Rewrite using Relm4

Yes, this is a monster commit but at this stage I'm the only one working
on this project anyway. Further commits will follow Best Practises™
again.

src/persist/data_manager.rs

@@ -0,0 +1,82 @@
+use std::env::var_os;
+use std::sync::OnceLock;
+
+use gtk4::gdk::Texture;
+
+use crate::persist::common::concat_os_str;
+use crate::persist::file_system_manager::FileSystemManager;
+use crate::persist::sqlite_manager::SqliteManager;
+use crate::views::overview::{FilmOverview, SeriesOverview};
+
+
+
+static SQLITE_MANAGER: OnceLock<SqliteManager> = OnceLock::new();
+static FILE_SYSTEM_MANAGER: OnceLock<FileSystemManager> = OnceLock::new();
+
+macro_rules! sqlite_manager {
+  () => {
+    SQLITE_MANAGER
+      .get()
+      .expect("SQLite manager should be initialized")
+  };
+}
+
+macro_rules! fs_manager {
+  () => {
+    FILE_SYSTEM_MANAGER
+      .get()
+      .expect("File system manager should be initialized")
+  };
+}
+
+
+
+pub struct DataManager {}
+
+impl DataManager {
+  pub async fn init() -> Result<(), DataManagerError> {
+    let data_dir = match var_os("XDG_DATA_HOME") {
+      Some(xdg_home_data_dir) => concat_os_str!(xdg_home_data_dir, "/zoodex"),
+      None => {
+        let home_dir = var_os("HOME").ok_or(DataManagerError::NoHomeDir)?;
+        concat_os_str!(home_dir, "/.local/share/zoodex")
+      }
+    };
+
+    let sqlite_manager = SqliteManager::new(data_dir.as_os_str()).await?;
+    SQLITE_MANAGER
+      .set(sqlite_manager)
+      .expect("SQLite manager should not already be initialized");
+
+    let fs_manager = FileSystemManager::new(data_dir.as_os_str());
+    FILE_SYSTEM_MANAGER
+      .set(fs_manager)
+      .expect("File system manager should not already be initialized");
+
+    Ok(())
+  }
+
+  pub async fn films_overview() -> Result<Vec<FilmOverview>, DataManagerError> {
+    sqlite_manager!().films_overview().await
+  }
+
+  pub async fn series_overview() -> Result<Vec<SeriesOverview>, DataManagerError> {
+    sqlite_manager!().series_overview().await
+  }
+
+  pub async fn poster(uuid: &str) -> Result<Option<Texture>, DataManagerError> {
+    fs_manager!().poster(uuid).await
+  }
+}
+
+
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum DataManagerError {
+  NoHomeDir,
+  CannotOpenSharedDB,
+  UnknownSharedDBError,
+  CannotOpenLocalDB,
+  UnknownLocalDBError,
+  UnknownTextureError,
+}