Add "Visual-Mode" (#192)

* Add "Visual-Mode"

This adds a "visual-mode" file selection feature where a range-selection follows the file-cursor.

Description of usage is added to the docs.

Also, the "normal" and the new "visual-mode-selection" are now preserved
when a `DirList` is reloaded.

Wrap-up of changes:
* Add command `toggle_visual`, mapped to `V`
* Add command `escape`, mapped to `ESCAPE`
* Add style `[visual_mode_selection]` for file entries which are
  "temporarily" selected by visual-mode
* For `JoshutoDirEntry`, the attribute `selected` has been renamed to
  `permanent_selected`, and a second selection-attribute
  `visual_mode_selected` has been added. "Setters" and "getters" have
  been adapted/added accordingly. The former "getter" for the `selecetd`
  attribute still exists and returns `True` for an entry which is
  "permanant selected" _or_ "visual-mode selected". So any higher logic
  which acts on selected files does not need to care about "how" and
  entry is selected.
* Each `JoshutoDirList` has an optional index of the file where
  visual-mode has been entered and re-calculates the "visual-mode
  selecetd" status for each entry any time the cursor-index changes.
* The footer has been extended so it shows a "VIS" marker when the user
  is in visual-mode.

This implementation of visual-mode is a bit different from the ranger
one, where the visual-selection is turned into a "normal selection" when
a command (like `copy-files`) is issued. This implementation keeps
both selections separate until the user toggles back to "normal mode".
Only then the visual-selection is taken over to the "normal selection".
The user also can withdraw the visual-selection with `escape`.

The `escape` command may be used also for other "reset"-actions in the
future.

* fix syntax for Rust stable

* cargo clippy

3 files changed, 84 insertions, 6 deletions

diff --git a/src/fs/dirlist.rs b/src/fs/dirlist.rs
index 096c9a0..567b8eb 100644
--- a/src/fs/dirlist.rs
+++ b/src/fs/dirlist.rs
@@ -15,6 +15,8 @@ pub struct JoshutoDirList {
     index: Option<usize>,
     /// The index in this dir list to start with when rendering the list
     viewport_index: usize,
+    /// The index in this dir list where visual mode has started or None if not in visual mode
+    visual_mode_anchor_index: Option<usize>,
     _need_update: bool,
 }
 
@@ -24,6 +26,7 @@ impl JoshutoDirList {
         contents: Vec<JoshutoDirEntry>,
         index: Option<usize>,
         viewport_index: usize,
+        visual_mode_anchor_index: Option<usize>,
         metadata: JoshutoMetadata,
     ) -> Self {
         Self {
@@ -32,6 +35,7 @@ impl JoshutoDirList {
             metadata,
             index,
             viewport_index,
+            visual_mode_anchor_index,
             _need_update: false,
         }
     }
@@ -55,6 +59,7 @@ impl JoshutoDirList {
             _need_update: false,
             index,
             viewport_index: if let Some(ix) = index { ix } else { 0 },
+            visual_mode_anchor_index: None,
         })
     }
 
@@ -62,6 +67,62 @@ impl JoshutoDirList {
         self.index
     }
 
+    pub fn get_visual_mode_anchor_index(&self) -> Option<usize> {
+        self.visual_mode_anchor_index
+    }
+
+    fn update_visual_mode_selection(&mut self) {
+        //! To be invoked any time the cursor index, the visual mode anchor index,
+        //! or the shown sub-set of entries changes.
+        if let Some(vmix) = self.visual_mode_anchor_index {
+            if let Some(cix) = self.index {
+                self.iter_mut().enumerate().for_each(|(i, entry)| {
+                    entry.set_visual_mode_selected(
+                        (if vmix > cix {
+                            cix..vmix + 1
+                        } else {
+                            vmix..cix + 1
+                        })
+                        .contains(&i),
+                    )
+                })
+            }
+        } else {
+            self.iter_mut()
+                .for_each(|entry| entry.set_visual_mode_selected(false))
+        }
+    }
+
+    fn visual_mode_enable(&mut self) {
+        if let Some(ix) = self.index {
+            self.visual_mode_anchor_index = Some(ix)
+        };
+        self.update_visual_mode_selection();
+    }
+
+    fn visual_mode_disable(&mut self) {
+        self.visual_mode_anchor_index = None;
+        self.iter_mut().for_each(|entry| {
+            if entry.is_visual_mode_selected() {
+                entry.set_permanent_selected(true)
+            }
+        });
+        self.update_visual_mode_selection();
+    }
+
+    pub fn visual_mode_cancel(&mut self) {
+        self.visual_mode_anchor_index = None;
+        self.update_visual_mode_selection();
+    }
+
+    pub fn toggle_visual_mode(&mut self) {
+        if self.get_visual_mode_anchor_index().is_none() {
+            self.visual_mode_enable()
+        } else {
+            self.visual_mode_disable()
+        }
+    }
+
     fn update_viewport(&mut self, ui_context: &UiContext, options: &DisplayOption) {
         if let Some(ix) = self.index {
             let height = ui_context.layout[0].height as usize;
@@ -106,6 +167,7 @@ impl JoshutoDirList {
         if !ui_context.layout.is_empty() {
             self.update_viewport(ui_context, options);
         }
+        self.update_visual_mode_selection();
     }
 
     pub fn iter(&self) -> Iter<JoshutoDirEntry> {
diff --git a/src/fs/entry.rs b/src/fs/entry.rs
index 8337bc4..f7dae32 100644
--- a/src/fs/entry.rs
+++ b/src/fs/entry.rs
@@ -12,7 +12,10 @@ pub struct JoshutoDirEntry {
     label: String,
     path: path::PathBuf,
     pub metadata: JoshutoMetadata,
-    selected: bool,
+    /// Directly selected by the user, _not_ by a current visual mode selection
+    permanent_selected: bool,
+    /// Temporarily selected by the visual mode range
+    visual_mode_selected: bool,
     _marked: bool,
 }
 
@@ -63,11 +66,23 @@ impl JoshutoDirEntry {
     }
 
     pub fn is_selected(&self) -> bool {
-        self.selected
+        self.permanent_selected || self.visual_mode_selected
     }
 
-    pub fn set_selected(&mut self, selected: bool) {
-        self.selected = selected;
+    pub fn is_permanent_selected(&self) -> bool {
+        self.permanent_selected
+    }
+
+    pub fn is_visual_mode_selected(&self) -> bool {
+        self.visual_mode_selected
+    }
+
+    pub fn set_permanent_selected(&mut self, selected: bool) {
+        self.permanent_selected = selected;
+    }
+
+    pub fn set_visual_mode_selected(&mut self, visual_mode_selected: bool) {
+        self.visual_mode_selected = visual_mode_selected;
     }
 
     pub fn get_ext(&self) -> &str {
@@ -102,7 +117,8 @@ impl JoshutoDirEntry {
             label,
             path,
             metadata,
-            selected: false,
+            permanent_selected: false,
+            visual_mode_selected: false,
             _marked: false,
         })
     }
diff --git a/src/fs/metadata.rs b/src/fs/metadata.rs
index fd192cc..616e09c 100644
--- a/src/fs/metadata.rs
+++ b/src/fs/metadata.rs
@@ -1,6 +1,6 @@
 use std::{fs, io, path, time};
 
-#[derive(Clone, Debug, PartialEq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub enum FileType {
     Directory,
     File,