Reimplementation (#1)

* refactor into separate modules

* update README

net/download.py

@@ -0,0 +1,79 @@
+"""Library for downloading files from the web with CLI output."""
+
+from pathlib import Path
+
+import requests
+from tqdm import tqdm
+
+from cli.clibella import Printer
+
+
+def download_file(
+        path_to_output_file,
+        url_to_file,
+        show_progress=False,
+        printer=None,
+):
+    """Downloads the file at the input URL to the specified path.
+
+    The file is downloaded via HTTP/HTTPS and saved to the specified path.
+    Optionally, displays a nice status bar.
+
+    Parameters
+    ----------
+    path_to_output_file : str or pathlike object
+        Path to a file as which the downloaded file is saved.
+    url_to_file : str
+        URL to the file to be downloaded.
+    show_progress : bool
+        When True, a progress bar is displayed on StdOut indicating the
+        progress of the download.
+    printer : clibella.Printer
+        A clibella.Printer used to print CLI output.
+    """
+
+    if '~' in str(path_to_output_file):
+        path_to_output_file = Path(path_to_output_file).expanduser()
+    path_to_output_file = Path(path_to_output_file).resolve()
+
+    if not path_to_output_file.parent.is_dir():
+        raise FileNotFoundError(
+            f"No such directory: '{path_to_output_file.parent}'."
+        )
+    if path_to_output_file.exists():
+        raise FileExistsError(
+            f"File already exists: '{path_to_output_file}'"
+        )
+
+    if printer is None:
+        p = Printer()
+    else:
+        p = printer
+
+    output_file_name = path_to_output_file.name
+    with open(path_to_output_file, "wb") as output_file:
+        p.info(f"Downloading '{output_file_name}'...")
+        file_response = requests.get(url_to_file, stream=True)
+        total_length = file_response.headers.get('content-length')
+
+        if total_length is None:  # no content length header
+            output_file.write(file_response.content)
+        else:
+            if (show_progress):
+                total_length = int(total_length)
+                progress_bar = tqdm(
+                    total=total_length,
+                    unit="B",
+                    unit_scale=True,
+                    unit_divisor=1024
+                )
+
+            for data in file_response.iter_content(chunk_size=4096):
+                output_file.write(data)
+                if (show_progress):
+                    progress_bar.update(len(data))
+
+            if (show_progress):
+                progress_bar.close()
+
+        p.ok(f"Received '{output_file_name}'.")