		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("Cache-Control", "no-store")
		_ = json.NewEncoder(w).Encode(map[string]string{"id": id})
	}))

	// GET /api/photos/<id> — serves the caller's own JPEG. Photos are immutable
	// per ID so we mark them as long-lived; the private cache keeps them per
	// user. Serving only from the caller's directory makes ownership implicit.
	mux.HandleFunc("/api/photos/", auth.requireUser(func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet && r.Method != http.MethodHead {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}
		id := strings.TrimPrefix(r.URL.Path, "/api/photos/")
		if !validUUID(id) {
			http.Error(w, "invalid id", http.StatusBadRequest)
			return
		}
		path := filepath.Join(photosDir, userID(r), id+".jpg")
		f, err := os.Open(path)
		if err != nil {
			http.NotFound(w, r)
			return
		}
		defer f.Close()
		stat, err := f.Stat()
		if err != nil {
			http.Error(w, "stat: "+err.Error(), http.StatusInternalServerError)
			return
		}
		w.Header().Set("Content-Type", "image/jpeg")
		w.Header().Set("Cache-Control", "private, max-age=31536000, immutable")
		http.ServeContent(w, r, path, stat.ModTime(), f)
	}))

	if *staticDir != "" {
		fileServer := http.FileServer(http.Dir(*staticDir))
		swVer := newSWVersion(*staticDir)
		mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
			// The service worker is rendered with a per-build hash of the static
			// assets, so any asset change yields a byte-different sw.js — that's
			// what makes the browser detect an update and show the reload prompt.
			if r.URL.Path == "/sw.js" {
				serveSW(w, *staticDir, swVer)
				return
			}
			// PWA: manifest.json must revalidate so updates propagate.
			if r.URL.Path == "/manifest.json" {
				w.Header().Set("Cache-Control", "no-cache")
			}
			// SPA fallback: unknown paths -> index.html (so deep links work).
			if !strings.HasPrefix(r.URL.Path, "/api/") {
				candidate := filepath.Join(*staticDir, filepath.FromSlash(r.URL.Path))
				if r.URL.Path != "/" {
					if info, err := os.Stat(candidate); err != nil || info.IsDir() {
						r.URL.Path = "/"
					}
				}
			}
			fileServer.ServeHTTP(w, r)
		})
	}

	srv := &http.Server{
		Addr:              *addr,
		Handler:           mux,
		ReadHeaderTimeout: 5 * time.Second,
	}
	log.Printf("puppy-tracker listening on %s (data=%s, static=%s)", *addr, *dataPath, *staticDir)
	log.Fatal(srv.ListenAndServe())
}