Better modularize clipboard code (add "clip" package; break up TOTP code

clip/copyArgument.go

@@ -0,0 +1,76 @@
+package clip
+
+import (
+	"errors"
+	"fmt"
+	"os"
+
+	"github.com/rwinkhart/go-boilerplate/back"
+	"github.com/rwinkhart/libmutton/crypt"
+)
+
+// CopyArgument copies a field from an entry to the clipboard.
+// If field is -1, it will one-time copy the TOTP code
+// (instead of keeping the clipboard up-to-date).
+func CopyArgument(targetLocation string, field int) error {
+	// ensure targetLocation exists and is a file
+	_, err := back.TargetIsFile(targetLocation, true)
+	if err != nil {
+		return err
+	}
+
+	decSlice, err := crypt.DecryptFileToSlice(targetLocation)
+	if err != nil {
+		return errors.New("unable to decrypt entry: " + err.Error())
+	}
+
+	// handle non-persistent TOTP copy
+	var copySubject string
+	var realField int
+	if field == -1 {
+		realField = 2
+	} else {
+		realField = field
+	}
+
+	// if field exists in entry...
+	if len(decSlice) > realField {
+		if decSlice[realField] == "" {
+			return errors.New("field is empty")
+		}
+
+		if realField == 2 { // TOTP mode
+			if field != -1 {
+				fmt.Println("Clipboard refreshing with the current TOTP code until this process is closed")
+			}
+			errorChan := make(chan error)
+			go TOTPCopier(decSlice[2], field, errorChan, nil) // "done" is not needed because the process runs until the program is killed
+			err = <-errorChan
+			if err != nil { // block until first successful copy
+				return errors.New("error encountered in TOTP refresh process: " + err.Error())
+			}
+		} else { // other
+			copySubject = decSlice[realField]
+		}
+	} else {
+		return errors.New("field does not exist in entry")
+	}
+
+	// copy field to clipboard; launch clipboard clearing process
+	err = CopyString(false, copySubject)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// ClipClearArgument reads the assigned clipboard contents from stdin and passes them to clipClearProcess.
+func ClipClearArgument() error {
+	assignedContents := back.ReadFromStdin()
+	if assignedContents == "" {
+		os.Exit(0) // use os.Exit instead of core.Exit, as this function runs out of a background subprocess that is invisible to the user (will never appear in GUI/TUI environment)
+	}
+	err := clipClearProcess(assignedContents)
+	return err
+}