1 files changed, 77 insertions, 0 deletions
diff --git a/crates/typst-cli/src/package.rs b/crates/typst-cli/src/package.rs
new file mode 100644
index 00000000..6853796b
--- /dev/null
+++ b/crates/typst-cli/src/package.rs
@@ -0,0 +1,77 @@
+use std::fs;
+use std::io::{self, Write};
+use std::path::{Path, PathBuf};
+
+use codespan_reporting::term::{self, termcolor};
+use termcolor::WriteColor;
+use typst::diag::{PackageError, PackageResult};
+use typst::file::PackageSpec;
+
+use super::color_stream;
+
+/// Make a package available in the on-disk cache.
+pub fn prepare_package(spec: &PackageSpec) -> PackageResult<PathBuf> {
+    let subdir =
+        format!("typst/packages/{}/{}-{}", spec.namespace, spec.name, spec.version);
+
+    if let Some(data_dir) = dirs::data_dir() {
+        let dir = data_dir.join(&subdir);
+        if dir.exists() {
+            return Ok(dir);
+        }
+    }
+
+    if let Some(cache_dir) = dirs::cache_dir() {
+        let dir = cache_dir.join(&subdir);
+
+        // Download from network if it doesn't exist yet.
+        if spec.namespace == "preview" && !dir.exists() {
+            download_package(spec, &dir)?;
+        }
+
+        if dir.exists() {
+            return Ok(dir);
+        }
+    }
+
+    Err(PackageError::NotFound(spec.clone()))
+}
+
+/// Download a package over the network.
+fn download_package(spec: &PackageSpec, package_dir: &Path) -> PackageResult<()> {
+    // The `@preview` namespace is the only namespace that supports on-demand
+    // fetching.
+    assert_eq!(spec.namespace, "preview");
+
+    let url = format!(
+        "https://packages.typst.org/preview/{}-{}.tar.gz",
+        spec.name, spec.version
+    );
+
+    print_downloading(spec).unwrap();
+    let reader = match ureq::get(&url).call() {
+        Ok(response) => response.into_reader(),
+        Err(ureq::Error::Status(404, _)) => {
+            return Err(PackageError::NotFound(spec.clone()))
+        }
+        Err(_) => return Err(PackageError::NetworkFailed),
+    };
+
+    let decompressed = flate2::read::GzDecoder::new(reader);
+    tar::Archive::new(decompressed).unpack(package_dir).map_err(|_| {
+        fs::remove_dir_all(package_dir).ok();
+        PackageError::MalformedArchive
+    })
+}
+
+/// Print that a package downloading is happening.
+fn print_downloading(spec: &PackageSpec) -> io::Result<()> {
+    let mut w = color_stream();
+    let styles = term::Styles::default();
+
+    w.set_color(&styles.header_help)?;
+    write!(w, "downloading")?;
+
+    w.reset()?;
+    writeln!(w, " {spec}")
+}