Add script hooks for image previews (#113)

This adds two configuration options, `preview_shown_hook_script`
and `preview_removed_hook_script` in the preview-section where the
user can configure external scripts which are called when a file preview
is shown or when the file preview widget disappears, respectively.

The `preview_shown_hook_script` gets the path of the file being previwed
as first argument and then the x and y coordinate and the width an
height of the preview area as second to fifth parameters.

To get the geometry information back from the UI rendering process, a
new struct `RenderResult` has been introduced which is given as mutable
reference to the rendering function.

The main-loop then checks for a changed preview and calls the hook
scripts.

Additionally, documentation has been added how these hooks can be used
to implement image previews.

6 files changed, 58 insertions, 7 deletions

diff --git a/src/ui/mod.rs b/src/ui/mod.rs
index 16ebd19..b782b1f 100644
--- a/src/ui/mod.rs
+++ b/src/ui/mod.rs
@@ -1,5 +1,29 @@
+use std::path;
+
 mod tui_backend;
 pub mod views;
 pub mod widgets;
 
 pub use tui_backend::*;
+
+#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
+pub struct Rect {
+    pub x: u16,
+    pub y: u16,
+    pub width: u16,
+    pub height: u16,
+}
+
+pub struct RenderResult {
+    pub file_preview_path: Option<path::PathBuf>,
+    pub preview_area: Option<Rect>,
+}
+
+impl RenderResult {
+    pub fn new() -> RenderResult {
+        RenderResult {
+            file_preview_path: None,
+            preview_area: None,
+        }
+    }
+}
diff --git a/src/ui/views/tui_command_menu.rs b/src/ui/views/tui_command_menu.rs
index bc94752..d62fa09 100644
--- a/src/ui/views/tui_command_menu.rs
+++ b/src/ui/views/tui_command_menu.rs
@@ -8,6 +8,7 @@ use crate::config::AppKeyMapping;
 use crate::context::AppContext;
 use crate::ui::views::TuiView;
 use crate::ui::widgets::TuiMenu;
+use crate::ui::RenderResult;
 use crate::util::to_string::ToString;
 
 const BORDER_HEIGHT: usize = 1;
@@ -26,7 +27,8 @@ impl<'a> TuiCommandMenu<'a> {
 
 impl<'a> Widget for TuiCommandMenu<'a> {
     fn render(self, area: Rect, buf: &mut Buffer) {
-        TuiView::new(self.context).render(area, buf);
+        let mut render_result = RenderResult::new();
+        TuiView::new(self.context, &mut render_result).render(area, buf);
 
         // draw menu
         let mut display_vec: Vec<String> = self
diff --git a/src/ui/views/tui_folder_view.rs b/src/ui/views/tui_folder_view.rs
index de3c8a0..1a07ce0 100644
--- a/src/ui/views/tui_folder_view.rs
+++ b/src/ui/views/tui_folder_view.rs
@@ -1,3 +1,5 @@
+use std::path;
+
 use tui::buffer::Buffer;
 use tui::layout::{Constraint, Direction, Layout, Rect};
 use tui::style::{Color, Style};
@@ -6,22 +8,26 @@ use tui::text::Span;
 use tui::widgets::{Block, Borders, Paragraph, Widget, Wrap};
 
 use crate::context::AppContext;
+use crate::ui;
 use crate::ui::widgets::{
     TuiDirList, TuiDirListDetailed, TuiFilePreview, TuiFooter, TuiTabBar, TuiTopBar,
 };
+use crate::ui::RenderResult;
 
 const TAB_VIEW_WIDTH: u16 = 15;
 
 pub struct TuiFolderView<'a> {
     pub context: &'a AppContext,
     pub show_bottom_status: bool,
+    pub render_result: &'a mut RenderResult,
 }
 
 impl<'a> TuiFolderView<'a> {
-    pub fn new(context: &'a AppContext) -> Self {
+    pub fn new(context: &'a AppContext, render_result: &'a mut RenderResult) -> Self {
         Self {
             context,
             show_bottom_status: true,
+            render_result,
         }
     }
 }
@@ -163,6 +169,8 @@ impl<'a> Widget for TuiFolderView<'a> {
         }
 
         // render preview
+        let mut file_preview_path: Option<path::PathBuf> = None;
+        let mut preview_area: Option<ui::Rect> = None;
         if let Some(list) = child_list.as_ref() {
             TuiDirList::new(list).render(layout_rect[2], buf);
         } else if let Some(entry) = curr_entry {
@@ -170,11 +178,21 @@ impl<'a> Widget for TuiFolderView<'a> {
                 match preview.status.code() {
                     Some(1) | None => {}
                     _ => {
-                        TuiFilePreview::new(entry, preview).render(layout_rect[2], buf);
+                        let rect = layout_rect[2];
+                        TuiFilePreview::new(entry, preview).render(rect, buf);
+                        file_preview_path = Some(entry.file_path_buf());
+                        preview_area = Some(ui::Rect {
+                            x: rect.x,
+                            y: rect.y,
+                            width: rect.width,
+                            height: rect.height,
+                        })
                     }
                 }
             }
         }
+        self.render_result.file_preview_path = file_preview_path;
+        self.render_result.preview_area = preview_area;
 
         let topbar_width = area.width;
         let rect = Rect {
diff --git a/src/ui/views/tui_textfield.rs b/src/ui/views/tui_textfield.rs
index d829852..b9426db 100644
--- a/src/ui/views/tui_textfield.rs
+++ b/src/ui/views/tui_textfield.rs
@@ -10,6 +10,7 @@ use crate::context::AppContext;
 use crate::event::AppEvent;
 use crate::ui::views::TuiView;
 use crate::ui::widgets::{TuiMenu, TuiMultilineText};
+use crate::ui::RenderResult;
 use crate::ui::TuiBackend;
 use crate::util::input;
 
@@ -96,7 +97,8 @@ impl<'a> TuiTextField<'a> {
                         return;
                     }
                     {
-                        let mut view = TuiView::new(context);
+                        let mut render_result = RenderResult::new();
+                        let mut view = TuiView::new(context, &mut render_result);
                         view.show_bottom_status = false;
                         frame.render_widget(view, area);
                     }
diff --git a/src/ui/views/tui_view.rs b/src/ui/views/tui_view.rs
index 2178475..a5f093c 100644
--- a/src/ui/views/tui_view.rs
+++ b/src/ui/views/tui_view.rs
@@ -4,23 +4,26 @@ use tui::widgets::Widget;
 
 use super::TuiFolderView;
 use crate::context::AppContext;
+use crate::ui::RenderResult;
 
 pub struct TuiView<'a> {
     pub context: &'a AppContext,
     pub show_bottom_status: bool,
+    pub render_result: &'a mut RenderResult,
 }
 
 impl<'a> TuiView<'a> {
-    pub fn new(context: &'a AppContext) -> Self {
+    pub fn new(context: &'a AppContext, render_result: &'a mut RenderResult) -> Self {
         Self {
             context,
             show_bottom_status: true,
+            render_result,
         }
     }
 }
 
 impl<'a> Widget for TuiView<'a> {
     fn render(self, area: Rect, buf: &mut Buffer) {
-        TuiFolderView::new(self.context).render(area, buf);
+        TuiFolderView::new(self.context, self.render_result).render(area, buf);
     }
 }
diff --git a/src/ui/widgets/tui_prompt.rs b/src/ui/widgets/tui_prompt.rs
index bc1b210..f1bd0d4 100644
--- a/src/ui/widgets/tui_prompt.rs
+++ b/src/ui/widgets/tui_prompt.rs
@@ -7,6 +7,7 @@ use tui::widgets::{Clear, Paragraph, Wrap};
 use crate::context::AppContext;
 use crate::event::AppEvent;
 use crate::ui::views::TuiView;
+use crate::ui::RenderResult;
 use crate::ui::TuiBackend;
 use crate::util::input;
 
@@ -31,7 +32,8 @@ impl<'a> TuiPrompt<'a> {
                 }
 
                 {
-                    let mut view = TuiView::new(context);
+                    let mut render_result = RenderResult::new();
+                    let mut view = TuiView::new(context, &mut render_result);
                     view.show_bottom_status = false;
                     frame.render_widget(view, f_size);
                 }