feat(telegram): split oversized videos into playable parts (#229)

* feat(telegram): split oversized videos losslessly

* fix(telegram): respect Premium upload limits

* fix(telegram): keep split videos in one album

pkg/storagetypes/context.go

@@ -0,0 +1,19 @@
+package storagetypes
+
+import "context"
+
+type sourceCaptionContextKey struct{}
+
+// WithSourceCaption records the source Telegram message caption for storage
+// backends that can preserve it. Calling this function with an empty caption
+// intentionally suppresses a backend-generated fallback caption.
+func WithSourceCaption(ctx context.Context, caption string) context.Context {
+	return context.WithValue(ctx, sourceCaptionContextKey{}, caption)
+}
+
+// SourceCaptionFromContext returns the source caption and whether the caller
+// explicitly supplied one.
+func SourceCaptionFromContext(ctx context.Context) (string, bool) {
+	caption, ok := ctx.Value(sourceCaptionContextKey{}).(string)
+	return caption, ok
+}

pkg/storagetypes/context_test.go

@@ -0,0 +1,24 @@
+package storagetypes
+
+import (
+	"context"
+	"testing"
+)
+
+func TestSourceCaptionContext(t *testing.T) {
+	if _, ok := SourceCaptionFromContext(context.Background()); ok {
+		t.Fatal("caption unexpectedly present on empty context")
+	}
+
+	tests := []string{"original caption", ""}
+	for _, want := range tests {
+		ctx := WithSourceCaption(context.Background(), want)
+		got, ok := SourceCaptionFromContext(ctx)
+		if !ok {
+			t.Fatalf("caption %q was not marked as present", want)
+		}
+		if got != want {
+			t.Fatalf("caption = %q, want %q", got, want)
+		}
+	}
+}