feat: add support for encrypted attachment (#45)

Reviewed-on: #45

crates/chat_ui/src/file.rs

@@ -0,0 +1,32 @@
+use std::path::{Path, PathBuf};
+
+use chat::FileAttachment;
+use gpui::SharedString;
+use nostr_sdk::prelude::*;
+
+/// A file attachment that has been uploaded, but not sent yet.
+///
+/// The local `path` is kept around so the composer can preview
+/// the file without downloading and decrypting it again.
+pub(crate) struct PendingFile {
+    pub file: FileAttachment,
+    pub path: PathBuf,
+}
+
+/// State of the encrypted file attachment of a message
+pub(crate) enum DecryptedFile {
+    Loading,
+    Ready(PathBuf),
+    Failed(SharedString),
+}
+
+/// Result of an upload, either plain or encrypted
+pub(crate) enum Uploaded {
+    Url(Url),
+    File(FileAttachment, PathBuf),
+}
+
+/// A `file://` url for a decrypted file, so it can be opened by the OS
+pub(crate) fn file_url(path: &Path) -> String {
+    format!("file://{}", path.display())
+}