plugin: add NewTerminalUI

Closes #611
Closes #591

Co-authored-by: Nicolas Dumazet <nicdumz.commits@gmail.com>

plugin/tui.go

@@ -0,0 +1,78 @@
+package plugin
+
+import (
+	"errors"
+	"fmt"
+
+	"filippo.io/age/internal/term"
+)
+
+// NewTerminalUI returns a [ClientUI] that uses the terminal to request inputs,
+// and the provided functions to display messages and errors.
+//
+// The terminal is reached directly through /dev/tty or CONIN$/CONOUT$,
+// bypassing standard input and output, so this UI can be used even when
+// standard input or output are redirected.
+func NewTerminalUI(printf, warningf func(format string, v ...interface{})) *ClientUI {
+	return &ClientUI{
+		DisplayMessage: func(name, message string) error {
+			printf("%s plugin: %s", name, message)
+			return nil
+		},
+		RequestValue: func(name, message string, isSecret bool) (s string, err error) {
+			defer func() {
+				if err != nil {
+					warningf("could not read value for age-plugin-%s: %v", name, err)
+				}
+			}()
+			if isSecret {
+				secret, err := term.ReadSecret(message)
+				if err != nil {
+					return "", err
+				}
+				return string(secret), nil
+			} else {
+				public, err := term.ReadPublic(message)
+				if err != nil {
+					return "", err
+				}
+				return string(public), nil
+			}
+		},
+		Confirm: func(name, message, yes, no string) (choseYes bool, err error) {
+			defer func() {
+				if err != nil {
+					warningf("could not read value for age-plugin-%s: %v", name, err)
+				}
+			}()
+			if no == "" {
+				message += fmt.Sprintf(" (press enter for %q)", yes)
+				_, err := term.ReadSecret(message)
+				if err != nil {
+					return false, err
+				}
+				return true, nil
+			}
+			message += fmt.Sprintf(" (press [1] for %q or [2] for %q)", yes, no)
+			for {
+				selection, err := term.ReadCharacter(message)
+				if err != nil {
+					return false, err
+				}
+				switch selection {
+				case '1':
+					return true, nil
+				case '2':
+					return false, nil
+				case '\x03': // CTRL-C
+					return false, errors.New("user cancelled prompt")
+				default:
+					warningf("reading value for age-plugin-%s: invalid selection %q", name, selection)
+				}
+			}
+		},
+		WaitTimer: func(name string) {
+			printf("waiting on %s plugin...", name)
+		},
+	}
+}