Add download callback to ClimaArtifactsHelper

The callback handles the condition when total size is unknown.
Total size is printed as  MB as an int if it is less than 1 GB, and GB with 2 decimal
places otherwise. The same applies to dowloaded size.

ClimaArtifactsHelper.jl/src/ClimaArtifactsHelper.jl

@@ -7,9 +7,10 @@ using Pkg.Artifacts
 import SHA: sha1
 import Downloads: download
 
-export create_artifact_guided, create_artifact_guided_one_file
+export create_artifact_guided, create_artifact_guided_one_file, download_progress_callback
 
 const MB = 1024 * 1024
+const GB = 1024 * MB
 
 # Mark files larger than this as "undownloadable". This will prevent them from
 # being mirrored by the Julia servers
@@ -214,4 +215,36 @@ function create_artifact_guided_one_file(
     create_artifact_guided(output_dir; artifact_name, append)
 end
 
+"""
+    download_size_string(bytes::Integer)
+
+Return a human-readable string for the given number of bytes.
+"""
+function download_size_string(bytes::Integer)
+    if bytes >= GB
+        size = round(bytes/GB, digits=2)
+        unit = "GB"
+    else
+        size = Int32(div(bytes, MB))
+        unit = "MB"
+    end
+    return "$size $unit"
+end
+
+"""
+    download_progress_callback(total::Integer, now::Integer)
+
+Print the download progress to the terminal. Designed to be used as a callback
+for Downloads.jl.
+"""
+function download_progress_callback(total::Integer, now::Integer)
+    if total == 0
+        print("Downloaded $(download_size_string(total))\r")
+    else
+        print(
+            "Downloaded $(download_size_string(now)) out of $(download_size_string(total)): $(div(now * 100, total))% \r",
+        )
+    end
+end
+
 end