feat(logs): add initial log loading and tab management improvements

- Implement fetchLastLines API to load initial log entries
- Add addInitialLogs function to useSSE hook for prepending logs
- Improve tab handling with better closable behavior and state management
- Add backend support for fetching last N lines from log files

backend/main.go

@@ -6,12 +6,14 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
+	"bufio"
 	"io/fs"
 	"log"
 	"net/http"
 	"os"
 	"os/signal"
 	"regexp"
+	"strings"
 	"sync"
 	"syscall"
 
@@ -28,6 +30,9 @@ var (
     username string
 )
 
+// Lista global de arquivos de log (apenas argumentos após flags)
+var logFiles []string
+
 // init() é executado antes de main(). É o lugar ideal para configurar flags.
 func init() {
     flag.StringVar(&port, "port", ":8080", "Porta para o servidor web (ex: :8080, 9090)")
@@ -118,7 +123,67 @@ func handleSSE(w http.ResponseWriter, r *http.Request) {
 // handleFiles lista os arquivos de log disponíveis
 func handleFiles(w http.ResponseWriter, r *http.Request) {
     w.Header().Set("Content-Type", "application/json")
-    json.NewEncoder(w).Encode(os.Args[1:])
+    json.NewEncoder(w).Encode(logFiles)
+}
+
+func handleLastLines(w http.ResponseWriter, r *http.Request) {
+    w.Header().Set("Content-Type", "application/json")
+    file := r.URL.Query().Get("file")
+    nParam := r.URL.Query().Get("n")
+    n := 200
+    if nParam != "" {
+        fmt.Sscanf(nParam, "%d", &n)
+    }
+    allowed := false
+    for _, f := range logFiles {
+        if f == file {
+            allowed = true
+            break
+        }
+    }
+    if !allowed {
+        w.WriteHeader(http.StatusBadRequest)
+        w.Write([]byte("arquivo inválido"))
+        return
+    }
+    entries, err := getLastLines(file, n)
+    if err != nil {
+        w.WriteHeader(http.StatusInternalServerError)
+        w.Write([]byte("erro ao ler arquivo"))
+        return
+    }
+    json.NewEncoder(w).Encode(entries)
+}
+
+func getLastLines(filename string, n int) ([]LogEntry, error) {
+    f, err := os.Open(filename)
+    if err != nil {
+        return nil, err
+    }
+    defer f.Close()
+    scanner := bufio.NewScanner(f)
+    buf := make([]string, 0, n)
+    for scanner.Scan() {
+        line := scanner.Text()
+        if len(buf) == n {
+            buf = buf[1:]
+        }
+        buf = append(buf, line)
+    }
+    if err := scanner.Err(); err != nil {
+        return nil, err
+    }
+    tsRe1 := regexp.MustCompile(`\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}`)
+    tsRe2 := regexp.MustCompile(`\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}`)
+    entries := make([]LogEntry, 0, len(buf))
+    for _, line := range buf {
+        t := tsRe1.FindString(line)
+        if t == "" {
+            t = tsRe2.FindString(line)
+        }
+        entries = append(entries, LogEntry{Filename: filename, Line: strings.TrimRight(line, "\r"), Timestamp: t})
+    }
+    return entries, nil
 }
 
 // startTailing inicia o monitoramento dos arquivos
@@ -184,7 +249,7 @@ func requestAuth(w http.ResponseWriter) {
 
 func main() {
     flag.Parse()
-    logFiles := flag.Args()
+    logFiles = flag.Args()
     if len(logFiles) < 1 {
         fmt.Println("Uso: web-tail-pro [opções] <arquivo1.log> <arquivo2.log> ...")
         fmt.Println("\nOpções:")
@@ -212,6 +277,7 @@ func main() {
     mux.Handle("/", http.FileServer(http.FS(distFS)))
     mux.HandleFunc("/logs", handleSSE)
     mux.HandleFunc("/api/files", handleFiles)
+    mux.HandleFunc("/api/last", handleLastLines)
 
     protectedHandler := authMiddleware(mux)