4 files changed, 254 insertions, 0 deletions
diff --git a/internal/config/config.go b/internal/config/config.go
new file mode 100644
index 0000000..3cfe5af
--- /dev/null
+++ b/internal/config/config.go
@@ -0,0 +1,50 @@
+package config
+
+import (
+	"flag"
+	"fmt"
+	"os"
+)
+
+// Configuration holds all the parameters for the SCP operation
+type Configuration struct {
+	Dest          string
+	RemoteUser    string
+	RemoteHost    string
+	RemotePath    string
+	Parallelism   int
+	LockDir       string
+	CipherOption  string
+	Verbose       bool
+	OnlyListFiles bool
+}
+
+// ParseArgs parses command-line arguments and returns a Configuration
+func ParseArgs() Configuration {
+	config := Configuration{
+		LockDir:      "/tmp/scp_lock",
+		Parallelism:  10,
+		CipherOption: "aes128-gcm@openssh.com",
+	}
+
+	flag.StringVar(&config.Dest, "d", "", "Destination directory (local)")
+	flag.StringVar(&config.RemoteUser, "u", "", "Remote username")
+	flag.StringVar(&config.RemoteHost, "h", "", "Remote hostname or IP")
+	flag.StringVar(&config.RemotePath, "r", "", "Remote path")
+	flag.IntVar(&config.Parallelism, "P", 10, "Number of parallel SCP processes")
+	flag.StringVar(&config.LockDir, "L", "/tmp/scp_lock", "Lock directory")
+	flag.StringVar(&config.CipherOption, "c", "aes128-gcm@openssh.com", "SSH cipher option")
+	flag.BoolVar(&config.Verbose, "v", false, "Verbose output")
+	flag.BoolVar(&config.OnlyListFiles, "l", false, "Only list files to be copied, don't copy")
+
+	flag.Parse()
+
+	// Check required parameters
+	if config.Dest == "" || config.RemoteUser == "" || config.RemoteHost == "" || config.RemotePath == "" {
+		flag.Usage()
+		fmt.Println("\nRequired flags: -d, -u, -h, -r")
+		os.Exit(1)
+	}
+
+	return config
+}
diff --git a/internal/local/files.go b/internal/local/files.go
new file mode 100644
index 0000000..e4b4f67
--- /dev/null
+++ b/internal/local/files.go
@@ -0,0 +1,30 @@
+package local
+
+import (
+	"os"
+	"path/filepath"
+)
+
+// GetFiles retrieves a map of files in the local destination directory
+func GetFiles(destDir string) (map[string]bool, error) {
+	files := make(map[string]bool)
+
+	err := filepath.Walk(destDir, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if !info.IsDir() {
+			// Get relative path
+			relPath, err := filepath.Rel(destDir, path)
+			if err != nil {
+				return err
+			}
+			files[relPath] = true
+		}
+
+		return nil
+	})
+
+	return files, err
+}
diff --git a/internal/remote/files.go b/internal/remote/files.go
new file mode 100644
index 0000000..5b89811
--- /dev/null
+++ b/internal/remote/files.go
@@ -0,0 +1,48 @@
+package remote
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"os/exec"
+
+	"gscp/internal/config"
+)
+
+// GetFiles retrieves the list of files from the remote server
+func GetFiles(config config.Configuration) ([]string, error) {
+	if config.Verbose {
+		log.Println("Getting remote file list...")
+	}
+
+	cmd := exec.Command("ssh", fmt.Sprintf("%s@%s", config.RemoteUser, config.RemoteHost),
+		fmt.Sprintf("find '%s' -type f | sed 's|^%s/||'", config.RemotePath, config.RemotePath))
+
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return nil, fmt.Errorf("error creating stdout pipe: %v", err)
+	}
+
+	if err := cmd.Start(); err != nil {
+		return nil, fmt.Errorf("error starting ssh command: %v", err)
+	}
+
+	var files []string
+	scanner := bufio.NewScanner(stdout)
+	for scanner.Scan() {
+		file := scanner.Text()
+		if file != "" {
+			files = append(files, file)
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		return nil, fmt.Errorf("error reading ssh output: %v", err)
+	}
+
+	if err := cmd.Wait(); err != nil {
+		return nil, fmt.Errorf("ssh command failed: %v", err)
+	}
+
+	return files, nil
+}
diff --git a/internal/transfer/transfer.go b/internal/transfer/transfer.go
new file mode 100644
index 0000000..a57b073
--- /dev/null
+++ b/internal/transfer/transfer.go
@@ -0,0 +1,126 @@
+package transfer
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"sync"
+
+	"gscp/internal/config"
+)
+
+// GetDiffFiles computes which files exist on remote but not on local
+func GetDiffFiles(remoteFiles []string, localFiles map[string]bool) []string {
+	var diffFiles []string
+
+	for _, remoteFile := range remoteFiles {
+		if !localFiles[remoteFile] {
+			diffFiles = append(diffFiles, remoteFile)
+		}
+	}
+
+	return diffFiles
+}
+
+// CopyFilesInParallel copies multiple files in parallel from remote to local
+func CopyFilesInParallel(files []string, config config.Configuration) int {
+	if len(files) == 0 {
+		log.Println("No files to copy")
+		return 0
+	}
+
+	var wg sync.WaitGroup
+	sem := make(chan struct{}, config.Parallelism)
+
+	totalFiles := len(files)
+	copiedFiles := 0
+	var mu sync.Mutex
+
+	for _, file := range files {
+		wg.Add(1)
+		go func(file string) {
+			defer wg.Done()
+
+			// Acquire semaphore
+			sem <- struct{}{}
+			defer func() { <-sem }()
+
+			if err := CopyFile(file, config); err != nil {
+				log.Printf("Error copying file %s: %v", file, err)
+			} else {
+				mu.Lock()
+				copiedFiles++
+				if config.Verbose && copiedFiles%10 == 0 {
+					log.Printf("Progress: %d/%d files copied (%.2f%%)",
+						copiedFiles, totalFiles, float64(copiedFiles)/float64(totalFiles)*100)
+				}
+				mu.Unlock()
+			}
+		}(file)
+	}
+
+	wg.Wait()
+	return copiedFiles
+}
+
+// CopyFile copies a single file from remote to local
+func CopyFile(file string, config config.Configuration) error {
+	// Create lock file path by replacing slashes with underscores
+	lockFileName := strings.ReplaceAll(file, "/", "_") + ".lock"
+	lockFilePath := filepath.Join(config.LockDir, lockFileName)
+
+	// Try to create and lock the file
+	lockFile, err := os.OpenFile(lockFilePath, os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		return fmt.Errorf("cannot create lock file: %v", err)
+	}
+	defer lockFile.Close()
+
+	// Create destination directory
+	destDir := filepath.Join(config.Dest, filepath.Dir(file))
+	if err := os.MkdirAll(destDir, 0755); err != nil {
+		return fmt.Errorf("failed to create directory %s: %v", destDir, err)
+	}
+
+	// Check if file already exists in destination
+	destFile := filepath.Join(config.Dest, file)
+	if _, err := os.Stat(destFile); err == nil {
+		// File already exists, skip
+		return nil
+	}
+
+	// Construct scp command
+	src := fmt.Sprintf("%s@%s:%s/%s", config.RemoteUser, config.RemoteHost, config.RemotePath, file)
+	args := []string{
+		"-q", // Quiet mode
+		"-c", config.CipherOption,
+		src,
+		destFile,
+	}
+
+	if config.Verbose {
+		log.Printf("Copying file: %s", file)
+	}
+
+	cmd := exec.Command("scp", args...)
+
+	// Capture stdout and stderr
+	var stdoutBuf, stderrBuf strings.Builder
+	cmd.Stdout = io.MultiWriter(os.Stdout, &stdoutBuf)
+	cmd.Stderr = io.MultiWriter(os.Stderr, &stderrBuf)
+
+	// Execute command
+	err = cmd.Run()
+	if err != nil {
+		return fmt.Errorf("scp failed: %v, stderr: %s", err, stderrBuf.String())
+	}
+
+	// Clean up lock file on success
+	os.Remove(lockFilePath)
+
+	return nil
+}