From 0f1637439f6825bc44be81fe90e7b37ba3ff5af7 Mon Sep 17 00:00:00 2001
From: Martyn Ranyard <m@rtyn.berlin>
Date: Tue, 5 May 2026 21:41:41 +0200
Subject: [PATCH] validating input files exist

---
 internal/fileflag/go.mod           |  3 +++
 internal/fileflag/inputfileflag.go | 22 ++++++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 internal/fileflag/go.mod
 create mode 100644 internal/fileflag/inputfileflag.go

diff --git a/internal/fileflag/go.mod b/internal/fileflag/go.mod
new file mode 100644
index 0000000..f9db92c
--- /dev/null
+++ b/internal/fileflag/go.mod
@@ -0,0 +1,3 @@
+module internal/fileflag
+
+go 1.26.2
diff --git a/internal/fileflag/inputfileflag.go b/internal/fileflag/inputfileflag.go
new file mode 100644
index 0000000..60d8b1b
--- /dev/null
+++ b/internal/fileflag/inputfileflag.go
@@ -0,0 +1,22 @@
+package fileflag
+
+import "os"
+
+type InputFileFlag string
+
+func (file *InputFileFlag) String() string {
+	return string(*file)
+}
+
+func (file *InputFileFlag) Set(v string) error {
+	_, err := os.OpenFile(v, os.O_RDONLY, 0o644)
+	if err != nil {
+		return err
+	}
+	*file = InputFileFlag(v)
+	return nil
+}
+
+func (file *InputFileFlag) Type() string {
+	return "inputFileName"
+}