From c4f3049a74bab0116e3db60f7deaad8ef8aa875b Mon Sep 17 00:00:00 2001
From: Jheison Martinez Bolivar <jheison.mb@gmail.com>
Date: Wed, 1 Apr 2026 10:05:18 -0500
Subject: [PATCH] feat: add texforge build --watch with configurable debounce
 delay

---
 Cargo.toml            |  5 ++-
 README.md             | 14 ++++++++
 src/cli/mod.rs        | 17 +++++++--
 src/commands/build.rs | 83 +++++++++++++++++++++++++++++++++++++++----
 4 files changed, 109 insertions(+), 10 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index bef5592..9ed65f7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "texforge"
-version = "0.3.0"
+version = "0.4.0"
 edition = "2021"
 rust-version = "1.75"
 description = "Self-contained LaTeX to PDF compiler CLI"
@@ -38,6 +38,9 @@ flate2 = "1.1"
 tar = "0.4"
 zip = { version = "2", default-features = false, features = ["deflate"] }
 
+# File watching for --watch mode
+notify = { version = "7", features = ["macos_fsevent"] }
+
 # Mermaid diagram rendering
 mermaid-rs-renderer = { version = "0.2", default-features = false }
 resvg = "0.46"
diff --git a/README.md b/README.md
index 34c6d59..fa6dfc6 100644
--- a/README.md
+++ b/README.md
@@ -138,6 +138,7 @@ sequenceDiagram
 | `texforge new <name> -t <template>` | Create with specific template |
 | `texforge init` | Initialize texforge in an existing LaTeX project |
 | `texforge build` | Compile to PDF |
+| `texforge build --watch` | Watch for changes and rebuild automatically |
 | `texforge clean` | Remove build artifacts |
 | `texforge fmt` | Format .tex files |
 | `texforge fmt --check` | Check formatting without modifying |
@@ -198,6 +199,19 @@ Both rendered to PNG via pure Rust — no browser, no Node.js, no `dot` binary r
 
 ---
 
+## Watch Mode
+
+`texforge build --watch` watches for `.tex` file changes and rebuilds automatically:
+
+```bash
+texforge build --watch            # rebuild after 10s of inactivity (default)
+texforge build --watch --delay 5  # custom delay in seconds
+```
+
+The terminal stays open showing build output. Press `Ctrl+C` to stop.
+
+---
+
 ## Linter
 
 `texforge check` runs static analysis without compiling:
diff --git a/src/cli/mod.rs b/src/cli/mod.rs
index 50f0bcf..5746ccd 100644
--- a/src/cli/mod.rs
+++ b/src/cli/mod.rs
@@ -28,7 +28,14 @@ enum Commands {
         template: Option<String>,
     },
     /// Compile project to PDF
-    Build,
+    Build {
+        /// Watch for file changes and rebuild automatically
+        #[arg(long)]
+        watch: bool,
+        /// Debounce delay in seconds before rebuilding (default: 10)
+        #[arg(long, default_value = "10")]
+        delay: u64,
+    },
     /// Format .tex files
     Fmt {
         /// Check formatting without modifying files
@@ -66,7 +73,13 @@ impl Cli {
             Commands::Clean => commands::clean::execute(),
             Commands::Init => commands::init::execute(),
             Commands::New { name, template } => commands::new::execute(&name, template.as_deref()),
-            Commands::Build => commands::build::execute(),
+            Commands::Build { watch, delay } => {
+                if watch {
+                    commands::build::watch(delay)
+                } else {
+                    commands::build::execute()
+                }
+            }
             Commands::Fmt { check } => commands::fmt::execute(check),
             Commands::Check => commands::check::execute(),
             Commands::Template { action } => match action {
diff --git a/src/commands/build.rs b/src/commands/build.rs
index eceea9d..2501890 100644
--- a/src/commands/build.rs
+++ b/src/commands/build.rs
@@ -1,6 +1,10 @@
 //! `texforge build` command implementation.
 
+use std::sync::mpsc;
+use std::time::Duration;
+
 use anyhow::Result;
+use notify::{RecursiveMode, Watcher};
 
 use crate::compiler;
 use crate::diagrams;
@@ -9,24 +13,89 @@ use crate::domain::project::Project;
 /// Compile project to PDF.
 pub fn execute() -> Result<()> {
     let project = Project::load()?;
-
     println!("Building project: {}", project.config.documento.titulo);
-
     std::fs::create_dir_all(project.root.join("build"))?;
-
-    // Pre-process embedded diagrams — works on copies in build/, originals untouched
     diagrams::process(&project.root, &project.config.compilacion.entry)?;
-
-    // Compile from build/ — all assets are mirrored there, diagrams use relative paths
     let build_dir = project.root.join("build");
     let entry_filename = std::path::Path::new(&project.config.compilacion.entry)
         .file_name()
         .map(|n| n.to_string_lossy().to_string())
         .unwrap_or(project.config.compilacion.entry.clone());
     compiler::compile(&build_dir, &entry_filename)?;
-
     let pdf_name = std::path::Path::new(&project.config.compilacion.entry).with_extension("pdf");
     println!("✅ build/{}", pdf_name.display());
+    Ok(())
+}
+
+/// Watch for .tex file changes and rebuild with debounce.
+pub fn watch(delay_secs: u64) -> Result<()> {
+    let project = Project::load()?;
+    let debounce = Duration::from_secs(delay_secs);
+
+    println!(
+        "Watching project: {} ({}s debounce — Ctrl+C to stop)",
+        project.config.documento.titulo, delay_secs
+    );
+
+    // Initial build
+    run_build(&project);
+
+    let (tx, rx) = mpsc::channel();
+    let mut watcher = notify::recommended_watcher(move |res| {
+        if let Ok(event) = res {
+            let _ = tx.send(event);
+        }
+    })?;
+
+    watcher.watch(&project.root, RecursiveMode::Recursive)?;
+
+    let build_dir = project.root.join("build");
+    let mut pending = false;
+    let mut last_event = std::time::Instant::now();
+
+    loop {
+        match rx.recv_timeout(Duration::from_millis(500)) {
+            Ok(event) => {
+                // Only react to .tex file changes, ignore build/
+                let relevant = event.paths.iter().any(|p| {
+                    !p.starts_with(&build_dir)
+                        && p.extension().and_then(|e| e.to_str()) == Some("tex")
+                });
+                if relevant {
+                    pending = true;
+                    last_event = std::time::Instant::now();
+                }
+            }
+            Err(mpsc::RecvTimeoutError::Timeout) => {}
+            Err(_) => break,
+        }
+
+        if pending && last_event.elapsed() >= debounce {
+            pending = false;
+            println!("\n--- rebuilding ---");
+            run_build(&project);
+        }
+    }
 
     Ok(())
 }
+
+fn run_build(project: &Project) {
+    let _ = std::fs::create_dir_all(project.root.join("build"));
+    if let Err(e) = diagrams::process(&project.root, &project.config.compilacion.entry) {
+        eprintln!("Error: {}", e);
+        return;
+    }
+    let build_dir = project.root.join("build");
+    let entry_filename = std::path::Path::new(&project.config.compilacion.entry)
+        .file_name()
+        .map(|n| n.to_string_lossy().to_string())
+        .unwrap_or(project.config.compilacion.entry.clone());
+    match compiler::compile(&build_dir, &entry_filename) {
+        Ok(()) => {
+            let pdf = std::path::Path::new(&project.config.compilacion.entry).with_extension("pdf");
+            println!("✅ build/{}", pdf.display());
+        }
+        Err(e) => eprintln!("Error: {}", e),
+    }
+}