feat: add support for S3 storage backend (#1080)

Co-authored-by: Alessandro (Ale) Segala <43508+ItalyPaleAle@users.noreply.github.com>

backend/internal/storage/s3_test.go

@@ -0,0 +1,44 @@
+package storage
+
+import (
+	"errors"
+	"testing"
+
+	s3types "github.com/aws/aws-sdk-go-v2/service/s3/types"
+	"github.com/aws/smithy-go"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestS3Helpers(t *testing.T) {
+	t.Run("buildObjectKey trims and joins prefix", func(t *testing.T) {
+		tests := []struct {
+			name     string
+			prefix   string
+			path     string
+			expected string
+		}{
+			{name: "no prefix no path", prefix: "", path: "", expected: ""},
+			{name: "prefix no path", prefix: "root", path: "", expected: "root"},
+			{name: "prefix with nested path", prefix: "root", path: "foo/bar/baz", expected: "root/foo/bar/baz"},
+			{name: "trimmed path and prefix", prefix: "root", path: "/foo//bar/", expected: "root/foo/bar"},
+			{name: "no prefix path only", prefix: "", path: "./images/logo.png", expected: "images/logo.png"},
+		}
+
+		for _, tc := range tests {
+			t.Run(tc.name, func(t *testing.T) {
+				s := &s3Storage{
+					bucket: "bucket",
+					prefix: tc.prefix,
+				}
+				assert.Equal(t, tc.expected, s.buildObjectKey(tc.path))
+			})
+		}
+	})
+
+	t.Run("isS3NotFound detects expected errors", func(t *testing.T) {
+		assert.True(t, isS3NotFound(&smithy.GenericAPIError{Code: "NoSuchKey"}))
+		assert.True(t, isS3NotFound(&smithy.GenericAPIError{Code: "NotFound"}))
+		assert.True(t, isS3NotFound(&s3types.NoSuchKey{}))
+		assert.False(t, isS3NotFound(errors.New("boom")))
+	})
+}