package main

import (
	"encoding/json"
	"errors"
	"flag"
	"io"
	"io/fs"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"sync"
	"time"
)

type Event struct {
	ID        string `json:"id"`
	Type      string `json:"type"`
	At        int64  `json:"at"`
	Note      string `json:"note"`
	PhotoID   string `json:"photoId,omitempty"`
	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) }

type Store struct {
	path string
	mu   sync.Mutex
	data map[string]Event
}

func newStore(path string) (*Store, error) {
	s := &Store{path: path, data: map[string]Event{}}
	if err := s.load(); err != nil {
		return nil, err
	}
	return s, nil
}

func (s *Store) load() error {
	f, err := os.Open(s.path)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			return nil
		}
		return err
	}
	defer f.Close()
	var evs []Event
	if err := json.NewDecoder(f).Decode(&evs); err != nil {
		if errors.Is(err, io.EOF) {
			return nil
		}
		return err
	}
	for _, e := range evs {
		s.data[e.ID] = e
	}
	return nil
}

// Caller must hold s.mu.
func (s *Store) saveLocked() error {
	if err := os.MkdirAll(filepath.Dir(s.path), 0o755); err != nil {
		return err
	}
	tmp := s.path + ".tmp"
	f, err := os.Create(tmp)
	if err != nil {
		return err
	}
	evs := make([]Event, 0, len(s.data))
	for _, e := range s.data {
		evs = append(evs, e)
	}
	enc := json.NewEncoder(f)
	enc.SetIndent("", "  ")
	if err := enc.Encode(evs); err != nil {
		f.Close()
		os.Remove(tmp)
		return err
	}
	if err := f.Close(); err != nil {
		return err
	}
	return os.Rename(tmp, s.path)
}

// sync merges client events into the store using last-write-wins by UpdatedAt,
// then returns the full merged set.
func (s *Store) sync(client []Event) ([]Event, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	for _, ce := range client {
		if ce.ID == "" {
			continue
		}
		existing, ok := s.data[ce.ID]
		if !ok || ce.UpdatedAt > existing.UpdatedAt {
			s.data[ce.ID] = ce
		}
	}
	if err := s.saveLocked(); err != nil {
		return nil, err
	}
	out := make([]Event, 0, len(s.data))
	for _, e := range s.data {
		out = append(out, e)
	}
	return out, nil
}

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

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

type cacheControlFS struct {
	root http.FileSystem
}

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

func main() {
	addr := flag.String("addr", ":8080", "listen address (e.g. :8080 or 0.0.0.0:8080)")
	dataPath := flag.String("data", "events.json", "path to events JSON file")
	staticDir := flag.String("static", "", "directory of static files to serve")
	flag.Parse()

	store, err := newStore(*dataPath)
	if err != nil {
		log.Fatalf("load store: %v", err)
	}

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

	mux := http.NewServeMux()

	mux.HandleFunc("/api/events/sync", 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(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(),
		})
	})

	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", 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()

		dstPath := filepath.Join(photosDir, 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 JPEG. Photos are immutable per ID
	// so we mark them as long-lived; both browser and SW can cache freely.
	mux.HandleFunc("/api/photos/", 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, 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", "public, max-age=31536000, immutable")
		http.ServeContent(w, r, path, stat.ModTime(), f)
	})

	if *staticDir != "" {
		fileServer := http.FileServer(http.Dir(*staticDir))
		mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
			// PWA: sw.js and manifest.json must revalidate so updates propagate.
			if r.URL.Path == "/sw.js" || 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())
}