Add safety check for package list validation

pkg/pacman/pacman.go

@@ -13,10 +13,21 @@ import (
 	"github.com/Riyyi/declpac/pkg/pacman/sync"
 )
 
-func Sync(packages []string) (*output.Result, error) {
+func Sync(packages []string, noCheck bool) (*output.Result, error) {
 	start := time.Now()
 	log.Debug("Sync: starting...")
 
+	explicitList, err := read.ExplicitList()
+	if err != nil {
+		return nil, err
+	}
+	explicitCount := len(explicitList)
+
+	if !noCheck && len(packages) < explicitCount/2 {
+		errMsg := "safety check: state packages (%d) less than half of explicitly installed (%d), override with --nocheck"
+		return nil, fmt.Errorf(errMsg, len(packages), explicitCount)
+	}
+
 	list, err := read.List()
 	if err != nil {
 		return nil, err

pkg/pacman/read/read.go

@@ -35,6 +35,25 @@ func List() ([]string, error) {
 	return list, nil
 }
 
+func ExplicitList() ([]string, error) {
+	start := time.Now()
+	log.Debug("ExplicitList: starting...")
+
+	cmd := exec.Command("pacman", "-Qqe")
+	output, err := cmd.Output()
+	if err != nil {
+		return nil, err
+	}
+
+	list := strings.Split(strings.TrimSpace(string(output)), "\n")
+	if len(list) > 0 && list[0] == "" {
+		list = nil
+	}
+
+	log.Debug("ExplicitList: done (%.2fs)", time.Since(start).Seconds())
+	return list, nil
+}
+
 func ListOrphans() ([]string, error) {
 	start := time.Now()
 	log.Debug("ListOrphans: starting...")