Improve performance of show commit

This change adds two caches that greatly speed up show commit. The first
is to cache the Unicode lengths so that they do not need to be
calculated for every render. The second is to ensure that the call to
libgit2 for retrieving the commit information is only made once and not
on every render loop. This should reduce the overall render time by
about ten fold.

10 files changed, 226 insertions, 226 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8e475d6..957ae88 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Support for 256-color terminals
 - Highlight of selected line(s) on 256-color terminals
 
+### Fixed
+- Performance issue with show commit
+
 ### Removed
 - Unused `errorColor` configuration
 
diff --git a/src/git_interactive.rs b/src/git_interactive.rs
index 60c59a2..87288fc 100644
--- a/src/git_interactive.rs
+++ b/src/git_interactive.rs
@@ -39,7 +39,6 @@ fn load_filepath(path: &PathBuf, comment_char: &str) -> Result<Vec<Line>, String
 pub struct GitInteractive {
 	filepath: PathBuf,
 	lines: Vec<Line>,
-	selected_commit_stats: Option<Commit>,
 	selected_line_index: usize,
 	visual_index_start: usize,
 }
@@ -52,7 +51,6 @@ impl GitInteractive {
 		Ok(GitInteractive {
 			filepath: path,
 			lines,
-			selected_commit_stats: None,
 			selected_line_index: 1,
 			visual_index_start: 1,
 		})
@@ -211,12 +209,10 @@ impl GitInteractive {
 		}
 	}
 
-	// TODO this is kind of clunky and might be replaceable with a RefCell
-	pub fn load_commit_stats(&mut self) -> Result<(), String> {
+	pub fn load_commit_stats(&self) -> Result<Commit, String> {
 		let selected_action = self.lines[self.selected_line_index - 1].get_action();
 		if *selected_action != Action::Exec && *selected_action != Action::Break {
-			self.selected_commit_stats = Some(Commit::from_commit_hash(self.get_selected_line_hash().as_str())?);
-			return Ok(());
+			return Ok(Commit::from_commit_hash(self.get_selected_line_hash().as_str())?);
 		}
 		Err(String::from("Cannot load commit for the selected action"))
 	}
@@ -225,10 +221,6 @@ impl GitInteractive {
 		!self.lines.is_empty() && *self.lines[0].get_action() == Action::Noop
 	}
 
-	pub fn get_commit_stats(&self) -> &Option<Commit> {
-		&self.selected_commit_stats
-	}
-
 	pub fn get_selected_line_hash(&self) -> &String {
 		self.lines[self.selected_line_index - 1].get_hash()
 	}
diff --git a/src/help/help.rs b/src/help/help.rs
index 7934d57..9d42287 100644
--- a/src/help/help.rs
+++ b/src/help/help.rs
@@ -93,7 +93,7 @@ impl<'h> ProcessModule for Help<'h> {
 		}
 
 		view.draw_view_lines(
-			view_lines,
+			&view_lines,
 			self.scroll_position.get_top_position(),
 			self.scroll_position.get_left_position(),
 			view_height - 3,
diff --git a/src/list/list.rs b/src/list/list.rs
index 869eada..a81b9d4 100644
--- a/src/list/list.rs
+++ b/src/list/list.rs
@@ -116,7 +116,7 @@ impl<'l> ProcessModule for List<'l> {
 		view.draw_title(true);
 
 		view.draw_view_lines(
-			view_lines,
+			&view_lines,
 			self.scroll_position.get_top_position(),
 			self.scroll_position.get_left_position(),
 			view_height - 2,
diff --git a/src/show_commit/data.rs b/src/show_commit/data.rs
new file mode 100644
index 0000000..fa16e7d
--- /dev/null
+++ b/src/show_commit/data.rs
@@ -0,0 +1,150 @@
+use crate::commit::Commit;
+use crate::constants::MINIMUM_FULL_WINDOW_WIDTH;
+use crate::display::DisplayColor;
+use crate::show_commit::util::get_stat_item_segments;
+use crate::view::{LineSegment, ViewLine};
+use std::cmp;
+use unicode_segmentation::UnicodeSegmentation;
+
+pub struct Data {
+	height: usize,
+	width: usize,
+	lines: Vec<ViewLine>,
+	line_lengths: Vec<usize>,
+	max_line_length: usize,
+}
+
+impl Data {
+	pub fn new() -> Self {
+		Self {
+			height: 0,
+			width: 0,
+			lines: Vec::new(),
+			line_lengths: Vec::new(),
+			max_line_length: 0,
+		}
+	}
+
+	pub fn reset(&mut self) {
+		self.height = 0;
+		self.width = 0;
+		self.lines.clear();
+		self.line_lengths.clear();
+		self.max_line_length = 0;
+	}
+
+	pub fn update(&mut self, commit: &Commit, window_width: usize, window_height: usize) {
+		if window_width != self.width || window_height != self.height {
+			self.reset();
+
+			self.height = window_height;
+			self.width = window_width;
+
+			let is_full_width = window_width >= MINIMUM_FULL_WINDOW_WIDTH;
+
+			let full_hash = commit.get_hash();
+			let author = commit.get_author();
+			let committer = commit.get_committer();
+			let date = commit.get_date();
+			let body = commit.get_body();
+			let file_stats = commit.get_file_stats();
+
+			let hash_line = if is_full_width {
+				format!("Commit: {}", full_hash)
+			}
+			else {
+				let max_index = cmp::min(full_hash.len(), 8);
+				format!("{:8} ", full_hash[0..max_index].to_string())
+			};
+
+			self.lines.push(ViewLine::new(vec![LineSegment::new_with_color(
+				hash_line.as_str(),
+				DisplayColor::IndicatorColor,
+			)]));
+			self.line_lengths.push(hash_line.len());
+
+			let date_line = if is_full_width {
+				format!("Date: {}", date.format("%c %z"))
+			}
+			else {
+				format!("{}", date.format("%c %z"))
+			};
+
+			self.lines
+				.push(ViewLine::new(vec![LineSegment::new(date_line.as_str())]));
+			self.line_lengths.push(date_line.len());
+
+			if let Some(a) = author.to_string() {
+				let author_line = if is_full_width {
+					format!("Author: {}", a)
+				}
+				else {
+					format!("A: {}", a)
+				};
+				self.lines
+					.push(ViewLine::new(vec![LineSegment::new(author_line.as_str())]));
+				self.line_lengths
+					.push(UnicodeSegmentation::graphemes(author_line.as_str(), true).count());
+			}
+
+			if let Some(c) = committer.to_string() {
+				let committer_line = if is_full_width {
+					format!("Committer: {}", c)
+				}
+				else {
+					format!("C: {}", c)
+				};
+				self.lines
+					.push(ViewLine::new(vec![LineSegment::new(committer_line.as_str())]));
+				self.line_lengths
+					.push(UnicodeSegmentation::graphemes(committer_line.as_str(), true).count());
+			}
+
+			match body {
+				Some(b) => {
+					for line in b.lines() {
+						self.lines.push(ViewLine::new(vec![LineSegment::new(line)]));
+						self.line_lengths
+							.push(UnicodeSegmentation::graphemes(line, true).count());
+					}
+				},
+				None => {},
+			}
+
+			self.lines.push(ViewLine::new(vec![LineSegment::new("")]));
+			self.line_lengths.push(0);
+
+			match file_stats {
+				Some(stats) => {
+					for stat in stats {
+						let stat_to_name = stat.get_to_name();
+						let stat_from_name = stat.get_from_name();
+						let stat_view_line = ViewLine::new(get_stat_item_segments(
+							*stat.get_status(),
+							stat_to_name.as_str(),
+							stat_from_name.as_str(),
+							is_full_width,
+						));
+						self.line_lengths.push(stat_view_line.get_length());
+						self.lines.push(stat_view_line);
+					}
+				},
+				None => {},
+			}
+		}
+	}
+
+	pub fn get_lines(&self) -> &Vec<ViewLine> {
+		&self.lines
+	}
+
+	pub fn get_max_line_length(&self, start: usize, end: usize) -> usize {
+		let mut max_length = 0;
+		for len in self.line_lengths[start..=end].iter() {
+			if *len > max_length {
+				max_length = *len;
+			}
+		}
+		max_length
+	}
+}
diff --git a/src/show_commit/mod.rs b/src/show_commit/mod.rs
index 9294506..ba21d8f 100644
--- a/src/show_commit/mod.rs
+++ b/src/show_commit/mod.rs
@@ -1,3 +1,4 @@
+mod data;
 #[allow(clippy::module_inception)]
 mod show_commit;
 mod util;
diff --git a/src/show_commit/show_commit.rs b/src/show_commit/show_commit.rs
index 561e967..810053e 100644
--- a/src/show_commit/show_commit.rs
+++ b/src/show_commit/show_commit.rs
@@ -1,5 +1,4 @@
 use crate::commit::Commit;
-use crate::constants::MINIMUM_FULL_WINDOW_WIDTH;
 use crate::display::DisplayColor;
 use crate::git_interactive::GitInteractive;
 use crate::input::{Input, InputHandler};
@@ -12,32 +11,46 @@ use crate::process::{
 	State,
 };
 use crate::scroll::ScrollPosition;
-use crate::show_commit::util::get_stat_item_segments;
-use crate::view::{LineSegment, View, ViewLine};
-use std::cmp;
-use unicode_segmentation::UnicodeSegmentation;
+use crate::show_commit::data::Data;
+use crate::view::View;
 
 pub struct ShowCommit {
+	commit: Option<Result<Commit, String>>,
+	data: Data,
 	scroll_position: ScrollPosition,
 }
 
 impl ProcessModule for ShowCommit {
-	fn activate(&mut self, _state: State, _git_interactive: &GitInteractive) {
+	fn activate(&mut self, _state: State, git_interactive: &GitInteractive) {
 		self.scroll_position.reset();
+		self.commit = Some(git_interactive.load_commit_stats());
 	}
 
-	fn process(&mut self, git_interactive: &mut GitInteractive, _view: &View) -> ProcessResult {
+	fn deactivate(&mut self) {
+		self.data.reset();
+	}
+
+	fn process(&mut self, _git_interactive: &mut GitInteractive, view: &View) -> ProcessResult {
+		let (view_width, view_height) = view.get_view_size();
 		let mut result = ProcessResultBuilder::new();
-		if let Err(e) = git_interactive.load_commit_stats() {
-			result = result.error(e.as_str(), State::List(false));
+
+		if let Some(commit) = &self.commit {
+			match commit {
+				Ok(c) => self.data.update(&c, view_width, view_height),
+				Err(e) => {
+					result = result.error(e.as_str(), State::List(false));
+					self.data.reset()
+				},
+			}
 		}
+
 		result.build()
 	}
 
 	fn handle_input(
 		&mut self,
 		input_handler: &InputHandler,
-		git_interactive: &mut GitInteractive,
+		_git_interactive: &mut GitInteractive,
 		view: &View,
 	) -> HandleInputResult
 	{
@@ -47,40 +60,24 @@ impl ProcessModule for ShowCommit {
 		let mut result = HandleInputResultBuilder::new(input);
 		match input {
 			Input::MoveCursorLeft => {
-				self.scroll_position.scroll_left(
-					view_width,
-					self.get_max_line_length(
-						git_interactive.get_commit_stats(),
-						view_height >= MINIMUM_FULL_WINDOW_WIDTH,
-					),
-				)
+				self.scroll_position
+					.scroll_left(view_width, self.get_max_line_length(view_height))
 			},
 			Input::MoveCursorRight => {
-				self.scroll_position.scroll_right(
-					view_width,
-					self.get_max_line_length(
-						git_interactive.get_commit_stats(),
-						view_height >= MINIMUM_FULL_WINDOW_WIDTH,
-					),
-				)
+				self.scroll_position
+					.scroll_right(view_width, self.get_max_line_length(view_height))
 			},
 			Input::MoveCursorDown => {
-				self.scroll_position.scroll_down(
-					view_height,
-					self.get_commit_stats_length(git_interactive.get_commit_stats()),
-				)
+				self.scroll_position
+					.scroll_down(view_height, self.get_commit_stats_length())
 			},
 			Input::MoveCursorUp => {
-				self.scroll_position.scroll_up(
-					view_height,
-					self.get_commit_stats_length(git_interactive.get_commit_stats()),
-				)
+				self.scroll_position
+					.scroll_up(view_height, self.get_commit_stats_length())
 			},
 			Input::Resize => {
-				self.scroll_position.scroll_up(
-					view_height as usize,
-					self.get_commit_stats_length(git_interactive.get_commit_stats()),
-				);
+				self.scroll_position
+					.scroll_up(view_height as usize, self.get_commit_stats_length());
 			},
 			_ => {
 				result = result.state(State::List(false));
@@ -89,105 +86,22 @@ impl ProcessModule for ShowCommit {
 		result.build()
 	}
 
-	fn render(&self, view: &View, git_interactive: &GitInteractive) {
-		let commit_data = git_interactive.get_commit_stats();
-		let (window_width, window_height) = view.get_view_size();
+	fn render(&self, view: &View, _git_interactive: &GitInteractive) {
+		let (_, window_height) = view.get_view_size();
 		let view_height = window_height - 2;
 
-		let is_full_width = window_width >= MINIMUM_FULL_WINDOW_WIDTH;
-
 		view.draw_title(false);
 
-		let commit = match commit_data {
+		match &self.commit {
 			None => {
 				view.draw_error("Not commit data to show");
 				return;
 			},
-			Some(c) => c,
-		};
-
-		let full_hash = commit.get_hash();
-		let author = commit.get_author();
-		let committer = commit.get_committer();
-		let date = commit.get_date();
-		let body = commit.get_body();
-		let file_stats = commit.get_file_stats();
-
-		let mut lines: Vec<ViewLine> = vec![];
-
-		lines.push(ViewLine::new(vec![LineSegment::new_with_color(
-			if is_full_width {
-				format!("Commit: {}", full_hash)
-			}
-			else {
-				let max_index = cmp::min(full_hash.len(), 8);
-				format!("{:8} ", full_hash[0..max_index].to_string())
-			}
-			.as_str(),
-			DisplayColor::IndicatorColor,
-		)]));
-
-		lines.push(ViewLine::new(vec![LineSegment::new(
-			if is_full_width {
-				format!("Date: {}", date.format("%c %z"))
-			}
-			else {
-				format!("{}", date.format("%c %z"))
-			}
-			.as_str(),
-		)]));
-
-		if let Some(a) = author.to_string() {
-			lines.push(ViewLine::new(vec![LineSegment::new(
-				if is_full_width {
-					format!("Author: {}", a)
-				}
-				else {
-					format!("A: {}", a)
-				}
-				.as_str(),
-			)]));
-		}
-
-		if let Some(c) = committer.to_string() {
-			lines.push(ViewLine::new(vec![LineSegment::new(
-				if is_full_width {
-					format!("Committer: {}", c)
-				}
-				else {
-					format!("C: {}", c)
-				}
-				.as_str(),
-			)]))
+			Some(c) => c.as_ref().unwrap(), // safe unwrap
 		};
 
-		match body {
-			Some(b) => {
-				for line in b.lines() {
-					lines.push(ViewLine::new(vec![LineSegment::new(line)]));
-				}
-			},
-			None => {},
-		};
-
-		lines.push(ViewLine::new(vec![LineSegment::new("")]));
-
-		match file_stats {
-			Some(stats) => {
-				for stat in stats {
-					lines.push(ViewLine::new(get_stat_item_segments(
-						*stat.get_status(),
-						stat.get_to_name().as_str(),
-						stat.get_from_name().as_str(),
-						is_full_width,
-					)))
-				}
-			},
-			None => {},
-		}
-
 		view.draw_view_lines(
-			lines,
+			self.data.get_lines(),
 			self.scroll_position.get_top_position(),
 			self.scroll_position.get_left_position(),
 			view_height,
@@ -201,13 +115,15 @@ impl ProcessModule for ShowCommit {
 impl ShowCommit {
 	pub fn new() -> Self {
 		Self {
+			commit: None,
+			data: Data::new(),
 			scroll_position: ScrollPosition::new(3, 6, 3),
 		}
 	}
 
-	fn get_commit_stats_length(&self, commit: &Option<Commit>) -> usize {
-		match commit {
-			Some(c) => {
+	fn get_commit_stats_length(&self) -> usize {
+		if let Some(commit) = &self.commit {
+			if let Ok(c) = commit {
 				let mut len = c.get_file_stats_length();
 
 				match c.get_body() {
@@ -216,94 +132,16 @@ impl ShowCommit {
 					},
 					None => {},
 				}
-				len + 3 // author + date + commit hash
-			},
-			None => 0,
+				return len + 3; // author + date + commit hash
+			}
 		}
+		0
 	}
 
-	fn get_max_line_length(&self, commit: &Option<Commit>, is_full_width: bool) -> usize {
-		match commit {
-			Some(c) => {
-				let full_hash = c.get_hash();
-				let author = c.get_author();
-				let committer = c.get_committer();
-				let body = c.get_body();
-				let file_stats = c.get_file_stats();
-
-				let mut max_line_length = if is_full_width {
-					full_hash.len() + 8 // 8 = "Commit: "
-				}
-				else {
-					cmp::min(full_hash.len(), 8)
-				};
-
-				max_line_length = cmp::max(
-					if is_full_width {
-						35 // "Date: Sun Jul 8 00:34:60 2001+09:30"
-					}
-					else {
-						29 // "Sun Jul 8 00:34:60 2001+09:30"
-					},
-					max_line_length,
-				);
-
-				if let Some(a) = author.to_string() {
-					max_line_length = cmp::max(
-						if is_full_width {
-							UnicodeSegmentation::graphemes(a.as_str(), true).count() + 8 // 8 = "Author: "
-						}
-						else {
-							UnicodeSegmentation::graphemes(a.as_str(), true).count() + 3 // 3 = "A: "
-						},
-						max_line_length,
-					);
-				}
-
-				if let Some(c) = committer.to_string() {
-					max_line_length = cmp::max(
-						if is_full_width {
-							UnicodeSegmentation::graphemes(c.as_str(), true).count() + 11 // 11 = "Committer: "
-						}
-						else {
-							UnicodeSegmentation::graphemes(c.as_str(), true).count() + 3 // 3 = "C: "
-						},
-						max_line_length,
-					);
-				};
-
-				if let Some(b) = body {
-					for line in b.lines() {
-						let line_length = UnicodeSegmentation::graphemes(line, true).count();
-						if line_length > max_line_length {
-							max_line_length = line_length;
-						}
-					}
-				}
-
-				if let Some(stats) = file_stats {
-					let additional_line_length = if is_full_width {
-						13 // stat name + arrow
-					}
-					else {
-						3 // stat name + arrow
-					};
-
-					for stat in stats {
-						let stat_line_length =
-							UnicodeSegmentation::graphemes(stat.get_to_name().as_str(), true).count()
-								+ UnicodeSegmentation::graphemes(stat.get_from_name().as_str(), true).count()
-								+ additional_line_length;
-
-						if stat_line_length > max_line_length {
-							max_line_length = stat_line_length;
-						}
-					}
-				}
-
-				max_line_length
-			},
-			None => 0,
-		}
+	fn get_max_line_length(&self, view_height: usize) -> usize {
+		self.data.get_max_line_length(
+			self.scroll_position.get_top_position(),
+			self.scroll_position.get_top_position() + view_height,
+		)
 	}
 }
diff --git a/src/view/line_segment.rs b/src/view/line_segment.rs
index b007204..320407e 100644
--- a/src/view/line_segment.rs
+++ b/src/view/line_segment.rs
@@ -6,6 +6,7 @@ pub struct LineSegment {
 	dim: bool,
 	reverse: bool,
 	text: String,
+	length: usize,
 	underline: bool,
 }
 
@@ -16,6 +17,7 @@ impl LineSegment {
 			color: DisplayColor::Normal,
 			reverse: false,
 			dim: false,
+			length: UnicodeSegmentation::graphemes(text, true).count(),
 			underline: false,
 		}
 	}
@@ -26,6 +28,7 @@ impl LineSegment {
 			color,
 			reverse: false,
 			dim: false,
+			length: UnicodeSegmentation::graphemes(text, true).count(),
 			underline: false,
 		}
 	}
@@ -43,10 +46,15 @@ impl LineSegment {
 			color,
 			reverse,
 			dim,
+			length: UnicodeSegmentation::graphemes(text, true).count(),
 			underline,
 		}
 	}
 
+	pub fn get_length(&self) -> usize {
+		self.length
+	}
+
 	pub fn draw(&self, left: usize, max_width: usize, selected: bool, display: &Display) -> (usize, usize) {
 		display.color(self.color, selected);
 		display.set_style(self.dim, self.underline, self.reverse);
diff --git a/src/view/view.rs b/src/view/view.rs
index f6fdb18..73eb264 100644
--- a/src/view/view.rs
+++ b/src/view/view.rs
@@ -62,7 +62,7 @@ impl<'v> View<'v> {
 		self.display.refresh();
 	}
 
-	pub fn draw_view_lines(&self, lines: Vec<ViewLine>, top: usize, left: usize, height: usize) {
+	pub fn draw_view_lines(&self, lines: &[ViewLine], top: usize, left: usize, height: usize) {
 		let number_of_lines = lines.len();
 
 		let scroll_indicator_index = get_scroll_position(top, number_of_lines, height);
diff --git a/src/view/view_line.rs b/src/view/view_line.rs
index 562c6f7..2e877af 100644
--- a/src/view/view_line.rs
+++ b/src/view/view_line.rs
@@ -23,6 +23,14 @@ impl ViewLine {
 		}
 	}
 
+	pub fn get_length(&self) -> usize {
+		let mut length = 0;
+		for s in self.segments.iter() {
+			length += s.get_length();
+		}
+		length
+	}
+
 	pub fn set_selected(mut self, selected: bool) -> Self {
 		self.selected = selected;
 		self