Thoroughly improve documentation 📝

1 files changed, 23 insertions, 15 deletions

diff --git a/src/bin/main.rs b/src/bin/main.rs
index 9e1403b2..6ca1ba56 100644
--- a/src/bin/main.rs
+++ b/src/bin/main.rs
@@ -1,16 +1,25 @@
 use std::env;
-use std::fs::File;
 use std::error::Error;
-use std::process;
+use std::fs::File;
 use std::io::Read;
 use std::path::{Path, PathBuf};
+use std::process;
 
 use typeset::Typesetter;
 use typeset::{font::FileSystemFontProvider, font_info};
 use typeset::export::pdf::PdfExporter;
 
 
+fn main() {
+    if let Err(err) = run() {
+        eprintln!("error: {}", err);
+        process::exit(1);
+    }
+}
+
+/// The actual main function.
 fn run() -> Result<(), Box<Error>> {
+    // Check the command line arguments.
     let args: Vec<String> = env::args().collect();
     if args.len() < 2 || args.len() > 3 {
         help_and_quit();
@@ -19,9 +28,10 @@ fn run() -> Result<(), Box<Error>> {
     // Open the input file.
     let mut file = File::open(&args[1]).map_err(|_| "failed to open source file")?;
 
-    // The output file name.
-    let output_filename = if args.len() <= 2 {
-        let source_path = Path::new(&args[1]);
+    let source_path = Path::new(&args[1]);
+
+    // Compute the output filename from the input filename by replacing the extension.
+    let dest_path = if args.len() <= 2 {
         let stem = source_path.file_stem().ok_or_else(|| "missing destation file name")?;
         let base = source_path.parent().ok_or_else(|| "missing destation folder")?;
         base.join(format!("{}.pdf", stem.to_string_lossy()))
@@ -29,6 +39,11 @@ fn run() -> Result<(), Box<Error>> {
         PathBuf::from(&args[2])
     };
 
+    // We do not want to overwrite the source file.
+    if dest_path == source_path {
+        return Err("source and destination path are the same".into());
+    }
+
     // Read the input file.
     let mut src = String::new();
     file.read_to_string(&mut src).map_err(|_| "failed to read from source file")?;
@@ -50,22 +65,15 @@ fn run() -> Result<(), Box<Error>> {
 
     // Export the document into a PDF file.
     let exporter = PdfExporter::new();
-    let output_file = File::create(&output_filename)?;
+    let output_file = File::create(&dest_path)?;
     exporter.export(&document, output_file)?;
 
     Ok(())
 }
 
-fn main() {
-    if let Err(err) = run() {
-        eprintln!("error: {}", err);
-        process::exit(1);
-    }
-}
-
 /// Print a usage message and quit.
 fn help_and_quit() {
-    let name = env::args().next().unwrap_or("help".to_string());
-    println!("usage: {} <source> [<destination>]", name);
+    let name = env::args().next().unwrap_or("typeset".to_string());
+    println!("usage: {} source [destination]", name);
     process::exit(0);
 }