Refactor AsyncView creation into Loader / PostProcessor abstraction

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

4 files changed, 53 insertions, 16 deletions

diff --git a/src/loader.rs b/src/loader.rs
new file mode 100644
index 0000000..2a2d573
--- /dev/null
+++ b/src/loader.rs
@@ -0,0 +1,19 @@
+/// Helper trait to load something and then postprocess it
+///
+/// the load() function might fail, but the PostProcessor::postprocess() function should never fail.
+pub trait Loader {
+    type Output: Sized;
+    type Error: Sized;
+    type PostProcessedOutput: Sized;
+    type PostProcessor: PostProcessor<Self::Output, Output = Self::PostProcessedOutput>;
+
+    fn load(self) -> Result<Self::Output, Self::Error>;
+    fn postprocessor(&self) -> Self::PostProcessor;
+}
+
+pub trait PostProcessor<Object: Sized> {
+    type Output: Sized;
+
+    fn postprocess(&self, o: Object) -> Self::Output;
+}
+
diff --git a/src/main.rs b/src/main.rs
index 26f9a47..174fd71 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -11,6 +11,7 @@ use env_logger::Env;
 mod mailstore;
 mod sidebar;
 mod main_view;
+mod loader;
 mod util;
 
 fn main() -> Result<()> {
diff --git a/src/main_view.rs b/src/main_view.rs
index 9048fb2..6f45296 100644
--- a/src/main_view.rs
+++ b/src/main_view.rs
@@ -11,6 +11,8 @@ use mailparse::ParsedMail;
 use async_std::sync::channel;
 
 use crate::mailstore::{ MailStore, Mail };
+use crate::loader::Loader;
+use crate::loader::PostProcessor;
 
 pub const MAIN_VIEW_NAME: &'static str = "main_view";
 
@@ -69,11 +71,10 @@ impl MainView {
         MainView { tabs }.with_name(MAIN_VIEW_NAME)
     }
 
-    pub fn maildir_loader(&mut self, pb: PathBuf) -> (MaildirLoader, MaildirLoaderPostProcessor) {
+    pub fn maildir_loader(&mut self, pb: PathBuf) -> MaildirLoader {
         debug!("Creating Loader for: {}", pb.display());
-        let maildir_loader = MaildirLoader { maildir_path: pb };
-        let postprocessor = MaildirLoaderPostProcessor;
-        (maildir_loader, postprocessor)
+        let maildir_loader = MaildirLoader(pb);
+        maildir_loader
     }
 
     pub fn add_tab<T: View>(&mut self, id: String, view: T) {
@@ -82,14 +83,17 @@ impl MainView {
 
 }
 
-pub struct MaildirLoader {
-    maildir_path: PathBuf
-}
+pub struct MaildirLoader(PathBuf);
+
+impl Loader for MaildirLoader {
+    type Output = Vec<String>;
+    type Error = String;
+    type PostProcessedOutput = cursive::views::ListView;
+    type PostProcessor = MaildirLoaderPostProcessor;
 
-impl MaildirLoader {
-    pub fn load(self) -> RResult<Vec<String>, String> {
-        debug!("Loading: {}", self.maildir_path.display());
-        MailStore::build_from_path(self.maildir_path).collect::<Result<MailStore>>()
+    fn load(self) -> Result<Self::Output, Self::Error> {
+        debug!("Loading: {}", self.0.display());
+        MailStore::build_from_path(self.0).collect::<Result<MailStore>>()
             .map(|store| {
                 store.cur_mail()
                     .iter()
@@ -107,11 +111,17 @@ impl MaildirLoader {
             })
             .map_err(|e| e.to_string())
     }
+
+    fn postprocessor(&self) -> Self::PostProcessor {
+        MaildirLoaderPostProcessor
+    }
 }
 
 pub struct MaildirLoaderPostProcessor;
-impl MaildirLoaderPostProcessor {
-    pub fn postprocess(&self, list: Vec<String>) -> cursive::views::ListView {
+impl PostProcessor<Vec<String>> for MaildirLoaderPostProcessor {
+    type Output = cursive::views::ListView;
+
+    fn postprocess(&self, list: Vec<String>) -> Self::Output{
         list.into_iter()
             .fold(cursive::views::ListView::new(), |view, elem| {
                 view.child("", cursive::views::TextView::new(elem))
diff --git a/src/sidebar.rs b/src/sidebar.rs
index d0427d5..48b7a6a 100644
--- a/src/sidebar.rs
+++ b/src/sidebar.rs
@@ -9,6 +9,9 @@ use cursive::views::NamedView;
 use cursive_tree_view::TreeView;
 
 use crate::main_view::MainView;
+use crate::main_view::MaildirLoader;
+use crate::loader::PostProcessor;
+use crate::loader::Loader;
 
 #[derive(Debug)]
 pub struct TreeEntry {
@@ -54,7 +57,7 @@ impl Sidebar {
             .flatten();
 
             if let Some(path) = borrow {
-                let (loader, processor) = {
+                let loader = { // Fetch the loader for the view to be created
                     let p = path.clone();
                     siv.call_on_name(crate::main_view::MAIN_VIEW_NAME, move |main_view: &mut MainView| {
                         Some(main_view.maildir_loader(p))
@@ -63,9 +66,12 @@ impl Sidebar {
                     .unwrap()
                 };
 
+                let postprocessor = loader.postprocessor();
+
+                // Construct the AsyncView with the loader job
                 let list_view = cursive_async_view::AsyncView::new_with_bg_creator(&mut siv,
-                    move || { loader.load() },
-                    move |list| { processor.postprocess(list) });
+                    || { loader.load() },
+                    move |list| { postprocessor.postprocess(list) });
 
                 let name = path.file_name()
                     .and_then(OsStr::to_str)
@@ -73,6 +79,7 @@ impl Sidebar {
                     .ok_or_else(|| anyhow!("UTF8 error"))
                     .unwrap();
 
+                // Add the AsyncView to the screen
                 siv.call_on_name(crate::main_view::MAIN_VIEW_NAME, move |main_view: &mut MainView| {
                     Some(main_view.add_tab(name, list_view))
                 });