Calling preview removed hook when help page shown (#125)

* Calling preview removed hook when help page shown

* Better function names and documentation

* syntax fix

3 files changed, 92 insertions, 52 deletions

diff --git a/src/commands/help.rs b/src/commands/help.rs
index a30235f..d47a0f4 100644
--- a/src/commands/help.rs
+++ b/src/commands/help.rs
@@ -27,6 +27,8 @@ pub fn help_loop(
         } else {
             widgets::get_keymap_table(keymap_t, &search_query[1..], sort_by)
         };
+
+        context.remove_external_preview();
         backend.render(TuiHelp::new(&keymap, &mut offset, &search_query));
 
         let event = match context.poll_event() {
diff --git a/src/context/app_context.rs b/src/context/app_context.rs
index 0bdcf28..57178ee 100644
--- a/src/context/app_context.rs
+++ b/src/context/app_context.rs
@@ -1,5 +1,7 @@
 use std::collections::HashSet;
+use std::process;
 use std::sync::mpsc;
+use std::thread;
 use tui::layout::Rect;
 
 use crate::config;
@@ -7,6 +9,8 @@ use crate::context::{
     CommandLineContext, LocalStateContext, MessageQueue, PreviewContext, TabContext, WorkerContext,
 };
 use crate::event::{AppEvent, Events};
+use crate::ui::views;
+use crate::ui::PreviewArea;
 use crate::util::search::SearchPattern;
 use crate::Args;
 use notify::{RecursiveMode, Watcher};
@@ -59,6 +63,9 @@ pub struct AppContext {
     watcher: notify::NullWatcher,
     // list of watched paths; seems not to be possible to get them from a notify::Watcher
     watched_paths: HashSet<path::PathBuf>,
+    // the last preview area (or None if now preview shown) to check if a preview hook script needs
+    // to be called
+    preview_area: Option<PreviewArea>,
 }
 
 impl AppContext {
@@ -94,9 +101,91 @@ impl AppContext {
             config,
             watcher,
             watched_paths,
+            preview_area: None,
         }
     }
 
+    /// Calls the "preview shown hook script" if it's configured.
+    ///
+    /// This method takes the current preview area as argument to check for both, the path of the
+    /// currently previewed file and the geometry of the preview area.
+    fn call_preview_shown_hook(&self, preview_area: PreviewArea) {
+        let preview_options = self.config_ref().preview_options_ref();
+        let preview_shown_hook_script = preview_options.preview_shown_hook_script.as_ref();
+        if let Some(hook_script) = preview_shown_hook_script {
+            let hook_script = hook_script.to_path_buf();
+            let _ = thread::spawn(move || {
+                let _ = process::Command::new(hook_script.as_path())
+                    .arg(preview_area.file_preview_path.as_path())
+                    .arg(preview_area.preview_area.x.to_string())
+                    .arg(preview_area.preview_area.y.to_string())
+                    .arg(preview_area.preview_area.width.to_string())
+                    .arg(preview_area.preview_area.height.to_string())
+                    .status();
+            });
+        }
+    }
+
+    /// Calls the "preview removed hook script" if it's configured.
+    fn call_preview_removed_hook(&self) {
+        let preview_options = self.config_ref().preview_options_ref();
+        let preview_removed_hook_script = preview_options.preview_removed_hook_script.as_ref();
+        if let Some(hook_script) = preview_removed_hook_script {
+            let hook_script = hook_script.to_path_buf();
+            let _ = thread::spawn(|| {
+                let _ = process::Command::new(hook_script).status();
+            });
+        }
+    }
+
+    /// Updates the external preview to the current preview in Joshuto.
+    ///
+    /// The function checks if the current preview content is the same as the preview content which
+    /// has been last communicated to an external preview logic with the preview hook scripts.
+    /// If the preview content has changed, one of the hook scripts is called. Either the "preview
+    /// shown hook", if a preview is shown in Joshuto, or the "preview removed hook", if Joshuto has
+    /// changed from an entry with preview to an entry without a preview.
+    ///
+    /// This function shall be called each time a change of Joshuto's preview can be expected.
+    /// (As of now, it's called in each cycle of the main loop.)
+    pub fn update_external_preview(&mut self) {
+        let layout = &self.ui_context_ref().layout;
+        let new_preview_area = views::calculate_preview(self, layout[2]);
+        match new_preview_area.as_ref() {
+            Some(new) => {
+                let should_preview = if let Some(old) = &self.preview_area {
+                    new.file_preview_path != old.file_preview_path
+                } else {
+                    true
+                };
+                if should_preview {
+                    self.call_preview_shown_hook(new.clone())
+                }
+            }
+            None => self.call_preview_removed_hook(),
+        }
+        self.preview_area = new_preview_area
+    }
+
+    /// Remove the external preview, if any is present.
+    ///
+    /// If the last preview hook script called was the "preview shown hook", this function will
+    /// call the "preview removed hook" to remove any external preview.
+    /// Otherwise it won't do anything.
+    ///
+    /// To restore the external preview, `update_external_preview` is called which will detect the
+    /// difference and call the "preview shown hook" again for the current preview (if any).
+    ///
+    /// This function can be called if an external preview shall be temporarily removed, for example
+    /// when entering the help screen.
+    pub fn remove_external_preview(&mut self) {
+        if let Some(_) = &self.preview_area {
+            self.call_preview_removed_hook();
+            self.preview_area = None;
+        }
+    }
+
+    /// Updates the file system supervision with the currently shown directories.
     pub fn update_watcher(&mut self) {
         // collect the paths that shall be watched...
         let mut new_paths_to_watch: HashSet<path::PathBuf> = HashSet::with_capacity(3);
diff --git a/src/run.rs b/src/run.rs
index 2430e3b..c344814 100644
--- a/src/run.rs
+++ b/src/run.rs
@@ -8,12 +8,9 @@ use crate::tab::JoshutoTab;
 use crate::ui;
 use crate::ui::views;
 use crate::ui::views::TuiView;
-use crate::ui::PreviewArea;
 use crate::util::input;
 use crate::util::to_string::ToString;
 
-use std::process;
-use std::thread;
 use termion::event::{Event, Key};
 use tui::layout::Rect;
 
@@ -36,8 +33,6 @@ pub fn run(
         preview_default::load_preview(context, backend);
     }
 
-    let mut preview_area: Option<PreviewArea> = None;
-
     while context.quit == QuitType::DoNot {
         // do the ui
         if let Ok(area) = backend.terminal_ref().size() {
@@ -48,7 +43,7 @@ pub fn run(
             backend.render(TuiView::new(context));
 
             // invoke preview hooks, if appropriate
-            preview_area = process_preview_on_change(&context, preview_area);
+            context.update_external_preview();
         }
 
         // wait for an event and pop it
@@ -132,49 +127,3 @@ fn calculate_ui_context(context: &mut AppContext, area: Rect) {
     };
     context.ui_context_mut().layout = layout;
 }
-
-fn process_preview_on_change(
-    context: &AppContext,
-    old_preview_area: Option<PreviewArea>,
-) -> Option<PreviewArea> {
-    let config = context.config_ref();
-    let preview_options = config.preview_options_ref();
-
-    let preview_shown_hook_script = preview_options.preview_shown_hook_script.as_ref();
-    let preview_removed_hook_script = preview_options.preview_removed_hook_script.as_ref();
-    let layout = &context.ui_context_ref().layout;
-    let new_preview_area = views::calculate_preview(&context, layout[2]);
-    match new_preview_area.as_ref() {
-        Some(new) => {
-            let should_preview = if let Some(old) = old_preview_area {
-                new.file_preview_path != old.file_preview_path
-            } else {
-                true
-            };
-            if should_preview {
-                if let Some(hook_script) = preview_shown_hook_script {
-                    let hook_script = hook_script.to_path_buf();
-                    let new2 = new.clone();
-                    let _ = thread::spawn(move || {
-                        let _ = process::Command::new(hook_script.as_path())
-                            .arg(new2.file_preview_path.as_path())
-                            .arg(new2.preview_area.x.to_string())
-                            .arg(new2.preview_area.y.to_string())
-                            .arg(new2.preview_area.width.to_string())
-                            .arg(new2.preview_area.height.to_string())
-                            .status();
-                    });
-                }
-            }
-        }
-        None => {
-            if let Some(hook_script) = preview_removed_hook_script {
-                let hook_script = hook_script.to_path_buf();
-                let _ = thread::spawn(|| {
-                    let _ = process::Command::new(hook_script).status();
-                });
-            }
-        }
-    }
-    new_preview_area
-}