feat: add fingerprint command to agent (#1726)

Co-authored-by: henrygd <hank@henrygd.me>

agent/fingerprint_test.go

@@ -0,0 +1,103 @@
+//go:build testing
+// +build testing
+
+package agent
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetFingerprint(t *testing.T) {
+	t.Run("reads existing fingerprint from file", func(t *testing.T) {
+		dir := t.TempDir()
+		expected := "abc123def456"
+		err := os.WriteFile(filepath.Join(dir, fingerprintFileName), []byte(expected), 0644)
+		require.NoError(t, err)
+
+		fp := GetFingerprint(dir, "", "")
+		assert.Equal(t, expected, fp)
+	})
+
+	t.Run("trims whitespace from file", func(t *testing.T) {
+		dir := t.TempDir()
+		err := os.WriteFile(filepath.Join(dir, fingerprintFileName), []byte("  abc123  \n"), 0644)
+		require.NoError(t, err)
+
+		fp := GetFingerprint(dir, "", "")
+		assert.Equal(t, "abc123", fp)
+	})
+
+	t.Run("generates fingerprint when file does not exist", func(t *testing.T) {
+		dir := t.TempDir()
+		fp := GetFingerprint(dir, "", "")
+		assert.NotEmpty(t, fp)
+	})
+
+	t.Run("generates fingerprint when dataDir is empty", func(t *testing.T) {
+		fp := GetFingerprint("", "", "")
+		assert.NotEmpty(t, fp)
+	})
+
+	t.Run("generates consistent fingerprint for same inputs", func(t *testing.T) {
+		fp1 := GetFingerprint("", "myhost", "mycpu")
+		fp2 := GetFingerprint("", "myhost", "mycpu")
+		assert.Equal(t, fp1, fp2)
+	})
+
+	t.Run("prefers saved fingerprint over generated", func(t *testing.T) {
+		dir := t.TempDir()
+		require.NoError(t, SaveFingerprint(dir, "saved-fp"))
+
+		fp := GetFingerprint(dir, "anyhost", "anycpu")
+		assert.Equal(t, "saved-fp", fp)
+	})
+}
+
+func TestSaveFingerprint(t *testing.T) {
+	t.Run("saves fingerprint to file", func(t *testing.T) {
+		dir := t.TempDir()
+		err := SaveFingerprint(dir, "abc123")
+		require.NoError(t, err)
+
+		content, err := os.ReadFile(filepath.Join(dir, fingerprintFileName))
+		require.NoError(t, err)
+		assert.Equal(t, "abc123", string(content))
+	})
+
+	t.Run("overwrites existing fingerprint", func(t *testing.T) {
+		dir := t.TempDir()
+		require.NoError(t, SaveFingerprint(dir, "old"))
+		require.NoError(t, SaveFingerprint(dir, "new"))
+
+		content, err := os.ReadFile(filepath.Join(dir, fingerprintFileName))
+		require.NoError(t, err)
+		assert.Equal(t, "new", string(content))
+	})
+}
+
+func TestDeleteFingerprint(t *testing.T) {
+	t.Run("deletes existing fingerprint", func(t *testing.T) {
+		dir := t.TempDir()
+		fp := filepath.Join(dir, fingerprintFileName)
+		err := os.WriteFile(fp, []byte("abc123"), 0644)
+		require.NoError(t, err)
+
+		err = DeleteFingerprint(dir)
+		require.NoError(t, err)
+
+		// Verify file is gone
+		_, err = os.Stat(fp)
+		assert.True(t, os.IsNotExist(err))
+	})
+
+	t.Run("no error when file does not exist", func(t *testing.T) {
+		dir := t.TempDir()
+		err := DeleteFingerprint(dir)
+		assert.NoError(t, err)
+	})
+}