2 files changed, 13 insertions, 6 deletions
diff --git a/src/epub.rs b/src/epub.rs
index 1e7402e..050e9cf 100644
--- a/src/epub.rs
+++ b/src/epub.rs
@@ -16,9 +16,6 @@ use tokio::fs::{self, File};
 use tokio_util::io::StreamReader;
 use zip::{CompressionMethod, ZipWriter, write::FileOptions};
 
-// TODO: make configurable.
-const MAX_CONCURRENT: usize = 4;
-
 /// Creates and writes container.xml.
 fn write_container_xml<W: Write>(out: &mut W, opf_full_path: &RelativePathBuf) -> Result<()> {
     // Prepare file contents.
@@ -41,12 +38,13 @@ pub async fn download_all_files(
     client: &Client,
     file_entries: &[FileEntry],
     dest_root: &Path,
+    max_concurrent: usize,
 ) -> Result<()> {
     let mut downloading = FuturesUnordered::new();
     let mut files_iter = file_entries.iter();
 
     // Start downloading the first n files.
-    for entry in files_iter.by_ref().take(MAX_CONCURRENT) {
+    for entry in files_iter.by_ref().take(max_concurrent) {
         downloading.push(download_one_file(client, entry, dest_root));
     }
 
diff --git a/src/main.rs b/src/main.rs
index 8712d4f..b4775d6 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -11,7 +11,7 @@ use crate::epub::{create_epub_archive, download_all_files};
 use crate::http_client::build_authenticated_client;
 use crate::models::{Chapter, EpubResponse, FileEntry, Paginated};
 use anyhow::{Context, Result, anyhow};
-use clap::Parser;
+use clap::{Parser, value_parser};
 use directories::{BaseDirs, UserDirs};
 use reqwest::Client;
 
@@ -28,6 +28,9 @@ struct Args {
     /// Do not download files. Use if they were already downloaded in a previous run.
     #[arg(long = "skip-download")]
     skip_download: bool,
+    /// Number of files to download in parallel. Limit is 8 (be polite).
+    #[arg(long, value_parser=value_parser!(u32).range(1..=8), default_value_t = 4)]
+    parallel: u32,
 }
 
 /// Fetches EPUB structural data (like the chapters URL).
@@ -132,7 +135,13 @@ async fn main() -> Result<()> {
     let epub_root = data_root.join("files").join(&args.bookid);
     if !args.skip_download {
         println!("Downloading files from the server...");
-        download_all_files(&client, &file_entries, &epub_root).await?;
+        download_all_files(
+            &client,
+            &file_entries,
+            &epub_root,
+            args.parallel.try_into()?, // Will work as 1..=8 will fit into any usize.
+        )
+        .await?;
     }
     println!("Generating the EPUB file...");
     create_epub_archive(&epub_data, &epub_root, &epub_path, &file_entries, &chapters)?;