Refactored, added comprehensive testing.

input/stdin.go

@@ -0,0 +1,28 @@
+package input
+
+import (
+	"io"
+	"os"
+)
+
+// DetectStdin checks if stdin contains piped data and reads it.
+// Returns content and true if stdin is a pipe/file, empty string and false if terminal.
+func DetectStdin() (string, bool) {
+	stat, err := os.Stdin.Stat()
+	if err != nil {
+		return "", false
+	}
+
+	// Terminal (character device) = no stdin data
+	if (stat.Mode() & os.ModeCharDevice) != 0 {
+		return "", false
+	}
+
+	// Pipe or file redirection detected
+	content, err := io.ReadAll(os.Stdin)
+	if err != nil {
+		return "", false
+	}
+
+	return string(content), true
+}