From c7281459f9097b4456216ecf945796fa707bc4fd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cau=C3=AA=20Baasch=20de=20Souza?= <cauebs@pm.me>
Date: Thu, 31 Jan 2019 16:31:02 -0200
Subject: [PATCH] Group file changes and rebuild book only once

---
 src/cmd/serve.rs |  4 ++--
 src/cmd/watch.rs | 42 ++++++++++++++++++++++++++++--------------
 2 files changed, 30 insertions(+), 16 deletions(-)

diff --git a/src/cmd/serve.rs b/src/cmd/serve.rs
index 9659d820..ac6acbdd 100644
--- a/src/cmd/serve.rs
+++ b/src/cmd/serve.rs
@@ -115,8 +115,8 @@ pub fn execute(args: &ArgMatches) -> Result<()> {
     }
 
     #[cfg(feature = "watch")]
-    watch::trigger_on_change(&book, move |path, book_dir| {
-        info!("File changed: {:?}", path);
+    watch::trigger_on_change(&book, move |paths, book_dir| {
+        info!("Files changed: {:?}", paths);
         info!("Building book...");
 
         // FIXME: This area is really ugly because we need to re-set livereload :(
diff --git a/src/cmd/watch.rs b/src/cmd/watch.rs
index d800ae7d..e19a5581 100644
--- a/src/cmd/watch.rs
+++ b/src/cmd/watch.rs
@@ -5,9 +5,10 @@ use clap::{App, ArgMatches, SubCommand};
 use mdbook::errors::Result;
 use mdbook::utils;
 use mdbook::MDBook;
-use std::path::Path;
+use std::path::{Path, PathBuf};
 use std::sync::mpsc::channel;
 use std::time::Duration;
+use std::thread::sleep;
 use {get_book_dir, open};
 
 // Create clap subcommand arguments
@@ -18,10 +19,12 @@ pub fn make_subcommand<'a, 'b>() -> App<'a, 'b> {
             "-d, --dest-dir=[dest-dir] 'Output directory for the book{n}\
              Relative paths are interpreted relative to the book's root directory.{n}\
              If omitted, mdBook uses build.build-dir from book.toml or defaults to `./book`.'",
-        ).arg_from_usage(
+        )
+        .arg_from_usage(
             "[dir] 'Root directory for the book{n}\
              (Defaults to the Current Directory when omitted)'",
-        ).arg_from_usage("-o, --open 'Open the compiled book in a web browser'")
+        )
+        .arg_from_usage("-o, --open 'Open the compiled book in a web browser'")
 }
 
 // Watch command implementation
@@ -34,8 +37,8 @@ pub fn execute(args: &ArgMatches) -> Result<()> {
         open(book.build_dir_for("html").join("index.html"));
     }
 
-    trigger_on_change(&book, |path, book_dir| {
-        info!("File changed: {:?}\nBuilding book...\n", path);
+    trigger_on_change(&book, |paths, book_dir| {
+        info!("Files changed: {:?}\nBuilding book...\n", paths);
         let result = MDBook::load(&book_dir).and_then(|b| b.build());
 
         if let Err(e) = result {
@@ -50,7 +53,7 @@ pub fn execute(args: &ArgMatches) -> Result<()> {
 /// Calls the closure when a book source file is changed, blocking indefinitely.
 pub fn trigger_on_change<F>(book: &MDBook, closure: F)
 where
-    F: Fn(&Path, &Path),
+    F: Fn(Vec<PathBuf>, &Path),
 {
     use self::notify::DebouncedEvent::*;
     use self::notify::RecursiveMode::*;
@@ -79,13 +82,24 @@ where
 
     info!("Listening for changes...");
 
-    for event in rx.iter() {
-        debug!("Received filesystem event: {:?}", event);
-        match event {
-            Create(path) | Write(path) | Remove(path) | Rename(_, path) => {
-                closure(&path, &book.root);
-            }
-            _ => {}
-        }
+    loop {
+        let first_event = rx.recv().unwrap();
+        sleep(Duration::from_millis(50));
+        let other_events = rx.try_iter();
+
+        let all_events = std::iter::once(first_event).chain(other_events);
+
+        let paths = all_events
+            .filter_map(|event| {
+                debug!("Received filesystem event: {:?}", event);
+
+                match event {
+                    Create(path) | Write(path) | Remove(path) | Rename(_, path) => Some(path),
+                    _ => None,
+                }
+            })
+            .collect();
+
+        closure(paths, &book.root);
     }
 }