feat: add emoji reaction support for files

- Implement `ReactionService` to manage file reactions in the database.
- Add `POST /d/{boxID}/f/{fileID}/react` endpoint to handle user reactions.
- Add `GET /emoji/{pack}/{file}` endpoint to serve custom emoji assets.
- Support loading custom emoji packs dynamically from the data directory.
- Update README with instructions on configuring emoji reaction packs.

backend/libs/handlers/download.go

@@ -2,12 +2,15 @@ package handlers
 
 import (
 	"bytes"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
 	"net/http"
+	"net/url"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
 	"time"
 
@@ -26,6 +29,7 @@ type downloadPageData struct {
 	DownloadCount int
 	MaxDownloads  int
 	ExpiresLabel  string
+	EmojiTabs     []emojiTabView
 }
 
 type boxView struct {
@@ -41,6 +45,28 @@ type fileView struct {
 	URL          string
 	DownloadURL  string
 	ThumbnailURL string
+	ReactURL     string
+	Reactions    []reactionView
+	Reacted      bool
+}
+
+type reactionView struct {
+	EmojiID string `json:"emojiId"`
+	URL     string `json:"url"`
+	Label   string `json:"label"`
+	Count   int    `json:"count"`
+}
+
+type emojiTabView struct {
+	ID     string
+	Label  string
+	Emojis []emojiOptionView
+}
+
+type emojiOptionView struct {
+	ID    string `json:"id"`
+	URL   string `json:"url"`
+	Label string `json:"label"`
 }
 
 type previewPageData struct {
@@ -70,13 +96,22 @@ func (a *App) DownloadPage(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	locked := a.uploadService.IsProtected(box) && !a.isBoxUnlocked(r, box)
+	visitorID := a.reactionVisitorID(w, r)
+	reactionsByFile, reactedByFile, err := a.reactionService.SummaryForBox(box.ID, visitorID)
+	if err != nil {
+		a.logger.Warn("failed to load file reactions", withRequestLogAttrs(r, "source", "reactions", "severity", "warn", "code", 4300, "box_id", box.ID, "error", err.Error())...)
+	}
 
 	files := make([]fileView, 0, len(box.Files))
 	if !(locked && box.Obfuscate) {
 		for _, file := range box.Files {
-			files = append(files, a.fileView(box, file))
+			files = append(files, a.fileViewWithReactions(box, file, reactionsByFile[file.ID], reactedByFile[file.ID]))
 		}
 	}
+	emojiTabs, err := a.emojiTabs()
+	if err != nil {
+		a.logger.Warn("failed to load emoji tabs", withRequestLogAttrs(r, "source", "reactions", "severity", "warn", "code", 4301, "box_id", box.ID, "error", err.Error())...)
+	}
 
 	expiresLabel := boxExpiryLabel(box.ExpiresAt, "Jan 2, 2006 15:04 MST")
 	title := "Shared files on Warpbox"
@@ -99,6 +134,7 @@ func (a *App) DownloadPage(w http.ResponseWriter, r *http.Request) {
 			DownloadCount: box.DownloadCount,
 			MaxDownloads:  box.MaxDownloads,
 			ExpiresLabel:  expiresLabel,
+			EmojiTabs:     emojiTabs,
 		},
 	})
 	a.logger.Info("download page viewed", withRequestLogAttrs(r, "source", "download", "severity", "user_activity", "code", 2003, "box_id", box.ID, "locked", locked)...)
@@ -310,6 +346,10 @@ func (a *App) DownloadZip(w http.ResponseWriter, r *http.Request) {
 }
 
 func (a *App) fileView(box services.Box, file services.File) fileView {
+	return a.fileViewWithReactions(box, file, nil, false)
+}
+
+func (a *App) fileViewWithReactions(box services.Box, file services.File, reactions []services.ReactionSummary, reacted bool) fileView {
 	return fileView{
 		ID:           file.ID,
 		Name:         file.Name,
@@ -319,9 +359,171 @@ func (a *App) fileView(box services.Box, file services.File) fileView {
 		URL:          fmt.Sprintf("/d/%s/f/%s", box.ID, file.ID),
 		DownloadURL:  fmt.Sprintf("/d/%s/f/%s/download", box.ID, file.ID),
 		ThumbnailURL: fmt.Sprintf("/d/%s/thumb/%s", box.ID, file.ID),
+		ReactURL:     fmt.Sprintf("/d/%s/f/%s/react", box.ID, file.ID),
+		Reactions:    a.reactionViews(reactions),
+		Reacted:      reacted,
 	}
 }
 
+func (a *App) ReactToFile(w http.ResponseWriter, r *http.Request) {
+	box, file, ok := a.loadFileForRequest(w, r)
+	if !ok {
+		return
+	}
+	if a.uploadService.IsProtected(box) && !a.isBoxUnlocked(r, box) {
+		http.Error(w, "password required", http.StatusUnauthorized)
+		return
+	}
+
+	if err := r.ParseForm(); err != nil {
+		http.Error(w, "invalid reaction", http.StatusBadRequest)
+		return
+	}
+	emojiID := strings.TrimSpace(r.FormValue("emoji_id"))
+	if !a.validEmojiID(emojiID) {
+		http.Error(w, "unknown emoji", http.StatusBadRequest)
+		return
+	}
+
+	visitorID := a.reactionVisitorID(w, r)
+	reactions, err := a.reactionService.Add(box.ID, file.ID, visitorID, emojiID)
+	if errors.Is(err, os.ErrExist) {
+		writeJSON(w, http.StatusConflict, map[string]any{"error": "already reacted"})
+		return
+	}
+	if err != nil {
+		a.logger.Warn("file reaction failed", withRequestLogAttrs(r, "source", "reactions", "severity", "warn", "code", 4302, "box_id", box.ID, "file_id", file.ID, "error", err.Error())...)
+		http.Error(w, "could not save reaction", http.StatusInternalServerError)
+		return
+	}
+
+	a.logger.Info("file reaction added", withRequestLogAttrs(r, "source", "reactions", "severity", "user_activity", "code", 2301, "box_id", box.ID, "file_id", file.ID, "emoji_id", emojiID)...)
+	writeJSON(w, http.StatusCreated, map[string]any{
+		"reactions": a.reactionViews(reactions),
+		"reacted":   true,
+	})
+}
+
+func (a *App) reactionViews(reactions []services.ReactionSummary) []reactionView {
+	views := make([]reactionView, 0, len(reactions))
+	for _, reaction := range reactions {
+		views = append(views, reactionView{
+			EmojiID: reaction.EmojiID,
+			URL:     emojiURL(reaction.EmojiID),
+			Label:   emojiLabel(reaction.EmojiID),
+			Count:   reaction.Count,
+		})
+	}
+	return views
+}
+
+func (a *App) emojiTabs() ([]emojiTabView, error) {
+	root := a.emojiRoot()
+	entries, err := os.ReadDir(root)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	tabs := make([]emojiTabView, 0, len(entries))
+	for _, entry := range entries {
+		if !entry.IsDir() {
+			continue
+		}
+		tabID := entry.Name()
+		files, err := os.ReadDir(filepath.Join(root, tabID))
+		if err != nil {
+			return nil, err
+		}
+		tab := emojiTabView{ID: tabID, Label: emojiTabLabel(tabID)}
+		for _, file := range files {
+			if file.IsDir() || !isEmojiFile(file.Name()) {
+				continue
+			}
+			emojiID := tabID + "/" + file.Name()
+			tab.Emojis = append(tab.Emojis, emojiOptionView{
+				ID:    emojiID,
+				URL:   emojiURL(emojiID),
+				Label: emojiLabel(emojiID),
+			})
+		}
+		sort.Slice(tab.Emojis, func(i, j int) bool { return tab.Emojis[i].ID < tab.Emojis[j].ID })
+		if len(tab.Emojis) > 0 {
+			tabs = append(tabs, tab)
+		}
+	}
+	sort.Slice(tabs, func(i, j int) bool { return tabs[i].ID < tabs[j].ID })
+	return tabs, nil
+}
+
+func (a *App) validEmojiID(id string) bool {
+	id = strings.TrimSpace(id)
+	if id == "" || strings.Contains(id, "\\") || strings.Contains(id, "..") || strings.HasPrefix(id, "/") {
+		return false
+	}
+	parts := strings.Split(id, "/")
+	if len(parts) != 2 || parts[0] == "" || parts[1] == "" || !isEmojiFile(parts[1]) {
+		return false
+	}
+	info, err := os.Stat(filepath.Join(a.emojiRoot(), parts[0], parts[1]))
+	return err == nil && !info.IsDir()
+}
+
+func (a *App) emojiRoot() string {
+	return filepath.Join(a.cfg.DataDir, "emoji")
+}
+
+func (a *App) reactionVisitorID(w http.ResponseWriter, r *http.Request) string {
+	const cookieName = "warpbox_reactor"
+	if cookie, err := r.Cookie(cookieName); err == nil && strings.TrimSpace(cookie.Value) != "" {
+		return cookie.Value
+	}
+	visitorID := services.RandomPublicToken(32)
+	http.SetCookie(w, &http.Cookie{
+		Name:     cookieName,
+		Value:    visitorID,
+		Path:     "/",
+		HttpOnly: true,
+		SameSite: http.SameSiteLaxMode,
+		Secure:   r.TLS != nil,
+		Expires:  time.Now().AddDate(1, 0, 0),
+	})
+	return visitorID
+}
+
+func isEmojiFile(name string) bool {
+	ext := strings.ToLower(filepath.Ext(name))
+	return ext == ".svg" || ext == ".webp" || ext == ".png" || ext == ".jpg" || ext == ".jpeg" || ext == ".gif"
+}
+
+func emojiTabLabel(id string) string {
+	label := strings.NewReplacer("-", " ", "_", " ").Replace(id)
+	if label == "" {
+		return "Emoji"
+	}
+	return strings.ToUpper(label[:1]) + label[1:]
+}
+
+func emojiLabel(id string) string {
+	base := strings.TrimSuffix(filepath.Base(id), filepath.Ext(id))
+	return strings.ReplaceAll(base, "-", " ")
+}
+
+func emojiURL(id string) string {
+	parts := strings.Split(id, "/")
+	if len(parts) != 2 {
+		return ""
+	}
+	return "/emoji/" + url.PathEscape(parts[0]) + "/" + url.PathEscape(parts[1])
+}
+
+func writeJSON(w http.ResponseWriter, status int, value any) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(value)
+}
+
 func (a *App) isBoxUnlocked(r *http.Request, box services.Box) bool {
 	if !a.uploadService.IsProtected(box) {
 		return true